Thermal conductive sheet, and method for manufacturing a thermal conductive sheet

Abstract

To provide a thermal conductive sheet that can alleviate stress under thermal cycling conditions while achieving both reliability and high thermal conductivity. [Solution] A thermal conductive sheet having a metal layer and a plurality of thermally conductive protrusions on at least a first surface of the metal layer, wherein when the contact area of ​​the protrusions, which have half the area of ​​the first surface and are located in the center centered on the centroid of the planar shape of the first surface, is denoted as Ac, and the contact area of ​​the protrusions, which are located in the peripheral part of the first surface other than the center, is denoted as Ap, the value obtained by dividing Ac by Ap (Ac / Ap) is 1.2 or more and 10 or less.

Description

Technical Field

[0001] The present invention relates to a heat conduction sheet and a method for manufacturing the heat conduction sheet.

Background Art

[0002] With the miniaturization of electronic devices such as power modules, image sensors, and high-performance computing (HPC), and the increase in the amount of information processing, the problem of heat generation has become more prominent, and the importance of heat diffusion from the heat source has increased. In LSI and the like in various electronic devices, if the LSI itself is exposed to high temperatures for a long time due to the heat generation of the elements used, there is a risk of malfunction or failure. Therefore, a heat conduction material is widely used to prevent the temperature rise of the LSI and the like. The heat conduction material can prevent the temperature rise of the device by diffusing the heat generated by the element or transmitting it to a heat dissipation member for discharging it to the outside of the system such as the atmosphere.

[0003] Heretofore, for the purpose of providing a wiring board or the like advantageous for improving the connection reliability of electronic components, an insulating board having a rectangular upper surface and a plurality of connection pads arranged linearly in the vertical and horizontal directions on the upper surface are provided. At least some of the plurality of connection pads arranged most outside are arranged in a convex or concave shape curved toward the outer periphery of the upper surface, and a plurality of pad conductors are arranged linearly. It has a plurality of openings arranged linearly, and at least a part of the upper surface is covered with a covering layer so that a part of the pad conductor is exposed at the opening. A wiring board characterized by being configured by the above has been reported (for example, see Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the conventional wiring board described in Patent Document 1 has a problem in that reliability issues can arise due to stress generation under thermal cycling conditions.

[0006] The present invention aims to solve the aforementioned conventional problems and achieve the following objectives. Specifically, the present invention aims to provide a thermal conductive sheet that can alleviate stress under thermal cycling conditions and achieve both reliability and high thermal conductivity. [Means for solving the problem]

[0007] The means to solve the aforementioned problem are as follows: <1> Metal layer, A thermal conductive sheet having a plurality of thermally conductive protrusions on at least a first surface of the metal layer, Let Ac be the contact area of ​​the convex portion which has half the area of ​​the first surface and is located at the center of the centroid of the planar shape of the first surface. When Ap is the contact area of ​​the convex portion located in the peripheral portion of the first surface other than the central portion, This thermal conductive sheet is characterized by having an Ac / Ap ratio of 1.2 to 10. <2> The metal layer further has a plurality of protrusions on the second surface opposite to the first surface. <1> This is the thermal conductive sheet described in [reference]. <3> The ratio of the contact area of ​​the plurality of protrusions with the first surface of the metal layer is 30% or more and 80% or less. <1> or <2> This is the thermal conductive sheet described in [reference]. <4> The ratio of the contact area of ​​the protrusion located at the center to the center of the first surface is 40% or more. <1> from <3> It is a thermal conductive sheet as described in one of the following. <5> The ratio of the contact area of ​​the protrusions arranged in the peripheral portion to the peripheral portion of the first surface is 70% or less. <1> from <4> It is a thermal conductive sheet as described in one of the following. <6> The thermal conductivity of the metal layer is 200 W / (m·K) or more. <1> from <5> It is a thermal conductive sheet as described in one of the following. <7> The metal layer comprises at least one of gold, silver, copper, and aluminum. <1> from <6> It is a thermal conductive sheet as described in one of the following. <8> The average thickness of the metal layer is 10 μm or more and 200 μm or less. <1> from <7> It is a thermal conductive sheet as described in one of the following. <9> The protrusion contains sinterable metal nanoparticles. <1> from <8> It is a thermal conductive sheet as described in one of the following. <10> The convex portion further comprises at least one of the following: a modified acrylate compound, an epoxy resin, an unsaturated polyester resin, a polyurethane resin, a bismaleimide resin, an alkyd resin, a phenolic resin, and a melamine resin. <9> This is the thermal conductive sheet described in [reference]. <11> The aforementioned <9> from <10> A method for manufacturing a heat conductive sheet as described in any of the following: The method for manufacturing a thermal conductive sheet is characterized by including a step of applying a composition containing the sinterable metal nanoparticles to at least a first surface of the metal layer to form the plurality of protrusions. <12> The aforementioned <1> from <8> A method for manufacturing a heat conductive sheet as described in any of the following: A step of applying a protective portion to at least a first surface of the metal layer, A step of forming the plurality of protrusions by plating the exposed surface of the metal layer to which the protective portion is not provided, A method for manufacturing a thermal conductive sheet, characterized by including the step of removing the protective portion. <13> The aforementioned <1> from <8> A method for manufacturing a heat conductive sheet as described in any of the following: A step of providing a protective portion on at least a first surface of a metal plate, A step of etching the exposed surface of the metal plate to which the protective portion is not provided to form the metal layer and the plurality of protrusions, A method for manufacturing a thermal conductive sheet, characterized by including the step of removing the protective portion.

Advantages of the Invention

[0008] According to the present invention, the above-mentioned various problems in the prior art can be solved, the above-mentioned object can be achieved, the stress under thermal cycle conditions can be relaxed, and a thermal conduction sheet that can achieve both reliability and high thermal conductivity can be provided.

Brief Description of the Drawings

[0009] [Figure 1] FIG. 1 is a plan view showing an example of the thermal conduction sheet of the present embodiment. [Figure 2] FIG. 2 is a cross-sectional view taken along the line A-A' of the thermal conduction sheet of FIG. 1. [Figure 3] FIG. 3 is a cross-sectional view taken along the line A-A' showing another example of the thermal conduction sheet of the present embodiment. [Figure 4] FIG. 4 is a plan view for explaining the central portion c and the peripheral portion p of the thermal conduction sheet of the present embodiment. [Figure 5] FIG. 5 is a schematic cross-sectional view showing an example of the process of the manufacturing method of the thermal conduction sheet of the first embodiment (Part 1). [Figure 6] FIG. 6 is a schematic cross-sectional view showing an example of the process of the manufacturing method of the thermal conduction sheet of the first embodiment (Part 2). [Figure 7] FIG. 7 is a schematic cross-sectional view showing an example of the process of the manufacturing method of the thermal conduction sheet of the first embodiment (Part 3). [Figure 8] FIG. 8 is a schematic cross-sectional view showing an example of the process of the manufacturing method of the thermal conduction sheet of the first embodiment (Part 4). [Figure 9] FIG. 9 is a schematic cross-sectional view showing an example of the process of the manufacturing method of the thermal conduction sheet of the second embodiment (Part 3). [Figure 10] FIG. 1 is a schematic cross-sectional view showing an example of the process of the manufacturing method of the thermal conduction sheet of the second embodiment (Part 4). [Figure 11] FIG. 11 is a schematic cross-sectional view showing an example of the process of the manufacturing method of the thermal conduction sheet of the third embodiment (Part 1). [Figure 12]Figure 12 is a schematic cross-sectional view showing an example of the process for manufacturing a heat conductive sheet according to the third embodiment (part 2). [Figure 13] Figure 13 is a schematic cross-sectional view showing an example of the process for manufacturing a heat conductive sheet according to the third embodiment (part 3). [Figure 14] Figure 14 is a schematic cross-sectional view showing an example of the process for manufacturing a thermal conductive sheet according to the third embodiment (part 4). [Figure 15] Figure 15 is a schematic cross-sectional view showing an example of the heat dissipation structure of this embodiment. [Modes for carrying out the invention]

[0010] (Thermal conductive sheet) The thermal conductive sheet of this embodiment is a thermal conductive sheet having a metal layer and a plurality of thermally conductive protrusions on at least a first surface of the metal layer. When the contact area of ​​the convex portion having half the area of ​​the first surface and positioned at the center of the centroid of the planar shape of the first surface is Ac, and the contact area of ​​the convex portion positioned at the peripheral part of the first surface other than the center is Ap, the value obtained by dividing Ac by Ap (Ac / Ap) is 1.2 or more and 10 or less.

[0011] Preferably, the thermal conductive sheet is a thermal conductive sheet having a plurality of protrusions on a second surface opposite to the first surface of the metal layer. Here, when the contact area of ​​the protrusions, which have half the area of ​​the second surface and are located in the center centered on the centroid of the planar shape of the second surface, is denoted as Ac, and the contact area of ​​the protrusions, which are located in the peripheral part of the second surface other than the center, is denoted as Ap, it is preferable that the value obtained by dividing Ac by Ap (Ac / Ap) is 1.2 or more and 10 or less.

[0012] The thermal conductive sheet of this embodiment has an area equal to half of the first surface, and when the contact area of ​​the convex portion located in the center centered on the centroid of the planar shape of the first surface is denoted as Ac, and the contact area of ​​the convex portion located in the peripheral portion of the first surface other than the center is denoted as Ap, the value obtained by dividing Ac by Ap (Ac / Ap) is 1.2 or more and 10 or less. By controlling the distribution of convex portions on the plane, it is possible to ensure the contact area with the substrate to be joined while mitigating stress that would normally be concentrated in the peripheral portion. Therefore, it is possible to provide a thermal conductive sheet that can reduce stress under thermal cycling conditions and achieve both reliability and high thermal conductivity.

[0013] Figures 1 and 2 are a plan view and a cross-sectional view of the AA' section of an example of a thermal conductive sheet according to this embodiment. The thermal conductive sheet 10 shown in Figures 1 and 2 has a metal layer 11 and a plurality of protrusions 12 on a first surface of the metal layer 11 and on a second surface opposite to the first surface. Here, as shown by the dashed line in Figure 4, the first surface of the metal layer 11 is divided into two equal-area parts: a central part c and a peripheral part p. The central part c has half the area of ​​the first surface and is the part centered on the centroid of the planar shape of the first surface (inside the rectangle shown by the dashed line in Figure 4), while the peripheral part p is the part of the first surface other than the central part c (outside the rectangle shown by the dashed line in Figure 4). Figure 4 is a plan view illustrating the central part c and peripheral part p of the heat conductive sheet of this embodiment, and the dashed line in Figure 4 is the boundary line dividing the central part c and peripheral part p into equal areas. When the contact area of ​​the convex part 12 located in the central part c is Ac, and the contact area of ​​the convex part 12 located in the peripheral part p is Ap, the value obtained by dividing Ac by Ap (Ac / Ap) is 1.2 or more and 10 or less. For example, in the thermal conductive sheet 10 shown in Figure 1, the area in contact with the multiple protrusions is 75% of the central part c of the first surface, and the area in contact with the multiple protrusions is 25% of the peripheral part p of the first surface, so Ac / Ap = 75 / 25 = 3.

[0014] As shown in Figure 3, which illustrates another example of the thermal conductive sheet of this embodiment, the thermal conductive sheet 10 may have a metal layer 11 and a plurality of protrusions 12 on a first surface (only one side). The thermal conductive sheet 10 shown in Figure 3 has a metal layer 11 and a plurality of protrusions 12 on a first surface of the metal layer 11. When the contact area of ​​the protrusions, which occupy half the area of ​​the first surface and are located at the center of the centroid of the planar shape of the first surface, is denoted as Ac, and the contact area of ​​the protrusions, which are located in the peripheral part of the first surface other than the center, is denoted as Ap, the value obtained by dividing Ac by Ap (Ac / Ap) is 1.2 or more and 10 or less.

[0015] <Metal layer> The material of the metal layer preferably contains a metal with high thermal conductivity, and more preferably consists of such a metal. From the viewpoint of thermal conductivity and safety, the aforementioned metals are preferably aluminum, nickel, iron, gold, silver, copper, zinc, and tin, and more preferably gold, silver, copper, aluminum, and nickel.

[0016] There are no particular restrictions on the thermal conductivity of the metal layer, and it can be appropriately selected according to the purpose. However, from the viewpoint of thermal conductivity, a value of 100 W / (m·K) or higher is preferred, and 200 W / (m·K) or higher is more preferred.

[0017] <<Convex part>> There are no particular limitations on the aforementioned protrusions, and they can be appropriately selected according to the purpose. Examples include metal formed by plating such as electrolytic plating or non-electrolytic plating; a metal material filled with a filler material if necessary; or a metal layer made of the same material as the metal layer cut from a metal plate. Among these, metals formed by electroplating are preferred. There are no particular restrictions on the metal formed by the electroplating, and it can be appropriately selected from the metals mentioned above depending on the purpose.

[0018] The aforementioned protrusion may be filled with a metal material, or it may be filled with a mixture of a metal material and a filler of any component. There are no particular restrictions on the type of metal material, and it can be appropriately selected according to the purpose. However, from the viewpoint of thermal conductivity and safety, aluminum, aluminum oxide, aluminum nitride, boron nitride, carbon resin, nickel, iron, gold, silver, copper, zinc, and tin are preferred, and gold, silver, copper, and nickel are more preferred. These may be used individually or in combination of two or more.

[0019] There are no particular restrictions on the shape of the metal material, and it can be appropriately selected according to the purpose. Examples include particles, plates, rods, and wires.

[0020] One embodiment of the metal material is preferably a sinterable metal nanoparticle, that is, a metal nanoparticle having sinterability. The protrusion may be filled with sinterable metal nanoparticles, filled with a mixture of sinterable metal nanoparticles and a binder resin of an optional component, or it may be a sintered product obtained by sintering sinterable metal nanoparticles.

[0021] Examples of the binder resin include modified acrylate compounds, epoxy resins, unsaturated polyester resins, polyurethane resins, bismaleimide resins, alkyd resins, phenolic resins, and melamine resins. These may be used individually or in combination of two or more.

[0022] As for the content of the metal material in the protrusions, from the viewpoint of thermal conductivity, 50% by mass or more is preferred, any of 60% by mass or more, 70% by mass or more, and 80% by mass or more is preferred, 90% by mass or more is even more preferred, 95% by mass or more is particularly preferred, and 99% by mass or more is most preferred.

[0023] The aforementioned filler is not particularly limited and can be appropriately selected according to the purpose, and examples include dispersants, surfactants, and binder resins.

[0024] [Area ratio] From the viewpoint of ensuring high thermal conductivity, the ratio of the contact area of ​​the plurality of protrusions with the first surface of the metal layer is preferably 30% to 80%, and more preferably 40% to 70%.

[0025] The ratio of the contact area of ​​the protrusion located on the center c to the center c of the first surface is preferably 40% or more, more preferably 50% or more, and even more preferably 60% or more. There is no particular upper limit, and it may be 100% or 90%.

[0026] The ratio of the contact area of ​​the protrusions arranged on the peripheral portion p to the peripheral portion p of the first surface is preferably 70% or less, and more preferably 60% or less. There is no particular lower limit, and it may be 10% or 20%.

[0027] [pattern] The pattern of the protrusions 12 when the heat conductive sheet is viewed in plan view is not particularly limited as long as (Ac / Ap) satisfies 1.2 or more and 10 or less, and can be appropriately selected according to the purpose. For example, a pattern in which multiple figures are arranged may be used, and the area of ​​the protrusions in the central part c may be large, or the arrangement density of the central part c of the multiple figures may be high and the arrangement density of the peripheral part p may be low.

[0028] In the case where the area of ​​the protrusion at the central part c is large, there are no particular restrictions on the length of the long side of the shape of the protrusion 12 at the central part c, and it can be appropriately selected according to the purpose, but it is preferable that it is 1 / 2 or less and 1 / 4 or more of the long side length of the thermal conductive sheet.

[0029] In a configuration where the arrangement density of the central part c of multiple figures is high and the arrangement density of the peripheral part p is low, there are no particular restrictions on the length of the long side of each protruding part 12 figure, and it can be appropriately selected according to the purpose, but it is preferably 10 μm or more and 1,000 μm or less, and more preferably 50 μm or more and 500 μm or less.

[0030] There are no particular restrictions on the thermal conductivity of the thermal conductive sheet, and it can be appropriately selected according to the purpose. However, from the viewpoint of thermal conductivity, a value of 100 W / (m·K) or higher is preferred, and 150 W / (m·K) or higher is more preferred.

[0031] There are no particular restrictions on the average thickness of the thermal conductive sheet, and it can be appropriately selected according to the purpose, but it is preferably 20 μm to 300 μm, more preferably 30 μm to 200 μm, and even more preferably 40 μm to 100 μm. The average thickness of the thermal conductive sheet can be determined by measuring the thickness of the thermal conductive sheet at 10 or more arbitrary points in the region having the protrusions and calculating the average value.

[0032] There are no particular restrictions on the average thickness of the metal layer, and it can be appropriately selected depending on the purpose, but it is preferably 10 μm to 200 μm, more preferably 20 μm to 100 μm, and even more preferably 30 μm to 75 μm. The "average thickness" can be determined by measuring at 10 or more arbitrary points and calculating the average value.

[0033] There are no particular restrictions on the average thickness of the protrusions, and they can be appropriately selected depending on the purpose, but a thickness of 5 μm to 100 μm is preferred, 10 μm to 75 μm is more preferred, and 20 μm to 50 μm is even more preferred.

[0034] The average thickness (T) of the aforementioned metal layer M The average thickness (T) of the protrusion relative to ) m ) ratio (T m / T M There are no particular restrictions on the value, and it can be selected appropriately depending on the purpose, but it is preferably 0.125 or more and 8 or less, and more preferably 0.2 or more and 4 or less, and more preferably 0.5 or more and 2 or less, from the viewpoint of further improving thermal conductivity and reliability.

[0035] In the case where the thermal conductive sheet has protrusions on both the first and second surfaces, for each protrusion on each surface, independently, the ratio (Ac / Ap), the pattern of the protrusions, the average thickness of the protrusions, and the ratio (T) are determined. m / T M Each of the following conditions can be set, and the conditions on the first surface and the conditions on the second surface may be different or the same.

[0036] (Method of manufacturing a thermal conductive sheet) There are no particular limitations on the method for manufacturing the thermal conductive sheet of this embodiment, and a suitable method can be selected depending on the purpose. Examples include a method of forming protrusions containing a metal material on a metal layer (first embodiment); a method of forming protrusions on a metal layer by plating (second embodiment); and a method of cutting out a metal part in which the metal layer and protrusions are integrated by etching a metal plate (third embodiment).

[0037] [First Embodiment] The method for manufacturing a heat conductive sheet in the first embodiment includes a protrusion forming step of forming a protrusion containing a metal material, and further includes, if necessary, other steps such as a protective part application step, a protective part removal step, a sintering step, and a polishing step. The heat conductive sheet of this embodiment described above can be suitably manufactured by the heat conductive sheet manufacturing method of the first embodiment.

[0038] Figures 5-8 show schematic cross-sectional views illustrating an example of the process for manufacturing a heat conductive sheet according to the first embodiment. This embodiment involves forming protrusions on the first and second surfaces (both sides) of the metal layer. First, a metal layer 11 is prepared (Figure 5), and protective portions 13 are formed on the first surface and optionally on the second surface of the metal layer 11 (Figure 6, protective portion application process). Next, a composition containing a metal material is applied to the exposed surface of the metal layer 11 where the protective portions 13 are not applied to form a plurality of protrusions 12 (Figure 7, protrusion formation process). Then, the protective portions 13 are removed (Figure 8, protective portion removal process), and a heat conductive sheet 10 having a metal layer 11 and a plurality of protrusions 12 on the first and second surfaces of the metal layer 11 can be manufactured.

[0039] <Protection application process> The protective portion application step is a step of applying a protective portion to at least a first surface of the metal layer, and can be suitably carried out by protective portion application means. When manufacturing a heat-conducting sheet having protrusions on both sides, the protective portion application step is a step of applying protective portions to the first surface and the second surface of the metal layer.

[0040] The pattern of the protective portion applied in the protective portion application step can be an inverse pattern of the convex portion pattern on the target heat conductive sheet. The protective portion can be suitably selected according to the desired embodiment, and examples include resist materials.

[0041] There are no particular restrictions on the method of applying the protective layer, and it can be appropriately selected according to the purpose. Examples include applying a protective layer with a desired pattern by imprinting; applying a protective layer with a desired pattern by inkjet, screen printing, etc.; and forming a protective layer with a desired pattern using resist. A method for forming a protective portion having a desired pattern using the resist includes, for example, applying the resist to at least a first surface of a metal layer, exposing and developing it to the desired pattern, and, if necessary, heating it after exposure or development to form the protective portion. The resist may be a negative type in which exposed areas remain after development, or a positive type in which unexposed areas remain after development.

[0042] <Protrusion formation process> The protrusion formation step is a step of forming the plurality of protrusions by applying a composition containing the metal material to at least a first surface of the metal layer, wherein the metal material is preferably the sinterable metal nanoparticles.

[0043] When the protective portion application step is performed, the convex portion formation step is a step of applying a composition containing the metal material to the exposed surface of the metal layer to which the protective portion has not been applied to form the plurality of convex portions, and can be suitably performed by a convex portion forming means.

[0044] The plurality of protrusions may be formed by applying the composition containing the metal material in a patterned manner without performing the protective portion application step. Methods for applying the composition in a pattern include, for example, applying the composition having a desired pattern by imprinting; or applying the composition having a desired pattern by inkjet printing, screen printing, etc.

[0045] The composition containing the metal material further comprises the metal material and, if necessary, a filler and a solvent. The content of the metal material in the composition is preferably 50% by mass or more, more preferably 60% by mass or more, 70% by mass or more, and 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more, based on the solid content of the composition.

[0046] The solvent is not particularly limited and can be appropriately selected depending on the purpose. Examples include terpineol, butyl carbitol, butyl carbitol acetate, and texanol.

[0047] The above composition can be prepared by mixing and dispersing the metal material, and optionally a filler and a solvent. The aforementioned composition may be a commercially available product, for example, a metal paste containing metal particles such as H 9890-6A (manufactured by Namics Corporation, a thermosetting conductive adhesive, silver paste).

[0048] <Protective part removal process> The protective part removal step is a step of removing the protective part, which can be suitably carried out by a protective part removal means. There are no particular restrictions on the method for removing the protective layer, and it can be appropriately selected depending on the purpose. For example, methods such as high-temperature heating, strong alkali, or organic solvent treatment can be used to remove the protective layer.

[0049] <Sintering process> The sintering step is a step of sintering the sinterable metal nanoparticles by heating, when the protrusions contain sinterable metal nanoparticles. The heating step may be performed simultaneously with the protective part removal step, or it may be performed when joining the heat conductive sheet to the substrate.

[0050] <Polishing process> The polishing step is a step of polishing the surfaces of the multiple protrusions formed on the metal layer. There are no particular restrictions on the method of polishing the surface of the metal layer, and known methods can be appropriately selected depending on the purpose. There are no particular restrictions on the timing of the polishing step, and it can be appropriately performed depending on the purpose, for example, after the convex part formation step, before the protective part removal step, after the protective part removal step, after the heating step, etc.

[0051] As a result of the polishing process, the surfaces of the multiple protrusions 12 on the obtained thermal conductive sheet become smooth and uniform, resulting in excellent adhesion to other components, reliability of the thermal conductive sheet, and excellent conductivity.

[0052] [Second Embodiment] The method for manufacturing a heat conductive sheet in the second embodiment includes a protective portion application step, a protrusion formation step in which protrusions are formed by plating, and a protective portion removal step, and further includes other steps such as a heating step and a polishing step as necessary. The heat conductive sheet of this embodiment described above can be suitably manufactured by the heat conductive sheet manufacturing method of the second embodiment.

[0053] Figures 5-6 and 9-10 show schematic cross-sectional views illustrating an example of the process for manufacturing a heat conductive sheet according to the second embodiment. In this embodiment, protrusions are formed on the first and second surfaces (both sides) of the metal layer. First, a metal layer 11 is prepared (Figure 5), and protective portions 13 are formed on the first surface and optionally on the second surface of the metal layer 11 (Figure 6, protective portion application process). Next, a plurality of protrusions 12 are formed by plating on the exposed surface of the metal layer 11 where the protective portions 13 are not applied (Figure 9, plating process). Then, the protective portions 13 are removed (Figure 10, protective portion removal process), and a heat conductive sheet 10 having the metal layer 11 and a plurality of protrusions 12 on the first and second surfaces of the metal layer 11 can be manufactured. For the protective part application step, protective part removal step, and other steps such as polishing step in the second embodiment, the items described in the first embodiment can be appropriately selected.

[0054] <Plating Process> The plating process is a process of forming the plurality of protrusions by plating the exposed surface of the metal layer that is not covered by the protective portion. There are no particular limitations on the method for forming multiple protrusions by plating, and it can be appropriately selected depending on the purpose. Examples include electroplating and electroless plating (chemical plating). Among these, electroplating is preferred from the viewpoint of throughput. There are no particular restrictions on the metal used for filling by the aforementioned plating, and it can be appropriately selected depending on the purpose. However, it is preferable that it contains at least one of nickel, gold, silver, and copper, and more preferably at least one of nickel, gold, silver, and copper.

[0055] [Third Embodiment] The method for manufacturing a thermal conductive sheet in the third embodiment includes a protective part formation step, an etching step, and a protective part removal step, and further includes other steps such as the polishing step as necessary.

[0056] Figures 11-14 show schematic cross-sectional views illustrating an example of the process for manufacturing a heat conductive sheet according to the third embodiment. In this embodiment, protrusions are formed on the first and second surfaces (both sides) of the metal layer. First, a metal plate 11' that will serve as a precursor to the metal layer 11 is prepared (Figure 11), and protective portions 13 are formed on the first surface and optionally on the second surface of the metal layer 11 (Figure 12, protective portion application process). Next, by removing the exposed surface of the metal plate 11' that does not have the protective portion 13 applied by etching, a metal layer 11 is obtained that integrally has the metal layer 11 and a plurality of protrusions 12 on the first and second surfaces of the metal layer 11 (Figure 13, etching process). Then, the protective portion 13 is removed (Figure 14, protective portion removal process), and a heat conductive sheet 10 having the metal layer 11 and a plurality of protrusions 12 on the first and second surfaces of the metal layer 11 can be manufactured.

[0057] The pattern of the protective portion applied in the aforementioned protective portion application step can be the same as the pattern of the protrusions on the target heat conductive sheet. The protective portion can be suitably selected according to the desired embodiment, and examples include resist materials.

[0058] (heat dissipation structure) The heat dissipation structure of this embodiment comprises a heat-generating element, the heat conductive sheet of this embodiment described above, and a heat dissipation member, and further comprises other members as necessary. The heat dissipation structure has the heat conductive sheet between the heat-generating element and the heat dissipation member. The heat dissipation structure may further have adhesive layers between its constituent members, if necessary.

[0059] There are no particular restrictions on the heat-generating element, and it can be appropriately selected according to the purpose. Examples include electronic components such as CPUs (Central Processing Units), MPUs (Micro Processing Units), and GPUs (Graphics Processing Units).

[0060] The heat dissipation member is not particularly limited as long as it is a structure that dissipates the heat generated by electronic components (heat-generating elements), and can be appropriately selected according to the purpose. Examples include heat spreaders, heat sinks, vapor chambers, and heat pipes. The heat spreader is a component for efficiently transferring heat from the electronic component to other components. There are no particular restrictions on the material of the heat spreader, and it can be appropriately selected according to the purpose, for example, copper, aluminum, etc. The heat spreader is usually in the shape of a flat plate. The heat sink is a component for releasing heat from the electronic component into the air. There are no particular restrictions on the material of the heat sink, and it can be appropriately selected depending on the purpose, for example, copper, aluminum, etc. The heat sink has, for example, a plurality of fins. The heat sink has, for example, a base portion and a plurality of fins provided so as to extend in a direction non-parallel to one surface of the base portion (for example, in a direction perpendicular to it). The heat spreader and the heat sink generally have a solid structure with no internal space. The vapor chamber is a hollow structure. A volatile liquid is sealed inside the hollow structure. Examples of the vapor chamber include a hollow heat spreader, a hollow heat sink, or a plate-shaped hollow structure. The heat pipe is a hollow structure that is cylindrical, substantially cylindrical, or flattened. A volatile liquid is sealed inside the hollow structure.

[0061] Here, Figure 15 is a schematic cross-sectional view showing an example of a semiconductor device as a heat dissipation structure. The thermal conductive sheet 7 in this embodiment dissipates heat generated by electronic components 3 such as semiconductor elements, and as shown in Figure 15, it is fixed to the main surface 2a of the heat spreader 2 that faces the electronic components 3, and is sandwiched between the electronic components 3 and the heat spreader 2. The thermal conductive sheet 1 is sandwiched between the heat spreader 2 and the heat sink 5. The thermal conductive sheet 1 may be the thermal conductive sheet of this embodiment, or it may be any other thermal conductive sheet.

[0062] The heat spreader 2 is formed, for example, in the shape of a rectangular plate and has a main surface 2a facing the electronic component 3 and side walls 2b erected along the outer circumference of the main surface 2a. The heat spreader 2 has a thermal conductive sheet 1 provided on the main surface 2a surrounded by the side walls 2b, and a heat sink 5 is provided on the other surface 2c opposite to the main surface 2a via the thermal conductive sheet 1. The higher the thermal conductivity of the heat spreader 2, the lower the thermal resistance and the more efficiently it absorbs heat from electronic components 3 such as semiconductor elements. For example, it can be formed using copper or aluminum, which have good thermal conductivity.

[0063] The electronic component 3 is, for example, a semiconductor element such as a BGA, and is mounted on the wiring board 6. The heat spreader 2 also has the leading edge of its side wall 2b mounted on the wiring board 6, thereby surrounding the electronic component 3 at a predetermined distance by the side wall 2b. Furthermore, by providing the heat conductive sheet 7 of this embodiment on the main surface 2a of the heat spreader 2, a heat dissipation member is formed that absorbs the heat emitted by the electronic component 3 and dissipates heat from the heat sink 5. [Examples]

[0064] The present invention will be described more specifically below based on examples, but the present invention is not limited to the following examples.

[0065] (Example 1) <Manufacturing of thermal conductive sheets> According to the manufacturing method shown in Figures 5-8, the thermal conductive sheet of Example 1 having multiple protrusions as shown in Figure 1 was manufactured by following the procedure below.

[0066] <<Formation of a protective layer>> On both sides of a copper plate (size: 10 mm x 10 mm, average thickness 40 μm, Figure 5) used as a metal layer, a resist ink (etching resist X-87, manufactured by Taiyo Ink Mfg. Co., Ltd.) was screen printed to an average thickness of 9 μm in the area corresponding to the protective portion 13 shown in Figure 6, and the protective portion was formed by heating at 100°C for 5 minutes (Figure 6).

[0067] A protective layer having an inverted pattern of the protrusions was formed on each surface of the metal layer so that the pattern of multiple protrusions on the first surface of the metal layer and the pattern of multiple protrusions on the second surface of the metal layer were similar and symmetrical across the metal layer. Here, the protrusion patterns shown in Figures 1 and 4 were formed, the size of the protrusions at the central part c shown in Figure 4 was 5 mm × 5 mm, the contact area Ac of the protrusions at the central part c was 50 [%], the multiple protrusions at the peripheral part p shown in Figure 4 were circular in shape with a diameter of 100 μm, the contact area Ap of the protrusions at the peripheral part p was 10 [%], the contact area of ​​the protrusions on the thermal conductive sheet was 30 [%], and the ratio (Ac / Ap) was 5.0.

[0068] <<Formation of protrusions>> By applying Ag sintering material (H 9890-6A, manufactured by Namics Corporation) to the metal layer with the protective layer and drying it, multiple protrusions were formed on both sides of the metal layer (Figure 7).

[0069] <<Removal of protective layer>> Next, the resist ink of the protective layer was sprayed with an 8% to 10% caustic soda solution to soften it, and then the protective layer was removed by washing with water to produce the thermal conductive sheet of Example 1, which has multiple protrusions on both sides of the metal layer (Figure 8).

[0070] <Fabrication of the joint> Next, a laminate was prepared by sandwiching the thermal conductive sheet from Example 1 between a copper substrate (5 mm × 5 mm × 0.3 mm) as the opposing substrate and a silicon substrate (SiC substrate having a 0.5 μm Au plating layer on its surface). Under an N2 atmosphere, the bonder (device name: SB6e, manufactured by SUSS MicroTech) was set to a load of 10 MPa and a temperature of 250 °C, and the bond was heated under pressure for a bonding time of 30 minutes. This sintered the sinterable silver nanoparticles contained in the protrusions to form a sintered body and bonded the laminate.

[0071] <Rating> The thermal conductivity and reliability of the obtained thermal conductive sheets and joints were evaluated as follows. The results are shown in Table 1.

[0072] <Thermal conductivity> In accordance with JIS R 1611, the thermal resistance of the bonded material was measured using a Netsch flash method thermal diffusivity / thermal conductivity measuring device (LFA467, manufactured by Netsch-Gereitebau) under conditions of a pulse width of 20 μsec. Next, the thermal resistance of the thermal conductive sheet was calculated by subtracting the thermal resistance of the opposing substrates used in the measurement: a copper substrate (5 mm × 5 mm × 0.3 mm) and a silicon substrate (a SiC substrate with a 0.5 μm Au plating layer on its surface). Then, the thermal conductivity W / (m·K) of the thermal conductive sheet was calculated by dividing the average thickness of the thermal conductive sheet, which had been measured in advance, by the thermal resistance. Thermal conductivity was evaluated according to the following criteria. The results are shown in Table 1. [Evaluation Criteria] ◎: Thermal conductivity is 150 W / m·K or higher. ○: The thermal conductivity is 100 W / m·K or more and less than 150 W / m·K. ×: The thermal conductivity is less than 100 W / m·K.

[0073] <Vitality> The reliability of the resulting bonded material was evaluated based on the rate of change in thermal conductivity before and after thermal cycling (-40°C to 150°C, 100 cycles) using a method compliant with JIS C 60068-2-14. The results are shown in Table 1. [Evaluation Criteria] ◎: The rate of change is 10% or less. ○: The rate of change is between 10% and 15%. △: The rate of change is between 15% and 20%. ×: The rate of change is 20% or more.

[0074] (Examples 2-5) In Example 1, the thermal conductive sheets of Examples 2 to 5 were manufactured and evaluated in the same manner as in Example 1, except that the pattern of multiple protrusions was changed as shown in Table 1. The results are shown in Table 1.

[0075] (Comparative Examples 1-4) In Example 1, the thermal conductive sheets of Comparative Examples 1 to 4 were manufactured and evaluated in the same manner as in Example 1, except that the pattern of multiple protrusions was changed as shown in Table 2. The results are shown in Table 2.

[0076] [Table 1]

[0077] [Table 2] [Explanation of symbols]

[0078] 1. Thermal conductive sheet 2 Heat spreader 2a Main surface 3. Heat-generating element (electronic component) 3a Top side 5 Heatsink 6 Wiring board 7. Thermal conductive sheet 10 Thermal conductive sheets 11 Metal layer 11' Metal plate before etching 12 Convex part 13 Protection part c center p Peripheral area

Claims

1. Metal layer, A thermal conductive sheet having a plurality of thermally conductive protrusions on at least a first surface of the metal layer, Let Ac be the contact area of ​​the convex portion which has half the area of ​​the first surface and is located at the center of the centroid of the planar shape of the first surface. When the contact area of ​​the convex portion located in the peripheral portion of the first surface, which is the portion other than the central part, is denoted as Ap, A thermal conductive sheet characterized in that the value obtained by dividing Ac by Ap (Ac / Ap) is between 1.2 and 10.

2. The thermal conductive sheet according to claim 1, further comprising a plurality of protrusions on a second surface of the metal layer opposite to the first surface.

3. The thermal conductive sheet according to claim 1, wherein the ratio of the contact area of ​​the plurality of protrusions with the first surface of the metal layer is 30% or more and 80% or less.

4. The thermal conductive sheet according to claim 1, wherein the ratio of the contact area of ​​the protrusion disposed at the center to the center of the first surface is 40% or more.

5. The thermal conductive sheet according to claim 1, wherein the ratio of the contact area of ​​the protrusions arranged in the peripheral portion to the peripheral portion of the first surface is 70% or less.

6. The thermal conductive sheet according to claim 1, wherein the thermal conductivity of the metal layer is 200 W / (m·K) or more.

7. The thermal conductive sheet according to claim 1, wherein the metal layer comprises at least one of gold, silver, copper, and aluminum.

8. The thermal conductive sheet according to claim 1, wherein the average thickness of the metal layer is 10 μm or more and 200 μm or less.

9. The thermal conductive sheet according to claim 1, wherein the protrusions contain sinterable metal nanoparticles.

10. The thermal conductive sheet according to claim 9, wherein the protrusions further comprise at least one of a modified acrylate compound, epoxy resin, unsaturated polyester resin, polyurethane resin, bismaleimide resin, alkyd resin, phenolic resin, and melamine resin.

11. A method for manufacturing a heat conductive sheet according to any one of claims 9 to 10, A method for manufacturing a thermal conductive sheet, characterized by including the step of applying a composition containing the sinterable metal nanoparticles to at least the first surface of the metal layer to form the plurality of protrusions.

12. A method for manufacturing a heat conductive sheet according to any one of claims 1 to 8, A step of applying a protective portion to at least the first surface of the metal layer, A step of forming the plurality of protrusions by plating the exposed surface of the metal layer to which the protective portion is not provided, A method for manufacturing a thermal conductive sheet, characterized by including the step of removing the protective portion.

13. A method for manufacturing a heat conductive sheet according to any one of claims 1 to 8, A step of providing a protective portion on at least the first surface of the metal plate, A step of etching the exposed surface of the metal plate to which the protective portion is not provided to form the metal layer and the plurality of protrusions, A method for manufacturing a thermal conductive sheet, characterized by including the step of removing the protective portion.

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