Thermally conductive sheet holder, method for manufacturing same, and method for attaching thermally conductive sheet

Abstract

A thermally conductive sheet holder 10 comprises: a thermally conductive sheet 15 having a first surface 15A and a second surface 15B on the opposite side from the first surface 15A; a carrier film 11 on the first surface 15A side; and a cover film 20 on the second surface 15B side. At least one of the first and second surfaces 15A, 15B has an adhesive component, the peel force between the cover film 20 and the second surface 15B is 0-55 mN / 25 mm, and the tack value of the second surface 15B is 4.0-9.0 N. The thermally conductive sheet holder 10 is a wound body 25, and the thermally conductive sheet 15 is not disposed in a region R having a length L of 2.0 turns or more of the wound body from the end 11E of the carrier film 11 on the outermost layer of the wound body.

Description

Thermal conductive sheet holder, method for manufacturing the same, and method for attaching a thermal conductive sheet.

[0001] The present invention relates to a thermal conductive sheet holder comprising a thermal conductive sheet, a method for manufacturing a thermal conductive sheet holder, and a method for attaching a thermal conductive sheet using the thermal conductive sheet holder.

[0002] Semiconductor packages are known to dissipate heat by sandwiching a heat dissipation material between a heat-generating element, such as a semiconductor chip, and a heat-sinking element called a heat spreader, which is made of aluminum, copper, or the like, and ensuring tight contact. Conventionally, thermal conductive grease has been widely used as the heat dissipation material placed between the semiconductor chip and the heat spreader. Semiconductor packages are generally heated to a certain temperature or higher during use. Because each component, such as the substrate, semiconductor chip, and heat spreader, has a different coefficient of thermal expansion, warping can occur when heated. Recently, with the increase in chip size, the gaps caused by warping have also increased, and thermal conductive grease cannot follow such warping, resulting in gaps. Therefore, the use of thermal conductive sheets as an alternative to thermal conductive grease is being considered.

[0003] Thermally conductive sheets are used to create a heat dissipation mechanism by being sandwiched between heat-generating elements such as semiconductor packages and heat sinks such as heat spreaders, ensuring close contact between them. To efficiently form this heat dissipation mechanism, there is a need to be able to automatically and accurately supply the thermally conductive sheets onto semiconductor packages and other surfaces. For this reason, for example, the supply of thermally conductive sheets in a form called reel packaging is being considered.

[0004] In reel packaging, it is known that a thermal conductive sheet holder is formed by winding a long carrier film, a plurality of thermal conductive sheets arranged on the carrier film at intervals along its longitudinal direction, and a cover film covering the plurality of thermal conductive sheets, in this order, into a roll (see, for example, Patent Document 1). In the thermal conductive sheet holder, the thermal conductive sheets are peeled off from the cover film and carrier film and then attached to semiconductor chips or the like.

[0005] International Publication No. 2022 / 079914

[0006] Thermal conductive sheets used in semiconductor chips generally contain a high density of thermal conductive filler, which tends to make them brittle. As a result, when peeling the cover sheet from the thermal conductive sheet, damage to the thermal conductive sheet, known as "crackling," can occur. Furthermore, in Patent Document 1, because the tack value of the thermal conductive sheet is high, problems can occur such as the thermal conductive sheet adhering to the cover film when peeling the cover film from the thermal conductive sheet, or difficulty in properly peeling the thermal conductive sheet from the carrier film. On the other hand, if the tack value of the thermal conductive sheet is low, problems can occur such as the thermal conductive sheet not being able to properly adhere to the semiconductor chip.

[0007] Furthermore, thermal conductive sheet holders may be stored for long periods after manufacturing, and during such long-term storage, the tack value may change over time. Therefore, in order to properly adhere the thermal conductive sheet to the surface of the semiconductor device even after long-term storage, it is necessary to suppress the change in tack value over time.

[0008] Therefore, the object of the present invention is to provide a method for attaching a thermal conductive sheet and a thermal conductive sheet holder that can properly fix the thermal conductive sheet to the surface of a semiconductor element without causing problems when peeling the cover sheet from the thermal conductive sheet, and can suppress changes in the tack value of the thermal conductive sheet over time.

[0009] As a result of diligent research, the inventors have found that the above problems can be solved by adjusting the peeling force between the cover film and the thermal conductive sheet, and the tack value of the cover film side surface (second surface) of the thermal conductive sheet within a predetermined range, while providing a region of a certain length or longer at the outermost circumference of the wound body where there is no thermal conductive sheet, and have completed the present invention as described below. The present invention provides the following [1] to

[13] . [1] A thermal conductive sheet holder comprising: a thermal conductive sheet having a first surface and a second surface opposite to the first surface; a carrier film laminated so as to cover the entire surface of the first surface of the thermal conductive sheet; and a cover film laminated so as to cover the entire surface of the second surface of the thermal conductive sheet, wherein at least one of the first surface and the second surface of the thermal conductive sheet has an adhesive component; the peel force between the cover film and the second surface of the thermal conductive sheet is 0 mN / 25 mm or more and 55 mN / 25 mm or less; the tack value of the second surface of the thermal conductive sheet is 4.0 N or more and 9.0 N or less; and the thermal conductive sheet holder is a wound body wound along the longitudinal direction, and the thermal conductive sheet is not arranged in a region with a length of 2.0 turns or more from the end of the outermost carrier film to the winding body. [2] The thermal conductive sheet holder according to [1], wherein the surface roughness Sa on the surface of the cover film in contact with the second surface is 5 μm or more. [3] The thermal conductive sheet holder according to [1] or [2], wherein the peel force between the carrier film and the first surface of the thermal conductive sheet is 55 mN / 25 mm or more and 130 mN / 25 mm or less. [4] The thermal conductive sheet holder according to any one of [1] to [3], wherein the second surface is a surface that adheres to the surface of a semiconductor element. [5] The thermal conductive sheet holder according to any one of [1] to [4], wherein the normal peel force of the cover film is 5 mN / 25 mm or more and 30 mN / 25 mm or less. [6] The thermal conductive sheet holder according to any one of [1] to [5], wherein the normal peel force of the carrier film is 5 mN / 25 mm or more and 30 mN / 25 mm or less. [7] The thermal conductive sheet holder according to any one of [1] to [6], wherein the tack value of the second surface is greater than the tack value of the first surface.[8] A thermal conductive sheet holder according to any one of [1] to [7] above, wherein the adhesive component comprises either a silicone resin or an acrylic resin. [9] A thermal conductive sheet holder according to any one of [1] to [8] above, wherein the adhesive component comprises an acrylic resin having a reactive double bond.

[10] A thermal conductive sheet holder according to any one of [1] to [9] above, wherein one or both of the first surface and the second surface of the thermal conductive sheet are cut surfaces and have the adhesive component.

[11] A thermal conductive sheet holder according to any one of [1] to

[10] above, wherein the thermal conductive sheet comprises an anisotropic filler oriented in the thickness direction.

[12] A method for manufacturing a thermal conductive sheet holder according to any one of [1] to

[11] above, comprising the steps of: setting a plurality of thermal conductive sheets on the carrier film or a base film constituting a part of the carrier film; and further laminating the cover film on the plurality of thermal conductive sheets so as to cover the plurality of thermal conductive sheets.

[13] A thermal conductive sheet holder comprising: a first step of preparing a thermal conductive sheet having a thermal conductive sheet having a first surface and a second surface opposite to the first surface; a carrier film provided so as to cover the entire surface of the first surface of the thermal conductive sheet; and a cover film provided so as to cover the entire surface of the second surface of the thermal conductive sheet; a second step of peeling the cover film from the second surface of the thermal conductive sheet; a third step of pressing the second surface of the thermal conductive sheet onto the surface of a semiconductor element; and a fourth step of peeling the carrier film from the first surface of the thermal conductive sheet, wherein at least one of the first surface and the second surface of the thermal conductive sheet has an adhesive component, the peeling force between the cover film and the second surface of the thermal conductive sheet is 0 mN / 25 mm or more and 55 mN / 25 mm or less, and the tack value of the second surface of the thermal conductive sheet is 4.0 N or more and 9.0 N or less. A method for attaching a thermal conductive sheet, wherein the thermal conductive sheet holder is a wound body wound along the longitudinal direction, and the thermal conductive sheet is not placed in a region extending for a length of 2.0 turns or more from the end of the carrier film on the outermost periphery of the wound body.

[0010] According to the present invention, the thermal conductive sheet can be properly fixed to the surface of a semiconductor element without causing problems when peeling the cover sheet from the thermal conductive sheet. Furthermore, it is possible to suppress changes in the tack value over time, even when stored for a long period of time.

[0011] This is a plan view of a thermal conductive sheet holder according to one embodiment of the present invention. This is a cross-sectional view of a thermal conductive sheet holder according to one embodiment of the present invention. This is a cross-sectional view of a thermal conductive sheet holder according to another embodiment of the present invention. This is a schematic side view of the thermal conductive sheet holder when it is wound into a coil. This is a schematic perspective view of the coil. This is a schematic side view showing how to transport the thermal conductive sheet holder according to one embodiment of the present invention and how to attach a thermal conductive sheet to a semiconductor element. This is a schematic side view showing how to press a lid onto the first surface of a thermal conductive sheet in one embodiment of the present invention.

[0012] Hereinafter, a thermal conductive sheet holder according to one embodiment of the present invention will be described in detail with reference to the drawings. In the following description, the longitudinal direction and width direction of the carrier film will be described as the longitudinal direction Y and width direction X of the thermal conductive sheet holder, respectively. Figure 1 shows a thermal conductive sheet holder according to one embodiment of the present invention, and Figure 2 is a cross-sectional view taken along the line II-II in Figure 1. As shown in Figures 1 and 2, the thermal conductive sheet holder 10 comprises a thermal conductive sheet 15 having a first surface 15A and a second surface 15B opposite to the first surface 15A, a carrier film 11 provided to cover the entire surface of the first surface 15A of the thermal conductive sheet 15, and a cover film 20 provided to cover the entire surface of the second surface 15B of the thermal conductive sheet 15. As will be described later, the first and second surfaces 15A and 15B are surfaces that are fixed to an adherend, but the second surface 15B is a surface that is fixed to the surface of a semiconductor element, for example. Furthermore, the first surface 15A becomes, for example, a surface that adheres to the lid.

[0013] The carrier film 11 is elongated and serves as a support for the thermal conductive sheets 15. Multiple thermal conductive sheets 15 are preferably provided on the carrier film 11. The multiple thermal conductive sheets 15 are arranged at intervals along the longitudinal direction Y on one surface of the carrier film 11. Each thermal conductive sheet 15 is laminated on the carrier film 11 in a manner that allows it to be peeled away from the carrier film 11. The cover film 20 is elongated, similar to the carrier film 11, and is peelably laminated on the multiple thermal conductive sheets 15 so as to cover them.

[0014] In this embodiment, the thermal conductive sheet holder 10 is provided with a plurality of thermal conductive sheets 15. As shown in Figures 1 and 2, the length of each thermal conductive sheet 15 along the width direction X is shorter than that of the carrier film 11 (base film 12, described later) and the cover film 20. Therefore, thermal conductive sheets 15 are not provided on both sides of the carrier film 11, and transport pin holes 14 are provided therein. Multiple transport pin holes 14 are arranged in parallel along the longitudinal direction Y on each side of the carrier film 11. Similarly, multiple transport pin holes 24 are provided on both sides of the cover film 20, arranged in parallel along the longitudinal direction Y. The transport pin holes 24 of the cover film 20 are positioned to overlap with the transport pin holes 14 of the carrier film 11. However, the transport pin holes 24 of the cover film 20 may be omitted, and the transport pin holes 14 of the carrier film 11 may also be omitted.

[0015] As described above, the cover film 20 has a larger outer shape than the thermal conductive sheet 15, and it is preferable that it is in close contact with the carrier film 11 in the outer portion of the thermal conductive sheet 15 where the thermal conductive sheet 15 is not provided. The cover film 20 is preferably adhered to the carrier film 11 in a way that allows it to be peeled off. In Figure 1, the cover film 20 is shown to be in close contact with both sides of the carrier film 11 on both sides of the film 20, which is the outer portion of the thermal conductive sheet 15. However, in addition to the parts on both sides of the films 11 and 20, the cover film 20 may also be in close contact with the carrier film 11 in the portion between the thermal conductive sheets 15, 15. As described above, by the carrier film 11 and the cover film 20 being in close contact with each other, the thermal conductive sheet 15 is protected from both sides and both sides by the carrier film 11 and the cover film 20, as shown in Figure 2, and is sealed inside the carrier film 11 and the cover film 20. However, the cover film 20 may only be in contact with the carrier film 11 without being adhered to it, or they may not be in contact with each other at all.

[0016] In one embodiment, the carrier film 11 has a long base film 12 and a release film 13 laminated on the base film 12, as shown in Figure 2, and each thermal conductive sheet 15 is preferably laminated on the release film 13. The carrier film 11 has a release film 13, which makes it easier to lower the peeling force P1, which will be described later. The base film 12 is a material that serves as the base for the carrier film 11 and is a long material. On the other hand, the release film 13 preferably has a shape that matches the thermal conductive sheet 15. That is, like the thermal conductive sheet 15, the release film 13 is arranged in parallel in multiples with intervals along the longitudinal direction Y, and its length along the width direction X is shorter than that of the carrier film 11 and the base film 12. Therefore, the release film 13 does not need to be provided on both sides of the carrier film 11 or between the thermal conductive sheets 15, 15. Therefore, it is preferable that the cover film 20 is in close contact with the base film 12 of the carrier film 11 on both sides of the film 20, and between the thermal conductive sheets 15, 15.

[0017] However, the release film 13 does not have to have a shape that matches the thermal conductive sheet 15. For example, multiple thermal conductive sheets 15 may be laminated on a single release film 13. Also, the carrier film 11 may not have a release film 13 and may be composed of a base film 12. In that case, each thermal conductive sheet 15 may be directly laminated on the base film 12 as shown in Figure 3.

[0018] As shown in Figure 4, the thermal conductive sheet holder 10 is wound into a roll along the longitudinal direction Y to form a winding body 25. The winding body 25 is wound around the outer circumference of the core 26. Although Figure 4 shows the outermost end portion 10E of the thermal conductive sheet holder 10 being unwound from the winding body 25 for illustrative purposes, the thermal conductive sheet holder 10 is wound up to the outermost end portion 10E before use. When in use, the thermal conductive sheet holder 10 is unwound from the winding body 25 and transported along the longitudinal direction Y.

[0019] As described above, the thermal conductive sheet holder 10 is provided with a plurality of thermal conductive sheets 15, but the thermal conductive sheets 15 are not arranged in a region R of a certain length L from the end 11E of the outermost carrier film 11 on the thermal conductive sheet holder 10. That is, in the thermal conductive sheet holder 10, the thermal conductive sheets 15 are arranged in a plurality along the length direction Y from a position at a certain length L from the end 11E toward the innermost end (not shown) of the carrier film 11. In the region R where the thermal conductive sheets 15 are not arranged, the cover film 20 is in close contact with the carrier film 11, and preferably adheres to the carrier film 11. In addition, in the thermal conductive sheet holder 10, both the cover film 20 and the carrier film 11 are provided up to the end portion 10E of the holder 10, and the end portion 10E of the thermal conductive sheet holder 10 is constructed by overlapping the cover film 20 with the end 11E of the carrier film 11.

[0020] In this embodiment, by not providing the thermal conductive sheet 15 in a region R of a certain length L on the end portion 10E side, airtightness between the carrier film 11 and the cover film 20 is ensured, and contact of the thermal conductive sheet 15 with the atmosphere is suppressed. Therefore, even if the thermal conductive sheet holder 10 is stored for a long period of time in the state of a wound body 25, the adhesive component contained in the thermal conductive sheet 15 is prevented from deteriorating over time, making it easier to maintain the tack value at a desired value. In addition, it is easier to prevent the thermal conductive sheet 15 from hardening.

[0021] The length L mentioned above is 2.0 turns or more in the winding body 25. When the length L is 2.0 turns or more, the thermal conductive sheet holder 10 is wound twice over the area in the winding body 25 where the thermal conductive sheet 15 is not provided, for one turn or more. As a result, airtightness is sufficiently improved, and deterioration of the adhesive component contained in the thermal conductive sheet 15 over time can be appropriately prevented. Preferably, the length L is 2.5 turns or more in the winding body 25, more preferably 3.0 turns or more. Furthermore, from the viewpoint of economy and workability during unwinding, the length L is often less than or equal to a certain length, for example, 10 turns or less, preferably 9 turns or less, and more preferably 8 turns or less.

[0022] Furthermore, the length L varies depending on the outer diameter of the core 26, but is typically 1.0 m or more, preferably 1.2 m or more, more preferably 2 m or more, and also, for example, 10 m or less, preferably 8 m or less, and more preferably 5 m or less. The outer diameter of the core 26 is not particularly limited, but for example, it is 50 mm or more and 300 mm or less, preferably 100 mm or more and 210 mm or less. Furthermore, the length of the thermal conductive sheet holder 10 wound around the winding body 25 is not particularly limited, but for example, it may be 5 m or more and 200 m or less, preferably 8 m or more and 100 m or less.

[0023] The core 26 of the winding body 25 may have a flange 27, as shown in Figure 5. The flange 27 protrudes radially outward from both ends in the axial direction of the outer surface of the core 26, preventing the winding body 25 from detaching from the core 26. The presence of the flange 27 also improves airtightness, suppressing the entry of air between the carrier film 11 and the cover film 20 from the side of the thermal conductive sheet holder 10, and more effectively preventing deterioration of the thermal conductive sheet 15 over time. Although not particularly limited, from the viewpoint of ensuring airtightness, the distance between the flanges 27 at both ends (also called the core width) should be slightly larger than the width of the thermal conductive sheet holder 10. In that case, the difference between the core width and the width of the thermal conductive sheet holder 10 should be greater than 0 mm and 5 mm or less, preferably 0.3 mm or more and 4 mm or less, and more preferably 0.5 mm or more and 3 mm or less.

[0024] The thermal conductive sheet holder 10 is not particularly limited, but the thermal conductive sheet 15 does not need to be placed in a region of a certain length L2 (not shown) from the innermost end of the winding body 25. The length L2 may be the same as length L, or it may be different. Furthermore, the thermal conductive sheet holder 10 is preferably wound with the cover film 20 side facing inward as shown in Figure 4, but it may also be wound with the carrier film 11 side facing inward (not shown).

[0025] The thermal conductive sheet holder 10 according to this embodiment satisfies the following requirements (1) and (2): (1) The peeling force between the cover film 20 and the second surface 15B of the thermal conductive sheet 15 (hereinafter sometimes referred to as "peeling force P2") is 0 mN / 25 mm or more and 55 mN / 25 mm or less. (2) The tack value of the second surface 15B of the thermal conductive sheet 15 (hereinafter sometimes referred to as "tack value T2") is 4.0 N or more and 9.0 N or less. With the above configuration, the thermal conductive sheet 15 can be properly fixed to the surface of a semiconductor element or the like without causing any problems when peeling the cover film 20 from the thermal conductive sheet 15.

[0026] On the other hand, if the peeling force P2 exceeds 55 mN / 25 mm or the tack value exceeds 9.0 N, when attempting to peel the cover film 20 from the thermal conductive sheet 15, damage to the thermal conductive sheet 15, known as "separation," may occur, or the thermal conductive sheet 15 may adhere to the cover film 20, making it impossible to properly peel off the cover film 20. Furthermore, if the tack value falls below 4.0 N, the thermal conductive sheet 15 becomes difficult to adhere to substrates such as semiconductor elements, making it difficult to achieve good mounting performance.

[0027] The peel force (peel force P2) between the cover film 20 and the second surface 15B of each thermal conductive sheet 15 is preferably 55 mN / 25 mm or less, more preferably 40 mN / 25 mm or less. Furthermore, the lower limit of the peel force P2 is not particularly limited, and it should be 0 mN / 25 mm or more. From the viewpoint of facilitating the retention of each thermal conductive sheet 15 by the cover film 20, the peel force P2 is preferably 1 mN / 25 mm or more, more preferably 3 mN / 25 mm or more. However, by sealing each thermal conductive sheet 15 between the cover film 20 and the carrier film 11 as described above, it is possible to properly retain each thermal conductive sheet inside the thermal conductive sheet holder 10 even if the peel force P2 is 0 mN / 25 mm.

[0028] The tack value T2 of the second surface 15B of the thermal conductive sheet 15 is preferably 4.0 N or more and 9.0 N or less, and more preferably 4.5 N or more and 8.0 N or less. By setting the tack value T2 within the above range, adhesion to the substrate such as a semiconductor element can be improved, and peeling defects such as separation can be prevented. The tack value T2 and the tack value T1, which will be described later, can be adjusted by the surface condition of the thermal conductive sheet, which will be described later. For example, they can be adjusted by appropriately changing the type of adhesive, basis weight, etc., while providing tackiness with an adhesive (adhesive component) as described later. The tack values ​​T1 and T2 can be measured by the measurement method described in the examples.

[0029] Furthermore, the tack value of the first surface 15A of the thermal conductive sheet 15 (hereinafter also referred to as "tack value T1") is, for example, 3.5N or more and 9.0N or less, preferably 4.0N or more and 9.0N or less, more preferably 4.5N or more and 8.5N or less, and even more preferably 5.0N or more and 8.0N or less. If the tack value T1 is above the lower limit, the adhesion of the first surface 15A to the adherend can also be improved. As a result, the thermal conductive sheet 15 can be fixed to the semiconductor element with high adhesive strength on the first surface 15A, while the opposite side can be appropriately fixed to a lid or the like. In addition, by setting the tack value T1 to below the upper limit, the thermal conductive sheet 15 can be appropriately peeled off from the carrier film 11.

[0030] In this embodiment, the tack value T2 of the second surface 15B may be the same as or different from the tack value T1 of the first surface 15A, but it is preferable that the tack value T2 of the second surface 15B is greater than the tack value T1 of the first surface 15A. In this embodiment, typically, the second surface 15B is fixed to a semiconductor element such as a semiconductor chip, and the first surface 15A is fixed to a lid. Since semiconductor chips generally have high smoothness, increasing the tack value T2 of the second surface 15B fixed to the semiconductor element as described above allows the thermal conductive sheet 15 to be properly fixed to the semiconductor element or lid. Furthermore, even if the tack value T2 is high, setting the peeling forces P1 and P2 as described above makes it less likely for problems such as separation or adhesion of the thermal conductive sheet 15 to the cover film 20 to occur when peeling the cover film 20 from the thermal conductive sheet 15. When the tack value T2 is greater than the tack value T1, the difference between T2 and T1 (T2-T1) is, for example, 0N or more and 5N or less, preferably 0.3N or more and 4.5N or less, and more preferably 0.5N or more and 4.0N or less.

[0031] The peeling force (hereinafter sometimes referred to as "peeling force P1") between the carrier film 11 and the first surface 15A of each thermal conductive sheet 15 is preferably 55 mN / 25 mm or more and 130 mN / 25 mm or less. By keeping the peeling force P1 below the above upper limit, it is possible to prevent peeling defects such as the thermal conductive sheet 15 not being able to be peeled off when attempting to peel the thermal conductive sheet 15 from the carrier film 11. Furthermore, by setting the peeling force P1 above a certain value, it is possible to prevent each thermal conductive sheet 15 from unexpectedly peeling off from the carrier film 11 when peeling off the cover film 20 or after peeling it off. From these viewpoints, the peeling force P1 is preferably 130 mN / 25 mm or less, more preferably 100 mN / 25 mm or less. Furthermore, the peeling force P1 is more preferably 60 mN / 25 mm or more, and even more preferably 65 mN / 25 mm or more. The peeling forces P1 and P2 can be adjusted as appropriate depending on the material and surface condition of the carrier film, cover film, and thermal conductive sheet. Furthermore, the peeling forces P1 and P2 can be measured using the measurement methods described in the examples. For example, peeling force P1 can be measured by measuring the peeling force on the film in contact with the thermal conductive sheet. If a release film is provided on the carrier film and the thermal conductive sheet is laminated on the release film, the peeling force of the thermal conductive sheet to the release film can be measured according to the method described in the examples and used as peeling force P1. Similarly, if the thermal conductive sheet is laminated directly on the base film, the peeling force of the thermal conductive sheet to the base film can be measured according to the method described in the examples and used as peeling force P1. The same applies to peeling forces P2 and P3, which will be described later.

[0032] It is preferable that the peeling force P1 is higher than the peeling force P2. By making the peeling force P1 higher than the peeling force P2, it is possible to prevent problems such as delamination occurring between the thermal conductive sheet 15 and the carrier film 11 when peeling the cover film 20 from the thermal conductive sheet 15. When the peeling force P1 is higher than the peeling force P2, the difference between the peeling force P1 and the peeling force P2 (P1-P2) is, for example, 30 mN / 25 mm or more and 130 mN / 25 mm or less, preferably 40 mN / 25 mm or more and 110 mN / 25 mm or less, and more preferably 50 mN / 25 mm or more and 100 mN / 25 mm or less.

[0033] In one embodiment of the present invention, the cover film 20 is preferably adhered to the carrier film 11 in areas where the thermal conductive sheet 15 is not provided, such as region R, as described above. Here, the cover film 20 is preferably adhered to the carrier film 11 in a manner that allows it to be peeled off with a peel force of a certain value or more. The peel force between the cover film 20 and the carrier film 11 (hereinafter also referred to as the "third peel force P3") is, for example, 2 mN / 25 mm or more, preferably 5 mN / 25 mm or more, and more preferably 7 mN / 25 mm or more. By having a third peel force P3 of a certain value or more, the thermal conductive sheet 15 is appropriately protected by the cover film 20 and the carrier film 11 during transport and storage. Alternatively, the third peel force P3 may be, for example, 30 mN / 25 mm or less, preferably 25 mN / 25 mm or less, and more preferably 20 mN / 25 mm or less. By having a third peel force P3 of a certain value or less, the cover film 20 can be easily peeled off and removed from the carrier film 11. As shown in Figures 2 and 3, in one embodiment, the cover film 20 may be peelably adhered to the base film 12 in the portion where the release film 13 is not provided, but it may also be adhered to the release film 13. Furthermore, the third peel force P3 can be appropriately adjusted depending on the material and surface condition of the carrier film and cover film. The peel force P3 can be measured by the measurement method described in the example.

[0034] The following describes in more detail each component constituting the thermal conductive sheet holder. <Thermal conductive sheet> The thermal conductive sheet typically includes a polymer matrix and a thermal conductive filler, and it is preferable that the thermal conductive filler is dispersed in the polymer matrix. It is preferable that the filling rate of the thermal conductive filler in the thermal conductive sheet is 51 volume% or more. By having a filling rate of 51 volume% or more, the thermal conductivity of the thermal conductive sheet 15 can be sufficiently improved, and the high-density, highly integrated semiconductor package can be sufficiently heat-dissipated. From the viewpoint of increasing thermal conductivity and further improving heat dissipation, the filling rate of the thermal conductive filler in the thermal conductive sheet 15 is preferably 55 volume% or more, more preferably 60 volume% or more, and even more preferably 62 volume% or more. From the viewpoint of facilitating the manufacture of the thermal conductive sheet, the filling rate of the thermal conductive filler in the thermal conductive sheet 15 is preferably 85 volume% or less, more preferably 83 volume% or less, and even more preferably 80 volume% or less.

[0035] (Adhesive) The thermal conductive sheet 15 is composed of a thermal conductive layer and has adhesive properties by containing an adhesive component on at least one of the first surface 15A and the second surface 15B. The adhesive component is preferably an adhesive. It is more preferable that the thermal conductive sheet 15 has adhesive properties by having an adhesive layer formed by an adhesive on at least one of its surfaces. By providing adhesive properties with an adhesive layer, the tack value can be more easily controlled. In order to increase the tack value T2 of the second surface 15B, it is preferable that the thermal conductive sheet 15 has an adhesive on at least the second surface 15B, and it is more preferable that both surfaces 15B and 15A have an adhesive (adhesive component) in order to increase both tack values ​​T1 and T2. The adhesive component contained on the surface of the thermal conductive sheet 15 is prevented from coming into contact with the atmosphere by increasing the airtightness of the thermal conductive sheet holder 10, and the tack values ​​T1 and T2 are less likely to change over time.

[0036] The basis weight of the adhesive on the first and second surfaces 15A and 15B of the thermal conductive sheet 15 is, for example, 0.03 mg / cm². ２ The above is preferable, and preferably 0.05 mg / cm³. ２ More preferably 0.08 mg / cm² ２More preferably 0.1 mg / cm³ ２ That is all. Also, for example, 0.5 mg / cm³ ２ The following is preferably 0.4 mg / cm ２ More preferably, 0.3 mg / cm² ２ More preferably, 0.2 mg / cm³ ２ The following applies: By ensuring that the basis weight of the adhesive on each surface is above a certain amount, a sufficient tack value can be secured. Furthermore, by keeping the basis weight below a certain amount, it is possible to prevent the thermal resistance value from decreasing due to the adhesive, making it easier to ensure good thermal conductivity. In addition, it is possible to prevent the tack value from becoming unnecessarily high due to the adhesive. Note that the basis weight of the adhesive refers to the amount of adhesive per unit area after solvent drying. Furthermore, if the tack value T2 of the second surface 15B is greater than the tack value T1 of the first surface 15A, it is preferable that the basis weight on the second surface 15B be greater than the basis weight on the first surface 15A.

[0037] Preferably, the adhesive (adhesive layer) on each surface of the thermal conductive sheet 15 is impregnated into the thermal conductive layer. Typically, it is preferable that only a portion of the adhesive is impregnated into the thermal conductive layer, but it may be entirely impregnated into the thermal conductive layer as long as the adhesive can exert adhesive force to the adherend. By impregnating the adhesive into the thermal conductive layer, the amount of adhesive present on the surface of the thermal conductive layer can be reduced, thereby suppressing a decrease in thermal conductivity due to the adhesive. Furthermore, even if the adhesive is impregnated into the thermal conductive layer of the thermal conductive sheet, high adhesion can be ensured. The principle is not entirely clear, but it is presumed that the pressure applied to the thermal conductive sheet, which is generally compressed during use, causes the impregnated adhesive to seep to the surface, thereby increasing adhesion. In addition, as will be described later, an appropriate amount of adhesive can be impregnated into the thermal conductive layer by impregnating it into bubbles formed by the volatilization of volatile substances. Furthermore, the adhesive may be formed to cover the entire surface of each surface of the heat conductive layer, or it may be formed to partially cover the surface as long as it can exert adhesive force to the adherend.

[0038] As the adhesive, an acrylic adhesive, a rubber adhesive, a urethane adhesive, a silicone adhesive, etc. can be used. Among these, a silicone adhesive and an acrylic adhesive are preferred, and an acrylic adhesive is more preferred. By using an acrylic adhesive among silicone adhesives and acrylic adhesives, a heat conductive sheet can be adhered to a lid such as a heat spreader and an adherend such as a semiconductor chip, and moreover, when used in a relatively high temperature environment of about 60 to 150 ° C in actual use, the adhesive strength is likely to improve during actual use. The silicone adhesive is an adhesive using a silicone resin as the main component of the adhesive, and the acrylic adhesive is an acrylic adhesive using an acrylic polymer (acrylic resin) as the main component of the adhesive.

[0039] In the present invention, the acrylic adhesive may or may not have a reactive double bond, but it is preferable to have a reactive double bond. By having a reactive double bond, the acrylic adhesive can maintain the adhered state and prevent peeling from the adherend even when heated to a high temperature in a reflow process or the like while adhered to an adherend such as a lid or a semiconductor element. Also, high adhesiveness can be maintained even when used in a relatively high temperature environment of about 150 ° C in actual use. Generally, it is known that the adhesive strength of an acrylic adhesive greatly decreases when heated at a high temperature. However, in the present invention, the acrylic adhesive can maintain or improve the adhesive strength to the adherend, contrary to the properties of conventional general acrylic adhesives, by having a reactive double bond. The principle is not clear, but it is presumed that the reactive double bonds in the acrylic adhesive react by heating, for example, bond to the adherend, or the mechanical strength of the adhesive is improved by crosslinking between the reactive double bonds. Further, in some cases, it also reacts with unreacted hydrosilyl groups in the organopolysiloxane constituting the polymer matrix, and these act in a complex manner to improve the adhesiveness.

[0040] The acrylic adhesive preferably contains an acrylic polymer as the main component of the adhesive, and the acrylic polymer has the reactive double bond described above. The acrylic adhesive can exhibit adhesiveness by containing an acrylic polymer. The acrylic polymer used in the acrylic adhesive preferably contains an acrylic polymer having a reactive double bond (acrylic polymer containing a reactive double bond). The acrylic polymer containing a reactive double bond preferably has a reactive double bond in the side chain. The reactive double bond is a saturated carbon-carbon double bond that does not form an aromatic ring. Typically, it is a group having a structure represented by H ２ C═CH−*, or H ２ C═CCH ３ −* (* represents a bond), and specifically includes a vinyl group, an acryloyl group, a methacryloyl group, etc. Further, the acrylic polymer containing a reactive double bond may have functional groups such as a hydroxyl group, a carboxyl group, an epoxy group, an amino group, etc. in the side chain in addition to the group having a reactive double bond, but it is preferable to have at least one of a hydroxyl group and a carboxyl group in the side chain, and it is more preferable to have both a hydroxyl group and a carboxyl group.

[0041] The weight average molecular weight of the acrylic polymer containing a reactive double bond is not particularly limited, but is, for example, about 100,000 or more and 1,200,000 or less, preferably about 200,000 or more and 1,000,000 or less. The weight average molecular weight is measured by gel permeation chromatography (GPC) and is determined as a polystyrene conversion value. By adjusting the molecular weight, the solid content concentration and viscosity of the adhesive containing an organic solvent described later can be adjusted. Specifically, when it is desired to adjust to a low viscosity while increasing the solid content concentration, the molecular weight may be decreased. When it is desired to adjust to a high viscosity while decreasing the solid content concentration, the molecular weight may be increased.

[0042] The reactive double bond-containing acrylic polymer can be obtained, for example, by reacting an acrylic polymer (hereinafter also referred to as acrylic polymer (X)) having a functional group such as a hydroxyl group, a carboxyl group, an epoxy group, an amino group, etc. in the side chain with a reactive double bond-containing compound (hereinafter also referred to as reactive double bond-containing compound (Y)) having a reactive group that reacts with the functional group and a reactive double bond.

[0043] As the acrylic polymer (X), it may be any one containing a structural unit derived from (meth)acrylate, but typically, it contains a structural unit derived from an alkyl (meth)acrylate as a main component. More specifically, examples of the acrylic polymer (X) include a copolymer of an alkyl (meth)acrylate and a functional group-containing monomer, a copolymer of an alkyl (meth)acrylate, a functional group-containing monomer, and other monomers other than these. Note that (meth)acrylate is used as a term meaning one or both of acrylate and methacrylate, and the same applies to other similar terms.

[0044] Alkyl (meth)acrylates are esters of (meth)acrylic acid and alkyl alcohols. The alkyl group in alkyl (meth)acrylates may be linear, branched, or cyclic. Examples of alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, isomiristyl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, and isobornyl (meth)acrylate. Alkyl (meth)acrylates may be used individually or in combination of two or more. The alkyl (meth)acrylate is preferably an alkyl (meth)acrylate having 1 to 12 carbon atoms in the alkyl group, and more preferably includes an alkyl acrylate having 2 to 8 carbon atoms in the alkyl group. The constituent units derived from the alkyl acrylate having 2 to 8 carbon atoms in the alkyl group are often the main component in the acrylic polymer (X), and in the acrylic polymer (X), they may be, for example, 50% by mass or more, preferably 60% by mass or more and 95% by mass or less, and more preferably 70% by mass or more and 90% by mass or less.

[0045] As mentioned above, the functional groups in the functional group-containing monomers include carboxyl groups, hydroxyl groups, amino groups, and epoxy groups, with carboxyl groups and hydroxyl groups being preferred among these. Examples of monomers containing carboxyl groups include (meth)acrylic acid and crotonic acid, with (meth)acrylic acid being more preferred among these. Examples of monomers containing hydroxyl groups include hydroxyl-containing (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, and 6-hydroxyhexyl (meth)acrylate, as well as allyl alcohol. Among these, hydroxyl-containing (meth)acrylates such as 2-hydroxyethyl (meth)acrylate are preferred. The constituent units derived from functional group-containing monomers in the acrylic polymer (X) are, for example, 1% by mass or more and 35% by mass or less, preferably 5% by mass or more and 30% by mass or less, and more preferably 10% by mass or more and 25% by mass or less. One functional group-containing monomer may be used alone, or two or more may be used in combination.

[0046] Other monomers include alkyl (meth)acrylates and monomers other than the functional group-containing monomers described above, and are not particularly limited as long as they can copolymerize with alkyl (meth)acrylates or functional group-containing monomers. Specifically, examples include styrene, α-methylstyrene, p-methylstyrene, p-chlorostyrene, styrene derivatives such as divinylbenzene, compounds having vinyl ester groups such as vinyl acetate and vinyl propionate, N-vinylpyrrolidone, N-vinylmorpholin, (meth)acrylonitrile, N-cyclohexylmaleimide, N-phenylmaleimide, N-laurylmaleimide, N-benzylmaleimide, n-propyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, tert-butyl vinyl ether, etc. Other monomers may be used individually or in combination of two or more.

[0047] The reactive double bond-containing compound (Y) is a compound having a reactive group that reacts with the functional group described above, and a reactive double bond. Examples of reactive groups include isocyanate groups, epoxy groups, carboxyl groups, and hydroxyl groups, among which isocyanate groups and epoxy groups are preferred, and isocyanate groups are more preferred. The amount of reactive double bonds contained in the acrylic adhesive can be adjusted by the amount of functional groups contained in the acrylic polymer (X) and the ratio of the functional groups that react with the reactive double bond-containing compound (Y). Furthermore, the amount of functional groups contained in the acrylic polymer (X) can be adjusted by the ratio of functional group-containing monomers used when synthesizing the acrylic polymer (X).

[0048] The acrylic polymer contained in the acrylic adhesive may consist of an acrylic polymer containing a reactive double bond, but it may also contain an acrylic polymer without a reactive double bond in addition to the acrylic polymer containing a reactive double bond. Furthermore, the acrylic polymer may consist of an acrylic polymer without a reactive double bond. An example of an acrylic polymer without a reactive double bond is the acrylic polymer (X) described above. In addition to the acrylic polymer described above, the acrylic adhesive may contain components commonly used in adhesives, and may appropriately contain additives such as crosslinking agents, tackifiers, fillers, antioxidants, UV inhibitors, plasticizers, and viscosity modifiers.

[0049] (Thermal Conducting Layer) The thermal conducting layer may include a polymer matrix and a thermally conductive filler. The polymer matrix is ​​an organic polymer matrix, such as an elastomer or rubber, and preferably a liquid polymer composition (curable polymer composition) consisting of a mixed system such as a main component and a curing agent, which is cured to form the matrix. The curable polymer composition may consist of, for example, uncrosslinked rubber and a crosslinking agent, or it may contain monomers, prepolymers, and a curing agent. Furthermore, the curing reaction may be room temperature curing or thermal curing.

[0050] The polymer matrix is ​​preferably an organopolysiloxane. In this invention, using an organopolysiloxane makes the polymer matrix flexible after curing, improving the filling properties of the thermally conductive filler. The organopolysiloxane is preferably a silicone rubber. Furthermore, the organopolysiloxane is preferably a curable silicone, and more preferably an addition-reaction silicone. In the case of an addition-reaction silicone, the curable polymer composition consists of an alkenyl group-containing organopolysiloxane (main component) and a hydrogen organopolysiloxane (curing agent), and the polymer matrix can be formed by curing these components. When an addition-reaction silicone is used, the reactive double bonds contained in the acrylic adhesive react with unreacted hydrosilyl groups due to high-temperature heating in processes such as reflow soldering, which is thought to improve adhesion to the adherend.

[0051] In addition to silicone rubber, various synthetic rubbers can be used as rubbers. Specific examples include acrylic rubber, nitrile rubber, isoprene rubber, urethane rubber, ethylene propylene rubber, styrene-butadiene rubber, butadiene rubber, fluororubber, and butyl rubber. When using these rubbers, the synthetic rubber may be crosslinked or left uncrosslinked (i.e., uncured) in the thermal conductive sheet. Uncrosslinked rubber is mainly used in flow orientation. When crosslinking (i.e., curing) is performed, as explained above, the polymer matrix may be a curable polymer composition consisting of uncrosslinked rubber made from these synthetic rubbers and a crosslinking agent, which is then cured. As for elastomers, thermoplastic elastomers such as polyester-based thermoplastic elastomers and polyurethane-based thermoplastic elastomers, as well as thermosetting elastomers formed by curing a mixed liquid polymer composition consisting of a main component and a curing agent, can also be used. For example, a polyurethane-based elastomer formed by curing a polymer composition containing a polymer having hydroxyl groups and an isocyanate can be cited.

[0052] Furthermore, the polymer composition for forming the polymer matrix may consist of an organic polymer alone, or it may consist of an organic polymer and a plasticizer. Plasticizers are preferably used when synthetic rubber is used, and by including a plasticizer, it is possible to increase the flexibility of the polymer matrix when it is not crosslinked. For example, when the polymer matrix is ​​an organopolysiloxane, silicone oil may be used as a plasticizer. That is, the curable polymer composition may consist of a main agent and a curing agent, or it may consist of a main agent, a curing agent, and a plasticizer. The polymer matrix content in the thermal conductive sheet, expressed as a volume-based filling rate (volume filling rate), may be, for example, 49 volume% or less of the total amount of the thermal conductive sheet, but 45 volume% or less is preferable, 39 volume% or less is more preferable, 37 volume% or less is even preferable, 14 volume% or more is preferable, 16 volume% or more is more preferable, and 19 volume% or more is even preferable.

[0053] (Thermal Conductive Filler) The thermal conductive filler contained in the thermal conductive layer is preferably dispersed in and retained within the polymer matrix. Examples of thermal conductive fillers include anisotropic fillers and non-anisotropic fillers, but it is preferable to use at least anisotropic fillers. The anisotropic filler is preferably oriented in the thickness direction of the thermal conductive sheet. This makes it easier to increase the thermal conductivity of the thermal conductive layer. When the anisotropic filler is oriented in the thickness direction, its long axis does not need to be strictly parallel to the thickness direction; it is considered oriented in the thickness direction even if its long axis is slightly tilted relative to the thickness direction. Specifically, even if the long axis is tilted by about 20°, it is considered oriented in the thickness direction. If the anisotropic filler is used, and such anisotropic filler constitutes the majority of the thermal conductive sheet (for example, more than 60%, preferably more than 80%, of the total number of anisotropic fillers), it is considered oriented in the thickness direction.

[0054] The content of the thermally conductive filler is preferably 150 parts by mass or more and 3000 parts by mass or less, more preferably 200 parts by mass or more and 1800 parts by mass or less, and even more preferably 300 parts by mass or more and 1000 parts by mass or less, per 100 parts by mass of polymer matrix. By having a thermally conductive filler content of 150 parts by mass or more, a certain level of thermal conductivity can be imparted to the thermal conductive layer. Furthermore, by having a content of 3000 parts by mass or less, the thermally conductive filler can be appropriately dispersed in the polymer matrix. In addition, it is possible to prevent the viscosity of the mixed composition, which will be described later, from becoming unnecessarily high.

[0055] (Anisotropic Filler) Anisotropic fillers are fillers that have anisotropy in shape and are oriented. Examples of anisotropic fillers include fibrous materials and flake-like materials. Anisotropic fillers have a high aspect ratio, specifically an aspect ratio greater than 2, and preferably an aspect ratio of 5 or more. By making the aspect ratio greater than 2, it becomes easier to orient the anisotropic filler in one direction, such as the thickness direction, and it is easier to improve the thermal conductivity in one direction, such as the thickness direction of the thermal conductive layer. Furthermore, there is no particular upper limit to the aspect ratio, but practically it is 100. Note that the aspect ratio is the ratio of the length in the long axis direction to the length in the short axis direction of the filler, and in the case of fibrous materials, it means fiber length / fiber diameter, and in the case of flake-like materials, it means the length in the long axis direction of the flake-like material / thickness.

[0056] The content of the anisotropic filler in the thermal conductive layer is preferably 10 parts by mass or more and 500 parts by mass or less per 100 parts by mass of polymer matrix, more preferably 30 parts by mass or more and 300 parts by mass or less, and even more preferably 50 parts by mass or more and 250 parts by mass or less. By setting the content of the anisotropic filler to 10 parts by mass or more, it becomes easier to improve thermal conductivity. Furthermore, by setting it to 500 parts by mass or less, the viscosity of the mixed composition described later becomes more appropriate, and the orientation of the anisotropic filler becomes good. In addition, the dispersibility of the anisotropic filler in the polymer matrix also becomes good.

[0057] When the anisotropic filler is a fibrous material, its average fiber length is preferably 10 μm to 300 μm, more preferably 20 μm to 200 μm, and even more preferably 30 μm to 100 μm. If the average fiber length is 10 μm or more, the anisotropic fillers will be in proper contact with each other within the thermal conductive layer, ensuring a heat transfer path and improving the thermal conductivity of the thermal conductive layer. On the other hand, if the average fiber length is 300 μm or less, the bulk of the anisotropic filler will be reduced, allowing for higher filling within the binder component. Furthermore, it is preferable that the average fiber length of the fibrous material is shorter than the thickness of the thermal conductive sheet. A shorter average fiber length prevents the fibrous material from protruding excessively from the surface of the thermal conductive sheet. The average fiber length can be calculated by observing the anisotropic filler under a microscope. More specifically, for example, the fiber lengths of 50 arbitrary anisotropic fillers can be measured using an electron microscope or an optical microscope, and the average value (arithmetic mean) can be taken as the average fiber length.

[0058] Furthermore, when the anisotropic filler is a flake-like material, its average particle size is preferably 5 μm to 300 μm, more preferably 10 μm to 200 μm, and even more preferably 15 μm to 100 μm. By setting the average particle size to 10 μm or more, the anisotropic fillers can easily come into contact with each other in the thermal conductive layer, ensuring a heat transfer path and improving the thermal conductivity of the thermal conductive layer. On the other hand, if the average particle size is 300 μm or less, the bulk of the thermal conductive sheet is reduced, making it possible to fill the binder component with a high concentration of anisotropic filler. Furthermore, when the orientation method is the flow orientation method, the average particle size is preferably 5 μm to 1000 μm, more preferably 10 μm to 750 μm, and even more preferably 15 μm to 500 μm. By setting the average particle size to 5 μm or more, the anisotropic fillers can easily come into contact with each other in the thermal conductive layer, ensuring a heat transfer path and improving the thermal conductivity of the thermal conductive layer. On the other hand, if the average particle size is 1000 μm or less, the bulk of the thermally conductive sheet is reduced, making it possible to highly pack the anisotropic filler into the binder component. The average particle size of the flake-like filler is D50, which can be calculated by observing the flake-like filler under a microscope and taking its longest axis as the diameter. More specifically, for example, by measuring the longest axis of 500 or more arbitrary flake-like fillers using an electron microscope or optical microscope, it means the particle size corresponding to the cumulative frequency of 50%. Specifically, it can be obtained from a particle size distribution curve with particle size on the horizontal axis and cumulative frequency on the vertical axis, using the flake-like filler as a sample. This particle size distribution curve is a number-based particle size distribution curve obtained by sequentially accumulating the flake-like fillers starting from the smallest particle size.

[0059] Anisotropic fillers can be made from known materials with thermal conductivity, but if they are oriented by magnetic field orientation as described later, it is preferable that they possess diamagnetism. On the other hand, if they are oriented by flow orientation or if the anisotropic filler is not oriented, diamagnetism is not required. Specific examples of anisotropic fillers include carbon-based materials represented by carbon fibers or flaky carbon powder, metal materials represented by metal fibers, metal oxides, boron nitride, metal nitrides, metal carbides, metal hydroxides, poly(p-phenylenebenzoxazole) fibers, etc. Among these, carbon-based materials are preferred because they have a low specific gravity and good dispersibility in the binder component, and graphitized carbon materials with high thermal conductivity are more preferred. Graphitized carbon materials possess diamagnetism when the graphite planes are aligned in a predetermined direction. Boron nitride is also a preferred anisotropic filler. Boron nitride is not particularly limited, but it is preferably used as a flaky material. The flaky boron nitride may or may not be aggregated, but it is preferable that some or all of it is not aggregated. Furthermore, boron nitride and the like also possess diamagnetism when their crystal planes are aligned in a predetermined direction.

[0060] Furthermore, while the anisotropic filler is not particularly limited, its thermal conductivity along the anisotropic direction (i.e., the long axis direction) is generally 30 W / m·K or higher, preferably 60 W / m·K or higher, more preferably 100 W / m·K or higher, and even more preferably 200 W / m·K or higher. The upper limit of the thermal conductivity of the anisotropic filler is not particularly limited, but for example, it is 2000 W / m·K or lower. The thermal conductivity can be measured by methods such as the laser flash method.

[0061] Anisotropic fillers may be used individually or in combination of two or more types. For example, at least two anisotropic fillers having different average particle sizes or average fiber lengths may be used. It is believed that using anisotropic fillers of different sizes allows smaller anisotropic fillers to be positioned between relatively larger ones, thereby enabling high-density filling of the anisotropic fillers within the binder component and improving thermal conductivity.

[0062] Furthermore, among the above, the anisotropic filler preferably contains a fibrous material. As will be described later, when a thermal conductive layer containing a fibrous material is sliced, the fibrous material tends to fall out, creating irregularities on the surface and reducing adhesion. However, in the present invention, by providing an adhesive layer, the acrylic adhesive layer fills the recesses, so that the adhesion can be sufficiently improved even in a thermal conductive layer containing a fibrous material. In addition, from the viewpoint of improving thermal conductivity, the thermal conductive layer preferably contains a flake-like material in addition to the fibrous material as an anisotropic filler. In this case, the content ratio of the flake-like material to the fibrous material (flak-like material / fibrous material) is, for example, 0.01 or more and 1 or less by mass, preferably 0.02 or more and 0.5 or less, and more preferably 0.1 or more and 0.3 or less.

[0063] Graphite carbon fibers are preferred as the carbon fibers used as the anisotropic filler. Flake-shaped graphite powder is preferred as the flake-shaped carbon powder. It is also preferable to use both graphite carbon fibers and flake-shaped graphite powder as the anisotropic filler. Graphite carbon fibers have graphite crystal planes aligned along the fiber axis, resulting in high thermal conductivity in that direction. Therefore, aligning the fiber axis in a predetermined direction can increase thermal conductivity in a specific direction. Similarly, flake-shaped graphite powder has graphite crystal planes aligned in the in-plane direction of the flake surface, resulting in high thermal conductivity in that in-plane direction. Therefore, aligning the flake surface in a predetermined direction can increase thermal conductivity in a specific direction. Graphite carbon fibers and flake-shaped graphite powder with a high degree of graphitization are preferred.

[0064] As the graphitized carbon materials such as the graphitized carbon fibers and flaky graphite powder mentioned above, the following raw materials can be graphitized. For example, condensed polycyclic hydrocarbon compounds such as naphthalene, PAN (polyacrylonitrile), and condensed heterocyclic compounds such as pitch can be used, but it is particularly preferable to use graphitized mesophase pitch, polyimide, or polybenzazole, which have a high degree of graphitization. For example, by using mesophase pitch, in the spinning process described later, the pitch is oriented in the direction of the fiber axis due to its anisotropy, and graphitized carbon fibers with excellent thermal conductivity in the direction of the fiber axis can be obtained. The manner in which mesophase pitch is used in graphitized carbon fibers is not particularly limited as long as it is spinnable, and mesophase pitch may be used alone or in combination with other raw materials. However, using mesophase pitch alone, that is, graphitized carbon fibers with a mesophase pitch content of 100%, is most preferable in terms of high thermal conductivity, spinnability, and quality stability.

[0065] Graphitized carbon fibers can be obtained by sequentially performing spinning, infusibility, and carbonization processes, followed by pulverization or cutting to a predetermined particle size and then graphitization, or by pulverization or cutting after carbonization and then graphitization. When pulverization or cutting is performed before graphitization, the condensation polymerization and cyclization reactions proceed more easily during the graphitization treatment on the newly exposed surface after pulverization, thereby increasing the degree of graphitization and obtaining graphitized carbon fibers with even greater thermal conductivity. On the other hand, when pulverizing spun carbon fibers after graphitization, the carbon fibers after graphitization are rigid and easy to pulverize, allowing for the acquisition of carbon fiber powder with a relatively narrow fiber length distribution in a short pulverization time.

[0066] As described above, the average fiber length of the graphitized carbon fiber is preferably 10 μm to 300 μm, more preferably 20 μm to 200 μm, and even more preferably 30 μm to 100 μm. Also, as described above, the aspect ratio of the graphitized carbon fiber is greater than 2, and preferably 5 or more. The thermal conductivity of the graphitized carbon fiber is not particularly limited, but the thermal conductivity in the fiber axis direction is preferably 400 W / m·K or more, more preferably 800 W / m·K or more.

[0067] When the thermal conductive layer contains an anisotropic filler, it may or may not be exposed on the surface of the thermal conductive layer (thermal conductive sheet), but exposure is preferable. When the anisotropic filler is exposed, it comes into contact with the adherend, such as a heat-generating element or heat sink, making it easier to lower the thermal resistance. Furthermore, when the anisotropic filler is exposed, it is difficult to improve adhesion to the adherend, but even in such cases, the present invention makes it easier to improve adhesion by providing an adhesive layer.

[0068] (Anisotropic Filler) The thermally conductive filler in the present invention may contain an anisotropic filler, and it is preferable to use the anisotropic filler and the anisotropic filler in combination. The anisotropic filler, in particular, when used in combination with anisotropic filler oriented in one direction such as the thickness direction, interposes in the gaps between the oriented anisotropic fillers, thereby further increasing thermal conductivity. The anisotropic filler is a filler that does not substantially have anisotropy in shape, and is a filler that does not align in a predetermined direction even in environments in which anisotropic fillers align in a predetermined direction, such as under magnetic field line generation or shear force action as described later.

[0069] The non-anisotropic filler has an aspect ratio of 2 or less, preferably 1.5 or less. When used in combination with anisotropic fillers, non-anisotropic fillers with a low aspect ratio are more easily positioned in the gaps of the anisotropic fillers, thus improving thermal conductivity. Furthermore, by setting the aspect ratio to 2 or less, it becomes possible to prevent an increase in the viscosity of the mixed composition described later, thereby enabling high-filling.

[0070] Specific examples of non-anisotropic fillers include metals, metal oxides, metal nitrides, metal hydroxides, carbon materials, and oxides, nitrides, and carbides of non-metals. The shapes of non-anisotropic fillers can be spherical, polyhedral, or amorphous powders. Examples of metals in non-anisotropic fillers include aluminum, copper, and nickel; examples of metal oxides include aluminum oxide (represented by alumina), magnesium oxide, and zinc oxide; and examples of metal nitrides include aluminum nitride. Examples of metal hydroxides include aluminum hydroxide. Furthermore, examples of carbon materials include spheroidal graphite. Examples of oxides, nitrides, and carbides of non-metals include quartz, boron nitride, and silicon carbide. Among these, aluminum oxide and aluminum are preferred because they have high thermal conductivity and are readily available in spherical form. Non-anisotropic fillers may be used individually or in combination of two or more types.

[0071] The average particle size of the non-anisotropic filler is preferably between 0.1 μm and 200 μm, more preferably between 0.3 μm and 100 μm, and more preferably between 0.5 μm and 70 μm. Furthermore, when the non-anisotropic filler is used in combination with the anisotropic filler, the average particle size of the non-anisotropic filler is preferably between 0.1 μm and 50 μm, more preferably between 0.3 μm and 35 μm, and even more preferably between 0.5 μm and 15 μm. By setting the average particle size to 50 μm or less, problems such as disrupting the orientation of the anisotropic filler are less likely to occur even when used in combination with the anisotropic filler. In addition, by setting the average particle size to 0.1 μm or more, the specific surface area of ​​the non-anisotropic filler does not become unnecessarily large, the viscosity of the mixed composition does not increase easily even when a large amount is added, and it becomes easier to fill the mixture with the non-anisotropic filler to a high degree. For example, the non-anisotropic filler may consist of at least two non-anisotropic fillers having different average particle sizes. The average particle size of the non-anisotropic filler can be measured by observation using an electron microscope or the like. More specifically, for example, the particle sizes of 500 or more arbitrary non-anisotropic fillers can be measured using an electron microscope or optical microscope, and D50 can be determined in the same way as for the flake-like filler.

[0072] The content of the non-anisotropic filler is preferably 50 parts by mass or more and 2500 parts by mass or less per 100 parts by mass of polymer matrix, more preferably 100 parts by mass or more and 1500 parts by mass or less, and even more preferably 200 parts by mass or more and 750 parts by mass or less. A content of 50 parts by mass or more allows for good thermal conductivity of the thermal conductive sheet. On the other hand, a content of 1500 parts by mass or less allows the non-anisotropic filler to be appropriately dispersed in the binder component, thereby enhancing thermal conductivity according to the content. Furthermore, it prevents the viscosity of the mixed composition from increasing excessively.

[0073] The ratio of the volume-based filling rate of non-anisotropic filler to the filling rate of anisotropic filler in a thermally conductive sheet is not particularly limited, but is preferably 0.5 to 10, more preferably 0.8 to 3, and preferably 1 to 2. By setting the filling rate ratio within the above range, the non-anisotropic filler is adequately filled between the anisotropic fillers, forming an efficient heat transfer path, and thus further improving the thermal conductivity of the thermally conductive sheet.

[0074] In the thermal conductive layer, the polymer matrix may contain other components as long as they do not impair its function as a thermal conductive layer. Specifically, at least one of the following can be used: dispersants, flame retardants, antioxidants, colorants, and anti-settling agents. Furthermore, when the curable polymer composition is crosslinked or cured as described above, additives such as crosslinking accelerators, curing accelerators, and curing catalysts may be added to promote crosslinking and curing. If the polymer matrix is ​​an organopolysiloxane, a platinum catalyst may be used as the curing catalyst. As for dispersants, there are no particular limitations, but examples include alkoxy group-containing organopolysiloxanes, hydroxyl group-containing organopolysiloxanes, and aromatic group-containing organopolysiloxanes. Examples of aromatic group-containing organopolysiloxanes include organopolysiloxanes having an aromatic structure, preferably a polycyclic aromatic structure such as pyrene or perylene.

[0075] The surface of the thermal conductive sheet (thermal conductive layer) is preferably a cut surface. Having a cut surface on the thermal conductive sheet allows for easier exposure of anisotropic fillers and other materials to the surface, as described above, thereby effectively lowering the thermal resistance. The thermal conductive sheet may have either one of its first and second surfaces 15A and 15B as a cut surface, or both as cut surfaces, but it is preferable that at least the surface on which the adhesive is applied is a cut surface. A cut surface, as described later, is a surface formed by cutting with a shear blade or laser. While cut surfaces often have significant irregularities due to the protrusion or detachment of anisotropic fillers, filling the depressions with adhesive reduces the air layer during use, improving adhesion while simultaneously improving thermal resistance.

[0076] Furthermore, it is preferable that the thermal conductive sheet has a polished surface. Having at least one surface of the thermal conductive sheet polished allows for a more effective reduction in thermal resistance. The thermal conductive sheet may have one polished surface or both surfaces polished, but it is preferable that the surface to which the adhesive is applied is polished, and it is particularly preferable that the surface to which the adhesive is applied is both a cut surface and a polished surface. Since polished surfaces tend to be relatively smooth, this, combined with the application of adhesive, makes it easier to improve adhesion to the substrate.

[0077] The above explanation assumes that an adhesive layer is provided on at least one surface of the thermal conductive sheet. However, as long as an adhesive (adhesive component) is present on at least one surface of the thermal conductive sheet, an adhesive layer is not necessary. For example, instead of providing an adhesive layer, the adhesive (adhesive component) can be incorporated into the thermal conductive layer to provide tackiness to at least one surface of the thermal conductive sheet. In this case, the adhesive can be incorporated into the thermal conductive layer by, for example, blending it into the mixed composition described later. Furthermore, at least one surface of the thermal conductive sheet does not need to be made tacky by an adhesive. For example, if the polymer matrix is ​​rubber, the tackiness of the rubber can provide tackiness to at least one surface of the thermal conductive layer. In this case, the rubber becomes the adhesive component. However, if the surface of the thermal conductive sheet is made tacky by the polymer matrix, it is preferable that the surface is not a cut surface, and is preferably composed of a skin layer described later. At the cut surface, the anisotropic filler is easily exposed or protrudes, making it difficult to provide tackiness with rubber. On the other hand, because the amount (volume %) of anisotropic filler in the skin layer is less than the amount (volume %) of anisotropic filler inside it, the anisotropic filler does not protrude to the surface, making it easier for the polymer matrix to impart adhesive force.

[0078] (Thickness of the thermal conductive sheet) The thickness of the thermal conductive sheet is not particularly limited, and is, for example, about 0.5 mm or less. However, from the viewpoint of suitability for use in semiconductor applications and from the viewpoint of preventing an increase in thermal resistance, it is preferable to make it relatively thin, preferably 0.4 mm or less, more preferably 0.3 mm or less, and even more preferably 0.2 mm or less. Furthermore, although the thickness of the thermal conductive sheet is not particularly limited, for practical purposes it is, for example, 0.01 mm or more, preferably 0.02 mm or more, and more preferably 0.05 mm or more. Note that the thickness of the thermal conductive sheet is the initial thickness measured without applying a load in the thickness direction.

[0079] (E-hardness of thermally conductive sheet) The thermally conductive sheet of the present invention preferably has a Type E hardness (hereinafter also referred to as "E-hardness") of 10 or more and 80 or less as defined in JIS K6253, more preferably 20 or more and 70 or less, and even more preferably 30 or more and 65 or less. If the E-hardness is above the lower limit, it becomes easier to increase the mechanical strength of the thermally conductive sheet. Also, if the E-hardness is below the upper limit, a certain degree of flexibility is imparted to the thermally conductive sheet, and it becomes easier to improve adhesion to the adherend.

[0080] [Method for Manufacturing a Thermally Conductive Sheet] The thermally conductive sheet of the present invention can be manufactured by a method comprising at least the following steps 1 to 3. However, the thermally conductive sheet of the present invention may be manufactured by a method other than the following manufacturing method. Step 1: A step of mixing a curable polymer composition and a thermally conductive filler to obtain a mixed composition. Step 2: A step of curing the mixed composition by heating to obtain a cured product. Step 3: A step of applying an adhesive to the surface of the cured product.

[0081] (Step 1) In Step 1, a mixed composition is preferably obtained by mixing a curable polymer composition and a thermally conductive filler, but it is preferable to further mix a volatile substance into the mixed composition. In addition, other components such as additives may be added to the mixed composition as needed.

[0082] In step 1, the mixing method and order are not particularly limited, as long as the above components can be mixed to obtain a mixed composition. The curable polymer composition, thermally conductive filler, volatile substances added as needed, and other components added as needed can be mixed in any order to obtain the mixed composition. The curable polymer composition may consist of, for example, a main agent and a curing agent (for example, in the case of addition-reaction type silicones, an alkenyl group-containing organopolysiloxane and a hydrogen organopolysiloxane). In such cases, the main agent, curing agent, thermally conductive filler, volatile substances added as needed, and other components can be mixed in any order to obtain the mixed composition. The mixed composition may be in the form of a one-component type or a two-component type consisting of a first agent and a second agent. In the two-component type, the first agent and the second agent are mixed at the time of use to obtain the mixed composition.

[0083] (Volatile Substances) The volatile substances used in this manufacturing method may be any components that volatilize in step 2, which will be described later. The volatile substances volatilize due to heating during curing, which allows for a higher proportion of the thermal conductive filler in the thermal conductive sheet. In addition, the viscosity of the mixed composition decreases due to the presence of volatile substances. This makes it easier to increase the amount of thermal conductive filler, and furthermore, it becomes easier to orient the anisotropic filler in a predetermined direction by magnetic field orientation, which will be described later. Moreover, as the volatile substances volatilize, many fine bubbles are formed in the cured product, which makes it easier for the adhesive to penetrate into the thermal conductive layer in step 3, which will be described later.

[0084] Furthermore, the volatile substance is preferably a compatible substance that is compatible with or dissolves in the curable polymer composition. When the volatile substance is compatible, the curable polymer composition and the volatile substance can be mixed uniformly, making it easier to reduce viscosity or increase the amount of thermally conductive filler. Moreover, the bubbles formed by the volatilization of the volatile substance can be made fine and uniform.

[0085] The volatile substance is preferably a substance that is liquid at room temperature (25°C) and 1 atmosphere. Examples of volatile substances include alkoxysilane compounds, hydrocarbon solvents, and alkoxysiloxane compounds. These compounds can increase the solubility or compatibility with the curable polymer composition, making it easier to reduce the viscosity of the mixed composition or to increase the amount of thermally conductive filler. In addition, it is easier to make the bubbles formed by the volatilization of the volatile substance fine and uniform. The volatile substance may be used alone or in combination of two or more types.

[0086] It is preferable to use an alkoxysilane compound as the volatile substance. By using an alkoxysilane compound, the surface of the heat-conductive sheet obtained by curing is free from roughness and other defects, resulting in a good appearance. The alkoxysilane compound used as the volatile substance is a compound having a structure in which one to three of the four bonds of the silicon atom (Si) are bonded to an alkoxy group, and the remaining bond is bonded to an organic substituent. By having an alkoxy group and an organic substituent, the alkoxysilane compound can improve compatibility with curable polymer compositions, particularly curable polymer compositions composed of organopolysiloxanes. Examples of alkoxy groups in alkoxysilane compounds include methoxy, ethoxy, protoxy, butoxy, pentoxy, and hexatoxy groups. The alkoxysilane compound may be contained in the curable polymer composition as a dimer.

[0087] Among alkoxysilane compounds, those having at least one of a methoxy group and an ethoxy group are preferred from the viewpoint of availability. The number of alkoxy groups in the alkoxysilane compound is preferably 2 or 3, and more preferably 3, from the viewpoint of compatibility and solubility with the curable polymer composition. Specifically, the alkoxysilane compound is preferably at least one selected from trimethoxysilane compounds, triethoxysilane compounds, dimethoxysilane compounds, and diethoxysilane compounds.

[0088] Examples of functional groups included in the organic substituents of alkoxysilane compounds include acryloyl groups, alkyl groups, carboxyl groups, vinyl groups, methacrylic groups, aromatic groups, amino groups, isocyanate groups, isocyanurate groups, epoxy groups, hydroxyl groups, and mercapto groups. When using a platinum catalyst as a curing catalyst for a curable polymer composition composed of organopolysiloxanes, it is preferable to select and use an alkoxysilane compound that does not easily affect the curing reaction of the organopolysiloxane. Specifically, when using an addition reaction type organopolysiloxane utilizing a platinum catalyst, it is preferable that the organic substituent of the alkoxysilane compound does not contain amino groups, isocyanate groups, isocyanurate groups, hydroxyl groups, or mercapto groups.

[0089] From the viewpoint of compatibility with curable polymer compositions composed of organopolysiloxanes, alkoxysilane compounds preferably include alkylalkoxysilane compounds having an alkyl group bonded to a silicon atom, i.e., alkoxysilane compounds having an alkyl group as an organic substituent. Therefore, dialkyldialkoxysilane compounds and alkyltrialkoxysilane compounds are preferred, and alkyltrialkoxysilane compounds are preferred among them. The number of carbon atoms in the alkyl group bonded to the silicon atom is preferably 1 to 16. Furthermore, in trialkoxysilane compounds such as trimethoxysilane compounds and triethoxysilane compounds, the number of carbon atoms in the alkyl group is preferably 6 or more, more preferably 8 or more, preferably 12 or less, and more preferably 10 or less. On the other hand, in dialkoxysilane compounds such as dimethoxysilane compounds and triethoxysilane compounds, the number of carbon atoms in the alkyl group may be 1 or more, preferably 10 or less, more preferably 6 or less, and more preferably 4 or less.

[0090] Examples of alkyl group-containing alkoxysilane compounds include methyltrimethoxysilane, dimethyldimethoxysilane, diethyldimethoxysilane, trimethylmethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, ethyltrimethoxysilane, n-propyltrimethoxysilane, di-n-propyldimethoxysilane, di-n-propyldiethoxysilane, isobutyltrimethoxysilane, isobutyltriethoxysilane, n-hexyltrimethoxysilane, n-hexyltriethoxysilane, methylcyclohexyldimethoxysilane, methylcyclohexyldiethoxysilane, n-octyltrimethoxysilane, n-octyltriethoxysilane, n-decyltrimethoxysilane, and n-decyltriethoxysilane. Among alkyl group-containing alkoxysilane compounds, n-decyltrimethoxysilane and n-octyltriethoxysilane are even more preferred from the viewpoint of compatibility with organopolysiloxanes constituting curable polymer compositions.

[0091] Alkoxysiloxane compounds used as volatile substances have two or more siloxane bonds and a structure in which an alkoxy group is bonded to at least one silicon atom. Alkoxysiloxane compounds have a structure in which an organic substituent is bonded to at least one silicon atom among the silicon atoms constituting the siloxane bond. By having an alkoxy group and an organic substituent, alkoxysiloxane compounds can improve compatibility with organopolysiloxanes constituting curable polymer compositions. Examples of alkoxy groups and organic substituents of alkoxysiloxane compounds are those exemplified in the description of alkoxysilane compounds above, and from the viewpoint of compatibility with organopolysiloxanes constituting curable polymer compositions, it is preferable to have at least an alkyl group.

[0092] Examples of alkoxysiloxane compounds include methyl methoxysiloxane oligomers, methylphenyl methoxysiloxane oligomers, methyl epoxy methoxysiloxane oligomers, methyl mercaptomethoxysiloxane oligomers, and methyl acryloyl methoxysiloxane oligomers. One or more alkoxysiloxane compounds can be used.

[0093] Aromatic hydrocarbon solvents are used as volatile substances. Among these, aromatic hydrocarbon solvents are preferred from the viewpoint of compatibility with curable polymer compositions. Examples of aromatic hydrocarbon solvents include those having about 6 to 10 carbon atoms, such as toluene, xylene, mesitylene, ethylbenzene, propylbenzene, butylbenzene, and t-butylbenzene, with toluene and xylene being preferred.

[0094] In the mixed composition, the content of volatile substances per 100 parts by mass of the curable polymer composition is preferably 6 parts by mass or more and 60 parts by mass or less. A content of 6 parts by mass or more makes it easier to exert the effects of the volatile substances, for example, allowing for the formation of an appropriate amount of fine bubbles in the polymer matrix. Furthermore, a content of 60 parts by mass or less allows for obtaining effects commensurate with the amount of volatile substances used. From these viewpoints, the above content of volatile substances is more preferably 8 parts by mass or more and 50 parts by mass or less, and even more preferably 10 parts by mass or more and 35 parts by mass or less. It is preferable that some or all of the volatile substances volatilize upon heating in step 2. Therefore, volatile substances do not necessarily have to be contained in the thermal conductive sheet, but they may be contained in the thermal conductive sheet in an amount less than that contained in the mixed composition.

[0095] Further details regarding components other than volatile substances in the mixed composition (i.e., curable polymer composition, thermally conductive filler, and other additives) are as described above. The content of thermally conductive filler in the mixed composition is also as described above. However, while the above descriptions indicate the content of each component based on 100 parts by mass of the polymer matrix, in the case of the mixed composition, the content should be based on 100 parts by mass of the curable polymer composition.

[0096] (Step 2) Step 2 is a step of curing the mixed composition by heating. The temperature at which the mixed composition is heated is not particularly limited as long as the curable polymer composition can be cured by heating, and it is sufficient to be higher than room temperature (25°C), but it is preferable to heat it at a temperature of 50°C or higher, more preferably 70°C or higher. The heating temperature is not particularly limited, but it is sufficient to be a temperature at which the heat conductive layer and the mixed composition do not deteriorate due to heat, for example, 200°C or lower, preferably 180°C or lower, more preferably 160°C or lower. The heating may be carried out in one stage or in two or more stages. If it is carried out in two or more stages, it is sufficient that the heating temperature is within the above range in at least one stage, but it is preferable that the heating temperature is within the above range in all stages, and it is preferable that at least the first stage of heating is carried out at a temperature lower than the boiling point of the volatile compound. The total heating time is, for example, 10 minutes or more and 24 hours or less. When the process is carried out in two or more stages, for example, the mixed composition may be partially cured in the first stage (primary curing), and then fully cured by heating in the second and subsequent stages (secondary curing). Alternatively, the curing may be completely cured in the primary curing stage, and the heating in the second and subsequent stages may not result in further curing.

[0097] As described later, when slicing a molded body obtained from a mixed composition to form a sheet-like molded body, it is also preferable to perform a first stage of heating before slicing for primary hardening, and then perform a second and subsequent stage of heating (secondary hardening) after slicing. Heating after slicing makes it easier for volatile substances to volatilize during the second and subsequent stages of heating. When hardening in two or more stages, the first stage (primary hardening) should be performed at a temperature of, for example, 50°C to 120°C, preferably 60°C to 100°C, and more preferably 70°C to 90°C. Furthermore, the heating in the second and subsequent stages (secondary hardening) should be performed at a higher temperature than the primary hardening, for example, 100°C to 200°C, preferably 120°C to 180°C, and more preferably 140°C to 160°C. The heating time in the first stage can be, for example, 5 minutes to 20 hours, and preferably 30 minutes to 12 hours. Furthermore, the heating time in the second and subsequent stages is, for example, about 10 minutes to 15 hours, preferably about 1 hour to 10 hours. By heating the molded body obtained from the mixed composition at a relatively low temperature in the first stage as described above, the volatile compounds are less likely to foam and produce large bubbles, and the molded body can be hardened so that the volatile compounds remain inside the molded body. Also, if the molded body is sliced ​​and then heated at a relatively high temperature in the second stage, the molded body is hardened, so even at high temperatures, it does not foam and produce large bubbles, and the spaces where the volatile compounds were present become fine bubbles. The size of the bubbles is, for example, 1 μm or less, preferably 0.2 μm or less. Furthermore, there is no particular lower limit to the size of the bubbles, but for example, it is 0.001 μm or more.

[0098] In step 2, the mixed composition may be molded into a predetermined shape such as a block or a sheet, and then heated to cure it. In step 2, if the mixed composition contains an anisotropic filler as a thermally conductive filler, the anisotropic filler may be oriented in one direction and then heated to cure it. The anisotropic filler can be oriented by the magnetic field orientation method or the flow orientation method, but it is preferable to align it by the magnetic field orientation method.

[0099] In the magnetic field orientation method, the mixed composition is injected into a mold or the like and then placed in a magnetic field to orient the anisotropic filler along the magnetic field. The oriented molded article is then obtained by curing the curable polymer composition. The curing of the mixed composition is carried out under the heating conditions described above. The oriented molded article is preferably in block form, but it may also be in sheet form. If it is in sheet form, the adhesive can be applied directly in step 3 without slicing the oriented molded article. On the other hand, if it is in block form, the orientation of the anisotropic filler can be enhanced.

[0100] In the magnetic field orientation method, a release film may be placed inside the mold in the area that comes into contact with the mixed composition. For example, a resin film with good release properties or a resin film with one side treated with a release agent can be used as the release film. Using a release film makes it easier to remove the oriented molded body from the mold. Also, when orientation and curing are performed in the mold, the surface of the resulting oriented molded body becomes a skin layer with a lower filling ratio of anisotropic filler than other parts. Therefore, if the sheet-like oriented molded body (sheet-like molded body) obtained by orientation and curing in the mold is applied directly to the third step, the thermal conductive sheet will have skin layers on both surfaces. Furthermore, if the sheet-like oriented molded body obtained by orientation and curing in the mold is cut along the surface direction (for example, divided into two parts), a thermal conductive sheet is obtained in which one surface is a skin layer and the other surface is the cut surface.

[0101] In the magnetic field orientation method, the viscosity of the mixed composition used is preferably between 10 Pa·s and 300 Pa·s in order to enable magnetic field orientation. A viscosity of 10 Pa·s or higher prevents the thermally conductive filler from settling. A viscosity of 300 Pa·s or lower ensures good fluidity, allowing the anisotropic filler to be properly oriented by the magnetic field without causing problems such as excessive orientation time. Viscosity is measured using a rotational viscometer (Brookfield viscometer DV-E, spindle SC4-14) at 25°C and a rotational speed of 10 rpm. However, when using a thermally conductive filler that is less prone to settling, or when combining it with additives such as settling inhibitors, the viscosity of the mixed composition may be less than 10 Pa·s.

[0102] In the magnetic field orientation method, examples of magnetic field source for applying magnetic field lines include superconducting magnets, permanent magnets, and electromagnets, but superconducting magnets are preferred because they can generate a magnetic field with a high magnetic flux density. The magnetic flux density of the magnetic field generated from these magnetic field source sources is preferably 1 to 30 Tesla. Setting the magnetic flux density to 1 Tesla or higher makes it possible to easily orient the anisotropic filler material made of carbon material or the like. Setting it to 30 Tesla or lower makes practical manufacturing possible.

[0103] In the flow orientation method, a shear force is applied to the mixed composition to produce a primary sheet in which the anisotropic filler is oriented along the planar direction. More specifically, in the flow orientation method, first, the mixed composition prepared in step 1 is flattened and stretched while applying a shear force to form a sheet (primary sheet). By applying a shear force, the anisotropic filler can be oriented in the shear direction. As a means of forming the sheet, for example, the mixed composition is coated onto a base film by a coating applicator such as a bar coater or doctor blade, or by extrusion molding or discharge from a nozzle, and then dried, semi-cured, or fully cured as needed. The thickness of the primary sheet is preferably 50 μm to 5000 μm. In the primary sheet, the anisotropic filler is oriented in one direction along the planar direction of the sheet. The mixed composition used in the flow orientation method has a relatively high viscosity so that a shear force is applied when stretching it into a sheet. Specifically, the viscosity of the mixed composition is preferably 3 Pa·s to 500 Pa·s.

[0104] The primary sheet may be used as a thermally conductive sheet without forming a block, as described later. Alternatively, multiple primary sheets may be stacked so that their orientation is the same, and then bonded together by heat pressing or the like, while being cured by heating as needed, to form a laminated block (a block-shaped oriented molded body). When forming a laminated block, at least one of the overlapping surfaces of the primary sheets may be irradiated with vacuum ultraviolet light before stacking the primary sheets. When the primary sheets are stacked with the surface irradiated with vacuum ultraviolet light as a buffer, the primary sheets can be strongly bonded together. When irradiating with vacuum ultraviolet light, the mixed composition may be fully cured when the primary sheets are made, and there is no need to cure it by heating or the like when stacking the primary sheets to form a laminated block. In the flow orientation method as well, the curing of the mixed composition should be carried out under the heating conditions described above.

[0105] As described above, when forming a block-shaped oriented molded body, it is preferable to cut the obtained oriented molded body perpendicular to the direction in which the anisotropic filler is oriented, for example, by slicing, to form a sheet-like molded body. Slicing can be done with a shear blade or laser, for example. When the sheet-like molded body is cut by slicing, some of the fibrous filler may be exposed from the matrix at each surface, which is the cut surface. Most of the exposed fibrous filler will remain oriented in the thickness direction without collapsing. However, in step 2, when the oriented molded body is cut by slicing, the fibrous filler contained in the oriented molded body may be cut to the extent that it does not impair the effects of the present invention.

[0106] The sheet-like molded body obtained by cutting may be directly coated with adhesive in step 3 described later, but it may also be subjected to further processing. For example, each surface, which is the cut surface, may be polished. Alternatively, as described above, secondary hardening may be performed. Note that secondary hardening may be performed after polishing or before polishing. Polishing the sheet-like molded body improves the surface condition of the sheet-like molded body, making it easier to further reduce the thermal resistance value. Polishing the sheet-like molded body makes it possible to smooth the sheet surface while exposing a certain amount of anisotropic filler material, such as fibrous filler, on the surface. It is also possible to make the fibrous filler material lie flat. Therefore, it becomes easier to make the surface of the thermally conductive sheet adhere to other components, and it becomes easier to make the sheet surface covered with fibrous filler material over a certain area or more, making it easier to reduce the thermal resistance value.

[0107] Polishing is preferably performed by polishing at least one surface of the obtained sheet-like molded body, but it is preferable to polish both sides of the sheet-like molded body. Surface polishing can be performed using, for example, abrasive paper, abrasive film, abrasive cloth, or abrasive belt. The properties of the abrasive paper are preferably such that the average particle size (D50) of the abrasive grains it contains is 0.1 μm or more and 100 μm or less, and more preferably 1 μm or more and 60 μm or less. Furthermore, the grit size of the abrasive grains in the abrasive paper is preferably #120 to #20000, preferably #300 to #15000, and more preferably #320 to #4000.

[0108] The polishing method can involve polishing the surface of the sheet-like molded body by continuously contacting it with abrasive paper in the same linear direction, polishing by moving back and forth over a certain distance, polishing by rotating in the same direction, or polishing by contacting it in various directions. The degree of polishing can be determined by observing the surface condition, for example, but in the case of reciprocating polishing, it is preferable to have 1 to 300 reciprocations, more preferably 2 to 200 reciprocations, and even more preferably 3 to 100 reciprocations. Polishing the surface of the sheet-like molded body may be performed in two polishing steps. For example, after the first polishing using abrasive paper with a large average particle size of abrasive grains, a second polishing may be performed using abrasive paper with a smaller average particle size of abrasive grains than that used in the first polishing.

[0109] (Step 3) In Step 3, an adhesive is applied to the surface of the cured product (thermal conductive layer), such as the sheet-like molded body obtained in Step 2, as described above. In this manufacturing method, it is preferable to impregnate the thermal conductive layer with the adhesive, but it is also preferable that the adhesive impregnates into the thermal conductive layer simply by applying it. The adhesive may be diluted with a diluent and applied to the surface of the sheet-like molded body as a diluted adhesive solution. Diluting the adhesive with a diluent makes it easier for the adhesive to impregnate the thermal conductive layer. The diluent is not particularly limited as long as it is a liquid at 25°C and 1 atm, is soluble or compatible with the adhesive, and volatilizes upon drying as described later, but organic solvents are preferably used.

[0110] The organic solvents used are not particularly limited, but include ketone compounds such as acetone, methyl ethyl ketone, and cyclohexanone; aromatic hydrocarbon compounds such as toluene, xylene, and tetramethylbenzene; glycol ether compounds such as cellosolve, methyl cellosolve, butyl cellosolve, carbitol, methyl carbitol, butyl carbitol, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol diethyl ether, tripropylene glycol monomethyl ether, and polyethylene glycol monoethyl ether; ester compounds such as ethyl acetate, butyl acetate, butyl lactate, cellosolve acetate, butyl cellosolve acetate, carbitol acetate, butyl carbitol acetate, propylene glycol monomethyl ether acetate, dipropylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, and propylene glycol monopropyl ether acetate; and aliphatic hydrocarbon compounds such as hexane, octane, and decane. Furthermore, from the viewpoint of properly impregnating the adhesive into the heat-conducting layer by spray coating as described later, it is preferable to include one of the following organic solvents as an organic solvent: cellosolve acetate, butyl cellosolve acetate, carbitol acetate, butyl carbitol acetate, propylene glycol monomethyl ether acetate, dipropylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, propylene glycol monopropyl ether acetate, or polyethylene glycol monoethyl ether, which do not have an excessively fast evaporation rate. In addition, it is preferable to further include an organic solvent with a lower boiling point than the above organic solvents. Specifically, examples include methyl ethyl ketone, methyl isobutyl ketone, hexane, ethyl acetate, butyl acetate, and toluene.

[0111] The dilution concentration with the diluent is not particularly limited, but it is preferable to adjust it so that the solid content concentration of the adhesive is, for example, 5% by mass or more and 50% by mass or less, preferably 8% by mass or more and 35% by mass or less, and more preferably 10% by mass or more and 25% by mass or less. Setting the solid content concentration to 5% by mass or more prevents excessive heating during drying and allows a predetermined amount of adhesive to be properly impregnated into the heat conduction layer along with the organic solvent. Setting it to 50% by mass or less prevents the amount of material used from becoming excessively large and allows the viscosity to be adjusted to facilitate impregnation, thus enabling the adhesive to be properly impregnated into the heat conduction layer. The amount of adhesive impregnated into the heat conduction layer can be adjusted by the viscosity, solid content concentration, type of solvent, etc. For example, if you want to increase the amount of adhesive impregnated, you should adjust the viscosity to be low and the solid content concentration to be high. If you want to decrease the amount of adhesive material impregnated, you should use a high viscosity and a low solid content concentration.

[0112] The method of applying the adhesive is not particularly limited, and any known application method may be used, but spray application is preferred. By spray application, the amount applied will not be excessively large, and the adhesive will be more easily absorbed into the heat conductive layer. Furthermore, by spray application and controlling the amount applied, it is possible to create areas on the surface of the heat conductive sheet with and without the adhesive layer. When spray application is used, it is preferable to spray an adhesive containing a fast-drying organic solvent such as ethyl acetate and a slow-drying organic solvent such as polyethylene glycol monoethyl ether or propylene glycol monomethyl ether acetate. More specifically, by including a slow-drying organic solvent, the organic solvent does not evaporate too much when the adhesive discharged from the spray adheres to the surface of the heat conductive layer, thereby making it easier for the adhesive to penetrate into the heat conductive layer. On the other hand, by including a fast-drying solvent, it is preferable to adjust the viscosity to one suitable for spraying.

[0113] The applied adhesive is then dried to allow the diluent to volatilize. The drying temperature should be such that the reaction of the reactive double bonds in the adhesive does not substantially proceed, for example, 80°C or lower, preferably 70°C or lower, and more preferably 60°C or lower. Furthermore, the drying temperature is not particularly limited in its lower limit and may be at room temperature, for example, 20°C or higher, but from the viewpoint of shortening the drying time, 30°C or higher is preferred, 40°C or higher is more preferred, and 45°C or higher is even more preferred. The drying time should be such that substantially all of the diluent contained in the applied adhesive volatilizes, for example, 1 minute or more, preferably 2 minutes or more, and more preferably 3 minutes or more. Furthermore, the drying time is not particularly limited, but from the viewpoint of workability, a shorter time is preferable, for example, 24 hours or less, preferably 3 hours or less, and more preferably 1 hour or less. From the viewpoint of efficiently volatilizing the diluent, drying may be performed under reduced pressure using a vacuum pump.

[0114] The above manufacturing method is merely an example, and the thermal conductive sheet does not need to be manufactured using the above method. For example, it may be manufactured by a method that omits step 3. In that case, the thermal conductive sheet does not need to have an adhesive layer; it is sufficient that the adhesive (adhesive component) is contained within the thermal conductive layer. In this case, the adhesive (adhesive component) may be incorporated into the mixed composition in step 1.

[0115] Furthermore, in this manufacturing method, a thermal conductive layer may be obtained by preparing at least a first and a second sheet, each containing a polymer matrix and a thermally conductive filler, and laminating the first and second sheets so that one surface of the first sheet and one surface of the second sheet are in contact. The first and second sheets may be obtained by the same manufacturing method as the thermal conductive layer (thermally conductive sheet) described above, for example, a sheet-like molded body obtained in step 2 may be used as the first and second sheets. However, the first sheet is preferably a sheet-like molded body obtained by cutting an oriented molded body by slicing or the like. In this case, it is preferable that anisotropic filler such as a fibrous filler is exposed on both surfaces of the first sheet. On the other hand, for the second sheet, the orientation of the anisotropic filler by the magnetic field described above and the hardening may be performed in a mold in which a hollow portion corresponding to the sheet shape is partitioned inside. When orientation and hardening are performed in such a mold, both surfaces of the resulting sheet-like oriented molded body become a skin layer in which the filling ratio of anisotropic filler is lower than in other parts. Furthermore, the sheet-like oriented molded body may be used as a second sheet. In the magnetic field molded body described above, the skin layer does not contain anisotropic filler, or the amount of anisotropic filler is reduced, and both surfaces of the second sheet are surfaces in which the anisotropic filler does not protrude. In addition, the skin layer becomes adhesive by using rubber or the like in the polymer matrix. Therefore, the second sheet is a sheet in which both surfaces are adhesive.

[0116] The first and second sheets described above can be assembled by overlapping them so that one surface of the second sheet, on which the skin layer is formed, is in contact with one surface of the first sheet, and then bonding them together to obtain a thermal conductive layer. As a result, the thermal conductive layer is formed by laminating the two sheets via an adhesive skin layer, thus obtaining a thermal conductive layer with high adhesive strength between the first and second sheets. In this way, one surface of the resulting thermal conductive layer becomes a surface where the anisotropic filler is exposed and is substantially non-adhesive, while the other surface becomes an adhesive surface with adhesive properties due to the polymer matrix.

[0117] In this case, one surface may be coated with adhesive in the third step described above to become an adhesive surface. On the other hand, the other surface may be used as an adhesive surface without the application of adhesive. Generally, when tackiness is provided by the rubber constituting the polymer matrix, the tack value provided by the adhesive is higher than the tack value provided by the rubber. For this reason, one surface with adhesive may be designated as the second surface 15B, and the other surface with tackiness provided by the rubber may be designated as the first surface 15A. The first and second sheets may be cured products obtained by hardening by heating, but they may also be semi-cured products. In the case of semi-cured products, the first and second sheets may be further heated after lamination to harden them.

[0118] <Carrier Film> The carrier film 11 preferably has a base film 12 and a release film 13 laminated on the base film 12, as shown in Figure 2. In this case, it is preferable to use an adhesive film as the base film 12. As the adhesive film, it is fine to use one with relatively low adhesive strength, also known as a so-called low-tack film. As the adhesive film, it is fine to use one in which the surface on the thermal conductive sheet 15 side is adhesive. The adhesive film may have an adhesive layer provided on the substrate and on one side of the substrate, and it is preferable to have the adhesive layer on the surface on the thermal conductive sheet 15 side. By making the base film 12 adhesive, it can be made to adhere to the release film 13 which has release properties to a certain extent. As a result, the thermal conductive sheet 15 has peelability from both the carrier film 11 and the cover film 20, and as described above, the cover film 20 and the carrier film 11 seal the thermal conductive sheet 15, making it easier to block out the atmosphere. Blocking out the atmosphere can suppress deterioration of the thermal conductive sheet 15 over time (such as a decrease in adhesive strength and hardening of the thermal conductive sheet).

[0119] Any known resin film may be used as the substrate for the slightly tacky film. The resin constituting the resin film is not particularly limited, and various resins such as polyethylene, polypropylene and other polyolefin resins, cyclic polyolefin resins, ethylene-vinyl acetate copolymer resins, polyester resins such as polyethylene terephthalate (PET), polyurethane resins, polyacrylic resins, polystyrene resins, polyimide resins, polyetherimide resins, and polyethernaphthalate resins can be used. These resins may be used individually or in combination of two or more. The tacky layer may be formed with a known adhesive, and specific examples of adhesives include acrylic adhesives, rubber adhesives, urethane adhesives, and silicone adhesives. The adhesive constituting the tacky layer should be appropriately selected so that the peeling force (third peeling force) from the cover film 20 falls within the desired range described above. The thickness of the base film 12 is not particularly limited, but is, for example, 50 to 150 μm, preferably 75 to 125 μm.

[0120] As the release film 13 in the carrier film 11, any known release film may be used. Preferably, the release film has a base material and a release agent layer on at least one side of the base material. If a release agent layer is provided, it is sufficient that the release agent layer be provided on at least the surface of the release film 13 that faces the thermal conductive sheet 15. By providing a release agent layer on the surface of the release film 13 that faces the thermal conductive sheet 15, it becomes easier to adjust the peeling force P1 between the carrier film 11 and each thermal conductive sheet 15.

[0121] A resin film is preferred as the base material, and the resin constituting the resin film is not particularly limited, but the resins listed above for the resin film of the base film can be appropriately selected and used, but among them, polyester resins such as PET are preferred. The resin constituting the base material of the base film may be used alone or two or more may be used in combination. The release agent layer is formed by a release agent. Examples of release agents include long-chain alkyl release agents, silicone release agents, and fluorine release agents. Among these, silicone release agents are preferred from the viewpoint of being able to lower the peel force P2. Furthermore, the release film 13 does not need to have a release agent layer on the surface facing the thermal conductive sheet 15, as long as the peel force P1 can be adjusted within a predetermined range. The thickness of the release film 13 is not particularly limited, but for example it is 10 to 100 μm, preferably 20 to 80 μm.

[0122] Furthermore, as shown in Figure 3, the carrier film 11 is not composed of a laminate of the base film 12 and the release film 13, but is composed of the base film 12 alone, and a plurality of thermal conductive sheets 15 may be directly laminated onto the base film 12. In this case, the base film 12 may be the adhesive film described above, but other materials may be used, for example, it may be composed of a resin film without an adhesive layer, or it may be composed of a release film alone. The release film alone used as the carrier film 11 may be a known release film as described above for the release film 13, and it is preferable that it has a base material and a release agent layer on at least one side of the base material. In this case, the release agent layer may be provided on the side facing the thermal conductive sheet 15. If the carrier film 11 is composed of the base film 12 and the base film 12 is not an adhesive film, the cover film 20 does not need to be adhered to the base film 12 in the portion where the thermal conductive sheet 15 is not provided. Similarly, even when a release film 13 is provided on the carrier film 11 as shown in Figure 2, the base film 12 does not have to be made of an adhesive film, and in that case as well, the cover film 20 does not have to be adhered to the base film 12 in the portion where the thermal conductive sheet 15 is not provided. The overall thickness of the carrier film 11 (i.e., the total thickness of the release film 13 and the base film 12 when a release film 13 is provided) is, for example, 50 to 200 μm, preferably 90 to 150 μm.

[0123] The normal peel force Q1 of the carrier film 11 is preferably 5 mN / 25 mm or more and 30 mN / 25 mm or less, more preferably 8 mN / 25 mm or more and 25 mN / 25 mm or less, and even more preferably 10 mN / 25 mm or more and 20 mN / 25 mm or less. By setting the normal peel force Q1 within the above predetermined range, it becomes easier to adjust the peel force P2 within the above predetermined range. The normal peel force Q1 can be appropriately adjusted depending on the material and surface condition of the carrier film. Note that for the carrier film 11, the normal peel force of the film constituting the surface that is adhered to the thermal conductive sheet should be measured. Therefore, if a release film 13 is provided, the normal peel force of the release film 13 should be measured, and if a release film 13 is not provided and the thermal conductive sheet 15 is directly laminated to the base film 12, the normal peel force of the base film 12 should be measured. Furthermore, in this specification, the normal peeling forces Q1 and Q2 are the peeling forces when a target film (for example, a cover film or carrier film) is attached to a predetermined adhesive tape by the method described in the examples, and the attached target film is peeled off the adhesive tape.

[0124] <Cover Film> The cover film 20 is usually arranged to cover a plurality of thermal conductive sheets 15. The cover film 20 is preferably a release film. The cover film 20 should be appropriately selected so that the peel force P2 to the plurality of thermal conductive sheets 15 and the peel force P3 to the carrier film 11 are the predetermined values ​​described above. A known release film can be used for the cover film 20. An example of a release film used for the cover film 20 is one which comprises a base material and a release agent layer on at least one side of the base material. If a release agent layer is provided, the release agent layer should be provided on at least the side of the cover film 20 that faces the thermal conductive sheets 15. By providing a release agent layer on the surface of the cover film 20 that faces the thermal conductive sheets 15, the peel force P2 can be easily reduced.

[0125] The cover film 20 can be a release film other than one having a release agent layer. For example, release papers such as paraffin paper, silicone resin-coated paper, or release-treated glassine paper may be used, as well as wax paper, cooking sheets, baking sheets, etc. Silicone rubber sheets, fluororubber sheets, etc. may also be used, or a resin film without a release agent layer may be used alone.

[0126] Preferably, the surface roughness Sa of the cover film 20 in contact with the second surface 15B of the thermal conductive sheet 15 is 5 μm or more. When the surface roughness Sa is 5 μm or more, the normal peel force Q2 and peel force P2 described later are easier to lower, and problems are less likely to occur when peeling the cover film 20 from the thermal conductive sheet 15. The surface roughness Sa is more preferably 5.5 μm or more, and even more preferably 6.0 μm or more. The surface roughness Sa of the cover film 20 can be made to be above a certain level by creating irregularities on the surface in contact with the second surface 15B. The irregularities are not particularly limited, but for example, they may be formed by embossing. The above surface roughness Sa is not particularly limited, but is preferably 10.0 μm or less, and more preferably 8.0 μm or less. By keeping the surface roughness Sa below a certain level, the cover film 20 adheres more easily to the carrier film 11, making it easier to ensure airtightness between the cover film 20 and the carrier film 11. The surface roughness Sa can be measured using a shape analysis laser microscope, for example, the VK-X160 laser microscope manufactured by Keyence Corporation. Specifically, a 10x lens is used for the laser microscope, the object to be measured is placed on the stage, and the measurement is performed in shape measurement mode. Subsequently, the obtained measurement results are opened in an analysis application, surface tilt correction (automatic) is performed, and then the surface roughness is measured. For surface roughness measurement, the entire area of ​​the image (1401.705 μm × 1051.279 μm) is specified, in accordance with JIS B0601:2001, and no cut filter is used. The surface roughness is measured at three random locations within the object to be measured, and the average value of the surface roughness obtained from each location is adopted.

[0127] The normal peel force Q2 of the cover film 20 is preferably 5 mN / 25 mm or more and 30 mN / 25 mm or less, more preferably 8 mN / 25 mm or more and 25 mN / 25 mm or less, and even more preferably 10 mN / 25 mm or more and 20 mN / 25 mm or less. By setting the normal peel force Q2 within a predetermined range, it becomes easier to adjust the peel force P2 within the above predetermined range. The normal peel force Q2 can be appropriately adjusted depending on the material and surface condition of the cover film, and in particular, if the surface roughness Sa is above a certain level, the normal peel force Q2 can be lowered. The thickness of the cover film 20 is not particularly limited, but for example it is 10 to 100 μm, preferably 20 to 75 μm. In this specification, the terms "sheet" and "film" are not clearly distinguished, and the term "sheet" used herein includes what is generally called "film," and the term "film" also includes what is generally called "sheet."

[0128] <Method for Manufacturing a Thermal Conductive Sheet Holder> The thermal conductive sheet holder of the present invention is preferably manufactured by arranging a plurality of pre-prepared thermal conductive sheets so as to be sandwiched between a carrier film and a cover film. More specifically, the thermal conductive sheets manufactured by the above manufacturing method are made into individual pieces, the plurality of individual thermal conductive sheets are placed on a carrier film or a base film constituting the carrier film, and then a cover film is further laminated on top of the plurality of thermal conductive sheets so as to cover the plurality of thermal conductive sheets.

[0129] The method for separating the thermal conductive sheet into individual pieces is not particularly limited and may be done by slicing with a cutter or by punching, but punching is preferred. When punching is performed, in order to perform the punching properly, it is preferable that the thermal conductive sheet is sandwiched between release films and the punching is performed with the release film laminated on both sides of the thermal conductive sheet. The release film used here may be appropriately selected from those described as release films used for carrier films, but a release film in which a release agent layer is provided on at least one side is preferred. The release film with the release agent layer should be laminated onto the thermal conductive sheet so that the side with the release agent layer is in contact with the thermal conductive sheet. The thermal conductive sheet with release films laminated on both sides should be punched together with the release films to separate them into individual pieces.

[0130] As described above, the heat conductive sheets, which have been separated into individual pieces along with the release film, can be attached to the base film with the release film still laminated on one side after one side of the release film has been peeled off and removed. At this time, the side on which the release film is provided is attached so that it is in contact with the base film. As a result, the release film and the heat conductive sheet are laminated on the base film in this order, and as shown in Figure 2, the heat conductive sheet 15 is attached to the carrier film 11 which comprises the base film 12 and the release film 13. Here, the method for attaching the separated heat conductive sheets to the base film is not particularly limited, but it is preferable to use a pick-and-place device or the like to pick up the separated heat conductive sheets and place them on the base film.

[0131] In the above example, the thermal conductive sheet 15 was placed on the base film 12, which constitutes part of the carrier film 11, while laminated on the release film 13. However, it is not necessary for the thermal conductive sheet 15 to be placed on the base film 12, which constitutes part of the carrier film 11. For example, the thermal conductive sheet 15, which has been cut into individual pieces by slicing or the like, may be placed on the base film 12 that constitutes the carrier film 11 without being laminated on the release film. Alternatively, the individual pieces of thermal conductive sheet 15 may be placed on the carrier film 11, on which the release film 13 has been pre-laminated on the base film 12. In either of these cases, it is preferable to pick up the individual pieces of thermal conductive sheet and place them on the base film.

[0132] Next, a cover film 20 is further laminated on top of the multiple thermal conductive sheets 15 so as to cover the multiple thermal conductive sheets 15, thereby obtaining a thermal conductive sheet holder 10. The cover film 20 is preferably attached by further laminating it onto a laminate formed by attaching multiple thermal conductive sheets 15 to a carrier film 11, and the lamination method is not particularly limited and may be carried out by known methods.

[0133] [Applications of the Thermally Conductive Sheet] The thermally conductive sheet 15 is preferably used in a heat dissipation mechanism in which it is interposed between a heat-generating element and a heat sink, and heat generated by the heat-generating element is transferred to the heat sink by thermal conduction, and heat is then dissipated from the heat sink. The thermally conductive sheet 15 is used in electronic equipment applications, semiconductor applications, etc., and is preferably used in semiconductor applications. In semiconductor applications, the thermally conductive sheet 15 may be used in any application, but it is preferably used in applications called TIM1, which is directly applied to semiconductor elements such as semiconductor chips, for example, between semiconductor elements such as semiconductor chips and lids such as heat spreaders. The thermally conductive sheet is preferably used by being placed between two members (adhered objects) such as a heat sink and a heat-generating element, and is preferably used in a state of close contact with each member (adhered object) and compressed, and is especially preferably placed between semiconductor elements and lids and used in a state of close contact with them and compressed.

[0134] The following describes a method for attaching a thermally conductive sheet to a semiconductor element as an embodiment of the present invention. The method for attaching a thermally conductive sheet according to an embodiment of the present invention comprises the following first to fourth steps. First step: A step of preparing a thermally conductive sheet holder. Second step: A step of peeling off a cover film from the second surface of the thermally conductive sheet. Third step: A step of pressing the second surface of the thermally conductive sheet onto the semiconductor surface of the semiconductor element. Fourth step: A step of peeling off the carrier film from the first surface of the thermally conductive sheet.

[0135] The following describes a bonding method according to one embodiment of the present invention with reference to Figure 6. In one embodiment of this manufacturing method, first, a thermal conductive sheet holder 10 is prepared (first step). The configuration of the thermal conductive sheet holder to be prepared and its manufacturing method are as described above. In the embodiment shown in Figure 6, the thermal conductive sheet holder 10 is wound up and prepared as a wound body 25. Then, the prepared thermal conductive sheet holder 10 is conveyed along the longitudinal direction Y in a roll-to-roll continuous process, and the second, third, and fourth steps are carried out in this order.

[0136] Specifically, the winding body 25 is attached to the dispensing roller 30, and the heat-conductive sheet holder 10 dispensed from the dispensing roller 30 is wound onto the take-up roller 31 and transported. A sprocket roller (not shown) is provided between the dispensing roller 30 and the take-up roller 31, and the pins of the sprocket roller are passed through transport pin holes 14, or transport pin holes 14, 24, and the heat-conductive sheet holder 10 is transported in the longitudinal direction Y by driving the sprocket roller. However, the heat-conductive sheet holder 10 may be transported by means other than driving the sprocket roller, and the pins passed through the pin holes may be used only for guiding or positioning.

[0137] During transport, the cover film 20 is peeled off the second surface 15B of the thermal conductive sheet 15 from the thermal conductive sheet holder 10. The method for peeling the cover film 20 from the thermal conductive sheet 15 is not particularly limited, but for example, it may be done by winding the cover film 20 onto a winding roller (not shown). Next, the second surface 15B of the thermal conductive sheet 15, which has been exposed by the peeling off of the cover film 20, is pressed against the semiconductor element 35.

[0138] The semiconductor element 35 is a semiconductor chip or the like, and may be mounted on a substrate 37 or the like, as shown in Figure 6. The semiconductor element 35 is preferably formed from a known semiconductor material such as silicon, silicon carbide, sapphire, gallium phosphide, indium phosphide, or gallium nitride, and among these, silicon is preferred. Therefore, the surface of the semiconductor element 35 to which the thermally conductive sheet 15 is fixed is preferably a silicon surface.

[0139] The thermal conductive sheet 15 is pressed from the back side of the carrier film 11 by a press device 32, peeling it off the carrier film 11 and pressing it onto the semiconductor element 35, thereby transferring it from the carrier film 11 to the semiconductor element 35. The semiconductor element 35 is, for example, placed on a transport device 36, and multiple semiconductor elements 35 are transported in a direction along the transport direction of the thermal conductive sheet holder 10, so that each of the multiple thermal conductive sheets 15 can be continuously transferred to each semiconductor element 35. On the other hand, the thermal conductive sheet holder 10 (i.e., the carrier film 11) from which the cover film 20 and thermal conductive sheet 15 have been peeled off is preferably wound onto a winding roller 31.

[0140] The first to fourth steps described above are preferably performed at a temperature of less than 180°C. Here, "performed at a temperature of less than 180°C" means that the first to fourth steps are performed at a temperature of less than 180°C for the thermal conductive sheet 15, and other similar expressions are used accordingly. In this invention, it is particularly preferable that the first to fourth steps be performed at a temperature of less than 180°C when using an acrylic adhesive having reactive double bonds as the adhesive. While the reactive double bonds in an acrylic adhesive may react when heated, if the first to fourth steps are performed at a temperature of less than 180°C, the reaction will not proceed, or even if the reaction proceeds, a certain amount of reactive double bonds will remain. Therefore, in the sixth step described later, the reactive double bonds can be reacted to maintain or improve the adhesive strength of the thermal conductive sheet 15 to the adherend (semiconductor element or lid). Furthermore, in order to minimize the reaction of the reactive double bonds, the first to fourth steps should be performed at the lowest possible temperature. Furthermore, the first to fourth steps can all be performed without heating the thermal conductive sheet holder 10 or the thermal conductive sheet 15, and it is desirable to perform them at a low temperature from the viewpoint of energy loss. From these viewpoints, the first to fourth steps are more preferably performed at a temperature of 150°C or lower, even more preferably at a temperature of 90°C or lower, and even more preferably at a temperature of 60°C or lower. There are no particular limitations, but for example, they may be performed at a temperature of 0°C or higher, and may also be performed at a temperature of 20°C or higher.

[0141] The laminate 40A, which comprises the semiconductor element 35 and the thermal conductive sheet 15 obtained through the above first to fourth steps, is then further subjected to the application of a lid 38 to the surface (first surface 15A) of the thermal conductive sheet 15 opposite to the second surface 15B on which the semiconductor element 35 is laminated, as shown in Figure 7 (fifth step). Examples of lids include heat spreaders. Heat spreaders are preferably made from metals such as aluminum and copper. The application of the lid 38 to the first surface 15A is not particularly limited, but is preferably done by pressurizing and heating, and more preferably by pressing with a heated press device 42. Here, the temperature of the thermal conductive sheet 15 during lid application may be, for example, 80°C or more and less than 180°C, preferably 100°C or more and 170°C or less, and more preferably 130°C or more and 160°C or less. The pressure applied during lid bonding is not particularly limited, but is, for example, 0.1 to 1.0 MPa, preferably 0.2 to 0.5 MPa. Furthermore, during lid bonding, the thermal conductive sheet 15 may also be pressed onto the semiconductor element 35. Therefore, in addition to the first to fourth steps, the fifth step may also be performed at a temperature of, for example, less than 180°C, more preferably at 170°C or lower, more preferably at 160°C or lower, more preferably at 80°C or higher, more preferably at 100°C or higher, and even more preferably at 130°C or higher. The press device 42 may also be a picker; for example, the lid 38 may be picked up and laminated onto the thermal conductive sheet 15.

[0142] By the first to fifth steps described above, a laminate 40 is obtained in which semiconductor elements 35 and lids 38 are laminated on both sides of the thermally conductive sheet 15. The obtained laminate 40 is preferably heated (sixth step). The sixth step is especially preferable when an acrylic adhesive having a reactive double bond is used as the adhesive. The heating in the sixth step allows the thermally conductive sheet 15 to maintain or improve its adhesive strength to the adherend (i.e., semiconductor elements 35, lids 38), contrary to the general properties of known acrylic adhesives as described above. In the sixth step, the laminate is preferably heated at a temperature of 180°C to 270°C, more preferably at 220°C to 260°C, and the heating time at the above temperature is preferably 1 minute to 10 minutes, and more preferably 3 minutes to 5 minutes.

[0143] The sixth step is preferably a reflow step. In the reflow step, the solder on the semiconductor element 35 and the substrate 37 is reflowed, and the components of the substrate 37 and the semiconductor element 35 are appropriately soldered. According to the bonding method of this embodiment, even though the thermal conductive sheet 15 is heated to a high temperature in the reflow step, the adhesive strength of the thermal conductive sheet 15 to the semiconductor element 35 and the lid 38 is not reduced, and in some cases, is improved, so that the thermal conductive sheet can be properly fixed to the surface of the semiconductor element and the lid.

[0144] The method of attaching the thermal conductive sheet described above is merely an example, and various embodiments can be adopted as long as they do not impair the effects of the present invention. For example, the fifth step may be omitted, and the lid may not be laminated on the first surface 15A of the thermal conductive sheet 15, and the laminate 40A without the lid may be heated in the sixth step. Furthermore, the sixth step may not be performed, and the present invention may be applied to semiconductor elements in which a reflow process is not carried out.

[0145] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way by these examples. The measurement method and evaluation method in these examples are as follows.

[0146] [Thickness of the thermal conductive sheet] The thickness of the thermal conductive sheet was measured using a thickness gauge.

[0147] [Tack Value] Equipment: A tack tester TA-500 (manufactured by UBM Co., Ltd.) was used, and the thermal conductive sheet was fixed to the stage with double-sided tape. The maximum load measured under the following measurement conditions was defined as the tack value (N). The double-sided tape used was Nichiban's "Nicetack NW-K15" double-sided tape. For each thermal conductive sheet, the tack values ​​T1 and T2 of the first and second surfaces were measured. (Measurement conditions) Probe diameter: 5 mmφ Probe material: Stainless steel Pressing load: 20 N Holding time: 10 seconds Pulling speed: 0.1 mm / s Measurement environment: 23°C, 50% RH

[0148] [Tack Values ​​After 6 Months] The windings obtained in each example and comparative example were stored for 6 months at room temperature of 23±5°C and humidity of 50±20%. After storage, the thermal conductive sheet holder was unwound from the winding, the cover film and carrier film were peeled off from the thermal conductive sheet, and the tack values ​​T3 and T4 of the first and second surfaces of the thermal conductive sheet removed from the thermal conductive sheet holder were measured.

[0149] [Peel Force P2 between Thermal Conductive Sheet and Cover Film] A 90° peel test was performed using a tensile testing machine in accordance with JIS K 6854-1. Specifically, a thermal conductive sheet with release film attached to both sides was prepared. The release film was peeled off one side, and the cover film was attached to the surface of the thermal conductive sheet at room temperature. At that time, a urethane rubber roller (44 mm in diameter) was used with a load of 500 g, and the thermal conductive sheet and cover film were pressed together by rolling it back and forth in the vertical direction once, then in the horizontal direction once, and then in the vertical direction once. After that, the sheet was cut to a width of 25 mm and a length of 150 mm, and the release film was peeled off from the other side of the thermal conductive sheet to obtain a measurement sample. The measurement sample was left for one day in an environment of 23°C and 50% RH before measurement. Using the measurement sample, the cover film was fixed, one end of the thermal conductive sheet was grasped with a chuck, and the average peel force obtained by pulling at 90° was defined as the peel force P2. The average peeling force was calculated using the maximum average value from the area where the peeling force was stable during the peel strength measurement. The peeling force was measured at 23°C and 50% RH, with a peeling speed of 50 mm / min.

[0150] [Peel Force P1 between Thermal Conductive Sheet and Carrier Film] Under the same measurement conditions as for peel force P2, the release film constituting the carrier film was attached to the thermal conductive sheet instead of the cover film, and the peel force was measured. The average peel force obtained was measured as peel force P1.

[0151] [Peel strength P3 between cover film and base film (carrier film)] A 90° peel test was performed using a tensile testing machine in accordance with JIS K 6854-1. Specifically, the cover film was attached to the base film without air bubbles, and a urethane rubber roller (44 mm in diameter) was used to apply a 500 g load. The roller was rolled sequentially in the vertical direction (one pass back and forth), horizontal direction (one pass back and forth), and vertical direction (one pass back and forth) to compress the film. The film was then cut to a width of 25 mm and a length of 150 mm to obtain a measurement sample. The measurement sample was left for one day in an environment of 23°C and 50% RH before measurement. Using the measurement sample, the base film was fixed, one end of the cover film was grasped with a chuck, and the average peel force obtained by pulling it at a 90° angle was defined as the peel force P3. The average peel force was the maximum average value of the area where the peel force was stable during the peel strength measurement. The peel force was measured in an environment of 23°C and 50% RH at a peeling speed of 50 mm / min.

[0152] [Surface Roughness Sa] was measured using a shape analysis laser microscope. Specifically, a 10x lens was used for the laser microscope, and the cover film measurement sample was placed on the stage and measured in shape measurement mode. Subsequently, the obtained measurement results were opened in an analysis application, and after performing surface tilt correction (automatic), the surface roughness was measured. For surface roughness measurement, the entire area of ​​the image (1401.705 μm × 1051.279 μm) was specified, in accordance with JIS B0601:2001, and no cut filter was used. Surface roughness was measured at three random locations within the measurement target, and the average value obtained from each location was adopted.

[0153] [Normal peel strength] The normal peel strength was measured in accordance with JIS Z0237:2009. Specifically, a measurement sample was obtained by laminating adhesive tape ("31B" manufactured by Nitto Denko Corporation) to the surface of the thermal conductive sheet side of the cover film. However, instead of using a 1 kg or 2 kg roller, a 463 g rubber roller was used for lamination. The obtained measurement sample was left for one day in an environment of 23°C and 50% RH. After that, using the measurement sample, the cover film was fixed in place, and one end of the adhesive tape was grasped with a chuck and pulled at 180° and a pulling speed of 300 mm / min. The peel strength obtained was defined as the normal peel strength (Q1) of the cover film. In addition, the peel strength measured under the same conditions using the release film that constitutes the carrier film instead of the cover film was defined as the normal peel strength (Q2) of the carrier film.

[0154] [Evaluation Method] For the thermal conductive sheet holders obtained in the examples and comparative examples, the film was pulled out by placing it on a reel holder, and the cover film was opened so that the angle between the cover film and the carrier film was 45 degrees, and 10 pieces of thermal conductive sheet were visually inspected. Next, the thermal conductive sheet was attached to a 0.7 mm thick silicon wafer from which the oxide film had been removed, and pressed down from the carrier film side with a urethane rubber roller, and the presence or absence of separation of the thermal conductive sheet, the adhesion of the thermal conductive sheet to the cover film, and the peelability from the base film were evaluated according to the following evaluation criteria. (Presence or absence of separation) A: When the 10 pieces of thermal conductive sheet were visually inspected after opening the cover film, there were no tears or defects. B: When the 10 pieces of thermal conductive sheet were visually inspected after opening the cover film, there were 1 or more but less than 3 pieces with tears or defects. C: When the 10 pieces of thermal conductive sheet were visually inspected after opening the cover film, there were 3 or more pieces with tears or defects. (Adhesion to cover film) A: When the cover film is opened, the 10 thermal conductive sheets are visually inspected and found to be not attached to the cover film and not misaligned. B: When the cover film is opened, the 10 thermal conductive sheets are visually inspected and found to be at least one attached to the cover film, or at least one misaligned or peeled off on the carrier film side, but the total number of sheets attached to the cover film or misaligned or peeled off on the carrier film side is less than three. C: When the cover film is opened, the 10 thermal conductive sheets are visually inspected and found to be at least three attached to the cover film, or at least three misaligned or peeled off on the carrier film side. (Removability from carrier film) A: When 10 thermal conductive sheets are bonded to a silicon wafer, the thermal conductive sheets peel off from the carrier film and there is no lifting of the thermal conductive sheets. B: When 10 thermal conductive sheets are bonded to a silicon wafer, one or more thermal conductive sheets do not peel off from the carrier film, or one or more thermal conductive sheets are lifted from the silicon wafer, but the total number of peeled or lifted sheets is less than 3.C: When 10 thermal conductive sheets are bonded to a silicon wafer, 3 or more thermal conductive sheets remain attached to the carrier film, or are floating away from the silicon wafer.

[0155] (Adhesion to Chip) A 3 mm x 3 mm thermal conductive sheet, obtained in each example and comparative example, was placed on a nickel-plated copper plate with an outer dimension of 50 mm x 50 mm and a thickness of 2 mm. A silicon die with a thickness of 600 μm and a thickness of 3 mm x 3 mm was then placed on top of the thermal conductive sheet. The resulting laminate was pressed in the thickness direction at a pressure of 1 MPa for 60 seconds at room temperature to adhere the thermal conductive sheet to the nickel-plated copper plate and the silicon die, thereby obtaining a sample for measurement. At this time, the silicon die was adhered to the second surface. The sample for measurement was placed on a hot plate heated to 250°C with the nickel-plated copper plate side facing down and heated for 3 minutes. Note that heating at 250°C for 3 minutes simulates a reflow process. After that, in a 25°C environment, the height was adjusted using a die shear tester ("Dage-S4000", Nordson) so that the tip of the tool was 300 μm above the surface of the thermal conductive sheet. Next, the tool was applied to the silicon die along the shear direction at a speed of 150 μm / s, and the load required for the joint to break was defined as the die shear strength.

[0156] The following components were used as raw materials for the thermal conductive sheet: (Polymer composition) Curable silicone: Addition reaction type organopolysiloxane consisting of an alkenyl group-containing organopolysiloxane as the main component and a hydrogen organopolysiloxane as the curing agent (however, containing a catalytic amount of platinum catalyst). (Volatile substance) n-decyltrimethoxysilane (Thermally conductive filler) Aluminum oxide 1: polyhedral shape, average particle size (D50) = 0.5 μm, aspect ratio 1.0 Aluminum oxide 2: polyhedral shape, average particle size (D50) = 3 μm, aspect ratio 1.0 Graphitized carbon fiber: average fiber length (arithmetic mean) 85 μm, diameter 10 μm, aspect ratio 8.5, thermal conductivity 900 W / m·K Scale graphite powder: average particle size (D50) = 15 μm, aspect ratio 10, thermal conductivity 550 W / m·K (Dispersant) Pyrene Wetter: organopolysiloxane containing pyrene as shown by the synthesis method described later

[0157] (Adhesive) The adhesives used in each example and comparative example are as follows: Acrylic adhesive: An adhesive in which the main adhesive component is an acrylic polymer having hydroxyl groups, carboxyl groups, and vinyl groups in the side chains, with 2-ethylhexyl acrylate as the main component. *Note that 100 parts by mass of a diluted solution of the adhesive diluted with ethyl acetate to a solid content concentration of 33% by mass was further diluted with 120 parts by mass of propylene glycol monomethyl ether acetate (solvent) to prepare a coating solution with a solid content concentration of 15% by mass, which was used in each example and comparative example.

[0158] (Cover film, release film, and base film) The cover film, release film, and base film used in each example and comparative example were as follows: TWR35X2: Silicone-based release paper, product name "TWR35X2", manufactured by Nippa Co., Ltd. Cooking sheet: product name "Lead Hot Cooking Sheet", manufactured by Lion Corporation G7 Shiro AA: Silicone-based release film, product name "G7 Shiro AA (N96)", manufactured by Lintec Corporation SP4107: Silicone-based release film, product name "Tokkuro Release Film SP4107", manufactured by Toyo Cloth Co., Ltd. SP8002-K2: product name "Tokkuro Release Film SP8002-K2", manufactured by Toyo Cloth Co., Ltd. Low-tack film: product name "NEION PET75-Y210", manufactured by Nichiei Shinka Co., Ltd.

[0159] (Synthesis of Pyrene Wetter) 98.6 g of an organosiloxane compound having a 1,3-diol group (n=210), 1.4 g of 1-pyrenecarboxaldehyde, 50 g of toluene as a solvent, and 0.6 g of a catalyst (Organo Corporation, "Amberlyst 15 dry") were reacted at 100°C for 24 hours in a nitrogen atmosphere. After the reaction, the catalyst was removed by filtration through a 5.0 μm PTFE filter, and the filtrate was concentrated using a rotary evaporator and a vacuum dryer to obtain pyrene dispersant 1. The reaction equation is shown below. １ The following reactions were confirmed to have occurred by 1H NMR measurement. A JEOL "ECX-400" NMR analyzer was used, and measurements were performed with deuterated chloroform as the solvent, at a sample concentration of 1% by weight, at 25°C, a measurement frequency of 400 MHz, and 8 cumulative measurements.

[0160] [Example 1] (Preparation of a thermally conductive sheet) Each component was mixed using a planetary mixer at 25°C for 50 minutes according to the formulation shown in Table 1 to obtain a mixed composition. Next, the mixed composition was poured into a mold set to a thickness sufficiently greater than that of the thermally conductive sheet, and an 8T magnetic field was applied in the thickness direction to orient the carbon fibers and flake graphite in the thickness direction. Then, the curable silicone was first cured by heating at 80°C for 8 hours to obtain a block-shaped oriented molded body. Next, the block-shaped oriented molded body was sliced ​​into a sheet with a thickness of approximately 120 μm using a shearing blade to obtain a sheet-shaped molded body with exposed carbon fibers. After that, the sheet-shaped molded body was heated at 150°C for 6 hours to perform secondary curing. Next, the sheet-shaped molded body was polished back and forth 75 times with coarse abrasive paper A (grit #800) having an average abrasive particle size (D50) of 20 μm, and then polished back and forth 10 more times with coarse abrasive paper B (grit #4000) having an average abrasive particle size (D50) of 3 μm.

[0161] An acrylic adhesive coating solution was spray-applied to both surfaces of the obtained polished sheet-like molded body, adjusting the discharge rate so that the basis weight after drying was the amount shown in Table 3. Then, by drying at 50°C for 3 minutes, a thermally conductive sheet was obtained with an acrylic adhesive layer on both surfaces of the thermal conductive layer. Fine bubbles were found within the thermal conductive layer, and it was confirmed that the acrylic adhesive had penetrated into these fine bubbles near both surfaces. The thermal conductive sheet had a filling rate of 60 vol% for thermally conductive fillers, 29 vol% for anisotropic fillers, and 30 vol% for non-anisotropic fillers, with the anisotropic fillers oriented in the thickness direction. The thickness of the thermal conductive sheet was 0.12 mm.

[0162] (Preparation of Thermal Conductive Sheet Holder) Release films were attached to both sides of the obtained thermal conductive sheet so that the surface with the release agent layer was in contact with the thermal conductive sheet. The thermal conductive sheet with release films attached to both sides was cut into 30 mm x 30 mm pieces to obtain multiple thermal conductive sheets with release films laminated on both sides. One release film was peeled off the obtained thermal conductive sheets, and then they were attached to a long base film (micro-adhesive film, product name "NEION PET75-Y210", manufactured by Nichiei Shinka Co., Ltd., thickness 85 μm) at 14 mm intervals using pick and place, and arranged in parallel along the longitudinal direction. At this time, the side with the release film was attached to the base film to obtain a laminate in which multiple thermal conductive sheets were attached on a carrier film. A cover film was attached to the obtained laminate so as to cover the thermal conductive sheets to obtain a thermal conductive sheet holder 10 as shown in Figures 1 and 2. The obtained thermal conductive sheet holder 10, with a width of 80 mm, was wound onto a bobbin core 26 (core width 81 mm) with an outer diameter of 6 inches (152.4 mm) as shown in Figure 4 to obtain a wound body 25. The thermal conductive sheet holder 10 was used in which, on the outermost circumference of the wound body 25, the thermal conductive sheet 15 was not provided in a region R with a length of 2 m from the end 11E of the carrier film 11. Instead, 100 thermal conductive sheets were arranged along the length direction Y from a position 2 m away from the end 11E toward the innermost end of the carrier film 11. Furthermore, at the innermost end of the carrier film 11, the thermal conductive sheet was not placed in a region with a length of 2 m.

[0163] [Examples 2-4, 6-9, Comparative Examples 1, 2, 4] The same procedure as in Example 1 was followed, except that the release film, cover film, adhesive application amount, and the thickness of the resulting thermal conductive sheet were changed as shown in Tables 3, 4, and 5.

[0164] [Example 5] The polished sheet-like molded body obtained in Example 1 was used as the first sheet. The components were mixed using a planetary mixer at 25°C for 50 minutes according to the formulations in Table 2 to obtain a mixed composition. Subsequently, release films were placed on the upper and lower surfaces of the mold, which were set to a predetermined thickness using spacers. The mixed composition was then injected, and an 8T magnetic field was applied in the thickness direction to orient the carbon fibers in the thickness direction. After heating at 150°C for 1.5 hours, the upper release film was peeled off, and the polymer matrix was cured by heating at 150°C for another 7 hours to obtain a second sheet with a thickness of 0.2 mm. Both surfaces of the second sheet consisted of a skin layer that did not contain anisotropic filler. The first sheet and the second sheet were stacked and pressed together using a roll press at room temperature (25°C) and a pressure of 1 MPa to bond them, obtaining a laminate with a two-layer structure. Of the resulting laminate, an acrylic adhesive coating solution was spray-applied to the surface of the first sheet side, adjusting the discharge rate so that the basis weight after drying was the amount shown in Table 3. Then, it was dried at 50°C for 3 minutes to obtain a thermally conductive sheet with an acrylic adhesive layer on one side of the thermally conductive layer.

[0165] [Examples 10, 11, Comparative Example 3] The procedure was carried out in the same manner as in Example 1, except that the length L of the region R where the thermal conductive sheet 15 is not provided at the outermost end 11E side of the wound body 25 was changed as shown in Tables 4 and 5.

[0166] *The values ​​for each component in Tables 1 and 2 are in parts by mass for each formulation. *The sheet hardness is the value measured for the cured product obtained from formulation 1 in each example and comparative example, and is substantially the same as the hardness of type E thermal conductive sheet. *The aluminum oxide in Table 1 is a mixture of aluminum oxide 1 and aluminum oxide 2 in a mass ratio of 1:10. *The aluminum oxide in Table 2 is aluminum oxide 2.

[0167]

[0168]

[0169]

[0170] As shown in Tables 3 and 4, in each embodiment, the peeling force P2 was within a predetermined range while the tack value was within a predetermined range. As a result, when peeling off the cover film, the thermal conductive sheet did not tear, and no adhesion of the thermal conductive sheet to the cover film was observed. Furthermore, the thermal conductive sheet could be properly fixed to semiconductor elements that are highly smooth and difficult to adhere to. Therefore, in each embodiment, the thermal conductive sheet could be efficiently attached to the semiconductor element with high adhesive strength. Moreover, since the thermal conductive sheet was not placed in a region with a length of 2.0 turns or more from the end of the outermost carrier film to the winding body, airtightness between the cover film and the carrier film could be ensured, preventing deterioration of the thermal conductive sheet over time even during long-term storage, and suppressing a decrease in the tack value. In contrast, in Comparative Example 4, the peeling force P2 was greater than the specified value, so when peeling off the cover film, the thermal conductive sheet to tear or the thermal conductive sheet to adhere to the cover film was observed, and the thermal conductive sheet could not be efficiently attached to the semiconductor element. Furthermore, in Comparative Example 1, the tack value T2 was too low, making it difficult to properly fix the thermal conductive sheet to the semiconductor element. In Comparative Example 2, the tack value T2 was too high, causing the thermal conductive sheet to adhere to the cover film, making it impossible to efficiently attach the thermal conductive sheet. Moreover, in Comparative Example 3, the region R where the thermal conductive sheet was not placed at the outermost end of the winding body was less than 2.0 turns in length, so sufficient airtightness between the cover film and the carrier film could not be ensured. As a result, when stored for a long period of time, deterioration of the thermal conductive sheet occurred over time, and a decrease in the tack value was observed.

[0171] 10 Thermal conductive sheet holder 10E End of thermal conductive sheet holder 11 Carrier film 11E End of carrier film 12 Base film 13 Release film 14, 24 Conveyor pin holes 15 Thermal conductive sheet 15A First surface 15B Second surface 20 Cover film 25 Winding body 26 Core 27 Flange 30 Feed roller 31 Take-up roller 32 Press device 35 Adhesion device (semiconductor element)

Claims

1. A thermal conductive sheet holder comprising: a thermal conductive sheet having a first surface and a second surface opposite to the first surface; a carrier film laminated so as to cover the entire surface of the first surface of the thermal conductive sheet; and a cover film laminated so as to cover the entire surface of the second surface of the thermal conductive sheet, wherein at least one of the first surface and the second surface of the thermal conductive sheet has an adhesive component; the peel force between the cover film and the second surface of the thermal conductive sheet is 0 mN / 25 mm or more and 55 mN / 25 mm or less; the tack value of the second surface of the thermal conductive sheet is 4.0 N or more and 9.0 N or less; and the thermal conductive sheet holder is a wound body wound along the longitudinal direction, and the thermal conductive sheet is not arranged in a region with a length of 2.0 turns or more from the end of the outermost carrier film to the wound body.

2. The thermal conductive sheet holder according to claim 1, wherein the surface roughness Sa on the surface of the cover film in contact with the second surface is 5 μm or more.

3. The thermal conductive sheet holder according to claim 1 or 2, wherein the peel force between the carrier film and the first surface of the thermal conductive sheet is 55 mN / 25 mm or more and 130 mN / 25 mm or less.

4. The thermal conductive sheet holder according to claim 1 or 2, wherein the second surface is a surface that adheres to the surface of a semiconductor element.

5. The thermal conductive sheet holder according to claim 1 or 2, wherein the normal peel force of the cover film is 5 mN / 25 mm or more and 30 mN / 25 mm or less.

6. The thermal conductive sheet holder according to claim 1 or 2, wherein the normal peeling force of the carrier film is 5 mN / 25 mm or more and 30 mN / 25 mm or less.

7. The thermal conductive sheet holder according to claim 1 or 2, wherein the tack value of the second surface is greater than the tack value of the first surface.

8. The thermal conductive sheet holder according to claim 1 or 2, wherein the adhesive component comprises either a silicone resin or an acrylic resin.

9. The thermally conductive sheet holder according to claim 1 or 2, wherein the adhesive component comprises an acrylic resin having a reactive double bond.

10. The thermal conductive sheet holder according to claim 1 or 2, wherein one or both of the first surface and the second surface of the thermal conductive sheet are cut surfaces and have the adhesive component.

11. The thermal conductive sheet holder according to claim 1 or 2, wherein the thermal conductive sheet comprises an anisotropic filler oriented in the thickness direction.

12. A method for manufacturing a thermal conductive sheet holder according to claim 1 or 2, comprising the steps of: placing a plurality of thermal conductive sheets on a carrier film or a base film constituting a part of the carrier film; and further laminating a cover film on the plurality of thermal conductive sheets so as to cover the plurality of thermal conductive sheets.

13. A thermal conductive sheet holder comprising: a first step of preparing a thermal conductive sheet having a thermal conductive sheet having a first surface and a second surface opposite to the first surface; a carrier film provided to cover the entire surface of the first surface of the thermal conductive sheet; and a cover film provided to cover the entire surface of the second surface of the thermal conductive sheet; a second step of peeling the cover film from the second surface of the thermal conductive sheet; a third step of pressing the second surface of the thermal conductive sheet onto the surface of a semiconductor element; and a fourth step of peeling the carrier film from the first surface of the thermal conductive sheet, wherein at least one of the first surface and the second surface of the thermal conductive sheet has an adhesive component, the peeling force between the cover film and the second surface of the thermal conductive sheet is 0 mN / 25 mm or more and 55 mN / 25 mm or less, and the tack value of the second surface of the thermal conductive sheet is 4.0 N or more and 9.0 N or less. A method for attaching a thermal conductive sheet, wherein the thermal conductive sheet holder is a wound body wound along the longitudinal direction, and the thermal conductive sheet is not placed in a region extending for a length of 2.0 turns or more from the end of the carrier film on the outermost periphery of the wound body.

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