Thermally-conductive sheet and method for manufacturing thermally-conductive sheet

Abstract

A thermally-conductive sheet according to the present invention comprises a metal layer and a plurality of protrusions on at least one first surface of the metal layer, wherein the protrusions contain sinterable metal particles.

Description

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

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

[0002] With the miniaturization of electronic devices such as power modules, image sensors, and high-performance computing (HPC), and the increase in information processing capacity, heat generation has become more pronounced, and the importance of heat dissipation from heat sources is increasing. In LSIs and other components of various electronic devices, prolonged exposure to high temperatures due to heat generated by the components used can lead to malfunctions or failures. For this reason, thermal conductive materials are widely used to prevent the temperature of LSIs and other components from rising. These thermal conductive materials can prevent the temperature of the equipment from rising by dissipating the heat generated by the components or by transferring it to a heat dissipation component that releases it to the outside of the system, such as the atmosphere.

[0003] To date, sheet-like heat-bonding materials have been reported in which a support made of plate-shaped metal and a bonding agent containing metal nanoparticles and metal fine particles and a solvent are attached to both sides of the support, with the organic material mainly composed of an alcohol having 18 or fewer carbon atoms or a derivative thereof, or a compound containing a carboxyl group, or a mixture thereof.

[0004] Japanese Patent Publication No. 2023-038748

[0005] However, the conventional thermal conductive sheet described in Patent Document 1 has the problem that, because the bonding agent adheres uniformly to the support, cracks occur in the bonding agent area during reliability tests, making practical application difficult. In addition, it requires a high-pressure press, which places a heavy load on the equipment, and it has the problem of poor reliability because it cannot relieve stress in response to the applied pressure.

[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 relieve stress in response to applied pressure and achieve both reliability and high thermal conductivity.

[0007] The means for solving the above problems are as follows: <1> A heat conductive sheet having a metal layer and a plurality of protrusions on at least a first surface of the metal layer, wherein the protrusions contain sinterable metal particles, and the aspect ratio (height / longest diameter) of the height of the protrusions to the longest diameter of the protrusions is 0.2 or more. <2> The heat conductive sheet according to <1>, further having a plurality of protrusions on a second surface of the metal layer opposite to the first surface. <3> The heat conductive sheet according to <1> or <2>, wherein the sinterable metal particles are at least one of gold, silver, copper, and nickel. <4> The heat conductive sheet according to any one of <1> to <3>, wherein the ratio of the contact area of ​​the plurality of protrusions to the first surface of the metal layer is 20% or more. <5> The heat conductive sheet according to any one of <1> to <4>, wherein the metal layer is at least one of gold, silver, copper, aluminum, and nickel. <6> The convex portion is a thermal conductive sheet according to any one of <1> to <5>, further comprising at least one of a modified acrylate compound, epoxy resin, unsaturated polyester resin, polyurethane resin, bismaleimide resin, alkyd resin, phenol resin, and melamine resin. <7> The first surface 1 mm of the metal layer ２ The volume of the aforementioned multiple protrusions is 0.003 mm². ３The thermal conductive sheet is as described in any of <1> to <6> above. <8> The thermal conductive sheet is as described in any of <1> to <7> above, wherein the ratio of the cross-sectional area of ​​the protrusion at 2 / 3 of its height to the cross-sectional area of ​​the protrusion at 1 / 3 of its height is 1 / 2 or less. <9> The thermal conductive sheet is as described in any of <1> to <8> above, wherein the height of the plurality of protrusions after being pressed at an applied pressure of 0.2 MPa, 300°C, for 5 minutes is 97% or less of the height of the plurality of protrusions before pressing. <10> The thermal conductive sheet is as described in any of <1> to <9> above, wherein when the contact area of ​​the protrusion that has 1 / 2 the area of ​​the first surface and is located in the center centered on the centroid of the planar shape of the first surface is Ac, and the contact area of ​​the protrusion located in the peripheral part of the first surface other than the central part is Ap, the value obtained by dividing Ac by Ap (Ac / Ap) is 1.2 or more and 10 or less. <11> A method for manufacturing a heat conductive sheet according to any one of <1> to <10> above, characterized in that it includes the step of applying a composition containing the sinterable metal particles 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 <11> above, comprising the steps of preparing a mold having a plurality of recesses corresponding to the plurality of protrusions, filling each recess with a composition containing the sinterable metal particles, and transferring the composition having a protrusion shape to at least the first surface of the metal layer to form the plurality of protrusions.

[0008] According to the present invention, the aforementioned problems in the conventional era can be solved, the aforementioned objectives can be achieved, and a thermal conductive sheet can be provided that can relieve stress in response to applied pressure and achieve both reliability and high thermal conductivity.

[0009] Figure 1 is a plan view showing an example of a heat conductive sheet according to this embodiment. Figure 2 is a cross-sectional view of the heat conductive sheet of Figure 1 along line A-A'. Figure 3 is a cross-sectional view of another example of the heat conductive sheet according to this embodiment along line A-A'. Figure 4 is a cross-sectional view of another example of the heat conductive sheet according to this embodiment along line A-A'. Figure 5 is a plan view illustrating the central part c and peripheral part p of the heat conductive sheet according to this embodiment. Figure 6 is a schematic cross-sectional view (part 1) showing an example of the process for manufacturing the heat conductive sheet according to the first embodiment. Figure 7 is a schematic cross-sectional view (part 2) showing an example of the process for manufacturing the heat conductive sheet according to the first embodiment. Figure 8 is a schematic cross-sectional view (part 1) showing an example of the process for manufacturing the heat conductive sheet according to the second embodiment. Figure 9 is a schematic cross-sectional view (part 2) showing an example of the process for manufacturing the heat conductive sheet according to the second embodiment. Figure 10 is a schematic cross-sectional view (part 3) showing an example of the process for manufacturing the heat conductive sheet according to the second embodiment. Figure 11 is a schematic cross-sectional view (part 4) showing an example of the process for manufacturing the heat conductive sheet according to the second embodiment. Figure 12 is a schematic cross-sectional view showing an example of a heat dissipation structure according to this embodiment. Figure 13 is a schematic cross-sectional view showing the thermal conductive sheet of Comparative Example 1.

[0010] (Thermal Conductive Sheet) The thermal conductive sheet of this embodiment is a thermal conductive sheet having a metal layer and a plurality of protrusions on at least a first surface of the metal layer. The protrusions contain sinterable metal particles. Preferably, the thermal conductive sheet further has a plurality of protrusions on a second surface of the metal layer opposite to the first surface.

[0011] The thermal conductive sheet of this embodiment has a metal layer and a plurality of protrusions on at least a first surface of the metal layer, and the protrusions contain sinterable metal particles, so that the thermal conductive sheet has thermal conductivity not only in the thickness direction but also in the planar direction, and thus has excellent thermal conductivity. Furthermore, since the protrusions containing sinterable metal particles are deformable in response to applied pressure, stress can be relieved in a laminate in which the thermal conductive sheet is provided between substrates such as a heating element and a heat dissipation member, lifting and peeling from the substrate can be reduced, and excellent adhesion to the substrate and excellent reliability can be achieved.Therefore, by providing a thermal conductive sheet between a heating element and a heat dissipation member, heat generated from the heating element can be efficiently dissipated through the thermal conductive sheet, stress can be relieved in response to applied pressure, and a thermal conductive sheet that can achieve both reliability and high thermal conductivity can be provided.

[0012] Figures 1 and 2 are schematic cross-sectional views and a schematic cross-sectional view along section A-A' of an example of a thermal conductive sheet according to this embodiment. Figure 1 is a plan view of Figure 2. 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 and a second surface opposite to the first surface of the metal layer 11, and each protrusion contains sinterable metal particles. As shown in Figures 1 and 2, a pattern of protrusions 12 is formed. The aspect ratio of the height h of the protrusion to the longest diameter d of the protrusion (height / longest diameter = h / d) is 0.2 or more.

[0013] As shown in Figure 3, which illustrates another example of the thermal conductive sheet of this embodiment, the thermal conductive sheet 10 may have 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 the first surface of the metal layer 11, and each protrusion contains sinterable metal particles. The pattern of the protrusions 12 on the first surface of the thermal conductive sheet 10 in Figure 3 is the same as in the plan view of Figure 1. The aspect ratio of the height h of the protrusions on the first surface to the longest diameter d of the protrusions (height / longest diameter = h / d) is 0.2 or more.

[0014] The shape of each protrusion in the thermal conductive sheet 10 may differ. For example, as shown in Figure 4, which illustrates a cross-sectional view A-A' of another example of the thermal conductive sheet of this embodiment, the shape may be cylindrical. Alternatively, the shape of each protrusion may be semicircular, a polygonal pyramid such as a square pyramid, or a polygonal prism such as a square prism, and can be appropriately selected according to the purpose.

[0015] Furthermore, the thermal conductive sheet may have a pattern of multiple protrusions 12 on the first surface and a pattern of multiple protrusions 12 on the second surface that are identical or not symmetrical across a metal layer, for example, they may be offset.

[0016] <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, aluminum, nickel, iron, gold, silver, copper, zinc, and tin are preferred as the metal, and gold, silver, copper, and aluminum are more preferred. These may be used individually or in combination of two or more. As the metal layer, for example, a metal foil to which a metal such as silver has been applied by sputtering or vapor deposition can be used.

[0017] The thermal conductivity of the metal layer is not particularly limited and can be appropriately selected depending on the purpose, but from the viewpoint of thermal conductivity, 50 W / (m·K) or higher is preferred, and 100 W / (m·K) or higher is more preferred. The thermal conductivity of the metal is not particularly limited and can be appropriately selected depending on the purpose, but from the viewpoint of thermal conductivity, 50 W / (m·K) or higher is preferred, 100 W / (m·K) or higher is more preferred, and 200 W / (m·K) or higher is even more preferred.

[0018] <<Protrusions>> The protrusions are not particularly limited as long as they contain sinterable metal particles and can be appropriately selected according to the purpose. For example, a composition containing sinterable metal particles and any component such as resin, curable material, curing agent, or solvent can be used. The sinterable metal particles are not particularly limited and can be appropriately selected according to the purpose. For example, gold, silver, copper, nickel, etc. The shape of the sinterable metal particles is not particularly limited and can be appropriately selected according to the purpose. For example, spherical, plate-shaped, rod-shaped, wire-shaped, etc.

[0019] From the viewpoint of sheet formation, the average particle size of the pre-sintered metal particles is preferably 10,000 nm or less, more preferably 3,000 nm or less, even more preferably 1,000 nm or less, and particularly preferably 500 nm or less. From the viewpoint of achieving good dispersibility of the sintered metal particles in the composition, the average particle size of the sintered metal particles is preferably 1 nm or more, more preferably 10 nm or more, and even more preferably 50 nm or more. The average particle size of the sintered metal particles can be determined by measuring the longest diameter of any 10 or more particles in an observation image using a scanning electron microscope (SEM) and calculating the average.

[0020] When sinterable metal particles constitute the composition, there are no particular restrictions on the content of sinterable metal particles in the composition, and it can be appropriately selected according to the purpose. However, from the viewpoint of improving thermal conductivity, it is preferable that the content is more than 40% by volume and 90% by volume or less, and more preferably 50% by volume or more and 80% by volume or less.

[0021] - Resin - There are no particular restrictions on the resin, and it can be appropriately selected depending on the purpose, but modified acrylate compounds, epoxy resins, unsaturated polyester resins, polyurethane resins, bismaleimide resins, alkyd resins, phenolic resins, and melamine resins are preferred. These may be used individually or in combination of two or more.

[0022] -Curable Material- There are no particular restrictions on the curable material, and it can be appropriately selected depending on the purpose, but curable silicone, curable epoxy resin, curable polyurethane resin, and curable polyester resin are preferred examples. These may be used individually or in combination of two or more.

[0023] Examples of curable silicones include silicones having alkoxy groups, silicones having epoxy groups (glycidoxy groups), silicones having acryloyl groups (methacryloyl groups), and silicones having hydrosilyl groups and vinyl groups. Examples of curable epoxy resins include glycidyl ether type epoxy resins, phenol novolac type epoxy resins, cresol novolac type epoxy resins, bisphenol A type epoxy resins, bisphenol F type epoxy resins, trisphenol type epoxy resins, tetraphenol type epoxy resins, phenol-xylylene type epoxy resins, naphthol-xylylene type epoxy resins, phenol-naphthol type epoxy resins, phenol-dicyclopentadiene type epoxy resins, alicyclic epoxy resins, and aliphatic epoxy resins. Examples of curable polyurethane resins include polyurethanes having acryloyl groups, polyurethanes having methacryloyl groups, urethane prepolymers containing terminal isocyanate groups, and epoxy-modified polyurethanes. Examples of curable polyester resins include polyesters having acryloyl groups, polyesters having methacryloyl groups, and epoxy-modified polyesters.

[0024] -Curing Agent- The curing agent is a curing agent corresponding to the curable material, and examples include polyfunctional carboxylic acids, acid anhydride curing agents, aliphatic amine curing agents, aromatic amine curing agents (e.g., imidazole curing agents), phenol curing agents, mercaptan curing agents, and other polyaddition curing agents, as well as catalytic curing agents such as imidazole. These may be used individually or in combination of two or more. Among these, aromatic amine curing agents are preferred, and imidazole curing agents are more preferred.

[0025] -Solvent- 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.

[0026] The composition can be prepared by mixing and dispersing the sinterable metal particles, and optionally a resin, a curing material, a curing agent, a solvent, etc. Commercially available products may be used as the composition, for example, H 9890-6A (manufactured by Namics Corporation, a thermosetting conductive adhesive, silver paste) can be used as a metal paste containing sinterable metal particles.

[0027] [Area Ratio] When the first surface of the thermal conductive sheet is viewed in plan view, the ratio of the contact area of ​​the plurality of protrusions on the first surface of the metal layer is preferably 20% to 80%, and more preferably 30% to 70%, in terms of reducing lifting and peeling from the substrate, providing excellent adhesion to the substrate, and offering superior reliability. In an embodiment in which the thermal conductive sheet has a plurality of protrusions on the second surface, when the second surface of the thermal conductive sheet is viewed in plan view, the ratio of the contact area of ​​the plurality of protrusions on the first surface of the metal layer is preferably 20% to 80%, and more preferably 30% to 70%, in terms of reducing lifting and peeling from the substrate, providing excellent adhesion to the substrate, and offering superior reliability.

[0028] The first surface 1 mm of the metal layer ２ The volume of the aforementioned multiple protrusions is 0.003 mm². ３ The above is preferable, and 0.003 mm ３ The above is 0.18 mm. ３ The following is more preferable: 0.003 mm ３ The above is 0.09 mm. ３ The following is even more preferable.

[0029] [Pattern] There are no particular restrictions on the pattern of the protrusions 12, and they can be appropriately selected according to the purpose. For example, a pattern in which multiple figures are arranged can be used. The shape of each protrusion may be a polygonal pyramid such as a square pyramid, a polygonal prism such as a square prism, a semicircle, a cone shape with a gentle slope at the top and a gradually steeper slope from the center to the base, or a parabolic shape. For example, it may be a structure consisting of multiple protrusions (moth-eye structure) as described in Japanese Patent Application Publication No. 2021-208526, and can be appropriately selected according to the purpose.

[0030] In one embodiment, from the viewpoint of adhesion between the substrate and the opposing substrate when manufacturing the laminate, it is preferable that each protrusion has a cross-sectional area at its top that is smaller than the cross-sectional area at its bottom or center in the height direction, and it is more preferable that the ratio of the cross-sectional area at 2 / 3 of the height of the protrusion to the cross-sectional area at 1 / 3 of the height of the protrusion is 1 / 2 or less. In this case, the shape of each protrusion can be a polygonal pyramid, a semicircle, a cone, a parabolic shape, etc. Furthermore, the bottoms of each protrusion may be in contact with each other or integrated.

[0031] When viewing the thermal conductive sheet from a plan view, a pattern of convex portions consisting of multiple shapes arranged regularly is preferred from the viewpoint of uniform thermal conductivity. Examples of such patterns include 45° staggered (see Figure 1), 60° staggered, parallel squares, 60° staggered regular hexagons, equilateral triangles, and alternating rectangles.

[0032] [Aspect Ratio] There are no particular restrictions on the shape and size of the protrusions, and they can be appropriately selected according to the purpose. However, the aspect ratio of the height h of the protrusion to the longest diameter d of the protrusion at the contact surface with the metal layer (height / longest diameter = h / d) should be 0.2 or more, preferably 0.2 to 10, and more preferably 0.3 to 6.

[0033] The longest diameter d of the protrusion at the contact surface with the metal layer is preferably 2 μm to 500 μm, and more preferably 5 μm to 100 μm. The height h of the protrusion is preferably 2 μm to 100 μm, and more preferably 5 μm to 50 μm.

[0034] Another configuration of the convex pattern is preferable in that, when the thermal conductive sheet is viewed in plan, the contact area Ac of the convex portion located in the center is larger than the contact area Ap of the convex portion located in the periphery, as this can further relieve stress when the thermal conductive sheets are joined. Here, as shown by the dashed line in Figure 5, 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 5), and 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 5). Figure 5 is a plan view illustrating the central part c and peripheral part p of the thermal conductive sheet of this embodiment, and the dashed line in Figure 5 is the boundary line that divides the central part c and peripheral part p into equal areas. When the contact area of ​​the protrusions 12 located in the central part c is Ac, and the contact area of ​​the protrusions 12 located in the peripheral part p is Ap, it is preferable that 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 shown in Figure 5, the ratio of the area in contact with the central part c of the first surface by the multiple protrusions is 75%, and the ratio of the area in contact with the peripheral part p of the first surface by the multiple protrusions is 25%, so Ac / Ap = 75 / 25 = 3.

[0035] 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, it is preferable that it is 10 W / (m·K) or higher, more preferably 20 W / (m·K) or higher, and even more preferably 30 W / (m·K) or higher.

[0036] 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 10 μm to 200 μm, and more preferably 30 μm to 150 μm.

[0037] 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 or more and 100 μm or less, and more preferably 15 μm or more and 50 μm or less.

[0038] The ratio (h / t) of the height h of the convex portion to the average thickness t of the metal layer is not particularly limited and can be appropriately selected according to the purpose. However, from the viewpoint of further improving the thermal conductivity and reliability, it is preferably 0.2 or more and 4 or less, and more preferably 0.5 or more and 2 or less.

[0039] In the case of the aspect having convex portions on both the first surface and the second surface of the heat conduction sheet, for the convex portions on each surface, independently, the shape of the convex portion, the longest diameter d, the height t, the aspect ratio (t / d), the ratio (h / t), and the pattern of the convex portion such as the distribution can be appropriately set, and the pattern of the convex portion 12 on the first surface and the pattern of the convex portion on the second surface may be different or the same.

[0040] The convex portion is deformable according to the applied pressure in the stacking direction when manufacturing the laminate. The degree of deformation can be appropriately selected according to the purpose. However, the height (t １ ) of the plurality of convex portions after pressing at an applied pressure of 0.2 MPa, 300 °C for 5 minutes is preferably 97% or less, more preferably <83% or less, and still more preferably 67% or less, with respect to the height (t) of the plurality of convex portions before pressing.

[0041] Since the heat conduction sheet has convex portions containing sinterable metal particles on its surface, and the convex portions are deformable and sinterable, for example, when adhering to other members such as a heating element or a heat radiating member, the stress can be relaxed according to the applied pressure, and it is excellent in adhesion and compressibility after heat treatment (accelerated life test), so it is also excellent in reliability. The heat conduction sheet has a metal layer and convex portions communicating in the thickness direction and the plane direction of the heat conduction sheet, so the stress can be relaxed. In addition, the problem that the film itself becomes brittle as in the case of a heat conduction sheet in which a heat conduction material is bound with a binder resin and the film collapses in a high-temperature test or the like is solved, and the collapse of the heat conduction sheet can be preferably prevented.

[0042] (Method for manufacturing a heat conduction sheet) There are no particular restrictions on the method for manufacturing the heat conduction sheet of the present embodiment, and it can be appropriately selected according to the purpose. For example, a method of forming a plurality of convex portions by applying a composition containing sinterable metal particles (First Embodiment); a method of forming a plurality of convex portions by transferring pre-formed convex portions (Second Embodiment), etc. can be mentioned.

[0043] [First Embodiment] The method for manufacturing the heat conduction sheet in the first embodiment includes a step of forming a plurality of convex portions by applying a composition containing sinterable metal particles on at least the first surface of the metal layer, and further includes other steps such as a polishing step as required. By the method for manufacturing the heat conduction sheet of the first embodiment, the heat conduction sheet of the present embodiment described above can be preferably manufactured.

[0044] Figs. 6 to 7 show schematic cross-sectional views showing an example of the process of the method for manufacturing the heat conduction sheet of the second embodiment. This aspect is an aspect of forming convex portions on the first surface and the second surface (both surfaces) of the metal layer. First, a metal layer 11 is prepared (Fig. 6). Next, a composition containing sinterable metal particles is applied in a pattern having a plurality of convex portion shapes on the first surface of the metal layer 11 to form a plurality of convex portions 12. Similarly, a composition containing sinterable metal particles is applied in a pattern having a plurality of convex portion shapes on the second surface of the metal layer 11 to form a plurality of convex portions 12 (Fig. 7). Thereby, a heat conduction sheet 10 having the metal layer 11 and a plurality of convex portions 12 on the first surface and the second surface of the metal layer 11 can be manufactured.

[0045] There are no particular restrictions on the method for applying the composition containing sinterable metal particles, and it can be appropriately selected according to the purpose. For example, a method of applying a composition having a desired pattern by imprinting; a method of applying a composition having a desired pattern by inkjet, screen printing, etc. can be mentioned.

[0046] [Second Embodiment] The composition containing sinterable metal particles may be applied by transferring pre-formed protrusions. The method for manufacturing a thermal conductive sheet in the second embodiment includes the steps of: preparing a mold having a plurality of recesses corresponding to the plurality of protrusions; filling each recess with a composition containing sinterable metal particles; and transferring the composition having a protrusion shape to at least a first surface of the metal layer to form the plurality of protrusions, and further including other steps as necessary. The thermal conductive sheet of this embodiment described above can be suitably manufactured by the method for manufacturing a thermal conductive sheet in the second embodiment.

[0047] Figures 8 to 11 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 a metal layer. First, a recess mold 22 having a plurality of recesses corresponding to a plurality of protrusions 12 is prepared. As shown in Figures 8 to 11, in the embodiment for manufacturing a heat-conductive sheet 10 having a plurality of protrusions 12 on both the first and second surfaces, a pair of recess molds 22, one for the first surface and one for the second surface, are prepared (Figure 8). For example, plastic can be used as the recess mold 22. Next, a composition 12' containing sinterable metal particles is filled into each recess of the recess mold 22 (Figure 9).

[0048] Then, the composition 12' containing the sinterable metal particles having multiple convex shapes is placed on the first and second surfaces of the metal layer 11, respectively, and laminated (Figure 10), and then transferred (Figure 11). Here, the composition 12' containing the sinterable metal particles may be transferred as is, or it may be pre-sintered with the metal layer 11. This makes it possible to manufacture a metal layer 11 and a heat conductive sheet 10 having multiple convex shapes 12 on the first and second surfaces of the metal layer 11 (Figure 11).

[0049] There are no particular limitations on the method for filling each recess of a mold with a composition containing sinterable metal particles, and a suitable method can be selected depending on the purpose. Examples include immersion, inkjet, dispensing, spray coating, slit coating, and spin coating methods.

[0050] (Laminate) The laminate of this embodiment comprises a base material and an opposing base material, and a thermal conductive sheet of this embodiment sandwiched between the base material and the opposing base material. In one embodiment, in order to further improve adhesion, it is preferable that the laminate further comprises a cured product of a filler filled between the plurality of metal protrusions.

[0051] - Substrate - There are no particular restrictions on the shape, structure, size, material, etc., of the substrate, and it can be appropriately selected according to the purpose. Examples of the substrate shape include plate-like and sheet-like shapes. Examples of the substrate structure include single-layer structure and laminated structure. The size of the substrate can be appropriately selected according to the application, etc.

[0052] Suitable materials for the substrate include, for example, silicon, aluminum, tungsten, molybdenum, glass, molding resin, stainless steel, and ceramics. Examples of ceramics include aluminum nitride, silicon carbide, alumina, and gallium nitride. Examples of molding resins include epoxy resin, silicone resin, urethane resin, and acrylic resin. The substrate is preferably a silicon substrate.

[0053] The average thickness of the substrate is not particularly limited and can be appropriately selected depending on the purpose. The substrate may also be the heat-generating element (electronic component) itself in the heat dissipation structure.

[0054] - Opposing Substrate - The opposing substrate is positioned opposite the substrate, and there are no particular restrictions on its shape, structure, size, material, etc., and it can be appropriately selected according to the purpose. Examples of the shape of the opposing substrate include plate-like and sheet-like shapes. Examples of the structure of the opposing substrate include single-layer structures and laminated structures. The size of the opposing substrate can be appropriately selected according to the application, etc. The material of the opposing substrate is a material that is easily wetted by solder, and includes at least one selected from copper, gold, platinum, palladium, silver, zinc, iron, tin, nickel, magnesium, indium, and alloys thereof. There are no particular restrictions on the average thickness of the opposing substrate and it can be appropriately selected according to the purpose. The opposing substrate may be the heat spreader itself in the heat dissipation structure.

[0055] - Filler - The filler is not particularly limited as long as it has curability and adhesive properties, and can be appropriately selected according to the purpose, but it is preferable that it contains a curable material, and further, if necessary, it contains a curing agent, filler, and other components.

[0056] --Curable Material-- There are no particular restrictions on the curable material, and it can be appropriately selected according to the purpose, but curable silicone, curable epoxy resin, curable polyurethane resin, and curable polyester resin are preferred examples. These may be used individually or in combination of two or more.

[0057] Examples of curable silicones include silicones having epoxy groups (glycidoxy groups), silicones having acryloyl groups (methacryloyl groups), and silicones having hydrosilyl groups and vinyl groups. Examples of curable epoxy resins include glycidyl ether type epoxy resins, phenol novolac type epoxy resins, cresol novolac type epoxy resins, bisphenol A type epoxy resins, bisphenol F type epoxy resins, trisphenol type epoxy resins, tetraphenol type epoxy resins, phenol-xylylene type epoxy resins, naphthol-xylylene type epoxy resins, phenol-naphthol type epoxy resins, phenol-dicyclopentadiene type epoxy resins, alicyclic epoxy resins, and aliphatic epoxy resins. Examples of curable polyurethane resins include polyurethanes having acryloyl groups, polyurethanes having methacryloyl groups, urethane prepolymers containing terminal isocyanate groups, and epoxy-modified polyurethanes. Examples of curable polyester resins include polyesters having acryloyl groups, polyesters having methacryloyl groups, and epoxy-modified polyesters.

[0058] --Curing Agent-- The curing agent is a curing agent corresponding to the curable material, and examples include polyfunctional carboxylic acids, acid anhydride curing agents, aliphatic amine curing agents, aromatic amine curing agents (e.g., imidazole curing agents), phenol curing agents, mercaptan curing agents, and other polyaddition curing agents, as well as catalytic curing agents such as imidazole. These may be used individually or in combination of two or more.

[0059] --Filler-- The filler may further contain a filler. Examples of the filler include metal powder, alloy powder, metal oxide, ceramic powder, and carbon powder. These may be used individually or in combination of two or more. There are no particular restrictions on the shape of the filler, and it can be appropriately selected according to the purpose, for example, spherical, flattened, granular, needle-shaped, etc.

[0060] When the filler contains the filler, there are no particular restrictions on the filler content in the filler, and it can be appropriately selected according to the purpose. However, from the viewpoint of improving mechanical strength, heat resistance, and thermal conductivity without impairing the adhesiveness of the filler, it is preferable that the content is greater than 0 vol% and 90 vol% or less, more preferably 40 vol% to 80 vol% or less, and even more preferably 50 vol% to 70 vol% or less.

[0061] The volume-average particle size of the filler is preferably 0.3 μm or more and 30 μm or less, and more preferably 0.5 μm or more and 10 μm or less. The volume-average particle size can be measured, for example, by a laser diffraction / scattering particle size distribution analyzer (Microtrac MT3300EXII).

[0062] --Other Ingredients-- There are no particular restrictions on other ingredients, and they can be selected as appropriate depending on the purpose. Examples include antioxidants.

[0063] (Method for manufacturing the laminate) The method for manufacturing the laminate of this embodiment preferably includes a step of heating the heat conductive sheet of this embodiment described above by sandwiching it between a base material and an opposing base material, and a step of filling the gaps between the deformed and sintered protrusions with a filler and hardening it (filler hardening step).

[0064] <Heating Process> The heating process involves sandwiching the heat-conducting sheet of this embodiment between a base material and an opposing base material and heating it. As a result, the convex portion deforms in accordance with the applied pressure, and the convex portion deforms and sintersects in accordance with the shapes of the base material and the opposing base material, so that the heat-conducting sheet and the base material, and the heat-conducting sheet and the opposing base material can be joined in a state where the stress is relieved.

[0065] The method of heating by sandwiching a heat conductive sheet between a substrate and an opposing substrate is not particularly limited as long as the substrate and the opposing substrate can be joined via the heat conductive sheet to form a heat conduction network, and can be appropriately selected according to the purpose. However, it is preferable to carry out the method at 350°C or below and under a pressure of 20 MPa or below.

[0066] <Filler curing process> The filler curing process is a process of filling and curing a filler between at least one of the substrate and the opposing substrate and the deformed and sintered protrusions. This makes it possible to further improve the adhesion between the heat conductive sheet and the substrate, and / or between the heat conductive sheet and the opposing substrate, which are joined in a state where stress has been relieved in the heating process.

[0067] - Heat Dissipation Structure - The laminate of this embodiment is preferably a heat dissipation structure. The heat dissipation structure preferably comprises a heating element as a base material, a heat dissipation member as an opposing base material, a metal layer sandwiched between the base material and the opposing base material, and a heat conductive sheet having a plurality of protrusions on at least a first surface of the metal layer, and a cured product of a filler filled between the plurality of protrusions, and further optionally includes other members. The heat dissipation structure has the heat conductive sheet between the heating element and the heat dissipation member. The heat dissipation structure may further have adhesive layers between each component as needed.

[0068] There are no particular restrictions on the heat-generating element, and it can be appropriately selected depending on the purpose. Examples include electronic components such as CPUs (Central Processing Units), MPUs (Micro Processing Units), and GPUs (Graphics Processing Units).

[0069] The heat dissipation member is not particularly limited as long as it is a structure that dissipates the heat generated by the electronic component (heat-generating element), 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 member for efficiently transferring the heat of the electronic component to other components. The material of the heat spreader is not particularly limited and can be appropriately selected according to the purpose. Examples include copper and aluminum. The heat spreader is usually in the shape of a flat plate. The heat sink is a member for releasing the heat of the electronic component into the air. The material of the heat sink is not particularly limited and can be appropriately selected according to the purpose. Examples include copper and aluminum. 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 non-parallel direction (for example, a perpendicular direction) with respect to one surface of the base portion. The heat spreader and the heat sink are generally solid structures 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 cylindrical, substantially cylindrical, or flattened cylindrical hollow structure. A volatile liquid is sealed inside the hollow structure.

[0070] Here, Figure 12 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 12, 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.

[0071] 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 heat 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 heat 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 the electronic component 3 such as a semiconductor element. For example, it can be formed using copper or aluminum, which have good thermal conductivity.

[0072] 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. The heat conductive sheet 7 of this embodiment is provided on the main surface 2a of the heat spreader 2, forming a heat dissipation member that absorbs the heat emitted by the electronic component 3 and dissipates the heat from the heat sink 5.

[0073] The present invention will be described more specifically below based on examples, but the present invention is not limited to the following examples.

[0074] (Example 1) <Manufacturing of thermal conductive sheet> A thermal conductive sheet of Example 1 having the convex pattern shown in Figures 2 and 11 was manufactured according to the manufacturing method shown in Figures 8 to 11 by following the procedure below.

[0075] <<Preparation of a master plate with a pattern of convex portions>> First, a master plate having the pattern of convex portions shown in Figures 2 and 11 was prepared. Here, the pattern of convex portions has multiple conical cones, with the longest diameter of each cone being 100 μm, the cone height being 30 μm, the aspect ratio being 0.3, the pitch (distance between the centers of adjacent circles) being 200 μm, and the ratio of the contact area of ​​the circles to the metal layer being 39.3%.

[0076] <<Preparation of a mold with multiple recesses>> Using the synthesized soluble polyimide resin composition, it was poured into a mold measuring 100 mm x 100 mm to a thickness of 0.5 mm or more, a master plate was pressed against it, and it was left to stand under vacuum for 2 hours. Then, it was plasticized by heating at 200°C for 3 hours to produce a mold with multiple recesses corresponding to the pattern of the protrusions (see Figure 8).

[0077] <<Preparation of Composition Containing Sinterable Metal Particles>> 20 parts by mass of a partially hydrolyzed methyl silicate (Colcoat N-103X, manufactured by Colcoat Co., Ltd.) were added to 20 parts by mass of silver nanowire particles (T-YP808, manufactured by Seikoh PMC Co., Ltd., solid content 0.5% by mass), and the mixture was uniformly mixed using a stirring device (Awatori Rentaro Automatic Revolving Mixer, manufactured by Thinky Co., Ltd.) to prepare a composition containing sinterable metal particles.

[0078] <<Filling with Composition>> Next, the obtained composition was filled into each recess of the mold under a nitrogen atmosphere at 60°C for 5 minutes, thereby creating a sheet for transferring convex parts by filling each recess of the mold with the composition.

[0079] <<Preparation of Thermal Conductive Sheet>> A transfer film having multiple protrusions prepared above is placed in contact with both sides of a copper plate (size: 20 mm x 20 mm, average thickness 30 μm) as a metal layer. Under pressurized heating conditions of 2 MPa pressure, 180°C, and 5 minutes, the multiple protrusions are transferred to each side of the metal layer while maintaining deformability and sinterability, thereby producing a thermal conductive sheet of Example 1 having a metal layer and multiple protrusions on both sides of the metal layer.

[0080] (Examples 2-5) Except for changing the maximum diameter of the contact surface of the protrusions and the aspect ratio of the protrusions as shown in Table 1, the thermal conductive sheets of Examples 2-5 were obtained in the same manner as in Example 1.

[0081] (Example 6) The thermal conductive sheet of Example 6 was obtained in the same manner as in Example 1, except that the pattern of the protrusions was changed from pattern 1 shown in Figure 2 to pattern 2 shown in Figure 4.

[0082] (Examples 7-10) Except for changing the maximum diameter of the contact surface of the protrusions and the aspect ratio of the protrusions as shown in Table 2 in Example 6, the thermal conductive sheets of Examples 7-10 were obtained in the same manner as in Example 6.

[0083] (Comparative Example 1) A thermal conductive sheet of Comparative Example 1 was obtained in the same manner as in Example 1, except that the metal layer itself was used without providing multiple protrusions.

[0084] (Comparative Example 2) A thermal conductive sheet for Comparative Example 2 was obtained in the same manner as in Example 1, except that pattern 1 shown in Figure 2 was changed to pattern 3 (Figure 13), which is a convex portion integrated with a metal layer and was fabricated by the following procedure. Here, Figure 13 is a schematic cross-sectional view showing the thermal conductive sheet of Comparative Example 1.

[0085] <<Fabrication of a thermal conductive sheet with multiple protrusions in Pattern 3>> On both sides of a copper plate (size: 20 mm x 20 mm, average thickness 100 μm), etching resist X-87 (manufactured by Taiyo Ink Manufacturing Co., Ltd.) was screen printed to an average thickness of 30 μm as a coating liquid for forming protective areas in areas other than the protrusions, and the protective areas were formed by heating at 100°C for 5 minutes.

[0086] The metal plate with the protective layer formed was plated using a nickel sulfamate bath under the following conditions: 50°C, pH 4.5, 10 mA / cm². ２ Plating was performed to form protrusions with an average thickness of 30 μm. Next, the protective layer was removed by immersion in 3% NaOH at 40°C for 15 seconds to produce a thermal conductive sheet of Comparative Example 1 having protrusions integrally on both sides of the metal layer.

[0087] (Comparative Example 3) A thermal conductive sheet for Comparative Example 3 was obtained in the same manner as in Comparative Example 2, except that the longest diameter of the contact surface of the protrusions and the aspect ratio of the protrusions were changed, as shown in Table 3.

[0088] (Comparative Example 4) A thermal conductive sheet for Comparative Example 4 was obtained in the same manner as in Example 1, except that the longest diameter of the contact surface of the protrusions and the aspect ratio of the protrusions were changed, as shown in Table 3.

[0089] (Comparative Example 5) A thermal conductive sheet for Comparative Example 5 was obtained in the same manner as in Example 6, except that the longest diameter of the contact surface of the protrusions and the aspect ratio of the protrusions were changed, as shown in Table 3.

[0090] <Evaluation> Next, the thermal conductivity, reliability, and compressibility of Examples 1 to 10 and Comparative Examples 1 to 5 were evaluated as follows. The results are shown in Table 1.

[0091] <Thermal Conductivity> In accordance with JIS R 1611, the thermal resistance of each thermal conductive sheet 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 nickel-plated copper plate (25 mm x 25 mm, average thickness 1.00 mm) and silicon plate (20 mm x 20 mm, average thickness 0.76 mm), which were the substrates used for measurement, from the measured values. Then, the thermal conductivity W / (m·K) of the thermal conductive sheet was calculated by dividing the average thickness of the thermal conductive sheet measured in advance by the thermal resistance. Thermal conductivity was evaluated according to the following criteria. The results are shown in Tables 1 to 3. [Evaluation Criteria] ◎: Thermal conductivity is 20 W / m·K or higher. ○: Thermal conductivity is 10 W / m·K or higher and less than 20 W / m·K. ×: The thermal conductivity is less than 10 W / m·K.

[0092] <Reliability> <<Fabrication of laminated bodies after compression>> Each heat conductive sheet was sandwiched between a nickel-plated copper plate (25 mm x 25 mm, average thickness 1.00 mm) and a silicon plate (20 mm x 20 mm, average thickness 0.76 mm). A mini press was used to heat and press the sheets for 5 minutes under the conditions of an upper plate temperature of 150°C on the copper plate side, a lower plate temperature of 150°C on the silicon plate side, and a set air pressure of 0.11 MPa (equivalent to 40 psi). After that, the sheets were heated in an oven (Perfect Oven PHH-202, manufactured by ESPEC Corporation) at 150°C for 1 hour.

[0093] <<Accelerated Life Testing and Reliability Evaluation>> The laminated material after compression was placed in an advanced accelerated life tester (EHS-212MD, manufactured by ESPEC Corporation) at 130°C and 85% humidity for 192 hours. After the accelerated life test, each thermal conductive sheet was observed using an ultrasonic imaging device (SAT, FS300IIIHR, manufactured by Hitachi Power Solutions, Ltd.) to inspect its adhesion to the substrate. A 50MHz, 7mm probe was used for the copper plate side, and a 25MHz probe was used for the silicon plate side. The results are shown in Tables 1 to 3. [Evaluation Criteria] ◎: No lifting or peeling of the thermal conductive sheet from the substrate. ○: Lifting and peeling of the thermal conductive sheet from the substrate is less than 0.1% of the observation field of view, which is within the practical range. ×: Lifting and peeling of the thermal conductive sheet from the substrate is 0.1% or more of the observation field of view, which is outside the practical range.

[0094] <Compressibility> Let t be the height of the protrusions of each thermal conductive sheet before pressing. Let t be the height of the protrusions of the thermal conductive sheet after applying a pressure of 20 MPa (high pressure) or 0.2 MPa (low pressure) at 300°C for 5 minutes. １ In this case, the deformation rate was calculated according to the following formula (1), and the compressibility was evaluated according to the following evaluation criteria. Formula (1): Deformation rate = 100 × (t １ / t) [%] [Evaluation Criteria] ◎: Deformation rate is 67% or less. ○: Deformation rate is greater than 67% but 83% or less. △: Deformation rate is greater than 83% but 97% or less, which is within the practical range. ×: Deformation rate is greater than 97%, which is outside the practical range.

[0095]

[0096]

[0097]

[0098] This application claims priority based on Japanese Patent Application No. 2024-172493, filed on 1 October 2024, and incorporates into this International Application by reference to the entire contents of Japanese Patent Application No. 2024-172493.

[0099] 1 Thermal conductive sheet 2 Heat spreader 2a Main surface 3 Heating element (electronic component) 3a Top surface 5 Heat sink 6 Wiring board 7 Thermal conductive sheet 10 Thermal conductive sheet 11 Metal layer 12 Protrusion 12' Composition containing sinterable metal particles 15 Substrate 16 Opposing substrate 22 Recessed type 100 Laminate

Claims

1. A thermal conductive sheet having a metal layer and a plurality of protrusions on at least a first surface of the metal layer, wherein the protrusions contain sinterable metal particles, and the aspect ratio (height / longest diameter) of the height of the protrusions to the longest diameter of the protrusions is 0.2 or more.

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 or 2, wherein the sinterable metal particles are at least one of gold, silver, copper, and nickel.

4. The thermal conductive sheet according to any one of claims 1 to 3, wherein the ratio of the contact area of ​​the plurality of protrusions with respect to the first surface of the metal layer is 20% or more.

5. The thermal conductive sheet according to any one of claims 1 to 4, wherein the metal layer is at least one of gold, silver, copper, aluminum, and nickel.

6. The thermal conductive sheet according to any one of claims 1 to 5, 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.

7. The first surface 1 mm of the metal layer ２ The volume of the aforementioned multiple protrusions is 0.003 mm². ３ The thermal conductive sheet according to any one of claims 1 to 6.

8. The thermal conductive sheet according to any one of claims 1 to 7, wherein the ratio of the cross-sectional area of ​​the protrusion at 2 / 3 height to the cross-sectional area of ​​1 / 3 height at the protrusion is 1 / 2 or less.

9. The thermal conductive sheet according to any one of claims 1 to 8, wherein the height of the plurality of protrusions after being pressed at an applied pressure of 0.2 MPa, 300°C, and for 5 minutes is 97% or less of the height of the plurality of protrusions before pressing.

10. A thermal conductive sheet according to any one of claims 1 to 9, wherein 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 portion of the first surface other than the central portion is Ap, and the value obtained by dividing Ac by Ap (Ac / Ap) is 1.2 or more and 10 or less.

11. A method for manufacturing a thermal conductive sheet according to any one of claims 1 to 10, characterized by comprising the step of applying a composition containing the sinterable metal particles to at least the first surface of the metal layer to form the plurality of protrusions.

12. A method for manufacturing a thermal conductive sheet according to claim 11, comprising the steps of: preparing a mold having a plurality of recesses corresponding to the plurality of protrusions, and filling each recess with a composition containing the sinterable metal particles; and transferring the composition having a protrusion shape to at least the first surface of the metal layer to form the plurality of protrusions.

Images