Laminate, and method for manufacturing laminate

Abstract

A laminate which has a first bonding layer, a metal layer and a second bonding layer, in this order, wherein recesses which connect to an outer peripheral edge of the metal layer are present in a first surface of the metal layer on the first bonding layer side thereof and in a second surface thereof on the second bonding layer side thereof.

Description

Laminate and method for manufacturing laminate

[0001] The present invention relates to a laminate and a method for manufacturing the laminate.

[0002] In LSIs (Large Scale Integration) and the like in various electronic devices, if the LSI itself is exposed to high temperatures for a long period of time due to heat generated by the elements used, this may lead to malfunction or failure. Therefore, thermal interface materials (TIMs) are widely used to prevent the temperature rise of LSIs and the like. The thermal interface materials can prevent the temperature rise of the equipment by diffusing the heat generated by the elements or by transferring it to a heat dissipation member that releases the heat outside the system, such as to the atmosphere.

[0003] For example, a method has been proposed to prevent the formation of voids in a solder joint formed between two metal surfaces, in which a slit solder layer having slits formed therein that serve as degassing paths is placed and heated (see, for example, Patent Document 1).

[0004] JP 2010-531738 A

[0005] However, when using a thermally conductive material containing solder or nanoparticles, residual volatile components contained in the thermally conductive material remain. When heated during bonding to a substrate, the material evaporates and expands, creating voids. This leads to poor adhesion to the substrate and poor thermal conductivity. During bonding, it is necessary to allow volatile components such as solvents and fluxes to escape to the outside of the thermally conductive material. This problem becomes particularly pronounced when bonding a large-area thermally conductive material to a heat-generating element, as the area of ​​the element increases.

[0006] The present invention aims to solve the above-mentioned problems in the prior art and to achieve the following object: That is, the present invention aims to provide a laminate that can suppress the generation of voids at the interface with the substrate, has excellent adhesion and thermal conductivity, and can be made large in area.

[0007] Means for solving the above problems are as follows. That is, <1> A laminate having a first bonding layer, a metal layer, and a second bonding layer in this order, wherein the metal layer has recesses communicating with the outer periphery of the metal layer on a first surface on the side of the first bonding layer and a second surface on the side of the second bonding layer. <2> The laminate according to <1>, wherein the recesses have a depth of 1 μm or more. <3> The laminate according to <1> or <2>, wherein the recesses have a shape pattern of at least one of a radial shape, a lattice shape, a linear shape, and an embossed shape. <4> The laminate according to any one of <1> to <3>, wherein the metal layer contains one or more elements selected from the group consisting of Cu, Al, Ag, Au, Fe, and Pt. <5> The laminate according to any one of <1> to <4>, wherein the first bonding layer and the second bonding layer have notches at positions corresponding to the recesses in the metal layer. <6> The laminate according to any one of <1> to <5>, wherein the first surface of the metal layer has a concave shape with a radius of curvature R represented by the following formula (1), wherein the radius of curvature R is 500 mm or more and 5000 mm or less. Formula (1): R = (x ２ +y ２) / 2 / y In the formula (1), x represents the distance between the center c and the end e on the first surface of the metal layer, and y represents the difference (Te-Tc) between the thickness Te of the end e and the thickness Tc of the center c of the metal layer. <7> The laminate according to any one of <1> to <6>, wherein the first bonding layer and / or the second bonding layer is a low-melting-point metal layer containing a low-melting-point metal. <8> The laminate according to <7>, wherein the low-melting-point metal is one or more selected from the group consisting of In, Ga, Sn, Zn, and Bi. <9> The laminate according to <7>, wherein the low-melting-point metal is at least one selected from the group consisting of Sn—Pb solder, Pb—Sn—Sb solder, Sn—Sb solder, Sn—Pb—Bi solder, Sn—Bi solder, Sn—Bi—Ag solder, Sn—Cu solder, Sn—Pb—Cu solder, Sn—In solder, Sn—Ag solder, Sn—Pb—Ag solder, Pb—Ag solder, and Sn—Ag—Cu solder. <10> The laminate according to any one of <7> to <9>, further comprising a polyfunctional carboxylic acid layer containing a trifunctional or higher polyfunctional carboxylic acid on the low-melting-point metal layer. <11> The laminate according to any one of <1> to <10>, wherein the first bonding layer and / or the second bonding layer is a thermally conductive particle-containing layer containing thermally conductive particles. <12> A method for producing a laminate, comprising: a recess forming step of forming recesses on a first surface and a second surface of a metal layer, the recesses communicating with the outer periphery of the metal layer; and a bonding layer forming step of forming a first bonding layer and a second bonding layer on the first surface and the second surface of the metal layer having the recesses. <13> The method for producing a laminate according to <12>, wherein the bonding layer forming step is a step of forming a bonding layer by transferring a bonding layer provided on a transfer substrate. <14> The method for producing a laminate according to <12> or <13>, wherein the first surface of the metal layer has a concave shape with a radius of curvature R represented by the following formula (1), wherein the radius of curvature R is 500 mm or more and 5000 mm or less. Formula (1): R=(x ２ +y ２) / 2 / y In the formula (1), x represents the distance between the center c and the end e on the first surface of the metal layer, and y represents the difference (Te-Tc) between the thickness Te of the end e and the thickness Tc of the center c of the metal layer. <15> The method for producing a laminate according to <14>, wherein the bonding layer-forming step is a step of forming a bonding layer by transferring a bonding layer provided on a transfer substrate using a pressing jig having a convex radius of curvature corresponding to the radius of curvature R. <16> The method for producing a laminate according to any one of <12> to <15>, wherein the first bonding layer and the second bonding layer have notched portions at positions corresponding to the recesses of the metal layer. <17> The method for producing a laminate according to <16>, wherein the bonding layer-forming step is a step of providing, in the recesses of the metal layer, spacers having a shape corresponding to the shape of the recesses of the metal layer and a total thickness of the recesses and the bonding layer, and applying a thermally conductive composition containing thermally conductive particles to form a thermally conductive particle-containing layer.

[0008] According to the present invention, the above-mentioned problems in the prior art can be solved, the above-mentioned objects can be achieved, and a laminate can be provided which can suppress the generation of voids at the interface with the substrate, has excellent adhesion and thermal conductivity, and can be made large in area.

[0009] FIG. 1 is a schematic diagram showing an example of a laminate of this embodiment. FIG. 2 is a schematic diagram showing another example of a laminate of this embodiment. FIG. 3 is a schematic diagram showing another example of a laminate of this embodiment. FIG. 4 is a schematic diagram showing another example of a laminate of this embodiment. FIG. 5 is an explanatory diagram of the radius of curvature R of the metal layer 12 in FIG. 4. FIG. 6 is a schematic diagram showing an example of a radial pattern of recesses in the metal layer. FIG. 7 is a schematic diagram showing an example of a lattice pattern of recesses in the metal layer. FIG. 8 is a schematic diagram showing an example of a linear pattern of recesses in the metal layer. FIG. 9 is an explanatory diagram (part 1) of a process for producing a laminate of this embodiment. FIG. 10 is an explanatory diagram (part 1) of a process for producing a laminate of this embodiment. FIG. 11 is an explanatory diagram (part 2) of a process for producing a laminate of this embodiment. FIG. 12 is an explanatory diagram (part 3) of a process for producing a laminate of this embodiment. FIG. 13 is an explanatory diagram (part 4) of a process for producing a laminate of this embodiment. FIG. 14 is an explanatory diagram (part 5) of a process for producing a laminate of this embodiment. Fig. 15 is an explanatory diagram (part 6) of the process of the method for manufacturing a laminate of this embodiment. Fig. 16 is an explanatory diagram (part 7) of the process of the method for manufacturing a laminate of this embodiment. Fig. 17 is an explanatory diagram (part 8) of the process of the method for manufacturing a laminate of this embodiment. Fig. 18 is an explanatory diagram (part 9) of the process of the method for manufacturing a laminate of this embodiment. Fig. 19 is an explanatory diagram (part 10) of the process of the method for manufacturing a laminate of this embodiment. Fig. 20 is a schematic cross-sectional view showing an example of a heat dissipation structure of this embodiment.

[0010] (Laminate) The laminate of this embodiment has a first bonding layer, a metal layer, and a second bonding layer, in this order, and further has other components as necessary. The metal layer has recesses on a first surface on the side of the first bonding layer and a second surface on the side of the second bonding layer, the recesses communicating with the outer periphery of the metal layer. The laminate may further have a first base material and a second base material, in which case the laminate has the first base material, the first bonding layer, the metal layer, the second bonding layer, and the second base material, in this order.

[0011] The present invention is based on the inventors' discovery of problems in the prior art. Specifically, the prior art method described in Patent Document 1, in which a slit solder layer having slits formed therein serving as degassing paths is used for heating, can remove a certain amount of volatile components through the slits serving as degassing paths. However, when the slits are formed in the solder layer and the solder layer is heated during bonding, the slits are blocked by the reflow of the solder layer at the beginning of heating, which can still result in the formation of voids. This problem becomes particularly pronounced when large-area elements are bonded using large-area slit solder layers as the elements become larger in size.

[0012] As a result of intensive research, the inventors have found that in the laminate of this embodiment, the metal layer has recesses on the first surface on the side of the first bonding layer and the second surface on the side of the second bonding layer that communicate with the outer periphery of the metal layer, so that the volatile components that volatilize and expand when heated can flow through the recesses that communicate with the outer periphery and be released outside the system, thereby further suppressing the generation of voids at the interface with the substrate, and realizing a laminate that has excellent adhesion and thermal conductivity and can be made large-area. In this case, it is preferable that the metal layer has recesses that communicate with the outer periphery on the entire surface of the first surface and the entire surface of the second surface from the viewpoint of the efficiency of releasing the volatile components outside the system.

[0013] <Metal Layer> The metal layer is a layer containing a metal, and has a recess communicating with the outer periphery of the metal layer on the first surface on the side of the first bonding layer and the second surface on the side of the second bonding layer. The metal is not particularly limited and can be selected appropriately depending on the purpose, but a metal with high thermal conductivity and relatively soft properties is preferred, and it preferably contains one or more metals selected from the group consisting of Cu, Al, Ag, Au, Fe, and Pt. The metal may be a single metal or an alloy containing two or more metals. Among these, a metal plate made of the metal is preferred, and a copper plate is more preferred from the viewpoints of thermal conductivity, stability, and economy.

[0014] The metal layer is not particularly limited in shape, structure, size, material, etc., as long as it is a layer containing a metal, and can be appropriately selected depending on the purpose. Examples of the shape of the metal layer include a plate, a sheet, and a foil. Examples of the structure of the metal layer include a single-layer structure and a laminated structure. The size of the metal layer can be appropriately selected depending on the application, etc., but it can be made large, for example, 100 mm ２ It can be made larger than 400 mm ２ More than 900 mm is preferable. ２ The above is more preferable.

[0015] The average thickness of the metal layer is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 50 μm to 1000 μm, more preferably 100 μm to 800 μm, and even more preferably 200 μm to 600 μm.

[0016] -Recess- The shape of the recess is not particularly limited and can be appropriately selected depending on the purpose. It may be an irregular shape, but is preferably, for example, a triangular prism, triangular pyramid, square prism, square pyramid, pentagonal prism, pentagonal pyramid, hexagonal prism, hexagonal pyramid, heptagonal prism, heptagonal pyramid, octagonal prism, octagonal pyramid, cylinder, cone, semicircle, or the like.

[0017] The depth of the recesses is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 1 μm or more, more preferably 1 μm to 15 μm. The maximum width of the recesses is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 5 μm or more, more preferably 10 μm to 100 μm. The pitch, which is the shortest distance between the centers of adjacent recesses, is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 10 μm or more, more preferably 10 μm to 100 μm.

[0018] The shape pattern of the recesses in the top view is preferably at least one of a radial shape, a lattice shape, a linear shape, and an embossed shape. From the viewpoint of maintaining the strength of the metal layer while reducing the thickness, it is preferable that the shape pattern of the recesses on the first surface of the metal layer and the shape pattern of the recesses on the second surface of the metal layer do not entirely overlap in the direction perpendicular to the metal layer, but they may partially overlap, and the metal layer may have through holes penetrating the first surface and the second surface.

[0019] [Aspect in which the first surface of the metal layer has a curved surface] The metal layer may have a first surface that has a curved surface. Specifically, in one embodiment, it is preferable that the first surface of the metal layer has a concave shape with a radius of curvature R expressed by the following formula (1). Formula (1): R=(x ２ +y ２ ) / 2 / y In the formula (1), x represents the distance between the center c and the end e of the first surface of the metal layer, and y represents the difference (Te-Tc) between the thickness Te of the end e and the thickness Tc of the center c of the metal layer. The unit is mm.

[0020] The first surface of the metal plate is the surface facing the heating element and preferably contacts the first substrate, which is a part of the heating element, via a first bonding layer. Here, the heating element may be deformed and become convex when mounted on a support substrate. When the heating element is bonded to a heat dissipation member via a thermally conductive member, adhesion to the thermally conductive member may be reduced, resulting in a problem of worsening thermal resistance around the heating element. In contrast, according to an embodiment in which the first surface of the metal layer has a curved surface, the laminate has a curved surface that follows the deformation of the heating element, thereby achieving even better adhesion and thermal conductivity.

[0021] Specifically, consider a case where the substrate of an IC, which is a heat generating element, is made of silicon, and the support substrate on which the IC is mounted is a printed circuit board (PCB), which is a composite material of wiring metal such as copper and resin. Here, the linear expansion coefficient of silicon is approximately 2.6 ppm / K, while the linear expansion coefficient of the PCB is approximately 9 ppm / K to 16 ppm / K. When mounting the PCB and IC using standard solder, they are mounted at high temperatures of 200°C to 300°C. In other words, when the PCB and IC are cooled from a high-temperature, distortion-free bonded state to room temperature, significant deformation occurs due to the difference in the linear expansion coefficients of the PCB and IC, resulting in convex distortion of the first substrate of the IC, which is a heat generating element. In fact, convex distortion of the first substrate is a problem in semiconductor manufacturing processes.

[0022] Assuming that the contact surface of the first substrate with the metal layer has a spherical convex shape, the convex shape can be expressed as a convex shape with a radius of curvature R' expressed by the following formula (2): Formula (2): R'=(x ２ +y ２ ) / 2 / y In the formula (2), x represents the distance between the center c and the end e of the contact surface of the first substrate, and y represents the difference (Te-Tc) between the thickness Te of the end e of the first substrate and the thickness Tc of the center c. The unit is mm.

[0023] The present inventors have confirmed that the radius of curvature R' of the first substrate can be appropriately changed depending on various conditions, such as the heating temperature during mounting of the heating element on the support substrate, the ratio of the length of one side of the support substrate (e.g., a printed circuit board (PCB)) to the first substrate during mounting (size ratio), etc. When the heating temperature during mounting is high (e.g., 200°C or higher) or when the size ratio of the support substrate (PCB) to the first substrate during mounting is large (e.g., 2 or higher), the radius of curvature R' tends to become smaller (i.e., deformation becomes larger), and can be, for example, 4000 mm or less, 3000 mm or less, or 2000 mm or less.

[0024] The radius of curvature R can be appropriately selected depending on the convex shape of the radius of curvature R' of the first substrate, but is preferably 500 mm or more and 5000 mm or less, and more preferably 1000 mm or more and 5000 mm or less. In addition, it is preferable that the radius of curvature R is equal to or larger than the radius of curvature R'.

[0025] When the first surface of the metal layer has a curved surface, the maximum thickness y of the metal layer, i.e., the difference (Te-Tc) between the thickness Te of the end e of the first base material and the thickness Tc of the center c, is preferably 50 μm to 1000 μm, more preferably 100 μm to 800 μm, and even more preferably 200 μm to 600 μm. Furthermore, the minimum thickness of the metal layer (for example, the thickness Tc of the center c) may be 0 μm (i.e., the metal layer has through holes penetrating the first and second surfaces) as long as the shape of the metal layer can be maintained, and from the viewpoint of thinning the laminate, it is preferably 0 μm to 300 μm, more preferably 0 μm to 100 μm, and even more preferably 0 μm to 100 μm.

[0026] When the first surface of the metal layer has a curved surface, the shape pattern of the recesses when viewed from above on the first surface is preferably radial, and more preferably radial around the center c of the metal layer, or a combination of circular and radial shapes around the center c of the metal layer.

[0027] <First substrate> The first substrate may be the heat generating element (electronic component) itself in the heat dissipation structure, or may be a component such as a lid (sealing cover) of the heat generating element. The shape, structure, size, material, etc. of the first substrate are not particularly limited and can be appropriately selected depending on the purpose. Examples of the shape of the first substrate include a plate shape and a sheet shape. Examples of the structure of the first substrate include a single-layer structure and a laminated structure. The size of the first substrate can be appropriately selected depending on the application, etc.

[0028] The material of the first substrate is a material that is difficult to wet with solder, and examples thereof include silicon (Si), aluminum, tungsten, molybdenum, glass, molded resin, stainless steel, and ceramics. These may be used alone or in combination of two or more. Examples of the ceramic include aluminum nitride, silicon carbide, alumina, and gallium nitride. Examples of the molded resin include epoxy resin, silicone resin, urethane resin, and acrylic resin. Among these, silicon (Si) is preferred as the material of the first substrate. There are no particular limitations on the average thickness of the first substrate, and it can be selected appropriately depending on the purpose.

[0029] <Second substrate> The second substrate may be the heat spreader itself in the heat dissipation structure, or may be a part of the heat spreader. The second substrate is disposed opposite the first substrate, and its shape, structure, size, material, etc. are not particularly limited and can be appropriately selected depending on the purpose. Examples of the shape of the second substrate include a plate shape and a sheet shape. Examples of the structure of the second substrate include a single-layer structure and a laminated structure. The size of the second substrate can be appropriately selected depending on the application, etc.

[0030] The material of the second substrate is a material that is easily wetted by solder, and examples thereof include copper, gold, platinum, palladium, silver, zinc, iron, tin, nickel, magnesium, indium, and alloys thereof. These may be used alone or in combination of two or more. Among these, copper is preferred as the material for the second substrate. The average thickness of the second substrate is not particularly limited and can be appropriately selected depending on the purpose. Hereinafter, the first substrate and the second substrate may be collectively referred to as "substrate".

[0031] <First Bonding Layer, Second Bonding Layer> The first bonding layer and the second bonding layer are collectively referred to as "bonding layers." The bonding layer is not particularly limited as long as it has thermal conductivity and can bond the metal layer and the substrate, and can be appropriately selected depending on the purpose. Examples include a low-melting-point metal layer and a thermally conductive particle-containing layer. Among these, a low-melting-point metal layer is preferred because it can effectively suppress the generation of voids without blocking the recesses of the metal layer during bonding and the release of volatile components to the outside of the system. The first bonding layer and the second bonding layer may be formed of the same material or different materials.

[0032] The shape of the bonding layer may be, for example, a plate or a sheet. The structure of the bonding layer may be a single-layer structure or a laminated structure. The size of the bonding layer may be appropriately selected depending on the application, etc.

[0033] [Aspect of the Bonding Layer Having a Cutout] The bonding layer preferably has a cutout at a position corresponding to the recess in the metal layer, and more preferably, the contact surface of the bonding layer with the metal layer has the same pattern as the upper surface of the metal layer. In this case, the bonding layer may be either a low-melting-point metal layer or a thermally conductive particle-containing layer, which is preferable in that it does not block the recess in the metal layer during bonding and can more effectively suppress the occurrence of voids. The cutout may be, for example, a recess or a cutout, but is preferably a cutout in order to thin the laminate and the bonding layer.

[0034] The method for forming the bonding layer having the cutout portion is not particularly limited and can be appropriately selected depending on the purpose. Examples include a method of embossing or die-cutting a sheet-like bonding layer provided on a transfer substrate; a method of transferring a sheet-like bonding layer provided on a transfer substrate onto a metal layer having a recess, and transferring the bonding layer having the cutout portion to the contact surface with the metal layer; and a method of providing a spacer having the shape of the recess of the metal layer and the total thickness of the recess and the bonding layer in the recess of the metal layer, and applying a thermally conductive composition containing thermally conductive particles to form a thermally conductive particle-containing layer.

[0035] <<Low-melting-point metal layer>> The low-melting-point metal layer is a layer containing a low-melting-point metal. The low-melting-point metal is not particularly limited and can be appropriately selected depending on the purpose, but is preferably one or more selected from the group consisting of In, Ga, Sn, Zn, and Bi; and / or a solder material. Among these, In is preferred from the viewpoints of lower hardness than other metal elements, high conformability to the surfaces of the first substrate and the second substrate, and high adhesion.

[0036] The solder material is preferably at least one selected from the group consisting of, for example, Sn—Pb solder, Pb—Sn—Sb solder, Sn—Sb solder, Sn—Pb—Bi solder, Sn—Bi solder, Sn—Bi—Ag solder, Sn—Cu solder, Sn—Pb—Cu solder, Sn—In solder, Sn—Ag solder, Sn—Pb—Ag solder, Pb—Ag solder, and Sn—Ag—Cu solder.

[0037] The low-melting-point metal layer may be formed into a sheet shape from the low-melting-point metal, or may be a commercially available product, such as an indium sheet (product name: 4N In sheet, manufactured by Nippon Invest Co., Ltd., average thickness: 100 μm), an indium sheet (product name: Indium sheet, manufactured by Axis Co., Ltd., average thickness: 100 μm), or a sheet-shaped solder (product name: M705 alloy, manufactured by Senju Metal Industry Co., Ltd., alloy composition (wt%): Sn-3.0Ag-0.5Cu, average thickness: 50 μm).

[0038] The melting point of the low-melting-point metal is preferably 100° C. or higher and 250° C. or lower, and more preferably 120° C. or higher and 200° C. or lower. The melting point of the low-melting-point metal is preferably lower than the heating temperature in the bonding step in the method for producing a laminate of the present embodiment, which will be described later.

[0039] The average thickness of the low melting point metal layer is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 20 μm or more and 500 μm or less, and more preferably 50 μm or more and 200 μm or less.

[0040] - Polyfunctional Carboxylic Acid Layer - It is preferable to further provide a polyfunctional carboxylic acid layer containing a trifunctional or higher polyfunctional carboxylic acid on the low-melting-point metal layer, as this can reduce contact resistance with the substrate and achieve excellent thermal conductivity and adhesion. Here, "on the low-melting-point metal layer" refers to the contact surface of the low-melting-point metal layer with at least one of the metal layer, the first substrate, and the second substrate. Among these, it is preferable to provide the polyfunctional carboxylic acid layer on the contact surface with the metal layer having a recess, as this can effectively expel volatile components including the polyfunctional carboxylic acid to the outside of the laminate during the bonding process of manufacturing the laminate. A laminate having a polyfunctional carboxylic acid layer on a low-melting-point metal layer can achieve a thermal conductivity of 20 W / (m·K) or more.

[0041] Here, it is known that if the contact surface between the low-melting-point metal layer and at least one of the metal layer, first substrate, and second substrate is oxidized, surface roughness and thermal resistance occur, and thermal conductivity decreases. Carboxylic acid can remove low-melting-point metal oxides according to the following reaction formula: By having a polyfunctional carboxylic acid layer on the low-melting-point metal layer, excellent thermal conductivity and adhesion can be achieved, and it is inferred that low-melting-point metal oxides are removed: Low-melting-point metal oxide + carboxylic acid → low-melting-point metal + reaction product with carboxylic acid + water

[0042] The content of the polyfunctional carboxylic acid per area of ​​the polyfunctional carboxylic acid layer is 0.002 μg / mm ２ 0.5 μg / mm or more ２ Preferably, 0.005 μg / mm ２ 0.2 μg / mm or more ２ More preferably, 0.01 μg / mm ２ 0.1 μg / mm or more ２ The following is even more preferred:

[0043] The polyfunctional carboxylic acid is not particularly limited and can be appropriately selected depending on the purpose as long as it is a trifunctional or higher polyfunctional carboxylic acid, but polyfunctional carboxylic acids represented by the following general formula (I) are more preferred. These may be used alone or in combination of two or more.

[0044] However, in the general formula (I), R １ ~R ３ R each independently represents an alkylene group, a lactone skeleton, or a bond. ４ represents a hydrogen atom or an alkyl group which may be substituted with a hydroxyl group. ５ represents an alkylene group having 1 to 3 carbon atoms or an alkenyl group having 2 to 3 carbon atoms.

[0045] R in the general formula (I) １ ~R ３ In the general formula (I), the alkylene group is preferably an alkylene group having 1 to 10 carbon atoms, and examples thereof include a methylene group, an ethylene group, a propylene group, an isopropylene group, a butylene group, a hexylene group, a heptylene group, an octylene group, a 2-ethylhexylene group, a tert-octylene group, and a cyclohexylene group. １ ~R ３ Examples of the lactone skeleton in the above formula include α-acetolactone, β-propiolactone, γ-butyrolactone, δ-valerolactone, and ε-caprolactone.

[0046] R １ ~R ３ When at least one of the groups has a caprolactone skeleton, each -R １ 0-, -R ２ 0-, -R ３ 0- is represented by the following general formula (i).

[0047] In the general formula (i), n represents an integer of 1 or more, preferably 1 to 10.

[0048] R ４ Examples of the alkyl group optionally substituted with a hydroxyl group in the formula (I) include a methyl group, an ethyl group, a propyl group, a -(CH ２ ) —OH, —(CH ２ ) ２ -OH, -(CH ２ ) ３ -OH and the like.

[0049] R ５Examples of the alkylene group having 1 to 3 carbon atoms in R include a methylene group, an ethylene group, a propylene group, and an isopropylene group. ５ Examples of the alkenyl group having 2 to 3 carbon atoms include a vinyl group, a 1-propenyl group, and an allyl group (2-propenyl group). ５ is preferably either an alkyl group having 2 to 3 carbon atoms or an alkenyl group having 2 carbon atoms, in view of achieving both excellent flux activity and curability.

[0050] The polyfunctional carboxylic acid represented by the general formula (I) can be synthesized by reacting a specific acid anhydride with a specific polyfunctional alcohol, as will be explained below.

[0051] [Method for producing polyfunctional carboxylic acid] The method for producing the polyfunctional carboxylic acid includes a step of esterifying an acid anhydride with a polyfunctional alcohol, and may further include other steps as necessary. The esterification reaction between the acid anhydride and the polyfunctional alcohol is not particularly limited and can be appropriately selected depending on the purpose.

[0052] Examples of the acid anhydride include succinic anhydride, glutaric anhydride, maleic anhydride, phthalic anhydride, benzoic anhydride, and oxalic anhydride. These may be used alone or in combination of two or more. Among these, succinic anhydride, glutaric anhydride, and maleic anhydride are preferred.

[0053] The polyfunctional alcohol is trifunctional or more, preferably trifunctional or tetrafunctional. Examples of the polyfunctional alcohol include lactone derivatives such as caprolactone derivatives, glycerin, trimethylolpropane, and pentaerythritol. These may be used alone or in combination of two or more. Among these, glycerin and caprolactone derivatives are preferred.

[0054] Examples of the caprolactone derivative include compounds having a caprolactone skeleton represented by the general formula (i). Commercially available caprolactone derivatives can be used, and examples of the commercially available products include PLACCEL 205, PLACCEL 205U, PLACCEL 303, and PLACCEL 410 (all manufactured by Daicel Corporation).

[0055] An example of the esterification reaction between a specific acid anhydride and a trifunctional alcohol is shown below. In the above reaction scheme, R １ ~R ３ represents an alkylene group, a lactone skeleton, or a bond. ４ represents a hydrogen atom or an alkyl group which may be substituted with a hydroxyl group. ５ represents an alkylene group having 1 to 3 carbon atoms or an alkenyl group having 2 to 3 carbon atoms.

[0056] The other steps are not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include a concentration step and a separation and purification step.

[0057] The polyfunctional carboxylic acid represented by the general formula (I) can exhibit a good fluxing effect. That is, the polyfunctional carboxylic acid represented by the general formula (I) remains liquid from room temperature to high temperatures, does not undergo reaction during film formation, and can improve the wettability of the coating liquid. When heated in stages, the first heating stage exerts a fluxing effect, and then the second heating stage and cooling to room temperature melts and solidifies the low-melting-point metal, resulting in lamination with the silicon substrate or opposing substrate to which it is to be applied. The first heating stage is preferably, for example, 120°C to 150°C. The second heating stage is preferably at a temperature above the melting point of the low-melting-point metal, for example, 150°C to 190°C.

[0058] The polyfunctional carboxylic acid is preferably liquid at 25°C and 150°C. Here, being liquid means having fluidity that allows application. Whether the polyfunctional carboxylic acid is liquid at 25°C and 150°C can be confirmed, for example, by visually confirming the fluidity at 25°C (room temperature) and by the presence or absence of an absorption peak up to 150°C by DSC. In terms of being liquid, the molecular weight of the polyfunctional carboxylic acid is preferably 800 g / mol or less, and more preferably 400 g / mol or more and 700 g / mol or less. The molecular weight of the polyfunctional carboxylic acid can be measured, for example, using Shodex (registered trademark) GPC-101 (product of Showa Denko K.K.).

[0059] <<Thermal Conductive Particle-Containing Layer>> The thermally conductive particle-containing layer contains thermally conductive particles, and further contains other components as needed. The thermally conductive particle-containing layer is preferably formed by curing a thermally conductive composition containing thermally conductive particles. The thermally conductive composition contains thermally conductive particles, a curing component, and a curing agent that cures the curing component, and preferably contains low-melting-point metal particles and a polymer, and further contains other components as needed.

[0060] -Thermal Conductive Particles- The thermal conductive particles are preferably at least one of copper particles, silver-coated particles, and silver particles. Examples of the silver-coated particles include silver-coated copper particles, silver-coated nickel particles, and silver-coated aluminum particles. The shape of the thermal conductive particles is not particularly limited and can be appropriately selected depending on the purpose. Examples include spherical, flat, granular, and acicular shapes. The volume average particle size of the thermal conductive particles is preferably 1 μm or more and 100 μm or less, more preferably 10 μm or more and 70 μm or less, and even more preferably 10 μm or more and 50 μm or less. A volume average particle size of 1 μm or more and 100 μm or less can increase the volume ratio of the thermal conductive particles to the low-melting-point metal particles, thereby achieving high thermal conductivity. The volume average particle size can be measured, for example, using a laser diffraction / scattering particle size distribution analyzer (Microtrac MT3300EXII, manufactured by Microtrac Bell Corporation).

[0061] -Low Melting Point Metal Particles- As the low melting point metal particles, solder particles specified in JIS Z3282-1999 are preferably used. Examples of the solder particles include Sn-Pb solder particles, Pb-Sn-Sb solder particles, Sn-Sb solder particles, Sn-Pb-Bi solder particles, Sn-Bi-Ag solder particles, Sn-Cu solder particles, Sn-Pb-Cu solder particles, Sn-In solder particles, Sn-Ag solder particles, Sn-Pb-Ag solder particles, Pb-Ag solder particles, and Sn-Ag-Cu solder particles. These may be used alone or in combination of two or more. Among these, solder particles containing Sn and at least one selected from Bi, Ag, Cu, and In are preferred, and Sn—Bi based solder particles, Sn—Bi—Ag based solder particles, Sn—Ag—Cu based solder particles, and Sn—In based solder particles are more preferred.

[0062] The shape of the low-melting-point metal particles is not particularly limited and can be appropriately selected depending on the purpose. Examples include spherical, flat, granular, and acicular shapes. The melting point of the low-melting-point metal particles is preferably 100°C or higher and 250°C or lower, more preferably 120°C or higher and 200°C or lower. It is preferable that the melting point of the low-melting-point metal particles be lower than the heat curing temperature of the thermal conductive composition, because the melted low-melting-point metal particles in the cured product of the thermal conductive composition can form a network (a continuous metal phase) via the thermally conductive particles, thereby achieving high thermal conductivity. The low-melting-point metal particles react with the thermally conductive particles under the heat curing conditions of the thermal conductive composition to form an alloy with a melting point higher than the low-melting-point metal particles, thereby preventing melting at high temperatures and improving reliability. Furthermore, the heat resistance of the cured product of the thermal conductive composition is improved. The heat curing treatment of the thermal conductive composition is performed, for example, at a temperature of 150°C or higher and 200°C for 30 minutes to 2 hours.

[0063] The volume average particle size of the low-melting-point metal particles is preferably 10 μm or less, and more preferably 1 μm or more and 5 μm or less. When the volume average particle size of the low-melting-point metal particles is 10 μm or less, the volume ratio of the low-melting-point metal particles to the thermally conductive particles can be reduced, thereby achieving high thermal conductivity. The volume average particle size of the low-melting-point metal particles can be measured in the same manner as the volume average particle size of the thermally conductive particles.

[0064] The volume average particle size of the thermally conductive particles is larger than the volume average particle size of the low-melting-point metal particles, and the volume average particle size ratio (A / B) of the thermally conductive particles A to the low-melting-point metal particles B is preferably 2 or more, more preferably 3 or more, and even more preferably 5 or more. The upper limit of the volume average particle size ratio (A / B) is preferably 20 or less, more preferably 10 or less. By using low-melting-point metal particles having a volume average particle size smaller than that of the thermally conductive particles, the thermally conductive particles become the main component in the thermally conductive composition, and the low-melting-point metal particles present between the thermally conductive particles melt when heated and alloy with the thermally conductive particles to form a network, thereby achieving high thermal conductivity.

[0065] -Curing Component- As the curing component, it is preferable to use at least one of an oxirane ring compound and an oxetane compound.

[0066] --Oxirane Ring Compound-- The oxirane ring compound is a compound having an oxirane ring, and examples thereof include epoxy resins. The epoxy resin is not particularly limited and can be appropriately selected depending on the purpose. Examples include glycidyl ether type epoxy resins, phenol novolac type epoxy resins, cresol novolac type epoxy resins, bisphenol A 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. These may be used alone or in combination of two or more.

[0067] --Oxetane Compound-- The oxetane compound is a compound having an oxetanyl group, and may be an aliphatic compound, an alicyclic compound, or an aromatic compound. The oxetane compound may be a monofunctional oxetane compound having only one oxetanyl group, or a polyfunctional oxetane compound having two or more oxetanyl groups.

[0068] The oxetane compound is not particularly limited and can be appropriately selected depending on the purpose. Examples thereof include 3,7-bis(3-oxetanyl)-5-oxa-nonane, 1,4-bis[(3-ethyl-3-oxetanylmethoxy)methyl]benzene, 1,2-bis[(3-ethyl-3-oxetanylmethoxy)methyl]ethane, 1,3-bis[(3-ethyl-3-oxetanylmethoxy)methyl]propane, ethylene glycol bis(3-ethyl-3-oxetanylmethyl)ether, triethylene glycol bis(3-ethyl-3-oxetanylmethyl)ether, tetraethylene glycol bis(3-ethyl-3-oxetanylmethyl)ether, 1,4 1,6-bis(3-ethyl-3-oxetanylmethoxy)butane, 1,6-bis(3-ethyl-3-oxetanylmethoxy)hexane, 3-ethyl-3-(phenoxy)methyloxetane, 3-ethyl-3-(cyclohexyloxymethyl)oxetane, 3-ethyl-3-(2-ethylhexyloxymethyl)oxetane, 3-ethyl-3-hydroxymethyloxetane, 3-ethyl-3-(chloromethyl)oxetane, 3-ethyl-3{[(3-ethyloxetan-3-yl)methoxy]methyl}oxetane, xylylenebisoxetane, 4,4'-bis[(3-ethyl-3-oxetanyl)methoxymethyl]biphenyl (OXBP), etc. These may be used alone or in combination of two or more.

[0069] As the oxetane compound, commercially available products can be used, and examples of the commercially available products include the "Aron Oxetane (registered trademark)" series sold by Toagosei Co., Ltd. and the "ETERNACOLL (registered trademark)" series sold by Ube Industries, Ltd.

[0070] Among the oxirane ring compounds and oxetane compounds, glycidyl ether type epoxy resins, phenol novolac type epoxy resins, cresol novolac type epoxy resins, phenol-dicyclopentadiene type epoxy resins, bisphenol A type epoxy resins, aliphatic epoxy resins, and 4,4'-bis[(3-ethyl-3-oxetanyl)methoxymethyl]biphenyl (OXBP) are preferred.

[0071] The content of the curing component is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 0.5% by mass or more and 60% by mass or less based on the total amount of the thermosetting composition.

[0072] Curing Agent—The curing agent is a curing agent corresponding to the curing component, and examples thereof include polyaddition-type curing agents such as acid anhydride-based curing agents, aliphatic amine-based curing agents, aromatic amine-based curing agents, phenol-based curing agents, and mercaptan-based curing agents, as well as catalyst-type curing agents such as imidazole. These may be used alone or in combination of two or more. Among these, acid anhydride-based curing agents are preferred. When the curing component is an epoxy resin, acid anhydride-based curing agents are preferred because they do not generate gas during thermal curing, can achieve a long pot life when mixed with the epoxy resin, and can achieve a good balance between the electrical, chemical, and mechanical properties of the resulting cured product. Examples of acid anhydride-based curing agents include cyclohexane-1,2-dicarboxylic acid anhydride and tricarboxylic acid monoanhydrides. Examples of tricarboxylic acid monoanhydrides include cyclohexane-1,2,4-tricarboxylic acid-1,2-anhydride.

[0073] The curing agent preferably has flux activity, as this improves the wettability of the molten low-melting-point metal particles to the thermally conductive particles. Examples of methods for imparting flux activity to the curing agent include introducing protonic acid groups, such as carboxyl groups, sulfonyl groups, and phosphate groups, into the curing agent by known methods. Among these, the introduction of carboxyl groups is preferred in terms of reactivity with the epoxy resin or oxetane compound used as the curing component. Examples of such groups include carboxyl-containing organic acids, such as glutaric acid and succinic acid. Alternatively, compounds modified from glutaric anhydride or succinic anhydride, or metal salts of organic acids, such as silver glutarate, may also be used.

[0074] The content of the curing agent is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 0.1% by mass or more and 30% by mass or less based on the total amount of the thermosetting composition.

[0075] -Polymer- The thermosetting composition preferably contains a polymer to impart flexibility and the like. The polymer is not particularly limited and can be appropriately selected depending on the purpose. Examples include polymers having at least one structure selected from a polybutadiene structure, a polysiloxane structure, a poly(meth)acrylate structure, a polyalkylene structure, a polyalkyleneoxy structure, a polyisoprene structure, a polyisobutylene structure, a polyamide structure, and a polycarbonate structure in the molecule. The content of the polymer is preferably 1% by mass or more and 50% by mass or less, more preferably 1% by mass or more and 30% by mass or less, and even more preferably 1% by mass or more and 10% by mass or less, based on the total amount of the thermosetting composition.

[0076] Other Components The thermosetting composition may contain other components as long as the effects of the present invention are not impaired. The other components are not particularly limited and can be appropriately selected depending on the purpose. Examples of the other components include non-metallic thermally conductive particles (e.g., aluminum nitride, alumina, carbon fiber, etc.), and additives (e.g., antioxidants, ultraviolet absorbers, curing accelerators, silane coupling agents, leveling agents, flame retardants, etc.).

[0077] The average thickness of the thermally conductive particle-containing layer is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 5 μm or more and 500 μm or less, and more preferably 20 μm or more and 200 μm or less.

[0078] In the laminate, the void area ratio at the interface between at least one of the first substrate and the second substrate and the metal layer is preferably 50% or less, more preferably 30% or less. Since the laminate has a metal layer, thermal resistance can be reduced, so a void area ratio of 50% allows significant heat conduction to the metal layer, achieving high thermal conductivity. The void area ratio at the interface between at least one of the first substrate and the second substrate and the metal layer can be determined, for example, as follows: A laminate having a metal layer with an average thickness of 100 μm between a 30 mm × 30 mm × 2 mm Si substrate and a 30 mm × 30 mm × 2 mm glass substrate is photographed from the glass substrate side using an optical microscope (manufactured by Olympus Corporation, product name: MX63) to capture an image 1 of the void at the interface between the glass substrate and the metal layer. Using an infrared microscope (Olympus Corporation, product name: MX63 and Hamamatsu Photonics K.K., product name: InGaAs Camera C12741-03) from the Si substrate side, image 2 of the voids at the interface between the Si substrate and the metal layer is photographed. The void area percentage (%) is calculated for the obtained interface void image 1 and void image 2 as follows. Using Microsoft Excel, the image is binarized at 50% black and white (threshold 128) and saved as a bitmap image. Next, the created binarized bitmap image is read into Excel as binary data, the number of pixels in the entire image and the number of pixels in the white parts are obtained, and the number of pixels in the white parts / the total number of pixels is counted to calculate the void area percentage (%). The void area percentage (%) may be evaluated for each of void image 1 (glass substrate) and void image 2 (Si substrate), or the value with the larger void area percentage may be used for evaluation.

[0079] Here, an embodiment of the laminate will be described in detail with reference to the drawings. In each drawing, the same components are denoted by the same reference numerals, and duplicated descriptions may be omitted. Furthermore, the number, position, shape, etc. of the following components are not limited to the present embodiment, and may be any number, position, shape, etc. that is preferable for implementing the present invention.

[0080] FIG. 1 is a schematic diagram showing an example of a laminate according to this embodiment, and FIG. 2 is a schematic diagram showing another example of a laminate according to this embodiment. The laminate 10 shown in FIG. 1 has a first bonding layer 111, a metal layer 12, and a second bonding layer 112, in this order. The metal layer 12 has a recess 13 (131) on a first surface facing the first bonding layer 111 and a recess 13 (132) on a second surface facing the second bonding layer 112, and the recess 13 communicates with the outer periphery of the metal layer 12. The first bonding layer 111 and the second bonding layer 112 are sheet-shaped low-melting-point metal layers, which can suitably suppress the occurrence of voids without blocking the recess 13 of the metal layer 12 during bonding.

[0081] 2 is a laminate in which the laminate 10 shown in FIG. 1 is bonded to a first substrate 21 and a second substrate 22, and has, in this order, the first substrate 21, a first bonding layer 111, a metal layer 12, a second bonding layer 112, and a second substrate 22. The laminate 10 shown in FIG. 1 is an embodiment in which the first surface of the metal layer 12 does not have a curved surface, and is suitable for cases in which the contact surface of the first substrate 21 with the laminate 10 is flat, as shown in FIG. 2, or when the contact surface of the first substrate 21 has a convex shape but sufficient bonding is ensured by the thickness or amount of the first bonding layer 111.

[0082] 3 is the same as the laminate 10 shown in FIG. 1 , except that the first bonding layer 111 has a notch at a location corresponding to the recess 131 of the metal layer 12. Similarly, the second bonding layer 112 has a notch at a location corresponding to the recess 132 of the metal layer 12. The first bonding layer 111 and the second bonding layer 112 may be low-melting point metal layers or thermally conductive particle-containing layers, which can more suitably suppress the occurrence of voids without blocking the recesses of the metal layers during bonding.

[0083] The laminate 40 shown in Fig. 4 is an embodiment of the laminate 30 shown in Fig. 3 in which the first surface of the metal layer 12 has a curved surface, and the first surface of the metal layer 12 has a concave shape with a radius of curvature R expressed by the following formula (1). Fig. 5 is an explanatory diagram of the radius of curvature R of the metal layer 12 in Fig. 4. Formula (1): R = (x ２ +y ２ ) / 2 / y In the formula (1), as shown in FIG. 5, x represents the distance between the center c and the end e on the first surface of the metal layer 12, and y represents the difference (Te-Tc) between the thickness Te of the end e and the thickness Tc of the center c of the metal layer 12. The unit is mm. The laminate 40 shown in FIG. 4 is suitable for a case where the contact surface of the first base material 21 with the laminate 10 has a convex shape.

[0084] Here, FIG. 6 shows an example of a radial pattern of recesses in the metal layer, FIG. 7 shows an example of a grid pattern of recesses in the metal layer, and FIG. 8 shows an example of a linear pattern of recesses in the metal layer. While FIG. 6 shows a radial pattern that combines a circular and radial pattern centered on the center c of the metal layer, a radial pattern alone is also possible. The shape of the recesses in the radial pattern, grid pattern, and linear pattern is, for example, a square prism, and the cross-sectional shape of the recess is approximately rectangular. Compared to a linear pattern, a grid pattern has contact points in multiple directions, allowing volatile components to move in multiple directions and facilitating the escape of the volatile components from the system. Furthermore, in a radial pattern, when heating and bonding proceed from the center to the edges of the laminate during bonding, the volatile components are sequentially evaporated and expelled from the center to the edges, and then the filling of the recesses with the bonding layer proceeds from the center to the edges, resulting in excellent adhesion.

[0085] (Method for Manufacturing Laminate) The method for manufacturing the laminate of this embodiment includes a recess forming step and a bonding layer forming step, and may include a bonding step, and further includes other steps as necessary.

[0086] <Recess Forming Step> The recess forming step is a step of forming recesses on the first and second surfaces of the metal layer, the recesses communicating with the outer periphery of the metal layer. The shapes of the metal layer and the recesses can be appropriately selected from the items described above for the metal layer in the laminate of this embodiment.

[0087] Examples of methods for forming a pattern consisting of recesses in the metal layer include a method in which a recess shape pattern is formed by directly etching the metal layer; and a method in which a recess shape pattern is formed on the metal layer by photolithography, a metal (e.g., copper) is deposited by electrolytic plating, and the resist pattern is removed to form a pattern on the surface of the metal layer.

[0088] <Bonding layer forming step> The bonding layer forming step is a step of forming a first bonding layer and a second bonding layer on the first surface and the second surface of the metal layer having the recess. The bonding layers can be appropriately selected from the items described above for the bonding layer in the laminate of this embodiment.

[0089] The method for forming a bonding layer on the metal layer having the recesses is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include the following methods (1) and (2): (1) A method for forming a bonding layer by transferring a bonding layer provided on a transfer substrate; (2) A method for forming a bonding layer that is a thermally conductive particle-containing layer by applying a thermally conductive composition containing thermally conductive particles.

[0090] [Aspect in which the bonding layer has a cutout] When the bonding layer has a cutout, the method for forming the bonding layer on the metal layer having the recess is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include the following methods (1-1), (1-2), and (2-1). (1-1) As shown in Figures 9 and 10, a sheet-like bonding layer provided on a transfer substrate 31 is embossed or punched to form a bonding layer 11 having a cutout (Figure 9), and then transferred onto a metal layer 12 having a recess to form a bonding layer 11 having a cutout (Figure 10).

[0091] (1-2) As shown in FIGS. 11 and 12, the metal layer 12 having the recesses is pressed against the sheet-like bonding layer 11 provided on the transfer substrate 31 in the direction of the arrow in the figure (FIG. 11), thereby transferring the bonding layer 11 onto the metal layer 12 having the recesses to form the bonding layer 11 having the notches (FIG. 12).

[0092] (2-1) As shown in FIGS. 13-14 and 12, a spacer 32 having the shape of the recess 13 of the metal layer 12 and the total thickness of the recess 13 and the bonding layer 11 is provided in the recess 13 of the metal layer 12 (FIG. 13), and a thermally conductive composition containing thermally conductive particles is applied to form the bonding layer 11, which is a thermally conductive particle-containing layer (FIGS. 14 and 12).

[0093] [Mode in which Metal Layer Has a Curved Surface] When the metal layer has a curved surface, the method for forming a bonding layer on the metal layer having a recess is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include the following methods (1-3), (1-4), and (2-2). (1-3) As shown in Figures 9 and 15 to 16, a bonding layer 11 having a cutout portion provided on a transfer substrate 31 (Figure 9) is transferred onto a metal layer 12 having a recess using a pressing jig 33 having a convex curvature radius corresponding to the curvature radius R (Figure 15), and a bonding layer 11 having a cutout portion is formed on the metal layer 12 having the recess (Figure 16).

[0094] (1-4) As shown in Figures 17 and 16, the sheet-like bonding layer 11 provided on the transfer substrate 31 is transferred onto the metal layer 12 having a recess using a pressing jig 33 having a convex radius of curvature corresponding to the radius of curvature R (Figure 17), and the bonding layer 11 having a cutout portion is formed on the metal layer 12 having the recess (Figure 18). Note that although an example of transferring the bonding layer 11 having a cutout portion has been described, the sheet-like bonding layer 11 may also be formed on the metal layer 12, and this can be achieved by appropriately adjusting conditions such as the type of transfer substrate 31, the type of bonding layer 11, and the pressing strength of the pressing jig 33.

[0095] (2-2) As shown in FIGS. 18-19 and 16, a spacer 32 having the shape of the recess 13 of the metal layer 12 and the total thickness of the recess 13 and the bonding layer 11 is provided in the recess 13 of the metal layer 12 (FIG. 18), and a thermally conductive composition containing thermally conductive particles is applied to form a bonding layer, which is a layer containing thermally conductive particles (FIGS. 19 and 16).

[0096] The thermally conductive particle-containing layer can be produced by applying a thermally conductive composition containing a curing component, a curing agent for curing the curing component, thermally conductive particles, and low-melting-point metal particles onto the metal layer and curing the composition. Examples of methods for applying the thermally conductive composition include inkjet coating, blade coating, gravure coating, gravure offset coating, bar coating, roll coating, knife coating, air knife coating, comma coating, U-comma coating, AKKU coating, smoothing coating, microgravure coating, reverse roll coating, four-roll coating, five-roll coating, dip coating, curtain coating, slide coating, and die coating.

[0097] <Bonding Step> The bonding step is a step of placing either the first substrate or the second substrate on the bonding layer of the laminate and heating to bond them together. This makes it possible to suitably manufacture a laminate further including either the first substrate or the second substrate. The bonding step preferably involves placing the laminate between the first substrate and the second substrate and heating to bond them together.

[0098] The heating conditions in the bonding step are not particularly limited as long as they are temperature conditions equal to or higher than the melting point of the low-melting-point metal contained in the bonding layer or equal to or higher than the sintering temperature of the thermally conductive particles contained in the thermally conductive particle-containing layer, and can be appropriately selected depending on the purpose. For example, when the melting point of the low-melting-point metal is defined as mp, heating at a temperature of mp+1°C or higher and mp+20°C or lower for 1 to 30 minutes is preferred, and heating at a temperature of mp+3°C or higher and mp+10°C or lower for 1 to 10 minutes is more preferred.

[0099] The laminate of this embodiment can be suitably used, for example, when forming a power LED module or a power IC module by bonding a thermal interface material (TIM), which fills the minute gap between a heat source such as an LSI and a heat sink to allow heat to flow smoothly between the two, and a heat dissipation substrate on which an LED chip or an IC chip is mounted, to the heat sink. Here, power LED modules include those of the wire bonding mounting type and those of the flip chip mounting type, and power IC modules include those of the wire bonding mounting type.

[0100] (Heat Dissipation Structure) The heat dissipation structure of this embodiment includes a heat generating element, the laminate of this embodiment, and a heat dissipation member, and may further include other members as necessary.

[0101] The heating element is not particularly limited and can be appropriately selected depending on the purpose. Examples of the heating element include electronic components such as a CPU (Central Processing Unit), an MPU (Micro Processing Unit), and a GPU (Graphics Processing Unit).

[0102] The heat dissipation member is not particularly limited as long as it is a structure that dissipates heat generated by an electronic component (heat-generating element) and can be appropriately selected depending on the purpose. Examples include a heat spreader, a heat sink, a vapor chamber, and a heat pipe. The heat spreader is a component for efficiently transferring heat from the electronic component to other components. The material of the heat spreader is not particularly limited and can be appropriately selected depending on the purpose, such as copper or aluminum. The heat spreader is typically flat. The heat sink is a component for dissipating heat from the electronic component into the air. The material of the heat sink is not particularly limited and can be appropriately selected depending on the purpose, such as copper or aluminum. The heat sink, for example, has multiple fins. The heat sink, for example, has a base and multiple fins extending in a non-parallel direction (e.g., a direction perpendicular to) one surface of the base. The heat spreader and the heat sink generally have solid structures without internal spaces. The vapor chamber is a hollow structure. A volatile liquid is sealed in the internal space of the hollow structure. Examples of the vapor chamber include a hollow structure of the heat spreader, and a plate-like hollow structure similar to the heat sink. The heat pipe is a cylindrical, approximately cylindrical, or flattened cylindrical hollow structure. A volatile liquid is sealed in the internal space of the hollow structure.

[0103] 20 is a schematic cross-sectional view showing an example of a semiconductor device as a heat dissipation structure. The laminate 7 of this embodiment dissipates heat generated by an electronic component 3 such as a semiconductor element, and as shown in FIG. 20, is fixed to the main surface 2a of the heat spreader 2 facing the electronic component 3, and is sandwiched between the electronic component 3 and the heat spreader 2. The thermally conductive sheet 1 is sandwiched between the heat spreader 2 and a heat sink 5.

[0104] The heat spreader 2 is formed, for example, in the shape of a rectangular plate, and has a main surface 2a facing the electronic components 3 and side walls 2b extending along the periphery of the main surface 2a. The heat spreader 2 has a thermally conductive sheet 1 provided on the main surface 2a surrounded by the side walls 2b, and a heat sink 5 provided on the other surface 2c opposite the main surface 2a via the thermally 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 components 3, such as semiconductor elements. Therefore, the heat spreader 2 can be made of, for example, copper or aluminum, which have good thermal conductivity.

[0105] The electronic component 3 is, for example, a semiconductor element such as an LSI, and is mounted on the wiring board 6. The tip surfaces of the side walls 2b of the heat spreader 2 are also mounted on the wiring board 6, so that the side walls 2b surround the electronic component 3 at a predetermined distance. The laminate 7 of this embodiment is provided on the main surface 2a of the heat spreader 2, thereby forming a heat dissipation member that absorbs heat generated by the electronic component 3 and dissipates the heat through the heat sink 5.

[0106] The laminate of this embodiment can achieve high thermal conductivity as a thermal interface material (TIM), and is therefore suitable for use in, for example, areas surrounding various electrical devices such as CPUs, MPUs, power transistors, LEDs, and laser diodes, where temperature can adversely affect the efficiency and lifespan of element operation.

[0107] This application claims priority based on Japanese Patent Application No. 2024-083966, filed on May 23, 2024, the entire contents of which are incorporated herein by reference.

[0108] REFERENCE SIGNS LIST 1 Thermally conductive sheet 2 Heat spreader 2a Main surface 3 Heat generating element (electronic component) 3a Upper surface 5 Heat sink 6 Wiring board 7 Laminate 10, 20, 30, 40 Laminate 11 Bonding layer 111 First bonding layer 112 Second bonding layer 12 Metal layer 13 Recess 131 Recess on first surface 132 Recess on second surface 21 First substrate 22 Second substrate 31 Transfer substrate 32 Spacer 33 Pressing jig

Claims

1. A laminate comprising a first bonding layer, a metal layer, and a second bonding layer in this order, wherein the metal layer has a recess on a first surface facing the first bonding layer and a second surface facing the second bonding layer that is in communication with the outer periphery of the metal layer.

2. The laminate according to claim 1, wherein the depth of the recess is 1 μm or more.

3. The laminate according to claim 1 or 2, wherein the pattern of the recesses is at least one of a radial pattern, a lattice pattern, a linear pattern, and an embossed pattern.

4. The laminate according to any one of claims 1 to 3, wherein the metal layer contains one or more elements selected from the group consisting of Cu, Al, Ag, Au, Fe, and Pt.

5. A laminate according to any one of claims 1 to 4, wherein the first bonding layer and the second bonding layer have cutouts at locations corresponding to the recesses in the metal layer.

6. The laminate according to any one of claims 1 to 5, wherein the first surface of the metal layer has a concave shape with a radius of curvature R expressed by the following formula (1), wherein the radius of curvature R is 500 mm or more and 5000 mm or less. Formula (1): R = (x ２ +y ２ ) / 2 / y In the formula (1), x represents the distance between the center c and the end e on the first surface of the metal layer, and y represents the difference (Te-Tc) between the thickness Te of the end e and the thickness Tc of the center c of the metal layer.

7. A laminate according to any one of claims 1 to 6, wherein the first bonding layer and / or the second bonding layer is a low-melting-point metal layer containing a low-melting-point metal.

8. The laminate according to claim 7, wherein the low-melting-point metal is at least one selected from the group consisting of In, Ga, Sn, Zn, and Bi.

9. The laminate according to claim 7, wherein the low melting point metal is one or more selected from the group consisting of Sn-Pb solder, Pb-Sn-Sb solder, Sn-Sb solder, Sn-Pb-Bi solder, Sn-Bi solder, Sn-Bi-Ag solder, Sn-Cu solder, Sn-Pb-Cu solder, Sn-In solder, Sn-Ag solder, Sn-Pb-Ag solder, Pb-Ag solder, and Sn-Ag-Cu solder.

10. A laminate according to any one of claims 7 to 9, further comprising a polyfunctional carboxylic acid layer containing a polyfunctional carboxylic acid having three or more functionalities on the low-melting point metal layer.

11. A laminate according to any one of claims 1 to 10, wherein the first bonding layer and / or the second bonding layer is a thermally conductive particle-containing layer containing thermally conductive particles.

12. A method for manufacturing a laminate, comprising: a recess forming step of forming recesses on a first surface and a second surface of a metal layer, the recesses communicating with the outer periphery of the metal layer; and a bonding layer forming step of forming a first bonding layer and a second bonding layer on the first surface and the second surface of the metal layer having the recesses.

13. The method for manufacturing a laminate according to claim 12, wherein the bonding layer forming step is a step of forming a bonding layer by transferring a bonding layer provided on a transfer substrate onto the metal layer having the recesses.

14. The method for producing a laminate according to claim 12 or 13, wherein the first surface of the metal layer has a concave shape with a radius of curvature R expressed by the following formula (1), wherein the radius of curvature R is 500 mm or more and 5000 mm or less. Formula (1): R = (x ２ +y ２ ) / 2 / y In the formula (1), x represents the distance between the center c and the end e on the first surface of the metal layer, and y represents the difference (Te-Tc) between the thickness Te of the end e and the thickness Tc of the center c of the metal layer.

15. A method for manufacturing a laminate according to claim 14, wherein the bonding layer forming step is a step of forming a bonding layer by transferring a bonding layer provided on a transfer substrate using a pressing jig having a convex radius of curvature corresponding to the radius of curvature R.

16. A method for manufacturing a laminate according to any one of claims 12 to 15, wherein the first bonding layer and the second bonding layer have cutouts at locations corresponding to the recesses in the metal layer.

17. A method for manufacturing a laminate according to claim 16, wherein the bonding layer forming step is a step of providing a spacer having the same shape as the recess of the metal layer and the total thickness of the recess and the bonding layer in the recess of the metal layer, and applying a thermally conductive composition containing thermally conductive particles to form a thermally conductive particle-containing layer.

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