Resin sheet

Abstract

To provide a novel resin sheet exhibiting a high heat dissipation effect and superior followability.SOLUTION: A resin sheet 1 includes a thermoplastic resin and a thermally conductive filler, wherein the resin sheet 1 has through-holes 19, and the number of the through-holes 19 in the resin sheet 1 is 4 to 400 per cm2. The average diameter of the through-holes 19 may be 50 to 1000 μm, and the pitch of the through-holes 19 may be 0.5 to 4 mm. The resin sheet 1 may include a plate-like filler and a linkage filler as the thermally conductive filler.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a resin sheet.

Background Art

[0002] A central processing unit (abbreviated as "CPU" in this specification) is a type of representative device that constitutes a computer. The amount of heat generated by the CPU increases dramatically during the operation of the computer. On the other hand, in recent years, with the high performance, miniaturization, and weight reduction of electronic devices, the high-density mounting of semiconductor packages, the high integration of LSIs, and the high speed of processing have advanced, and countermeasures against heat generated in electronic devices have become extremely important.

[0003] In a normal electronic device, a heat spreader is mounted on a CPU arranged on a circuit board via a thermal interface material (abbreviated as "TIM" in this specification), and this heat spreader is arranged in contact with a heat sink. Thereby, in the electronic device, the heat generated by the CPU is conducted to the heat spreader via the TIM, and further, the heat is conducted in the plane direction by this plate-shaped heat spreader, and the heat is dissipated to the outside of the electronic device via the heat sink (see Patent Document 1).

[0004] Conventionally, the reasons for adopting such a heat dissipation structure for the CPU are as follows. That is, the heat spreader is made of metal, graphite, or the like, has a high thermal conductivity in its plane direction, and has high heat dissipation performance. On the other hand, it does not have followability with respect to the object to be cooled (CPU), has insufficient adhesion to the object to be cooled (CPU), and further does not have insulation. On the other hand, TIM has a certain degree of followability with respect to the object to be cooled (CPU), has good adhesion, and further has insulation. However, its thermal conductivity is insufficient. Therefore, by combining and using these (heat spreader and TIM) and adopting the above-described heat dissipation structure, these drawbacks are complemented.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in such conventional electronic devices, as long as TIM is an essential component, the heat dissipation structure is limited, and the configuration of the electronic device is also limited. And as a substitute for TIM, considering that insulation and followability are required, it is appropriate to use a resin sheet. However, a resin sheet with high heat dissipation effect and good followability has not been sufficiently studied so far. Note that, so far, the CPU has been taken as an example for explanation, but the same problems can occur in other devices equipped with a heat generating body similar to the CPU.

[0007] An object of the present invention is to provide a novel resin sheet having a high heat dissipation effect and good followability.

Means for Solving the Problems

[0008] The present invention adopts the following configuration. [1] A resin sheet, wherein the resin sheet includes a thermoplastic resin and a thermally conductive filler, the resin sheet has through holes, and the number of the through holes in the resin sheet is 4 to 400 per cm 2 A resin sheet which is [2] The resin sheet according to [1], wherein the average diameter of the through holes is 50 to 1000 μm. [3] The resin sheet according to [1] or [2], wherein the pitch of the through holes is 0.5 to 4 mm.

[0009] [4] The resin sheet according to any one of [1] to [3], wherein the resin sheet contains a plate-shaped filler and a connecting filler as the thermally conductive filler. [5] The resin sheet according to [4], wherein the average particle diameter of the connecting filler is 2 μm or less. [6] Using a test piece that is one sheet of the resin sheet or a laminate of two or more sheets of the resin sheet and has a thickness of T0, and applying a pressure of 12 kPa in the thickness direction of the test piece for 10 minutes in an environment of 100 °C, when measuring the thickness T1 of the test piece at the site where the pressure is applied, the following formula: R = (T0 - T1) / T0 × 100 The resin sheet according to any one of [1] to [5], wherein the embedding rate R calculated by the formula is 30% or more.

[0010] [7] The resin sheet according to any one of [1] to [6], wherein the relative permittivity of the resin sheet at a frequency of 10 GHz, measured in accordance with the TM0m0 mode cavity resonator perturbation method, is 4 or less. [8] The resin sheet according to any one of [1] to [7], wherein the dielectric loss tangent of the resin sheet at a frequency of 10 GHz, measured in accordance with the TM0m0 mode cavity resonator perturbation method, is 0.01 or less. [9] The resin sheet according to any one of [4] to [8], wherein the plate-shaped filler is made of boron nitride or aluminum oxide.

[0011]

[10] The resin sheet according to any one of [4] to [9], wherein the connecting filler is made of magnesium hydroxide.

[11] The resin sheet according to any one of [1] to

[10] , wherein the thermoplastic resin is an ethylene-vinyl acetate copolymer.

[12] The resin sheet according to any one of [4] to

[11] , wherein the ratio of the content of the connecting filler to the content of the plate-shaped filler in the resin sheet is 60 to 300% by volume.

[13] The resin sheet according to any one of [4] to

[12] , wherein the average particle diameter of the plate-shaped filler is 5 μm or more.

Advantages of the Invention

[0012] According to the present invention, a novel resin sheet with high heat dissipation effect and good followability is provided.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Modes for Carrying Out the Invention

[0014] ◇Resin Sheet The resin sheet according to an embodiment of the present invention includes a thermoplastic resin and a heat conductive filler, the resin sheet has through holes, and the number of the through holes in the resin sheet is 4 to 400 pieces / cm 2 is. The resin sheet of this embodiment contains the heat conductive filler, so that the heat conductivity is high and the heat dissipation property is high in both the direction parallel to its surface and its thickness direction. The resin sheet of this embodiment contains a thermoplastic resin, so it can maintain a sheet-like shape, and furthermore, it has high flexibility when heated. The resin sheet of this embodiment has through holes, and the number of the through holes in the resin sheet is 4 to 400 per cm 2 By virtue of this, even without applying pressure to the resin sheet, in a heating environment, the resin sheet has good followability with respect to its application object. In this specification, when the resin sheet is heated without applying pressure to the resin sheet, the followability of the resin sheet with respect to its application object may be simply referred to as "the followability of the resin sheet". By using the resin sheet of this embodiment having such characteristics to cover, preferably embed, a heat-generating body such as a CPU (central processing unit), a high effect of suppressing heat generation in various electronic devices can be obtained. Further, not limited to the CPU, high effects of suppressing heat generation can also be obtained in other devices having a heat-generating body similar to the CPU.

[0015] In this specification, not limited to the case of a resin sheet, the "direction parallel to the surface" may be referred to as the "plane direction". In this specification, the "heat-generating body" means a structure that can generate heat.

[0016] In this specification, applying pressure to the resin sheet, unless otherwise specified, means pressing the resin sheet against the application object in order to bond the resin sheet to the application object. In order to improve the heat dissipation effect of the heat-generating body by bonding a heat-dissipating resin sheet to the heat-generating body (application object), it is desirable that the resin sheet follows the heat-generating body and is in good contact with the heat-generating body. Therefore, usually, the resin sheet is pressed against the heat-generating body (that is, pressure is applied to the resin sheet) to bond the resin sheet to the heat-generating body. In contrast, the resin sheet of the present embodiment can be placed on the heating element in either a heating environment or a non-heating environment (i.e., at room temperature). Subsequently, even without applying pressure to the resin sheet, when the resin sheet is finally placed in a heating environment, the resin sheet can follow the object to be applied well and adhere well to it.

[0017] The resin sheet of the present embodiment has insulation properties.

[0018] FIG. 1 is a front view schematically showing an example of the resin sheet of the present embodiment. In the following descriptions, for the sake of clarity in understanding the features of the present invention, the figures used may sometimes show the main parts enlarged for convenience, and the dimensional ratios and the like of each component are not necessarily the same as the actual ones.

[0019] The resin sheet 1 shown here has a large number of through holes 19 penetrating from one surface 1a to the other surface 1b. The shape of the main surfaces (one surface 1a and the other surface 1b) of the resin sheet 1 is rectangular. However, the shape of the main surface of the resin sheet of the present embodiment is not limited to this and can be arbitrarily selected according to the purpose.

[0020] In the resin sheet 1, the through holes 19 are provided at equal intervals in two directions perpendicular to each other in the same direction as the outer peripheral direction of the resin sheet 1. That is, in the two directions of the resin sheet 1, the distances between adjacent through holes 19 can be regarded as all being constant or approximately constant. However, the arrangement form of the through holes in the resin sheet of the present embodiment is not limited to this. For example, the distances between adjacent through holes may be different at least in part, or the through holes may be provided in directions other than the two perpendicular directions.

[0021] <<Through hole>> When the resin sheet is placed on the object to which it is to be applied (heating element), and in this state, when the resin sheet is placed in a heating environment, even without applying pressure to the resin sheet, the resin sheet follows the object to which it is applied well and adheres well. That is, even if there are convex portions on the surface of the object to which it is applied, the resin sheet adheres well to the surfaces of both the convex portions and other portions (non-convex portions), and has good followability with respect to the uneven surface. The reason why the resin sheet exhibits such good followability is that the resin sheet has through-holes.

[0022] A comparative resin sheet that is the same as such a resin sheet in terms of composition and thickness, but does not have through-holes, when heated without applying pressure thereto, has low followability with respect to the uneven surface. For example, the adhesiveness to the surface of the convex portion becomes low, and the comparative resin sheet may float. When the comparative resin sheet is heated without applying pressure, for example, a part of the comparative resin sheet whose flexibility has increased due to heating comes into contact with and adheres to the object to which it is applied. However, in the void portion surrounded by such an adhered portion and where the comparative resin sheet and the object to which it is applied do not contact each other, it is presumed that the gas expands as the comparative resin sheet is heated, and as a result, the followability of the comparative resin sheet becomes low. On the other hand, when the resin sheet of the present embodiment is used, when the resin sheet whose flexibility has increased due to heating comes into contact with and adheres to the object to which it is applied, the gas existing between the resin sheet and the object to which it is applied is discharged to the outside through the through-holes of the resin sheet. As a result, it is presumed that even without applying pressure to the resin sheet, the resin sheet adheres well to the object to which it is applied in a heating environment and exhibits good followability.

[0023] The shape of the opening of the through-hole on the surface of the resin sheet and the shape of the opening of the through-hole in a cross-section perpendicular to its longitudinal direction are not particularly limited. For example, they may be circular; elliptical; polygonal shapes such as triangular and quadrangular; shapes formed by combining two or more shapes selected from the group consisting of circular, elliptical, and polygonal shapes, etc. However, from the viewpoint of ease of forming the through-hole, the shape is preferably circular.

[0024] In this specification, unless otherwise specified, "the opening of the through-hole" means both the opening of the through-hole on the surface of the resin sheet described above and the opening of the through-hole in a cross-section perpendicular to its longitudinal direction.

[0025] When the shape of the opening of the through-hole is other than circular, the diameter of the through-hole means the maximum length (maximum diameter) among the lengths of line segments connecting two different points of the opening.

[0026] The number of through-holes in the resin sheet (the number of through-holes per unit area of the resin sheet that the resin sheet has) is 4 to 400 holes / cm 2 and preferably 8 to 200 holes / cm 2 and more preferably 10 to 100 holes / cm 2 When the number of the through-holes is equal to or more than the lower limit value, the followability of the resin sheet becomes good. When the number of the through-holes is equal to or less than the upper limit value, the heat dissipation effect of the resin sheet becomes higher.

[0027] The average diameter of the through-holes in the resin sheet is preferably 50 to 1000 μm, more preferably 100 to 1000, and even more preferably 300 to 1000. When the average diameter of the through-holes is equal to or more than the lower limit value, the followability of the resin sheet becomes better. When the average diameter of the through-holes is equal to or less than the upper limit value, the heat dissipation effect of the resin sheet becomes higher.

[0028] In the resin sheet, the distance between adjacent through-holes is preferably 0.5 to 5 mm, more preferably 0.5 to 3 mm, and even more preferably 1 to 3 mm. When the distance between the through-holes is equal to or greater than the lower limit value, it is possible to suppress the number of through-holes from becoming excessive. When the distance between the through-holes is equal to or less than the upper limit value, the followability of the resin sheet becomes better. In this specification, the "distance between adjacent through-holes" means the distance between the centers of the openings of one through-hole and the other through-hole that are adjacent to each other.

[0029] Furthermore, in the resin sheet, the distance between adjacent through-holes is preferably such that all of them are constant or can be regarded as being substantially constant. The followability of such a resin sheet becomes higher. In this specification, "the distance is substantially constant" means that although the distance is not strictly constant, it is not possible to clearly recognize by visual inspection that the distances are different. That is, in the resin sheet, the pitch of the through-holes is preferably 0.5 to 4 mm, more preferably 0.5 to 2 mm, and even more preferably 1 to 2 mm. When the pitch of the through-holes is within such a range, the followability of the resin sheet becomes particularly high.

[0030] The position of the through-holes in the resin sheet is not particularly limited, but it is preferable that the through-holes are provided uniformly without bias over the entire area of the resin sheet. The followability of such a resin sheet becomes higher.

[0031] <<Thermoplastic resin>> The thermoplastic resin is not particularly limited as long as it can maintain the sheet-like shape of the resin sheet and increase the flexibility of the resin sheet during heating.

[0032] The resin sheet can be manufactured, for example, by molding (pressure-heat molding) a resin composition, which will be described later, for manufacturing the resin sheet. In this case, it is preferable that the thermoplastic resin has a melting point lower than the heating temperature (molding temperature) during the molding of the resin composition. By molding the resin composition at a temperature higher than the melting point of the thermoplastic resin, a resin sheet with higher uniformity can be obtained.

[0033] The melting point of the thermoplastic resin is preferably 90°C or lower, and for example, it may be either 80°C or lower, or 70°C or lower. By using a thermoplastic resin with a melting point below the upper limit value, a resin sheet with higher uniformity can be obtained. The lower limit value of the melting point of the thermoplastic resin is not particularly limited. For example, thermoplastic resins with a melting point of 35°C or higher can be more easily obtained or manufactured. In one embodiment, the melting point of the thermoplastic resin may be, for example, any one of 35 - 90°C, 35 - 80°C, and 35 - 70°C. However, these are only examples of the melting point of the thermoplastic resin.

[0034] The melt flow rate of the thermoplastic resin (which may be referred to as "MFR" in this specification) is preferably 1 - 40 g / 10 min, and for example, it may be either 5 - 40 g / 10 min, or 10 - 40 g / 10 min. When the MFR of the thermoplastic resin is at or above the lower limit value, the followability of the resin sheet to the object to which it is applied becomes higher. For example, when covering a heating element with the resin sheet, the heating element can be easily covered with the resin sheet. When the MFR of the thermoplastic resin is at or below the upper limit value, the shape of the resin sheet can be more stably maintained. In this specification, unless otherwise specified, MFR means a value measured in accordance with JIS K7210:1999.

[0035] As the preferred thermoplastic resin, for example, ethylene-vinyl acetate copolymer (EVA) and the like can be mentioned. The ethylene-vinyl acetate copolymer has a lower melting point than other resins, and when heated, it exhibits an endothermic effect at the melting point or a temperature near it. Therefore, the resin sheet containing the ethylene-vinyl acetate copolymer has higher heat dissipation due to its heat storage latent heat function. In addition, the ethylene-vinyl acetate copolymer has flexibility, impact resistance, and adhesiveness. When covering the heating element with the resin sheet containing the ethylene-vinyl acetate copolymer, the resin sheet easily adheres to the heating element. Further, since the ethylene-vinyl acetate copolymer has polarity, it can be compounded with a flame retardant (for example, magnesium hydroxide, etc.), and flame retardancy can be easily imparted to the resin sheet.

[0036] In the ethylene-vinyl acetate copolymer, the ratio of the amount (parts by mass) of the structural unit derived from vinyl acetate to the total amount (parts by mass) of the structural units (which may be referred to as "vinyl acetate content" in this specification) is preferably 10 to 40% by mass, and may be, for example, either 20 to 40% by mass or 30 to 40% by mass. When the ratio (vinyl acetate content) is equal to or higher than the lower limit value, the followability and adhesiveness of the resin sheet to the object to which it is applied become higher. For example, when covering the heating element with the resin sheet, the heating element can be easily covered with the resin sheet, and the resin sheet easily adheres to the heating element. When the ratio is equal to or lower than the upper limit value, the workability during the production of the resin sheet becomes higher.

[0037] The thermoplastic resin contained in the resin sheet may be only one kind, or two or more kinds. When there are two or more kinds, their combinations and ratios can be arbitrarily selected according to the purpose.

[0038] The thermoplastic resin contained in the resin sheet is preferably an ethylene-vinyl acetate copolymer in that the effects of the present invention can be obtained more significantly.

[0039] In the resin sheet, the ratio ([content of thermoplastic resin (parts by mass)] / [total mass of resin sheet (parts by mass)] × 100) of the content (parts by mass) of the thermoplastic resin to the total mass (parts by mass) of the resin sheet is preferably 20% by mass or more, more preferably 25% by mass or more, and even more preferably 30% by mass or more. When the ratio is at least the lower limit value, the effect obtained by the resin sheet containing the thermoplastic resin becomes higher. In the resin sheet, the ratio of the content (parts by mass) of the thermoplastic resin to the total mass (parts by mass) of the resin sheet is preferably 45% by mass or less, and more preferably 40% by mass or less. When the ratio is at most the upper limit value, the effect obtained by the resin sheet containing components other than the thermoplastic resin becomes higher. In one embodiment, the ratio may be any one of, for example, 20 to 45% by mass, 25 to 45% by mass, and 30 to 45% by mass, or any one of 20 to 40% by mass, 25 to 40% by mass, and 30 to 40% by mass. However, these are merely examples of the ratio. The ratio is usually the same as the ratio ([content of thermoplastic resin (parts by mass)] / [total content of components that do not vaporize at normal temperature in the resin composition (parts by mass)] × 100) of the content (parts by mass) of the thermoplastic resin to the total content (parts by mass) of components that do not vaporize at normal temperature in the resin composition described below.

[0040] In this specification, "normal temperature" means a temperature without particularly cooling or heating, that is, an ordinary temperature, and examples thereof include a temperature of 15 to 25°C.

[0041] <<Thermally Conductive Filler>> The thermally conductive filler is not particularly limited as long as it can improve the thermal conductivity of the resin sheet. Examples of the thermally conductive filler include plate-like fillers and connecting fillers.

[0042] The heat conductive filler contained in the resin sheet may be only one type or two or more types. When there are two or more types, their combinations and ratios can be arbitrarily selected according to the purpose.

[0043] <Plate-shaped filler> In the resin sheet, the plate-shaped filler is likely to be oriented such that its plane direction is the same as or close to the plane direction of the resin sheet. Therefore, since the resin sheet contains the plate-shaped filler, the thermal conductivity of the resin sheet in its plane direction becomes higher, and the heat dissipation property in its plane direction becomes higher. For example, when using fillers other than plate-shaped fillers, such as polyhedral fillers or card house-shaped fillers (fillers in which plate-shaped fillers aggregate to form secondary particles), instead of plate-shaped fillers, the heat dissipation property of the resin sheet in its plane direction tends not to be as high as when using plate-shaped fillers. Furthermore, card house-shaped fillers do not contribute to improving the flexibility of the resin sheet during heating.

[0044] The aspect ratio ([particle diameter of the plate-shaped filler] / [thickness of the plate-shaped filler]) of the plate-shaped filler is preferably 10 to 50, and may be any of, for example, 10 to 30, 20 to 40, and 30 to 50. When the aspect ratio of the plate-shaped filler is within such a range, the effect obtained by the resin sheet containing the plate-shaped filler becomes higher.

[0045] As the particle diameter of the plate-shaped filler, for example, the maximum value of the length of the line segment connecting two different points on the outer periphery of the plate-shaped filler can be adopted. As the thickness of the plate-shaped filler, for example, the maximum value of the distance between the main surfaces of the plate-shaped filler can be adopted. As the aspect ratio of the plate-shaped filler, for example, the average value of the aspect ratios of 50 randomly selected plate-shaped fillers can be adopted.

[0046] The average particle diameter of the plate-shaped filler is preferably 5 μm or more, and for example, it may be either 6.5 μm or more, or 8 μm or more. When the average particle diameter of the plate-shaped filler is at least the above lower limit value, the effect obtained by using the plate-shaped filler becomes higher. The upper limit value of the average particle diameter of the plate-shaped filler is not particularly limited. For example, a plate-shaped filler having an average particle diameter of 15 μm or less is more easily available. In one embodiment, the average particle diameter of the plate-shaped filler may be, for example, any one of 5 to 15 μm, 6.5 to 15 μm, and 8 to 15 μm. However, these are examples of the average particle diameter of the plate-shaped filler.

[0047] In this specification, not limited to the case of the plate-shaped filler, the "average particle diameter" means, unless otherwise specified, the particle diameter (D50) at 50% cumulative of the particles when the particle size distribution of the particles is measured on a volume basis by the laser diffraction particle size distribution measurement method.

[0048] The thermal conductivity of the plate-shaped filler may be, for example, any one of 5 W / m·K or more, 10 W / m·K or more, 25 W / m·K or more, and 40 W / m·K or more. The upper limit value of the thermal conductivity of the plate-shaped filler is not particularly limited. For example, a plate-shaped filler having a thermal conductivity of 400 W / m·K or less is more easily available. In one embodiment, the thermal conductivity of the plate-shaped filler may be, for example, any one of 5 to 400 W / m·K, 10 to 400 W / m·K, 25 to 400 W / m·K, and 40 to 400 W / m·K. However, these are examples of the thermal conductivity of the plate-shaped filler.

[0049] Not limited to the plate-shaped filler, the thermal conductivity of the filler can be measured, for example, by a method of preparing a sintered body of the filler and measuring it using a known thermal conductivity measuring device such as the laser flash method or the hot disk method, or a method of measuring it using a thermal property microscope or the like.

[0050] In terms of being able to more easily lower the relative permittivity of the resin sheet described below, the relative permittivity of the plate-like filler is preferably 5.5 or less, and more preferably 4.5 or less. On the other hand, the lower limit value of the relative permittivity of the plate-like filler is not particularly limited. For example, plate-like fillers with a relative permittivity of 3.5 or more are more easily prepared or obtained.

[0051] Examples of the material of the plate-like filler include metal nitrides such as boron nitride; metal oxides such as aluminum oxide.

[0052] The plate-like filler contained in the resin sheet may be only one type or two or more types. When there are two or more types, their combinations and ratios can be arbitrarily selected according to the purpose.

[0053] The plate-like filler preferably consists of boron nitride (BN) or aluminum oxide (Al2O3) (that is, it is a boron nitride filler or an aluminum oxide filler). A resin sheet containing such a plate-like filler not only has high heat dissipation, but also has better fluidity during heating and higher followability to the object to which the resin sheet is applied. For example, when covering a heating element with the resin sheet, the heating element can be easily covered with the resin sheet.

[0054] More preferably, the plate-like filler consists of boron nitride (BN) (that is, it is a boron nitride filler). A resin sheet containing such a plate-like filler not only has the above-mentioned preferable characteristics, but also has more preferable characteristics as described below because its relative permittivity is lower.

[0055] In the resin sheet, the ratio ([content (volume part) of plate-like filler in resin sheet] / [total volume (volume part) of resin sheet]×100) of the content (volume part) of the plate-like filler to the total volume (volume part) of the resin sheet is preferably 10% by volume or more, and for example, it may be any one of 15% by volume or more, 20% by volume or more, and 25% by volume or more. When the ratio is at least the lower limit value, the effect obtained by using the plate-like filler becomes higher. In the resin sheet, the ratio of the content (volume part) of the plate-like filler to the total volume (volume part) of the resin sheet is preferably 35% by volume or less, and for example, it may be any one of 30% by volume or less, 25% by volume or less, and 20% by volume or less. When the ratio is at most the upper limit value, the effect obtained by using fillers other than the plate-like filler, such as the connecting filler, becomes higher. In one embodiment, the ratio may be, for example, any one of 10 - 35% by volume, 15 - 35% by volume, 20 - 35% by volume, and 25 - 35% by volume, or any one of 10 - 30% by volume, 15 - 30% by volume, 20 - 30% by volume, and 25 - 30% by volume, or any one of 10 - 25% by volume, 15 - 25% by volume, and 20 - 25% by volume, or 10 - 20% by volume. However, these are merely examples of the ratio.

[0056] <Connecting filler> In the resin sheet, the connecting filler can be widely distributed in both the plane direction and the thickness direction of the resin sheet. Furthermore, as will be described later, the size of the connecting filler is small. Therefore, the connecting filler can connect the plate-like fillers to each other through itself by maintaining contact with the plate-like filler in both the plane direction and the thickness direction of the resin sheet. As a result, since the resin sheet contains the connecting filler, the thermal conductivity of the resin sheet becomes higher in both its plane direction and thickness direction, and the heat dissipation property in its plane direction and thickness direction becomes higher. When the resin sheet does not contain the connecting filler, the heat dissipation property of the resin sheet in its plane direction and thickness direction does not become this high.

[0057] The average particle diameter of the connecting filler is preferably 2 μm or less, more preferably 1.5 μm or less, and may be, for example, either 1.2 μm or less or 0.9 μm or less. When the average particle diameter of the connecting filler is equal to or less than the above upper limit value, the effect of connecting the plate-like fillers by the connecting filler becomes higher. The lower limit value of the average particle diameter of the connecting filler is not particularly limited. For example, a connecting filler having an average particle diameter of 0.5 μm or more is more easily available, and by using such a connecting filler, the heat dissipation property of the resin sheet can be more easily improved. In one embodiment, the average particle diameter of the connecting filler may be, for example, any one of 0.5 to 2 μm, 0.5 to 1.5 μm, 0.5 to 1.2 μm, and 0.5 to 0.9 μm. However, these are merely examples of the average particle diameter of the connecting filler.

[0058] The shape of the connecting filler is not particularly limited, but preferably has a shape having a plane, and more preferably is plate-shaped. Since the connecting filler has a plane, particularly when it is plate-shaped, the contact area between the connecting filler and the plate-like filler becomes larger. As described above, since the plate-like filler is likely to be oriented in the same direction as the plane direction of the resin sheet or in a direction close to the plane direction of the resin sheet, even if the connecting filler has a plane, as the overall shape of the connecting filler deviates from the plate shape, the contact area between the connecting filler and the plate-like filler tends to become smaller. However, when the average particle diameter of the connecting filler is 2 μm or less, the effect of maintaining the contact between the connecting filler and the plate-like filler becomes higher.

[0059] The connecting filler is preferably a non-aggregate (not an aggregate). The lower the content of the connecting filler that is an aggregate in the resin sheet, the more improved the fluidity of the resin sheet during heating, and the higher the followability of the resin sheet to the object to which it is applied. For example, when covering a heating element with the resin sheet, the heating element can be easily covered with the resin sheet.

[0060] The thermal conductivity of the connecting filler may be, for example, any one of 5 W / m·K or more, 10 W / m·K or more, 25 W / m·K or more, and 40 W / m·K or more. The upper limit value of the thermal conductivity of the connecting filler is not particularly limited. For example, a connecting filler having a thermal conductivity of 400 W / m·K or less is more easily available. In one embodiment, the thermal conductivity of the connecting filler may be, for example, any one of 5 to 400 W / m·K, 10 to 400 W / m·K, 25 to 400 W / m·K, and 40 to 400 W / m·K. However, these are examples of the thermal conductivity of the connecting filler.

[0061] Examples of the material of the connecting filler include metal hydroxides such as magnesium hydroxide.

[0062] The surface of the connecting filler may or may not be treated with a surface treatment agent. By using a surface-treated connecting filler, for example, the affinity between the connecting filler and a resin such as a thermoplastic resin is improved, and the fluidity of the resin sheet is improved, so that the followability and adhesiveness of the resin sheet to the object to which it is applied are higher. Examples of the surface treatment of the connecting filler include surface treatment with a fatty acid or an organosilicon compound (silane coupling agent).

[0063] The connecting filler contained in the resin sheet may be only one type or two or more types. In the case of two or more types, their combinations and ratios can be arbitrarily selected according to the purpose.

[0064] The connecting filler preferably consists of magnesium hydroxide (Mg(OH)2) (that is, it is a magnesium hydroxide filler). Since magnesium hydroxide is also a flame retardant, a resin sheet containing such a connecting filler has high heat dissipation and high flame retardancy.

[0065] The flame-retardant resin sheet such as the above resin sheet containing a magnesium hydroxide filler can meet, for example, the grades V-0, V-1 or V-2 of the UL94 standard.

[0066] In the resin sheet, the ratio ([content (volume part) of the connecting filler in the resin sheet] / [total volume (volume part) of the resin sheet]×100) of the content (volume part) of the connecting filler to the total volume (volume part) of the resin sheet is preferably in a numerical range that satisfies the ratio of the content of the connecting filler to the content of the above plate-shaped filler. For example, it is preferably 6% by volume or more. For example, it may be any one of 9.8% by volume or more, 14% by volume or more, 20% by volume or more, and 25% by volume or more. When the ratio is equal to or higher than the lower limit value, the effect obtained by using the connecting filler becomes higher. In the resin sheet, the ratio of the content (volume part) of the connecting filler to the total volume (volume part) of the resin sheet is preferably 49% by volume or less. For example, it may be any one of 33% by volume or less and 21% by volume or less. When the ratio is equal to or lower than the upper limit value, the effect obtained by using fillers other than the connecting filler, such as the plate-shaped filler, becomes higher. In one embodiment, the ratio may be, for example, any one of 6 to 49% by volume, 9.8 to 49% by volume, 14 to 49% by volume, 20 to 49% by volume, and 25 to 49% by volume, or any one of 6 to 33% by volume, 9.8 to 33% by volume, 14 to 33% by volume, and 20 to 33% by volume, or any one of 6 to 21% by volume, 9.8 to 21% by volume, and 14 to 21% by volume. However, these are examples of the ratio.

[0067] <Combination of plate-shaped filler and connecting filler> The resin sheet preferably contains either or both of a plate-shaped filler and a connecting filler as the heat conductive filler, and more preferably contains both the plate-shaped filler and the connecting filler. In the resin sheet containing both the plate-shaped filler and the connecting filler, the thermal conductivity is particularly high and the heat dissipation property in both the plane direction and the thickness direction is particularly high.

[0068] When the resin sheet contains a plate-shaped filler and a connecting filler, in the resin sheet, the ratio of the content of the connecting filler to the content of the plate-shaped filler ([content of the connecting filler in the resin sheet (volume part)] / [content of the plate-shaped filler in the resin sheet (volume part)] × 100) is preferably 60% by volume or more, and may be any of, for example, 65% by volume or more, 70% by volume or more, 90% by volume or more, and 200% by volume or more. By the ratio being at least the lower limit value, in addition to the effect obtained by containing the plate-shaped filler being sufficient, the effect obtained by using the connecting filler becomes higher, and these effects are obtained in a well-balanced manner. In the resin sheet, the ratio of the content of the connecting filler to the content of the plate-shaped filler is preferably 300% by volume or less, and may be any of, for example, 250% by volume or less, 140% by volume or less, 110% by volume or less, and 80% by volume or less. By the ratio being at most the upper limit value, in addition to the effect obtained by containing the connecting filler being sufficient, the effect obtained by using the plate-shaped filler becomes higher, and these effects are obtained in a well-balanced manner. In one embodiment, the ratio is preferably 60 to 300% by volume, and may be, for example, any one of 65 to 300% by volume, 70 to 300% by volume, 90 to 300% by volume, and 200 to 300% by volume, or any one of 60 to 250% by volume, 65 to 250% by volume, 70 to 250% by volume, and 90 to 250% by volume, or any one of 60 to 140% by volume, 65 to 140% by volume, 70 to 140% by volume, and 90 to 140% by volume, or any one of 60 to 110% by volume, 65 to 110% by volume, 70 to 110% by volume, and 90 to 110% by volume, or any one of 60 to 80% by volume, 65 to 80% by volume, and 70 to 80% by volume. However, these are only examples of the ratio.

[0069] <<Other components>> The resin sheet may or may not contain other components that do not fall under either the thermoplastic resin or the thermally conductive filler, as long as the effects of the present invention are not impaired. The other components can be arbitrarily selected according to the purpose and are not particularly limited.

[0070] The other components contained in the resin sheet may be only one type or two or more types. When there are two or more types, their combinations and ratios can be arbitrarily selected according to the purpose.

[0071] Examples of the other components include additives known in the art. Examples of the additives include antioxidants, antistatic agents, viscosity reducers, thickeners, infrared absorbers, ultraviolet absorbers, antiblocking agents, and the like.

[0072] In the resin sheet, the ratio (([content of thermoplastic resin in resin sheet (parts by mass)] + [content of thermally conductive filler in resin sheet (parts by mass)]) / [total mass of resin sheet (parts by mass)] × 100) of the total content (parts by mass) of the thermoplastic resin and the thermally conductive filler to the total mass (parts by mass) of the resin sheet is preferably 80% by mass or more, more preferably 90% by mass or more, and may be, for example, any one of 95% by mass or more, 97% by mass or more, and 99% by mass or more. When the ratio is at least the lower limit value, the heat dissipation property and the followability of the resin sheet become higher in a well-balanced manner. On the other hand, the ratio is 100% by mass or less. The ratio is usually the same as the ratio (([content of thermoplastic resin in resin composition (parts by mass)] + [content of thermally conductive filler in resin composition (parts by mass)]) / [total content of components that do not vaporize at room temperature in resin composition (parts by mass)] × 100) of the total content (parts by mass) of the thermoplastic resin and the thermally conductive filler to the total content (parts by mass) of components that do not vaporize at room temperature in the resin composition described below.

[0073] The thickness of the resin sheet is preferably 0.1 mm or more, more preferably 0.3 mm or more, and may be, for example, 0.5 mm or more. When the thickness of the resin sheet is at least the lower limit value, the heat dissipation property of the resin sheet becomes higher. On the other hand, the thickness of the resin sheet is preferably 5 mm or less, and may be, for example, any one of 3.5 mm or less, 1.5 mm or less, and 0.7 mm or less. When the thickness of the resin sheet is at most the upper limit value, the flexibility of the resin sheet during heating becomes higher, and as a result, the followability of the resin sheet becomes higher. For example, when covering a heating element with the resin sheet, the heating element can be easily covered with the resin sheet. In one embodiment, the thickness of the resin sheet may be, for example, any one of 0.1 to 5 mm, 0.1 to 3.5 mm, 0.1 to 1.5 mm, and 0.1 to 0.7 mm, or any one of 0.3 to 5 mm, 0.3 to 3.5 mm, 0.3 to 1.5 mm, and 0.3 to 0.7 mm, or any one of 0.5 to 5 mm, 0.5 to 3.5 mm, 0.5 to 1.5 mm, and 0.5 to 0.7 mm. However, these are merely examples of the thickness of the resin sheet. As will be described later, it is preferable to adjust the thickness of the resin sheet according to the thickness of the object to which the resin sheet is applied.

[0074] <<Properties of the Resin Sheet>> <Embedding Ratio R> Using a test piece that is one resin sheet and has a thickness of T0, or a laminate of two or more resin sheets and has a thickness of T0, and applying a pressure of 12 kPa in the thickness direction of the test piece for 10 minutes in an environment of 100°C, when measuring the thickness T1 of the test piece at the site where the pressure is applied, the following formula: R = (T0 - T1) / T0 × 100 The embedding ratio R calculated by the formula is preferably 30% or more. Since the resin sheet with the embedding ratio R within such a range has higher flexibility during heating, it can cover the object to which it is applied better. For example, in a heating environment, such a resin sheet can cover the object to which it is applied by following the object well, and furthermore, at least a part of the object to which it is applied is embedded in the resin sheet, so that the heat dissipation effect of the resin sheet becomes higher. Hereinafter, with reference to the drawings, the method for calculating the embedding ratio R will be described in more detail.

[0075] FIG. 2 is a cross-sectional view for schematically explaining the method for calculating the embedding ratio R of the test piece using the resin sheet. In the figures after FIG. 2, the same components as those shown in the already explained figures are denoted by the same reference numerals as in the case of the already explained figures, and their detailed explanations are omitted.

[0076] For example, in order to measure T1 (the thickness of the test piece at the pressed portion after heating and pressing), as shown in FIG. 2(a), the test piece 10 is placed on a plane, and the pushing material 9 is placed near the center of one surface 10a, which is the upward exposed surface of the test piece 10. The pushing material 9 is a means for contacting the test piece 10, applying pressure, and pushing the test piece 10 in. The test piece 10 is either a single resin sheet itself or a laminate of two or more resin sheets. Regardless of which of these the test piece 10 is, in the thickness direction of the test piece 10, the thickness of the test piece 10 in a state where no pressure is applied to the test piece 10 is T0. T0 is not particularly limited, and for example, it may be any of 500 μm or more, 1000 μm or more, and 1500 μm or more, and may also be any of 3500 μm or less, 3000 μm or less, and 2500 μm or less.

[0077] In FIG. 2, the display of the contents of the test piece 10 (resin sheet) is omitted. Also in the figures after FIG. 3 and in the cross-sectional view of the resin sheet of the present embodiment, the display of the contents of the resin sheet is omitted.

[0078] The constituent material of the pushing material 9 is not particularly limited as long as it is hard, and examples thereof include various ceramics. The shape of the pushing material 9 is not particularly limited as long as the contact portion with the test piece 10 is a plane, and for example, it may be any of a prismatic shape, a frustum of a pyramid shape, a cylindrical shape, a frustum of a cone shape, an elliptical column shape, an elliptical frustum shape, etc. The area of the contact surface (in other words, the pushing surface) 9b of the pushing material 9 with the test piece 10 may be smaller than the area of one surface 10a of the test piece 10, but it is preferably 0.05 to 0.30 times the area of one surface 10a of the test piece 10.

[0079] Next, a weight 8 is placed on the other surface (the upward exposed surface that does not contact one surface 10a of the test piece 10) 9a of the pushing material 9 in this state. The weight 8 may be placed on a partial area of the other surface 9a of the pushing material 9 or on the entire surface. The hammer 8 placed on the pressing member 9 may be one or two or more. In this way, by placing the hammer 8 on the pressing member 9 and stacking the test piece 10, the pressing member 9, and the hammer 8 in this order to form the laminate 100, a pressure of 12 kPa is applied to the test piece 10 in the thickness direction by the pressing member 9 and the hammer 8.

[0080] Next, the laminate 100 in this state is immediately placed in an environment of 100°C and left standing for 10 minutes. As described above, a pressure of 12 kPa is applied to the test piece 10 in the thickness direction of the test piece 10 for 10 minutes in an environment of 100°C. When the laminate 100 is placed in an environment of 100°C, the heated test piece 10 softens, is pushed in by the pressing member 9, and the contact portion of the test piece 10 with the pressing member 9 sinks in. Next, after 10 minutes have elapsed, immediately measure the thickness T1 of the test piece 10 at the portion where the pressure is applied in the laminate 100 in the state of being heated and pressurized.

[0081] As described above, since T0 and T1 can be measured, the embedding rate R of the test piece 10 is calculated by the above formula using these measured values.

[0082] In terms of being able to better cover the heating element with the resin sheet, the embedding rate R is preferably 35% or more, and for example, it may be any one of 40% or more, 45% or more, and 50% or more. On the other hand, the upper limit value of the embedding rate R is not particularly limited. For example, a resin sheet with an embedding rate R of 68% or less or 60% or less can be manufactured more easily. In one embodiment, the embedding rate R may be, for example, any one of 30 - 68%, 35 - 68%, 40 - 68%, 45% - 68%, and 50 - 68%, or any one of 30 - 63%, 35 - 63%, 40 - 63%, 45 - 63%, and 50 - 63%. However, these are examples of the embedding rate R.

[0083] The embedding rate R of the resin sheet can be adjusted, for example, by adjusting the type and content of the components contained in the resin sheet, particularly the type and content of the thermoplastic resin.

[0084] <Thermal conductivity in the plane direction> The thermal conductivity of the resin sheet in the plane direction is preferably 2 W / m·K or more, more preferably 2.4 W / m·K or more, and may be, for example, 2.8 W / m·K or more. The resin sheet with the thermal conductivity equal to or higher than the lower limit value has high heat dissipation in its plane direction. The upper limit value of the thermal conductivity of the resin sheet in the plane direction is not particularly limited. For example, a resin sheet with the thermal conductivity of 15 W / m·K or less can be manufactured more easily. In one embodiment, the thermal conductivity of the resin sheet in the plane direction may be, for example, any one of 2 to 15 W / m·K, 2.4 to 15 W / m·K, and 2.8 to 15 W / m·K. Not limited to the resin sheet, more specifically, the thermal conductivity in the plane direction of the resin sheet is the thermal conductivity of the resin sheet in a direction parallel to one surface or the other surface of the resin sheet.

[0085] The thermal conductivity of the resin sheet in the plane direction can be measured, for example, by the hot disk method in accordance with ISO 22007-2. For example, the thermal conductivity can be measured using a hot disk method thermal property measuring device manufactured by Kyoto Electronics Industry Co., Ltd. (for example, "TPS 2500 S", "TPS 500 S", etc.).

[0086] The thermal conductivity of the resin sheet in the plane direction can be adjusted, for example, by adjusting the type of the thermoplastic resin and its content in the resin sheet; the type of the thermally conductive filler and its content in the resin sheet; the thickness of the resin sheet, etc.

[0087] [Relative permittivity] The relative permittivity of the resin sheet at a frequency of 10 GHz, measured in accordance with the TM0m0 mode cavity resonator perturbation method, is preferably 4 or less, and may be, for example, any one of 3.75 or less, 3.65 or less, and 3.55 or less. The resin sheet having a relative permittivity at a frequency of 10 GHz equal to or less than the above upper limit value has high insulation properties. For example, in a circuit in an object to which the resin sheet is attached, it is particularly suitable as a covering for a heating element on a circuit board because it has a high effect of suppressing the generation of electrical signal noise. The lower limit value of the relative permittivity at a frequency of 10 GHz is not particularly limited. For example, the resin sheet having a relative permittivity at a frequency of 10 GHz of 1 or more can be manufactured more easily. In one embodiment, the relative permittivity at a frequency of 10 GHz may be, for example, any one of 1 to 4, 1 to 3.75, 1 to 3.65, and 1 to 3.55. However, these are examples of the relative permittivity at a frequency of 10 GHz. The relative permittivity at a frequency of 10 GHz is preferably a measured value at normal temperature (for example, under a temperature condition of 23 °C).

[0088] The relative permittivity of the resin sheet at a frequency of 1 GHz, measured in accordance with the TM0m0 mode cavity resonator perturbation method, is preferably 4 or less, and may be, for example, any one of 3.9 or less, and 3.8 or less. The resin sheet having a relative permittivity at a frequency of 1 GHz equal to or less than the above upper limit value has high insulation properties. For example, in a circuit in an object to which the resin sheet is attached, it is particularly suitable as a covering for a heating element on a circuit board because it has a high effect of suppressing the generation of electrical signal noise. The lower limit value of the relative permittivity at a frequency of 1 GHz is not particularly limited. For example, the resin sheet having a relative permittivity at a frequency of 1 GHz of 1 or more can be manufactured more easily. In one embodiment, the relative permittivity at a frequency of 1 GHz may be, for example, any one of 1 to 4, 1 to 3.9, and 1 to 3.8. However, these are examples of the relative permittivity at a frequency of 1 GHz. The relative permittivity at a frequency of 1 GHz is preferably a measured value at room temperature (for example, under temperature conditions of 23°C).

[0089] The relative permittivity of the resin sheet can be adjusted by adjusting the types and contents of the components contained in the resin sheet regardless of the frequency.

[0090] [Dielectric loss tangent] The dielectric loss tangent of the resin sheet at a frequency of 10 GHz, measured in accordance with the TM0m0 mode cavity resonator perturbation method, is preferably 0.01 or less, and may be, for example, any of 0.0065 or less, 0.0055 or less, and 0.0045 or less. The resin sheet with a dielectric loss tangent within such a range at a frequency of 10 GHz has high radio wave permeability and is suitable for constituting an electronic device equipped with an antenna. The lower limit value of the dielectric loss tangent at a frequency of 10 GHz is not particularly limited. For example, the resin sheet with a dielectric loss tangent of 0.001 or more at a frequency of 10 GHz can be manufactured more easily. In one embodiment, the dielectric loss tangent at a frequency of 10 GHz may be, for example, any of 0.001 to 0.01, 0.001 to 0.0065, 0.001 to 0.0055, and 0.001 to 0.0045. However, these are examples of the dielectric loss tangent at a frequency of 10 GHz. The dielectric loss tangent at a frequency of 10 GHz is preferably a measured value at room temperature (for example, under temperature conditions of 23°C).

[0091] The dielectric loss tangent of the resin sheet at a frequency of 1 GHz, measured in accordance with the TM0m0 mode cavity resonator perturbation method, is preferably 0.01 or less, and may be, for example, any of 0.009 or less and 0.008 or less. The resin sheet with a dielectric loss tangent within such a range at a frequency of 1 GHz has high radio wave permeability and is suitable for constituting an electronic device equipped with an antenna. The lower limit value of the dielectric loss tangent at a frequency of 1 GHz is not particularly limited. For example, the resin sheet with a dielectric loss tangent of 0.001 or more at a frequency of 1 GHz can be manufactured more easily. In one embodiment, the dielectric tangent at a frequency of 1 GHz may be, for example, any one of 0.001 to 0.01, 0.001 to 0.009, and 0.001 to 0.008. However, these are examples of the dielectric tangent at a frequency of 1 GHz. The dielectric tangent at a frequency of 1 GHz is preferably a measured value at room temperature (for example, under temperature conditions of 23°C).

[0092] The dielectric tangent of the resin sheet can be adjusted by adjusting the types and contents of the components contained in the resin sheet regardless of the frequency.

[0093] In the resin sheet, it is preferable that both the relative permittivity at a frequency of 10 GHz and the relative permittivity at a frequency of 1 GHz are within the above numerical ranges. In the resin sheet, it is preferable that both the dielectric tangent at a frequency of 10 GHz and the dielectric tangent at a frequency of 1 GHz are within the above numerical ranges. In the resin sheet, it is more preferable that the relative permittivity at a frequency of 10 GHz, the relative permittivity at a frequency of 1 GHz, the dielectric tangent at a frequency of 10 GHz, and the dielectric tangent at a frequency of 1 GHz are all within the above numerical ranges.

[0094] [Density] The density of the resin sheet is preferably 2 g / cm 3 or less, and for example, may be 1.7 g / cm 3 or less. Various electronic devices configured by mounting such a resin sheet are suitable as, for example, portable electronic devices because in addition to suppressing heat generation, they are lightweight. The lower limit value of the density of the resin sheet is not particularly limited. For example, a resin sheet with a density of 1 g / cm 3 or more can be more easily realized. In one embodiment, the density of the resin sheet is, for example, 1 to 2 g / cm 3 , and may be any one of 1 to 1.7 g / cm 3 . However, these are examples of the density of the resin sheet. The density of the resin sheet can be adjusted, for example, by adjusting the types and contents of the components contained in the resin sheet.

[0095] The density of the resin sheet can be measured by a known method. For example, it can be measured in accordance with JIS K 7112:1999 or JIS K 0061:2022 (density gradient tube method).

[0096] The resin sheet may be irradiated with an electron beam. In that case, the resin sheet is preferably irradiated with an electron beam under the condition of an absorbed dose of 20 to 300 kGy. The accelerating voltage of the electron beam irradiation is preferably 100 to 300 kV. By irradiating the resin sheet with an electron beam, the resin sheet is partially crosslinked, and the heat resistance and repairability of the resin sheet are improved.

[0097] <<Resin Composition and Method for Producing the Same>> The resin sheet of the present embodiment can be produced, for example, by using a resin composition containing the thermoplastic resin, the thermally conductive filler, and, if necessary, the other components.

[0098] The resin composition may contain a solvent in addition to the above-described components. The resin composition containing a solvent may have improved handleability. In this specification, unless otherwise specified, not only components capable of dissolving a solute in a solution but also components serving as a dispersion medium in a dispersion are referred to as "solvent".

[0099] The solvent is preferably an organic solvent, and more preferably an organic solvent that can be removed by vaporization when the resin composition is heated.

[0100] The content of the solvent in the resin composition can be arbitrarily selected according to the purpose and is not particularly limited.

[0101] The resin composition may be manufactured by adjusting the types and contents of the contained components so that the resin sheet contains the target components (constituent materials) in the target contents. For example, the ratio of the contents of the components that do not vaporize at normal temperature in the resin composition is usually the same as the ratio of the contents of the components in the resin sheet.

[0102] The resin composition can be manufactured by blending the thermoplastic resin, the thermally conductive filler, the other components as necessary, and the solvent as necessary. The order of addition during the blending of each component is not particularly limited, and two or more components may be added simultaneously. The method of mixing each component during blending is not particularly limited, and it may be appropriately selected from known methods. The temperature and time during the addition and mixing of each component are not particularly limited as long as each blended component does not deteriorate, and can be adjusted as appropriate.

[0103] The resin composition may be, for example, a kneaded product obtained by kneading the thermoplastic resin, the thermally conductive filler, and the other components as necessary.

[0104] ◇ Method for manufacturing the resin sheet The resin sheet can be manufactured, for example, by molding the resin composition to produce a resin sheet having no through holes (which may be referred to as an "unprocessed resin sheet" in this specification), and forming the through holes in the resin sheet having no through holes (the unprocessed resin sheet).

[0105] The resin composition can be molded by a known method. For example, when molding under vacuum conditions, the resin composition can be molded by vacuum heating press.

[0106] The molding temperature (pressurizing temperature) of the resin composition is preferably a temperature higher than the melting point of the thermoplastic resin. For example, it may be any one of a temperature 15°C or more higher than the melting point of the thermoplastic resin, a temperature 35°C or more higher than the melting point of the thermoplastic resin, and a temperature 55°C or more higher than the melting point of the thermoplastic resin. When the molding temperature is at or above the lower limit value, a resin sheet with higher uniformity can be obtained. The upper limit value of the molding temperature is not particularly limited. For example, if the molding temperature is equal to or lower than a temperature 75°C higher than the melting point of the thermoplastic resin, excessive heating can be avoided.

[0107] The pressure during the molding of the resin composition is not particularly limited as long as the effect of pressurization can be sufficiently obtained, but it is preferably 3 MPa or more. For example, it may be either 8 MPa or more, or 13 MPa or more. When the pressure is at or above the lower limit value, a resin sheet with higher uniformity can be obtained. The upper limit value of the pressure is not particularly limited. For example, if the pressure is 20 MPa or less, excessive pressurization can be avoided.

[0108] The molding time (pressurizing time) of the resin composition is not particularly limited as long as the effect of pressurization can be sufficiently obtained. For example, it can be arbitrarily set according to the pressure during molding as described above, but it is preferably 0.5 minutes or more. When the molding time is at or above the lower limit value, a resin sheet with higher uniformity can be obtained. The upper limit value of the molding time is not particularly limited. For example, if the molding time is 10 minutes or less, excessive pressurization can be avoided.

[0109] The molding of the resin composition is preferably carried out under reduced pressure. For example, it is more preferably carried out under vacuum conditions where the pressure is 0.05 MPa or less. By molding under reduced pressure in this way, a resin sheet with higher uniformity can be obtained.

[0110] The method for forming the through holes in the raw resin sheet may be a known method.

[0111] For example, by using a hole-making means configured to include a support and a plurality of needles provided on one surface of the support, pressing the needles against the raw resin sheet and penetrating them, and forming the through-holes in the raw resin sheet, a target resin sheet can be manufactured.

[0112] The support is for fixing and holding the needles in a state where the tip for inserting the needles faces outward (in a direction away from the support). As long as such an object can be achieved, the constituent material thereof may be any of metal, resin, etc., and is not particularly limited. As long as the constituent material of the needles has a mechanical strength sufficient to form through-holes in the raw resin sheet, it may be any of metal, resin, etc., and is not particularly limited. The hole-making means having a large number of the needles may be in the form of a pincushion, and a pincushion may be used as the hole-making means.

[0113] The arrangement form of the needles in the hole-making means may be the same as or different from the arrangement form of the assumed through-holes in the resin sheet. Even if the arrangement form of the needles in the hole-making means is different from the arrangement form of the assumed through-holes in the resin sheet, for example, by forming the through-holes by the hole-making means in the raw resin sheet two or more times while shifting the position of the hole-making means, a resin sheet having the target arrangement form of the through-holes may be obtained.

[0114] For example, by irradiating the raw resin sheet with laser light, disappearing the irradiated portion of the raw resin sheet, and forming the through-holes in the raw resin sheet, a target resin sheet can also be manufactured. The irradiation conditions of the laser light may be appropriately adjusted so as to appropriately form the through-holes, and are not particularly limited.

[0115] ◇ Method of using the resin sheet By using the resin sheet of the present embodiment to cover the surface of a heat-generating body such as a CPU, which is the object to which it is applied, heat generation in various electronic devices can be suppressed.

[0116] Figure 3 is a cross-sectional view for schematically explaining an example of the method of using the resin sheet. The circuit board 7 shown in Fig. 3(a), which is an object to which the resin sheet of the present embodiment is applied, is not particularly limited and may be a known one. On one surface 7a of the circuit board 7, a heat-generating body 5 such as a CPU is provided via a connection portion 6.

[0117] In the method of use of the present embodiment, first, as shown in Fig. 3(a), the resin sheet 1 is brought into contact with the exposed surface 5a of the heat-generating body 5 and disposed on one surface 7a of the circuit board 7. At this stage, one surface 1a of the resin sheet 1 may not be in contact with the one surface 7a of the circuit board 7 at all as shown here, or a part of the region may be in contact with any location on the one surface 7a of the circuit board 7.

[0118] When the resin sheet 1 is disposed on one surface 7a of the circuit board 7, at least both the vicinity region of the connection portion 6 and the heat-generating body 5 in the circuit board 7 are covered with the region of the resin sheet 1 having the through holes. These regions are likely to form voids without gas escaping when covered with a resin sheet having no through holes.

[0119] In the method of use of the present embodiment, then, the resin sheet 1 disposed on the circuit board 7 in this state is heated. As a result, at this time, even without applying pressure to the resin sheet 1, as shown in Fig. 3(b), the resin sheet 1 adheres well to both the exposed surface 5a of the heat-generating body 5, which is the object to be applied, and the one surface 7a of the circuit board 7, and exhibits good followability. For example, the resin sheet 1 can be adhered not only to the upper surface (the surface opposite to the side of the connection portion 6) of the exposed surface 5a of the heat-generating body 5 but also to at least a part of the side surface.

[0120] In this state, generation of voids is suppressed between one surface 7a of the circuit board 7 and one surface 1a of the resin sheet 1, and also between the exposed surface 5a of the heating element 5 and one surface 1a of the resin sheet 1. As a result, the other surface 1b of the resin sheet 1 reflects the shape of the heating element 5 protruding on the circuit board 7 and becomes convex in the region covering the heating element 5.

[0121] In FIG. 3(b), the resin sheet 1 is shown in a state where it does not contact one surface 7a of the circuit board 7 in the vicinity of the connection portion 6 and does not contact the exposed surface (side surface) of the connection portion 6. However, for example, by adjusting the heating temperature of the resin sheet 1, the thickness of the resin sheet 1, or the composition of the resin sheet 1, it is also possible to suppress the occurrence of such a non-contact state.

[0122] As described above, the resin sheet 1 has good followability to the object to which it is applied even without applying pressure in a heating environment. Such a heat-dissipating resin sheet has not been known conventionally.

[0123] The heating temperature of the resin sheet 1 is preferably 150°C or higher, and may be, for example, either 200°C or higher and 240°C or higher. When the heating temperature is at or above the lower limit value, the followability of the resin sheet 1 during heating becomes higher. On the other hand, the heating temperature of the resin sheet 1 is preferably 300°C or lower in terms of suppressing the deterioration of the resin sheet 1. More specifically, as the heating temperature of such a resin sheet 1, for example, the heating temperature in the solder reflow process can be mentioned.

[0124] The time (heating time) when heating the resin sheet 1 at the above-described heating temperature is preferably 1 to 10 minutes.

[0125] The resin sheet 1 may be heated step by step. For example, the resin sheet 1 may be heated in the first stage at 150 to 190°C for 1 to 9 minutes, and then heated in the second stage at 200°C or higher for 1 to 9 minutes. And it is preferable that the total heating time of the first stage and the second stage is 1 to 10 minutes.

[0126] In the state where the heating element 5 is covered with the resin sheet 1 in this way, the heat generated by the heating element 5 is conducted in the resin sheet 1 along its surface direction D S and is radiated into the atmosphere, for example. Also, the heat generated by the heating element 5 is conducted in the resin sheet 1 along its thickness direction D T and is radiated into the atmosphere, for example. Furthermore, the heat conducted along the thickness direction D T of the resin sheet 1 may also be radiated into the atmosphere through the circuit board 7.

[0127] Fig. 3(b) shows a state in which one heating element 5 is provided on one surface 7a of the circuit board 7. However, the number of heating elements provided on one surface 7a of the circuit board 7 may be only one or two or more. When there are two or more heating elements provided on one surface 7a of the circuit board 7, these two or more heating elements may be the same as each other or different from each other. That is, all of the two or more heating elements may be the same, all may be different, or only some may be the same.

[0128] When there are two or more heating elements provided on one surface 7a of the circuit board 7, at least some of these heating elements may be covered separately by two or more resin sheets 1 instead of integrally.

[0129] After heating and causing the resin sheet 1 to follow the circuit board 7 and the heating element 5, a heat spreader may be provided on the resin sheet 1. The heat spreader may be a known one, and examples of its constituent materials include metals such as copper; carbon materials such as graphite, etc.

[0130] As described so far, since the resin sheet of the present embodiment has high flexibility during heating, it has excellent characteristics of following and covering the heating element in a heating environment. Therefore, the heat dissipation property of the resin sheet of the present embodiment is extremely excellent. On the other hand, for example, a conventional heat dissipation sheet such as a graphite sheet is excellent in heat dissipation, but does not have followability with respect to the object to be cooled and also has insufficient adhesion to the object to be cooled. Therefore, it is unsuitable as a heat dissipation structure provided alone on the heating element. Further, a heat dissipation sheet such as a graphite sheet is also a conductive sheet, and due to its conductivity (because it does not have insulating properties), it cannot be used in the vicinity of the antenna. For example, a thermal interface material (TIM) has adhesion to the object to be cooled and further has insulating properties, but is insufficient in heat dissipation and followability with respect to the object to be cooled. For example, a heat dissipation material that is liquid at normal temperature is also known. However, the use of the liquid heat dissipation material is limited to a sealed space, and moreover, its filling operation is complicated and its repairability is also poor. The resin sheet of the present embodiment can solve all such conventional problems.

Example

[0131] Hereinafter, the present invention will be described in more detail with specific examples. However, the present invention is not limited to the examples shown below at all. The raw materials and materials used in the examples and comparative examples are shown below.

[0132] [Thermoplastic resin] Thermoplastic resin (a1): Ethylene-vinyl acetate copolymer (EVA) (manufactured by Mitsui Dow Polychemical Co., Ltd., "Evaflex (registered trademark) EV150", melting point of about 60 ° C, MFR 30 g / 10 min, density 0.96 g / cm 3 , vinyl acetate content 33% by mass) The MFR of the EVA is a measured value when a load of 2.16 kg is applied under a temperature condition of 190 ° C in accordance with JIS K7210:1999.

[0133] [Plate-shaped filler] Plate-shaped filler (b1): Plate-shaped boron nitride filler (manufactured by Tokuyama Corporation, "K03", average particle diameter 9 μm, density 2.3 g / cm 3 , thermal conductivity 60 W / m·K, aspect ratio 30, relative permittivity 4) [Connecting filler] Connecting filler (c1): Magnesium hydroxide filler surface-treated with a higher fatty acid (manufactured by Kyowa Chemical Industry Co., Ltd., "KISUMA (registered trademark) 5B", magnesium hydroxide content of 95% by mass or more, higher fatty acid content of 5% by mass or less, average particle diameter of 0.83 μm, thermal conductivity of 8 W / m·K) Connecting filler (c2): Magnesium hydroxide filler (manufactured by Kyowa Chemical Industry Co., Ltd., "KISUMA (registered trademark) 8", average particle diameter of 1.38 μm, thermal conductivity of 8 W / m·K)

[0134] [Example 1] [Manufacture of resin sheet] A pellet-shaped resin composition was prepared by melt-kneading 33.3 parts by mass of a thermoplastic resin (a1), 16.7 parts by mass of a plate-shaped filler (b1), 5.0 parts by mass of a connecting filler (c1), and 45.0 parts by mass of a connecting filler (c2) using a twin-screw extruder. Furthermore, the obtained resin composition was sandwiched between a pair of hot plates and vacuum-heat pressed at a pressure of 15 MPa for 1 minute while heating at 120°C under a vacuum condition of a pressure of 0.02 MPa or less to obtain an unprocessed resin sheet having a single-layer structure (size: 150 mm × 150 mm, thickness: 1 mm).

[0135] A metal support and a large number of needles made of metal and having substantially the same length provided on one surface of this support were provided, and all of these large number of needles were arranged at substantially equal intervals and facing in the same direction. By using a hedgehog-shaped hole-forming means, a large number of through-holes were formed in the unprocessed resin sheet obtained above to obtain a target resin sheet (thickness: 1 mm) as shown in Table 1. In the obtained resin sheet, the number of through-holes was 6.25 holes / cm 2 The average diameter of the through-holes was 688 μm, and the pitch of the through-holes was 4 mm.

[0136] In Table 1, "content of plate-shaped filler (volume %)" means "the ratio (volume %) of the content (volume part) of the plate-shaped filler to the total volume (volume part) of the resin sheet in the resin sheet". "Content of connecting filler (volume %)" means "the ratio (volume %) of the content (volume part) of the connecting filler to the total volume (volume part) of the resin sheet in the resin sheet". "Ratio of the content of the connecting filler to the content of the plate-shaped filler (volume %)" means "the ratio (volume %) of the content (volume part) of the connecting filler to the content (volume part) of the plate-shaped filler in the resin sheet".

[0137] <<Evaluation of Resin Sheet>> <Calculation of Embedding Ratio R> Two resin sheets (thickness 1 mm) obtained by the above method were laminated in their thickness directions and cut into a size of 3.5 cm × 3.5 cm to produce a test piece with a thickness T0 of 2 mm and a square planar shape. Next, the obtained test piece was placed on a plane, and a cylindrical pressing material made of ceramic with a diameter of 16 mm and a height of 14 mm was placed near the center of the upward exposed surface of the test piece. At this time, one plane instead of the curved surface of the pressing material was brought into contact with the exposed surface of the test piece. Further, one weight was placed on the entire other plane (the upward exposed surface not in contact with the exposed surface of the test piece) of the pressing material in this state. In this way, by laminating the test piece, the pressing material, and the weight in this order, a pressure of 12 kPa was applied to the test piece in its thickness direction. Then, this laminate was immediately transferred to an environment of 100 °C and left standing for 10 minutes. Thereby, a pressure of 12 kPa was applied to the test piece in its thickness direction for 10 minutes in an environment of 100 °C. Next, after 10 minutes had elapsed, immediately, the thickness T1 of the test piece at the part where the pressure was applied in the laminate in this state was measured. And the embedding ratio R of the test piece (resin sheet) was calculated by the above formula. The results are shown in Table 1.

[0138] <Confirmation of Followability of Resin Sheet> The resin sheet (thickness: 1 mm) obtained above was cut into pieces of 25 mm × 50 mm in size. An object 9 to which the resin sheet is to be applied, as shown in FIG. 4, was prepared. The object 9 to which the resin sheet is to be applied has, on one surface of a heat-resistant resin substrate 91, four flat rectangular parallelepiped-shaped first members 92 and one flat rectangular parallelepiped-shaped second member 93 that is smaller than the first member 92, which are arranged linearly. The first member 92 and the second member 93 are elements for electronic devices. The thickness of the first member 92 is 1 mm, and the size of the main surface of the first member 92 is 10 mm × 12 mm or 12 mm × 12 mm. The thickness of the second member 93 is 0.8 mm, and the size of the main surface of the second member 93 is 4.5 mm × 3 mm.

[0139] The resin sheet 1 was placed on the surface of the object 9 to which the resin sheet is to be applied, on the side where the first member 92 and the second member 93 are provided, so as to cover the first member 92 and the second member 93. At this time, a part of two of the first members 92 at both ends was exposed without being covered by the resin sheet 1 as shown in FIG. 4. The remaining two first members 92 and the second member 93 were all covered entirely with the resin sheet 1. The four first members 92, the one second member 93, and the vicinity regions of the substrate 91 where these first members 92 and second member 93 are located were all covered with the region of the resin sheet 1 having its through holes. In FIG. 4, the illustration of the through holes of the resin sheet 1 is omitted.

[0140] Such a laminate of the resin sheet and its application object was placed inside an oven and heat-treated at 180 °C for 5 minutes. Then, the temperature inside the oven was raised, and the laminate was further heat-treated at 250 °C for 2 minutes. Then, immediately, the laminate was taken out of the oven and allowed to cool to room temperature in the atmosphere, and then its appearance was visually observed. And the followability of the resin sheet to the application object in the laminate after the heat treatment in these two steps was evaluated according to the following criteria. The results are shown in Table 1. Further, the imaging data of the laminate (resin sheet) after the heat treatment in these two steps is shown in FIG. 5. (Evaluation Criteria) A: The resin sheet is in close contact with all of the exposed surface of the substrate, the exposed surface of the first member, and the exposed surface of the second member, without any voids or with the generation of voids being significantly suppressed, and the resin sheet has high followability. B: A narrow part of the resin sheet is not in close contact with any of the exposed surface of the substrate, the exposed surface of the first member, and the exposed surface of the second member, but most of the other areas of the resin sheet are in close contact, and the resin sheet has good followability. C: A wide area of the resin sheet is not in close contact with any of the exposed surface of the substrate, the exposed surface of the first member, and the exposed surface of the second member, and the resin sheet has low followability.

[0141] <Measurement of Thermal Conductivity of Resin Sheet in Plane Direction> For the resin sheet obtained above, in accordance with ISO 22007-2, using a hot disk method thermal property measurement device ("TPS 500 S" manufactured by Kyoto Electronics Industry Co., Ltd.), the thermal conductivity in its plane direction was measured. At this time, two resin sheets were sandwiched between heat insulating materials, and a sensor with a diameter of 7 mm was inserted between these resin sheets to measure the thermal conductivity of the resin sheet. The results are shown in Table 1.

[0142] <Measurement of Relative Permittivity and Dielectric Loss Tangent of Resin Sheet> At room temperature, a test piece of a predetermined size was cut out from the resin sheet obtained above, and for this test piece, in accordance with the TM0m0 mode cavity resonator perturbation method, the relative permittivity at frequencies of 1 GHz and 10 GHz, and the dielectric loss tangent at frequencies of 1 GHz and 10 GHz were measured. The results are shown in Table 1.

[0143] <Measurement of Density of Resin Sheet> In accordance with JIS K 7112:1999, the density of the resin sheet obtained above was measured. The results are shown in Table 1.

[0144] <<Manufacture and Evaluation of Resin Sheet>> [Example 2] Using the raw resin sheet obtained in Example 1, a target resin sheet (thickness: 1 mm) was obtained in the same manner as in Example 1, except that the number of formed through-holes was increased. More specifically, as the resin sheet, one having 25 through-holes / cm 2 with an average through-hole diameter of 703 μm and a through-hole pitch of 2 mm was manufactured. Then, this resin sheet was evaluated in the same manner as in Example 1. The results are shown in Table 1. Further, imaging data of the laminate (resin sheet) when confirming the followability of the resin sheet are shown in FIG. 5.

[0145] [Example 3] A raw resin sheet with a single-layer structure (thickness: 0.4 mm) was manufactured in the same manner as in Example 1, except that the conditions during vacuum heating press of the resin composition were changed. Then, a target resin sheet (thickness: 0.4 mm) was obtained in the same manner as in Example 1, except that this raw resin sheet was used. In the obtained resin sheet, the number of through-holes was 6.25 through-holes / cm 2 with an average through-hole diameter of 718 μm and a through-hole pitch of 4 mm. The obtained resin sheet was evaluated in the same manner as in Example 1. The results are shown in Table 1. Further, imaging data of the laminate (resin sheet) when confirming the followability of the resin sheet are shown in FIG. 6. Note that when calculating the embedding rate R, five resin sheets (thickness: 0.4 mm) were laminated in their thickness directions, and a test piece with a thickness T0 of 2 mm was prepared in the same manner as in Example 1 for the rest.

[0146] <<Evaluation of Resin Sheet>> [Comparative Example 1] The raw resin sheet with a single-layer structure (thickness: 1 mm) obtained in Example 1 was used as a comparative resin sheet having no through-holes, and this comparative resin sheet was evaluated in the same manner as the resin sheet in Example 1. The results are shown in Table 2. Further, imaging data of the laminate (resin sheet) when confirming the followability of the resin sheet are shown in FIG. 5.

[0147] [Comparative Example 2] The as - received resin sheet with a single - layer structure (thickness: 0.4 mm) obtained in Example 3 was used as a comparative resin sheet having no through - holes, and this comparative resin sheet was evaluated in the same manner as the resin sheet in Example 1. The results are shown in Table 2. Further, the imaging data of the laminate (resin sheet) when confirming the followability of the resin sheet is shown in FIG. 7.

[0148]

Table 1

[0149]

Table 2

[0150] As is clear from the above results, in Examples 1 to 3, the followability of the resin sheet was good, and even without applying pressure to the resin sheet in a heating environment, the resin sheet adhered well to the object to which it was applied. As shown in FIG. 5, in Examples 1 to 2, the surface of the resin sheet clearly reflected the shape of the exposed surfaces of the object to which it was applied, that is, the substrate, the first member, and the second member. In particular, in Example 2, the shape of the exposed surface of the object to which it was applied was reflected more highly than in Example 1, and the followability of the resin sheet was particularly high. As shown in FIG. 6, also in Example 3, the surface of the resin sheet clearly reflected the shape of the exposed surface of the object to which it was applied, and its accuracy was comparable to that of Example 2. When the resin sheets of Examples 1 to 3 were peeled off from the object to which they were applied, the shapes of the first member and the second member were clearly transferred onto these resin sheets. The resin sheets of Examples 1 to 3 had through - holes, and the number thereof was 6.25 - 25 holes / cm 2 and, particularly in the resin sheet of Example 2, the number of through - holes was 25 holes / cm 2

[0151] ​In Examples 1 to 3, the average diameter of the through-holes was 688 to 718 μm, and the pitch of the through-holes was 2 to 4 mm.

[0152] Furthermore, the resin sheets of Examples 1 to 3 contained a heat conductive filler and had high thermal conductivity and high heat dissipation in both the direction parallel to the surface and the thickness direction thereof. For example, the thermal conductivity in the plane direction of the resin sheets of Examples 1 to 3 was 3 W / m·K.

[0153] Note that the resin sheets of Examples 1 to 3 contained a plate-like filler and a connecting filler as the heat conductive filler, and in the resin sheets of Examples 1 to 3, the ratio of the content of the connecting filler to the content of the plate-like filler was 99.1% by volume.

[0154] Furthermore, the resin sheets of Examples 1 to 3 contained a thermoplastic resin and had high flexibility when heated. In Examples 1 to 3, the embedding rate R was 60.5% or more (60.5 to 61.2%).

[0155] Thus, the resin sheets of Examples 1 to 3 had both high heat dissipation and high flexibility when heated, had high followability to the object to be applied without applying pressure in a heating environment, and had a high heat dissipation effect.

[0156] Furthermore, the relative permittivity of the resin sheets of Examples 1 to 3 satisfied the condition of 4 or less in both cases of frequencies of 1 GHz and 10 GHz. The dielectric loss tangent of the resin sheets of Examples 1 to 3 satisfied the condition of 0.01 or less in both cases of frequencies of 1 GHz and 10 GHz. The density of the resin sheets of Examples 1 to 3 satisfied the following conditions. 3 The following conditions were satisfied.

[0157] On the other hand, in Comparative Examples 1 to 2, the followability of the resin sheet was low, and in a state where no pressure was applied to the resin sheet in a heating environment, it was not sufficiently adhered to the object to be applied. As shown in FIGS. 5 and 7, in Comparative Examples 1 and 2, the surface of the resin sheet did not reflect the shape of the exposed surface of the object to be applied, particularly the first member. More specifically, in the region away from the peripheral edge of the upper surface of the first member (the region closer to the center), the resin sheet tended to float from the first member. The resin sheet of Comparative Example 1 had the same composition and thickness as the resin sheets of Examples 1 and 2, but did not have through holes. Similarly, the resin sheet of Comparative Example 2 had the same composition and thickness as the resin sheet of Example 3, but did not have through holes.

Industrial Applicability

[0158] The present invention can be used as a new heat dissipation means in an electronic device equipped with a CPU, and is not limited to the CPU. It can also be used as a new heat dissipation means in other devices equipped with a heat generating body similar to the CPU.

Explanation of Reference Numerals

[0159] 1 ··· Resin sheet 5 ··· Heat generating body 6 ··· Connection part 7 ··· Circuit board 8 ··· Weight 9 ··· Pushing material 10 ··· Test piece 19 ··· Through hole D S ··· Plane direction of the resin sheet D T ··· Thickness direction of the resin sheet T0 ··· Thickness of the test piece T1 ··· Thickness of the test piece at the pressurized part after heating and pressurization

Claims

1. A resin sheet, The resin sheet contains a thermoplastic resin and a heat conductive filler, The resin sheet has through holes, The number of the through holes in the resin sheet is 4 to 400 pieces / cm ２ A resin sheet.

2. The resin sheet according to claim 1, wherein an average diameter of the through holes is 50 to 1000 μm.

3. The resin sheet according to claim 1 or 2, wherein a pitch of the through holes is 0.5 to 4 mm.

4. The resin sheet according to claim 1 or 2, wherein the resin sheet contains a plate-shaped filler and a connecting filler as the heat conductive filler.

5. The resin sheet according to claim 4, wherein an average particle diameter of the connecting filler is 2 μm or less.

6. Using one piece of the resin sheet or a laminate of two or more pieces of the resin sheet, and a test piece having a thickness of T ０ For the test piece, a pressure of 12 kPa is applied in the thickness direction of the test piece for 10 minutes in an environment of 100 °C, and the thickness T of the test piece at the site where the pressure is applied １ When measured, the following formula: R = (T ０ - T １ ) / T ０ × 100 The resin sheet according to claim 1 or 2, wherein an embedding rate R calculated by the formula is 30% or more.

7. The resin sheet according to claim 1 or 2, wherein a relative permittivity of the resin sheet at a frequency of 10 GHz measured in accordance with the TM0m0 mode cavity resonator perturbation method is 4 or less.

8. The resin sheet according to claim 1 or 2, wherein the dielectric loss tangent of the resin sheet at a frequency of 10 GHz, measured in accordance with the TM0m0 mode cavity resonator perturbation method, is 0.01 or less.

9. The resin sheet according to claim 4, wherein the plate-like filler is made of boron nitride or aluminum oxide.

10. The resin sheet according to claim 4, wherein the connecting filler is made of magnesium hydroxide.

11. The resin sheet according to claim 1 or 2, wherein the thermoplastic resin is an ethylene-vinyl acetate copolymer.

12. The resin sheet according to claim 4, wherein the ratio of the content of the connecting filler to the content of the plate-like filler in the resin sheet is 60 to 300% by volume.

13. The resin sheet according to claim 4, wherein the average particle diameter of the plate-like filler is 5 μm or more.

Images