Thermally-conductive sheet and thermally-conductive sheet production method

Abstract

This thermally-conductive sheet includes: a metal layer; and a plurality of protrusions having thermal conductivity on at least a first surface of the metal layer. When a contact area of the protrusions arranged in a central portion having an area of 1 / 2 of the first surface and being centered on the centroid of the planar shape of the first surface is defined as Ac, and a contact area of the protrusions arranged in a peripheral portion that is a portion other than the central portion of the first surface is defined as Ap, a value obtained by dividing Ac by Ap (Ac / Ap) is 1.2-10.

Description

Thermal Conductive Sheet and Method for Manufacturing the Same

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

[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 LSIs 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 thermal conductive material is widely used to prevent the temperature rise of the LSI and the like. The thermal conductive material can prevent the temperature rise of the device by diffusing the heat generated by the element or transmitting it to a heat radiating member for releasing it to the outside of the system such as the atmosphere.

[0003] Conventionally, for the purpose of providing a wiring board or the like that is 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. Among the plurality of connection pads, at least those arranged on the outermost side are arranged in a convex or concave shape curved toward the outer periphery of the upper surface, and a plurality of conductor pads for pads, and a plurality of linearly arranged openings are provided. A wiring board has been reported that is composed of a covering layer that covers at least a part of the upper surface so that a part of the conductor for the pad is exposed at the opening (see, for example, Patent Document 1).

[0004] Japanese Patent Application Laid-Open No. 2017-152678

[0005] However, the conventional wiring board described in Patent Document 1 has a problem that reliability problems may occur due to the generation of stress under thermal cycle conditions.

[0006] An object of the present invention is to solve the above-mentioned conventional problems and achieve the following object. That is, an object of the present invention is to provide a thermal conductive sheet that can relieve stress under thermal cycle conditions and can 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 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 Ac, and the contact area of ​​the protrusions, which are located in 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. <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 ratio of the contact area of ​​the plurality of protrusions to the first surface of the metal layer is 30% or more and 80% or less. <4> The thermal conductive sheet according to any one of <1> to <3>, wherein the ratio of the contact area of ​​the protrusions arranged in the center to the center of the first surface is 40% or more. <5> The thermal conductive sheet according to any one of <1> to <4>, wherein the ratio of the contact area of ​​the protrusions arranged in the periphery to the periphery of the first surface is 70% or less. <6> The thermal conductive sheet according to any one of <1> to <5>, wherein the thermal conductivity of the metal layer is 200 W / (m·K) or more. <7> The thermal conductive sheet according to any one of <1> to <6>, wherein the metal layer contains at least one of gold, silver, copper, and aluminum. <8> The thermal conductive sheet according to any one of <1> to <7>, 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 any one of <1> to <8>, wherein the protrusions contain sinterable metal nanoparticles. <10> The thermal conductive sheet according to <9> further comprises at least one of a modified acrylate compound, epoxy resin, unsaturated polyester resin, polyurethane resin, bismaleimide resin, alkyd resin, phenol resin, and melamine resin.<11> A method for manufacturing a heat conductive sheet according to any one of <9> to <10> above, characterized in that it includes the 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> A method for manufacturing a heat conductive sheet according to any one of <1> to <8> above, characterized in that it includes the steps of applying a protective portion to at least a first surface of the metal layer, forming the plurality of protrusions by plating the exposed surface of the metal layer to which the protective portion is not applied, and removing the protective portion. <13> A method for manufacturing a heat conductive sheet according to any one of <1> to <8> above, characterized in that it includes the steps of applying a protective portion to at least a first surface of a metal plate, etching the exposed surface of the metal plate to which the protective portion is not applied to form the metal layer and the plurality of protrusions, and removing the protective portion.

[0008] According to the present invention, it is possible to solve the aforementioned problems in the conventional method, achieve the aforementioned objectives, and provide a thermal conductive sheet that can alleviate stress under thermal cycling conditions 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 plan view illustrating the central part c and peripheral part p of the heat conductive sheet according to this embodiment. Figure 5 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 6 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 7 is a schematic cross-sectional view (part 3) 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 4) showing an example of the process for manufacturing the heat conductive sheet according to the first embodiment. Figure 9 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 10 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 11 is a schematic cross-sectional view (part 1) showing an example of the process for manufacturing the heat conductive sheet according to the third embodiment. 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 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 is a schematic cross-sectional view showing an example of the process for manufacturing a heat conductive sheet according to the third embodiment (part 4). Figure 15 is a schematic cross-sectional view showing an example of a heat dissipation structure according to this embodiment.

[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 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 Ac, and the contact area of ​​the protrusions, which are located in 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 along the A-A' section, respectively, of an example of a heat-conducting sheet according to this embodiment. The heat-conducting 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. 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), 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 4). Figure 4 is a plan view illustrating the central part c and peripheral part p of the heat-conducting sheet according to this embodiment, and the dashed line in Figure 4 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, the value obtained by dividing Ac by Ap (Ac / Ap) is 1.2 or more and 10 or less. For example, in the heat conductive sheet 10 shown in Figure 1, the proportion of the area in contact with the central part c of the first surface by the multiple protrusions is 75%, and the proportion 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.

[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 the first surface of the metal layer 11. 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 defined 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 defined 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, aluminum, nickel, iron, gold, silver, copper, zinc, and tin are preferred as the metal, and gold, silver, copper, aluminum, and nickel are more preferred.

[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 a value of 200 W / (m·K) or higher is more preferred.

[0017] <<Protrusions>> There are no particular restrictions on the protrusions, and they can be appropriately selected according to the purpose. Examples include metals formed by electroplating, non-electroplating, etc.; metals filled with a filler material if necessary; and metals 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 metals formed by electroplating, and they can be appropriately selected from the metals according to the purpose.

[0018] The protrusions may be filled with a metal material, or they 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, but 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 limit to the 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 can be given, 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 length of the long side of the heat 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 according to 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 of the protrusion (T) relative to ) ｍ ) ratio (T ｍ / T Ｍ There are no particular restrictions on this, and it can be appropriately selected according to 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 for 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. For example, 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); a method of cutting out a metal part in which the metal layer and the protrusions are integrated by etching a metal plate (third embodiment).

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

[0038] FIGS. 5 to 8 show schematic cross-sectional views illustrating an example of the process of the method for manufacturing a heat conduction sheet according to the first embodiment. This aspect is an aspect in which convex portions are formed on the first surface and the second surface (both surfaces) of the metal layer. First, a metal layer 11 is prepared (FIG. 5), and a protective portion 13 is formed on the first surface and optionally the second surface of the metal layer 11 (FIG. 6, protective portion applying step). Next, a composition containing a metal material is applied onto the exposed surface of the metal layer 11 to which the protective portion 13 is not applied to form a plurality of convex portions 12 (FIG. 7, convex portion forming step). Next, the protective portion 13 is removed (FIG. 8, protective portion removing step), and 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.

[0039] <Protective Portion Applying Step> The protective portion applying step is a step of applying a protective portion on at least the first surface of the metal layer, and can be preferably carried out by a protective portion applying means. When manufacturing a heat conduction sheet having convex portions on both of its surfaces, the protective portion applying step is a step of applying a protective portion on the first surface and the second surface of the metal layer.

[0040] As a pattern of the protective portion applied by the protective portion applying step, it can be an inverted pattern of the pattern of the convex portion in the target heat conduction sheet. The protective portion can be preferably selected according to the target aspect, and examples thereof include a resist material.

[0041] The method of applying the protective portion is not particularly limited and can be appropriately selected according to the purpose. For example, a method of applying a protective portion having a desired pattern by imprint; a method of applying a protective portion having a desired pattern by inkjet, screen printing, etc.; a method of forming a protective portion having a desired pattern with a resist, etc. can be mentioned. As a method of forming a protective portion having a desired pattern with the resist, for example, a method of forming a protective portion by applying a resist on at least the first surface of the metal layer, exposing and developing it to a desired pattern, and heating it after exposure and / or after development as necessary can be mentioned. The resist may be a negative type in which the exposed portion remains after development, or a positive type in which the non-exposed portion remains after development.

[0042] <Convex portion forming step> The convex portion forming step is a step of forming the plurality of convex portions by applying a composition containing the metal material to at least the first surface of the metal layer, and the metal material is preferably the sinterable metal nanoparticles.

[0043] When the protective portion applying step is carried out, the convex portion forming step is a step of forming the plurality of convex portions by applying a composition containing the metal material onto the exposed surface of the metal layer on which the protective portion is not applied, and it can be preferably carried out by a convex portion forming means.

[0044] Even if the protective portion applying step is not carried out, the composition containing the metal material may be applied in a pattern to form the plurality of convex portions. Examples of the method of applying the composition in a pattern include 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, or the like.

[0045] The composition containing the metal material contains the metal material, and further, 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 any one of 60% by mass or more, 70% by mass or more, and 80% by mass or more, still 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 according to the purpose. Examples thereof include terpineol, butyl carbitol, butyl carbitol acetate, and texanol.

[0047] The composition can be prepared by mixing and dispersing the metal material, and if necessary, a filler and a solvent. As the composition, a commercially available product may be used. Examples thereof include H 9890-6A (manufactured by Namics Corporation, thermosetting conductive adhesive, silver paste) as a metal paste containing metal particles.

[0048] <Protective Part Removal Process> The protective part removal process is a process of removing the protective part, which can be suitably carried out by protective part removal means. There are no particular restrictions on the method of removing the protective part, and it can be appropriately selected according to the purpose. For example, methods of removing the protective part include high-temperature heating, strong alkali, organic solvent treatment, etc.

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

[0050] <Polishing Process> The polishing process is a process 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 carrying out the polishing process, and it can be appropriately done depending on the purpose, for example, after the protrusion formation process, before the protective part removal process, after the protective part removal process, after the heating process, 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 of forming protrusions by plating, and a protective portion removal step, and further includes other steps such as a heating step and a polishing step as needed. The heat conductive sheet of this embodiment described above can be suitably manufactured by the method for manufacturing a heat conductive sheet in 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. 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 step). Next, a plurality of protrusions 12 are formed by plating on the exposed surface of the metal layer 11 where the protective portion 13 is not applied (Figure 9, plating step). Then, the protective portion 13 is removed (Figure 10, protective portion removal step), 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 portion application step, protective portion removal step, and other steps such as the polishing step in the second embodiment, the matters 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 restrictions on the method of forming the plurality of protrusions by plating, and can be appropriately selected according to the purpose, for example, electroplating and electroless plating (chemical plating). Among these, electroplating is preferred from the viewpoint of throughput. There are no particular restrictions on the metal to be filled by the plating, and can be appropriately selected according to the purpose, but it is preferable to include at least one of nickel, gold, silver, and copper, and it is more preferable to include at least one of nickel, gold, silver, and copper.

[0055] [Third Embodiment] The method for manufacturing a heat 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 to 14 show schematic cross-sectional views illustrating an example of the process for manufacturing a heat conductive sheet according to the third embodiment. This embodiment involves forming protrusions on the first and second surfaces (both sides) of the metal layer. First, a metal plate 11', which will serve as a precursor for 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 step). 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 includes the metal layer 11 and a plurality of protrusions 12 on the first and second surfaces of the metal layer 11 (Figure 13, etching step). Then, the protective portion 13 is removed (Figure 14, protective portion removal step), 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-conducting sheet of this embodiment described above, and a heat-dissipating member, and further comprises other members as necessary. The heat dissipation structure has the heat-conducting sheet between the heat-generating element and the heat-dissipating member. The heat dissipation structure may further have adhesive layers between each component as necessary.

[0059] 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).

[0060] 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.

[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 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.

[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. 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.

[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 a thermal conductive sheet> A thermal conductive sheet of Example 1 having a plurality of protrusions as shown in Figure 1 was manufactured according to the manufacturing method shown in Figures 5 to 8 by following the procedure below.

[0066] <<Formation of 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 layer 13 shown in Figure 6, and the protective layer 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>> Ag sintering material (H 9890-6A, manufactured by Namics Corporation) was applied to the metal layer on which the protective layer had been formed, and by drying, 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] <Preparation of the bonded body> Next, a laminate is prepared by sandwiching the thermal conductive sheet of 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). ２ Under atmospheric conditions, a bonder (device name: SB6e, manufactured by SUSS MicroTech) was set to a load of 10 MPa and a temperature of 250°C. By pressurizing and heating for a bonding time of 30 minutes, the sinterable silver nanoparticles contained in the protrusions were sintered to form a sintered body, and the laminate was bonded.

[0071] <Evaluation> 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 (SiC substrate with a 0.5 μm Au plating layer on the 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 measured in advance by the thermal resistance. The 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. ○: Thermal conductivity is 100 W / m·K or higher and less than 150 W / m·K. ×: The thermal conductivity is less than 100 W / m·K.

[0073] <Reliability> The reliability of the obtained joints 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] ◎: Rate of change is 10% or less. ○: Rate of change is 10% or more and less than 15%. △: Rate of change is 15% or more and less than 20%. ×: Rate of change is 20% or more.

[0074] (Examples 2-5) Except for changing the pattern of multiple protrusions as shown in Table 1, the thermal conductive sheets of Examples 2-5 were manufactured and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0075] (Comparative Examples 1-4) Except for changing the pattern of multiple protrusions as shown in Table 2, the thermal conductive sheets of Comparative Examples 1-4 were manufactured and evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0076]

[0077]

[0078] This application claims priority based on Japanese Patent Application No. 2024-172495, filed on 1 October 2024, and incorporates into this International Application by reference to the entire contents of Japanese Patent Application No. 2024-172495.

[0079] 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 11' Metal plate before etching 12 Protrusion 13 Protective part c Center p Peripheral part

Claims

1. 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 Ac, and the contact area of ​​the protrusions, which are located in 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.

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 ratio of the contact area of ​​the plurality of protrusions with respect to the first surface of the metal layer is 30% or more and 80% or less.

4. The thermal conductive sheet according to any one of claims 1 to 3, 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 any one of claims 1 to 4, wherein the ratio of the contact area of ​​the protrusions arranged on the peripheral portion to the peripheral portion of the first surface is 70% or less.

6. The thermal conductive sheet according to any one of claims 1 to 5, wherein the thermal conductivity of the metal layer is 200 W / (m·K) or more.

7. The thermal conductive sheet according to any one of claims 1 to 6, wherein the metal layer comprises at least one of gold, silver, copper, and aluminum.

8. The thermal conductive sheet according to any one of claims 1 to 7, 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 any one of claims 1 to 8, 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 thermal conductive sheet according to any one of claims 9 to 10, characterized by comprising 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, comprising the steps of: providing a protective portion on at least the first surface of the metal layer; forming the plurality of protrusions by plating the exposed surface of the metal layer to which the protective portion is not provided; and removing the protective portion.

13. A method for manufacturing a thermal conductive sheet according to any one of claims 1 to 8, comprising the steps of: providing a protective portion on at least the first surface of a metal plate; 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; and removing the protective portion.

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