Heat sink and semiconductor package

Abstract

To provide a heat sink having a good balance between thermal conductivity and coefficient of linear expansion and excellent heat dissipation performance.SOLUTION: A heat sink having a structure in which three or more layers are laminated includes a first layer that is at least one of the two outermost layers in the thickness direction of the laminated structure. The first layer is composed of a first material. The first material is a material containing carbon fibers dispersed in a metallic phase mainly composed of copper, the volume ratio of the carbon fibers to the entire first material is 5.0 vol.% or more, the thickness of the first layer is 0.15 mm or more and 0.35 mm or less, and a value obtained by subtracting the thermal conductivity in the thickness direction of the first layer from the thermal conductivity in the plane direction orthogonal to the thickness direction of the first layer is 40 W / m K or more.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a heat sink and a semiconductor package.

Background Art

[0002] In the semiconductor field, a heat sink is used to efficiently dissipate heat generated from semiconductor elements and prevent overheating of the semiconductor elements. As the heat sink, metals such as copper with high thermal conductivity have been used. Due to the difference in the linear expansion coefficients between the metal that is the heat sink and the semiconductor element or the ceramic package, thermal stress is generated at these interfaces, which may cause damage to the semiconductor element or the like. For this reason, a composite material of a metal with high thermal conductivity and a metal with a small linear expansion coefficient is used as the heat sink. For example, Patent Document 1 discloses a heat sink in which a copper (Cu) layer and a molybdenum-copper (Mo-Cu) composite layer are alternately laminated, and the outermost layer is made of a copper layer. By making the laminated outermost copper layer thin, a heat sink having excellent thermal conductivity in the plate thickness direction and a small thermal expansion coefficient is obtained.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] According to the structure described in Patent Document 1, heat generated from a semiconductor element arranged to be in contact with the central portion of the surface is likely to be transmitted in the plate thickness direction of the heat sink, and the thermal expansion in the plane direction of the heat sink can be reduced. However, due to the progress of semiconductor technology, the heat generation from semiconductor elements tends to be greater than before. There is a demand for a heat sink that has higher heat dissipation performance than before and is less likely to be damaged by thermal stress. The present disclosure aims to provide a heat sink having a good balance between thermal conductivity and linear expansion coefficient and being more excellent in heat dissipation performance than before.

Means for Solving the Problems

[0005] The heat sink of the present disclosure is a heat sink having a structure in which three or more layers are laminated, and includes a first layer which is at least one of the outermost layers in the thickness direction of the laminated structure. The first layer is made of a first material, and the first material is a material containing carbon fibers dispersed in a metal phase mainly composed of copper. The volume ratio of the carbon fibers in the entire first material is 5.0% by volume or more. The thickness of the first layer is 0.15 mm or more and 0.35 mm or less. The value obtained by subtracting the thermal conductivity in the thickness direction of the first layer from the thermal conductivity in the plane direction orthogonal to the thickness direction of the first layer is 40 W / m·K or more.

[0006] Also, the heat sink of the present disclosure is a heat sink having a structure in which three or more layers are laminated, and includes a first layer which is at least one of the outermost layers in the thickness direction of the laminated structure. The thickness of the first layer is 0.15 mm or more and 0.35 mm or less. The first layer is made of a first material, and the first material is a material containing a plurality of carbon fibers dispersed in a metal phase mainly composed of copper. The volume ratio of the carbon fibers in the entire first material is 5.0% by volume or more. Each of the plurality of carbon fibers has an orientation in the plane direction, and the orientation ratio of the orientation is 76% or more.

[0007] Also, the semiconductor package of the present disclosure includes the above-described heat sink and a semiconductor element disposed on the surface of the first layer.

Advantages of the Invention

[0008] According to the heat sink of the present disclosure, a heat sink with an excellent heat dissipation performance can be obtained with a good balance between the thermal conductivity and the linear expansion coefficient. A heat sink can be obtained.

Brief Description of the Drawings

[0009]

Figure 1

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Figure 6A

Figure 6B

Figure 6C

Figure 6D

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Figure 12

MODE FOR CARRYING OUT THE INVENTION

[0010] [Description of Embodiments of the Present Disclosure] In the conventional technology for improving the heat conduction in the thickness direction of a heat sink, the heat transferred from the heating element to the heat sink is transmitted isotropically in the thickness direction and the plane direction of the heat sink. For this reason, in the thin surface layer, the surface heat is transmitted to the back surface before spreading in the plane direction. In other words, the heat flow concentrates in the plate thickness direction directly below the heat source. The inventor of the present application has focused on such heat flow and found a problem that it is difficult to obtain the effect of heat conduction in the thickness direction in the peripheral portion of the heat sink not in contact with the heating element. In particular, when the area of the entire surface of the heat sink is larger than the area of the portion where the heating element is in contact with the heat sink, the portion where the heating element is not in contact hardly contributes to heat dissipation, and the performance of the heat sink cannot be fully exhibited.

[0011] Hereinafter, embodiments of the present disclosure will be listed and described. (1) A heat sink according to an embodiment of the present disclosure is a heat sink having a structure in which three or more layers are laminated. The heat sink includes a first layer which is at least one of the outermost layers in the thickness direction of the laminated structure, and the first layer is made of a first material. The first material is a material containing carbon fibers as an additive phase dispersed in a metal phase mainly composed of copper. The volume ratio of the carbon fibers as the additive phase in the entire first material is 5.0% by volume or more. The thickness of the first layer is 0.15 mm or more and 0.35 mm or less. The value obtained by subtracting the heat conductivity in the thickness direction of the first layer from the heat conductivity in the plane direction orthogonal to the thickness direction of the first layer is 40 W / m·K or more. Note that the thickness direction of the laminated structure is the direction in which the three or more layers are laminated, and the plane direction is a direction perpendicular to the thickness direction.

[0012] By adding carbon fibers to the outermost layer which is the surface layer in contact with the heating element, the heat conductivity can be changed as compared with the case of using only copper. Here, by providing a difference between the heat conductivity in the thickness direction and the heat conductivity in the plane direction of the first layer, and making heat more easily transmitted in the plane direction than in the thickness direction, heat transfer over the entire surface easily contributes to heat dissipation. When heat spreads in the plane direction in the first layer having a surface in contact with the heating element, heat in the thickness direction becomes more easily transmitted over the entire surface. As a result, a heat sink with an excellent heat dissipation performance can be obtained with a good balance between heat conductivity and linear expansion coefficient.

[0013] (2) The heat sink according to another embodiment of the present disclosure is a heat sink having a structure in which three or more layers are laminated, and includes a first layer which is at least one of the outermost layers in the thickness direction of the laminated structure. The thickness of the first layer is 0.15 mm or more and 0.35 mm or less. The first layer is made of a first material. The first material is a material containing a plurality of carbon fibers dispersed in a metal phase mainly composed of copper. The volume ratio of the carbon fibers in the entire first material is 5.0% by volume or more. Each of the plurality of carbon fibers has an orientation in the plane direction, and the orientation ratio of the orientation is 76% or more.

[0014] By adding carbon fibers to the outermost layer which is the surface layer in contact with the heating element, the thermal conductivity can be changed compared to the case of using only copper. Here, since each of the plurality of carbon fibers has an in-plane orientation, the in-plane thermal conductivity can be made higher than the thermal conductivity in the thickness direction. By making heat transfer easier in the plane direction, heat transfer over the entire surface can contribute more easily to heat dissipation. Thereby, a balance between the thermal conductivity and the linear expansion coefficient is good, and a heat sink with excellent heat dissipation performance can be obtained.

[0015] (3) The thermal conductivity of the first layer in the thickness direction may be 250 W / m·K or more, and the linear expansion coefficient of the first layer in the plane direction when the temperature changes from room temperature to 300 °C may be 18.1 ppm / K or less.

[0016] In order to obtain high heat dissipation performance of the entire heat sink, it is preferable that the thermal conductivity in the thickness direction of the first layer is high. Also, considering use at high temperatures, it is preferable that the linear expansion coefficient in the plane direction is below a certain value. According to the configuration of the above embodiment (3), a balance between the thermal conductivity in the thickness direction and the linear expansion coefficient in the plane direction is good, and a heat sink with excellent heat dissipation performance can be obtained.

[0017] (4) The second layer in contact with the first layer may have a thermal conductivity in the thickness direction of the second layer of 140 W / m·K or more, and a linear expansion coefficient in the plane direction of the second layer of 8.0 ppm / K or less when the temperature changes from room temperature to 300 °C.

[0018] The second layer is provided for the purpose of reducing the coefficient of linear thermal expansion in the plane direction of the entire heat sink. A heat sink with a good balance between thermal conductivity and coefficient of linear thermal expansion and excellent heat dissipation performance can be obtained.

[0019] (5) The second layer may be composed of a second material containing molybdenum or tungsten.

[0020] Molybdenum and tungsten are materials suitable for adjusting the thermal conductivity and coefficient of linear thermal expansion of the second layer. Molybdenum or tungsten may be used alone in the second layer. Also, desired performance can be obtained with a material in which molybdenum or tungsten is combined with copper. Thereby, a heat sink with a good balance between the thermal conductivity in the thickness direction and the coefficient of linear thermal expansion in the plane direction and excellent heat dissipation performance can be obtained.

[0021] (6) In the case of a heat sink in which three layers are laminated, both of the outermost layers may be the first layer, and the layer between the two outermost layers may be the second layer.

[0022] Laminating the first layer, the second layer, and the first layer in this order is a preferable combination when the number of laminated layers is three. With this three-layer structure, a heat sink with a good balance between the thermal conductivity in the thickness direction and the coefficient of linear thermal expansion in the plane direction and excellent heat dissipation performance can be obtained. Also, by making the layer structure symmetric in the lamination direction, warping of the heat sink itself is less likely to occur.

[0023] (7) In the case of a heat sink in which an odd number of layers of five or more are laminated, both of the outermost layers are the first layer, a pair of layers each in contact with one of the two outermost layers are both the second layer, and the third layer in contact with the surface of the pair of second layers opposite to the surface in contact with the first layer may be composed of copper or a copper alloy.

[0024] When using a 5-layer laminate as a heat sink, it is preferable to laminate in the order of the first layer, the second layer, the third layer, the second layer, and the first layer. Here, the third layer is mainly a layer for obtaining heat conduction performance and is preferably composed of a material mainly containing copper. The third layer may be copper or a copper alloy. The same material as the first layer may be used for the third layer. Also, pure copper composed of copper and inevitable impurities is preferably used for the third layer. With this 5-layer structure, a good balance between the thermal conductivity in the thickness direction and the linear expansion coefficient in the plane direction can be achieved, and a heat sink with excellent heat dissipation performance can be obtained.

[0025] (8) Also, a semiconductor package according to an embodiment of the present disclosure includes any one of the above heat sinks and a semiconductor element disposed on the surface of the first layer.

[0026] By using the heat sink with excellent heat dissipation performance as described above, a semiconductor package that suppresses the occurrence of malfunction or damage due to overheating can be obtained.

[0027] [Details of Embodiments of the Present Disclosure] Hereinafter, specific examples of the heat sink according to the embodiment of the present disclosure will be described with reference to the drawings. The same reference numerals in the drawings indicate the same or corresponding parts. The sizes and positional relationships of the members shown in each drawing are expressed for the purpose of clarifying the description and do not necessarily represent the actual dimensional relationships. The configuration described in one embodiment is applicable to other embodiments unless otherwise specified. Although terms indicating specific directions and positions are used in the following description, the use of these terms is for facilitating the understanding of the invention with reference to the drawings, and the technical scope of the present invention is not limited by the meanings of these terms. Examples of terms indicating specific directions and positions include, for example, "up", "upper surface", "front", "surface", etc.

[0028] FIG. 1 is a perspective view showing an example of a heat sink according to an embodiment. The heat sink 1 in FIG. 1 has a front surface 2 and a back surface 3, and is a plate-like body having a rectangular shape in plan view. In the following description, the direction of the surfaces constituting the front surface 2 and the back surface 3 of the heat sink 1 is defined as the X-Y plane, and the thickness direction of the plate is defined as the Z direction. A heat generating body (not shown) to be cooled is disposed on a part or all of the front surface 2. The heat transmitted from the heat generating body to the front surface 2 is transmitted in the thickness direction, that is, the Z direction, and is radiated from the back surface 3. Metals, liquids, etc. as other heat transfer media may be in contact with the back surface 3. The heat sink 1 has a structure in which a plurality of layers are stacked in the Z direction, and one surface of the outermost layer is exposed as the front surface 2, and one surface of the other outermost layer is exposed as the back surface 3.

[0029] FIG. 2 is a schematic diagram for explaining a cross section obtained by cutting the heat sink 1 in FIG. 1 in the Z direction along line A-A. The heat sink 1 has a plurality of layers in the Z direction. In this embodiment, the case of five layers is shown. Hereinafter, for convenience of explanation, the layers having the front surface 2 arranged at the upper part of the figure are sequentially referred to as the first layer 101, the second layer 102, the third layer 103, the fourth layer 104, and the fifth layer 105. The first layer 101 is made of a first material 10. The second layer 102 in contact with the first layer 101 is made of a second material 20. The third layer 103 is made of a third material 30. The fourth layer 104 is made of the same second material 20 as the second layer 102. The fifth layer 105 having the back surface 3 is made of the first material 10. The thickness of each layer can be arbitrarily selected. In the embodiment shown in FIG. 2, the first layer 101 and the fifth layer 105, and the second layer 102 and the fourth layer 104 have the same thickness. As a result, the heat sink 1 of this embodiment has a laminated structure that is symmetric up and down with respect to the center in the thickness direction.

[0030] The first material 10 is a material containing an additive phase mainly composed of carbon fibers 13 in a metal phase 11 mainly composed of copper. Here, the "metal phase 11 mainly composed of copper" is a metal phase in which the copper content in the metal phase is 50 mass percent or more. The metal phase 11 mainly composed of copper preferably contains 70 mass percent or more copper, and most preferably pure copper. Pure copper is a metallic material composed of copper and inevitable impurities. Carbon fiber is a fiber obtained by subjecting a precursor of an organic fiber to heat carbonization treatment and composed of 90% or more carbon by mass ratio. Carbon fiber includes fibrous substances made of carbon. Alternatively, carbon fiber refers to so-called commercially available carbon fiber, that is, fibers made by carbonizing acrylic fiber or pitch (by-products such as petroleum, coal, and coal tar) at high temperature. It is preferable that the carbon fiber has a higher thermal conductivity than copper in the longitudinal direction of the fiber.

[0031] By using such a material, it is possible to make the value obtained by subtracting the thermal conductivity in the thickness direction from the thermal conductivity in the plane direction of the first layer 101 be 40 W / m·K or more. Since the thermal conductivity in the plane direction is higher than the thermal conductivity in the thickness direction, heat is likely to be transmitted in the plane direction. For example, the heat transmitted to a part of the surface 2 of the first layer 101 is transmitted in the plane direction and then in the thickness direction within the first layer 101. Therefore, the entire first layer 101 can contribute to heat conduction in the thickness direction. The heat transmitted from the surface 2 of the first layer 101 to the surface in contact with the second layer 102 is then transmitted in the thickness direction in order from the second layer 102. Therefore, it is possible to efficiently transmit heat in the thickness direction for the entire heat sink 1.

[0032] Figure 3 shows a state where carbon fibers 13 exist in the metal phase 11. Figure 3 is a diagram schematically showing an enlarged cross section of the region B indicated by the dashed line in Figure 2. A plurality of carbon fibers 13 are dispersed in the metal phase 11. The shape of the carbon fibers 13 is not constant. The individual carbon fibers 13 may exist separately from each other, or a plurality of carbon fibers 13 may exist in contact with each other.

[0033] The shape of the carbon fiber 13 has an elongated shape. The direction in which the carbon fiber extends is defined as the longitudinal direction. Hereinafter, the longitudinal direction, inclination, and orientation ratio of the carbon fiber 13 will be described.

[0034] Figure 4 shows one of the carbon fibers 13 in the cross-section in the thickness direction of the first layer 101 shown in Figure 3. As shown in Figure 4, each carbon fiber 13 is divided by a length L0. The length of L0 is 20 μm. The carbon fiber 13 divided by the length of L0 is herein referred to as a carbon fiber piece 14 for convenience. As shown in Figure 5, for this carbon fiber piece 14, a line segment in contact with the outer periphery of the carbon fiber piece 14 is drawn, and the widths L1 and L2 of the line segments in two orthogonal directions are obtained. Here, L1 is determined such that the value of L1 / L2, which is the ratio of L1 to L2, becomes the maximum. The direction of L1 in this case is defined as the longitudinal direction of the carbon fiber piece 14. The angle θ formed by the longitudinal direction of the carbon fiber piece 14 and the X-Y plane, which is the horizontal axis in Figure 4, that is, the angle formed by the carbon fiber piece 14 with respect to the plane parallel to the surface is obtained. The angle is defined as the angle measured on the acute angle side between the line segment obtained by projecting the longitudinal direction of the carbon fiber piece 14 onto the X-Y plane from the Z direction and the longitudinal direction.

[0035] For the angles θ of a plurality of carbon fiber pieces 14 with respect to a plurality of carbon fibers obtained within the observation field of view, the ratio of the number of carbon fiber pieces 14 whose angle θ falls within a certain range is expressed as a percentage and defined as the orientation ratio of the entire carbon fiber 13 in the first layer 101. For example, when the angle θ is set to 20 degrees or less, if the orientation ratio of 20 degrees or less is high, it means that most of the carbon fiber pieces 14 are inclined in a direction close to the X-Y plane.

[0036] The second material 20 is a material containing molybdenum or tungsten. It is preferable to use a material with a smaller coefficient of linear expansion for the second layer 102 compared to the first layer 101. By reducing the coefficient of linear expansion of the second layer 102, the coefficient of linear expansion in the plane direction of the entire heat sink 1 can be reduced. As the material containing molybdenum or tungsten, known materials used for the heat sink 1 can be applied. For example, the material constituting the second layer 102 may be a material composed of molybdenum or tungsten and inevitable impurities. The material constituting the second layer 102 is preferably a composite material in which copper is impregnated in a porous body obtained by sintering molybdenum or tungsten powder. By using the composite material, the thermal conductivity and the coefficient of linear expansion can be adjusted to a desired range. Note that the material containing molybdenum or tungsten may be any of a material containing molybdenum, a material containing tungsten, and a material containing both molybdenum and tungsten.

[0037] The third material 30 is preferably a material mainly composed of copper, but is not particularly limited. The same material as the first material 10 can also be used as the third material 30. Using a material with good heat conduction for the third layer 103 has the effect of increasing the thermal conductivity in the thickness direction of the entire heat sink 1. Pure copper is preferably used for the third material 30.

[0038] As described above, the case where the number of layers of the heat sink 1 is five has been described as an example, but the number of layers may be three or more. An example of the heat sink 1 in the case of three layers is shown in FIG. 6A. In the case of three layers, the third layer 103 and the fourth layer 104 shown in FIG. 2 do not exist. The heat sink 1 in FIG. 6A is composed of the first material 10, the second material 20, and the first material 10 in this order from the front surface 2 to the back surface 3. In the case of seven or more layers, it is preferable to increase the repetition of the layers of the third material 30 and the second material 20. FIG. 6B shows a typical structure in the case of seven layers. The heat sink 1 in FIG. 6B is composed of the first material 10, the second material 20, the third material 30, the second material 20, the third material 30, the second material 20, and the first material 10 in this order from the front surface 2 to the back surface 3.

[0039] In an embodiment of the present disclosure, regardless of the number of layers, the first layer including surface 2 is made of the first material 10. Surface 2 is the surface in contact with the heat-generating body to be cooled, and the heat sink 1 transfers heat from surface 2 toward back surface 3. When the number of layers is odd, it is preferable that surface 2 and back surface 3 are made of the same first material 10. The number of layers can also be even. In this case, there are no particular limitations other than that surface 2 is made of the first material 10 and the second layer is made of the second material 20. FIG. 6C shows an example of a four-layer configuration as an example when the number of layers is even. The heat sink 1 in FIG. 6C is configured in the order of the first material 10, the second material 20, the third material 30, and the second material 20 from surface 2 toward back surface 3.

[0040] Various modifications of the structure described above are conceivable and are not limited to the above configuration. For example, FIG. 6D shows another configuration example of the heat sink 1 in the case of three layers. The heat sink 1 shown in FIG. 6D is configured such that the first layer having surface 2 is made of the first material 10, the second layer is made of the second material 20, and the material having back surface 3 is made of the third material 30.

[0041] (Semiconductor Package) FIG. 7 is a diagram for explaining an example of a semiconductor package 50 including a heat sink according to the present disclosure. A semiconductor element 53 is disposed on a surface 2 of the heat sink 1. Current is supplied to the semiconductor element 53 via terminals 51. Further, a case member 52 for sealing the semiconductor element 53 is provided on the surface 2 of the heat sink 1. It is the function of the heat sink 1 to quickly transfer the heat generated from the semiconductor element 53 to the outside and maintain the temperature of the semiconductor element 53. Therefore, the back surface of the heat sink 1 is used in contact with a metal plate or other cooling medium (not shown). The heat sink 1 according to the present disclosure easily transfers the heat generated from the semiconductor element 53 in the plane direction in the first layer constituting the surface 2. The heat spreading in the plane direction is transmitted in the thickness direction through the entire heat sink 1. Further, since the linear expansion coefficient in the plane direction of the heat sink 1 is close to that of materials such as ceramics used for the semiconductor element 53 and the case member 52, damage at each material and joint surface is less likely to occur due to temperature changes. Compared with the case of using a conventional heat sink, heat from the semiconductor element 53 is more likely to be transmitted to the back surface, and a semiconductor package 50 having high cooling performance and durability can be obtained. Note that there are many types of configurations of the semiconductor package 50, and it is not limited to the above example. Regardless of the configuration difference, the semiconductor package 50 of the present disclosure includes a structure in which the semiconductor element 53 is disposed so that heat from the semiconductor element 53 is applied to the surface 2 of the heat sink 1 of the present disclosure, and the cooling effect is obtained by transmitting the heat to the back surface of the heat sink 1.

[0042] <Example> (Manufacture of Heat Sink) The five-layer heat sink shown in FIG. 2 was manufactured as described below.

[0043] (Preparation of First Material) Spherical copper powder (Cu-At-100 manufactured by Fukuda Metal Foil & Powder Co., Ltd.) was made to have an average particle size of 30 μm by removing coarse powder with a sieve having an opening of 45 μm. Further, fibrous powder shape (Mild Fiber ZY-300-25M manufactured by Nippon Graphite Fiber Corporation) collected while sieving using a sieve with an opening of 250 μm for pulverization was prepared. This spherical copper powder and the fibrous powder shape were mixed so that the volume ratio was from 100:0 to 79:21. The average length in the longitudinal direction of the carbon fiber used was 120 μm, and the average diameter was 8 μm. After loading the mixed powder into a carbon mold with a diameter of 30 mm, heating was performed at 950 °C for 10 minutes while applying a pressure of 30 MPa with an electric current plasma sintering apparatus to obtain a sintered body. Note that the average length and average diameter in the longitudinal direction were imaged at 200 times using a scanning electron microscope (SEM) in a state of being dispersed on a carbon tape, and the major axis lengths of 100 or more fibers were measured and averaged. Here, the major axis length is defined as the length that becomes maximum when the transmission image of the fiber is sandwiched between two parallel lines. The average diameter was similarly imaged at 500 times using SEM, and the cross-sectional lengths of 100 or more fibers with a major axis length of 50 μm or more were measured and averaged. Here, the cross-sectional length is a value obtained by measuring and averaging the widths in the direction orthogonal to the direction of the major axis length at positions of 1 / 4, 1 / 2, and 3 / 4 of the major axis length. Fig. 12 is an explanation of the above-described measurement method for the average length and average diameter in the longitudinal direction. The method for obtaining the major axis length is the same as in the case of Fig. 5, and the obtained major axis length is LL1, the position of length LL2 is the 3 / 4 position, the position of length LL3 is the 1 / 2 position, and the position of length LL4 is the 1 / 4 position. The cross-sectional lengths at each position are shown as W1, W2, and W3.

[0044] (Preparation of the second material) For use as the second layer and the fourth layer, a molybdenum (Mo) plate with a predetermined thickness was prepared.

[0045] (Preparation of the third material) For use as the third layer, a pure copper plate with a predetermined thickness was prepared.

[0046] (Manufacture of the laminate) The first material, the second material, and the third material prepared as described above were each processed into a disk shape with a diameter of 30 mm. Each disk-shaped material was stacked in the order of the first material, the second material, the third material, the second material, and the first material, and loaded into a graphite mold with an inner diameter of 32 mm. The filled laminated sample was joined by hot pressing under the conditions of a temperature of 1000 °C, a time of 60 minutes, and a pressure of 50 MPa. The overall thickness after hot pressing was made 1 mm. The copper powder contained in the first material is deformed into a flat shape following the direction of pressing in the hot pressing. By arranging the carbon fibers, which are in a fibrous shape, along the flat shape of the copper powder, the carbon fibers have orientation in the first material. Note that since the thickness of the first material becomes smaller by hot pressing according to the filling rate of the copper powder, the thickness is adjusted in advance so as to obtain a desired thickness after hot pressing. In this experimental example, the manufacturing was performed only by hot pressing, but it can also be performed by rolling.

[0047] (Evaluation) For each layer material before lamination and the joined laminate, the thermal conductivity in the plane direction and the thickness direction and the linear expansion coefficient in the plane direction were measured.

[0048] (Measurement sample for measuring the thermal conductivity in the plane direction) A sample for measuring the thermal conductivity in the plane direction of the first material was prepared as follows. FIG. 8 is a diagram for explaining the procedure for creating a measurement sample for the thermal conductivity in the plane direction. FIG. 8 shows the procedure for cutting out the first material 10 from the heat sink 1 to create a sample. FIG. 8(a) shows the heat sink 1 to be evaluated. The heat sink 1 is a laminate. The first material 10 constituting the first layer of the laminate is cut out from the laminate. Let the thickness of the cut-out first material be t mm. The material is cut into flakes having a length of A mm and a width of 2 mm as shown in FIG. 8(b). The length A is from 1 mm to 10 mm, preferably 10 mm. In this measurement, the length A was set to 10 mm.

[0049] The following procedure will be described with reference to FIGS. 8(c) and 8(d). Let X be the ceiling value of the decimal part of the value obtained by dividing 10 by t, and let Y be the ceiling value of the decimal part of the value obtained by dividing 10 by A. The number of wafers to be prepared is the product of X and Y. Next, stack X wafers to produce Y blocks with a height of approximately 10 mm, a length of A mm, and a width of 2 mm. Here, place amorphous silver powder with an average particle size of approximately 4 μm (AgC-74SE manufactured by Fukuda Metal Foil Powder Industry Co., Ltd.) between each of the wafers to be stacked. The amount of amorphous silver powder used is in the range of 0.2 g ± 30% per 100 mm 2 between each layer. Next, place this block in a graphite mold with a rectangular inner dimension of A (mm) × 2 (mm) for the opening. While applying a load of 4.9 N to 9.8 N from above, soften and bond the silver powder by heat treatment at 900 °C for 10 minutes in an inert gas. By arranging Y of the obtained blocks side by side, a measurement sample with a height of approximately 10 mm, a length of approximately 10 mm, and a width of 2 mm is completed (FIG. 8(d)). Here, when arranging Y blocks side by side, they may be bonded with an adhesive member that can withstand heat up to about 800 °C, such as silver brazing foil or a ceramic adhesive. Also, the outer periphery of the block may be fixed by winding it with a stainless steel wire or the like.

[0050] (Measurement sample for measuring the thermal conductivity in the thickness direction) The measurement samples for the thermal conductivity in the thickness direction of the first material, the second material, the third material, or the laminate were prepared as follows. FIG. 9 is a diagram for explaining the procedure for creating a measurement sample for the thermal conductivity in the thickness direction. FIG. 9 shows the procedure for cutting out the first material from the heat dissipation plate 1 to create a sample. FIG. 9(a) shows the heat dissipation plate 1 to be evaluated. The heat dissipation plate 1 is a laminate. Cut out the first material 10 that constitutes the first layer of the laminate from the laminate. When the second material or the third material is the measurement target, the procedure is the same except that the target to be cut out is different. Let the thickness of the cut-out material to be measured be t mm. Cut the material into wafers with a size of length B mm and width C mm as shown in FIG. 9(b). The length B and the length C are each from 1 mm to 10 mm, preferably 10 mm. In this measurement, both the length B and the width C were set to 10 mm.

[0051] The following procedure will be described with reference to FIGS. 9(c) and 9(d). Let X1 be the ceiling value of the decimal part of the value obtained by dividing 2 by t, Y1 be the ceiling value of the decimal part of the value obtained by dividing 10 by B, and Y2 be the ceiling value of the decimal part of the value obtained by dividing 10 by C. The number of thin slices to be prepared for the material is the product of X1, Y1, and Y2. First, stack X1 thin slices to produce blocks with a height of about 2 mm, a length of B m, and a width of C mm, the number of which is the product of Y1 and Y2. Here, amorphous silver powder with an average particle size of 4 μm is placed between each of the stacked thin slices. The amount of amorphous silver powder used is in the range of 0.2 g ± 30% per 100 mm 2 or so. Next, place this block into a rectangular graphite mold with an inner dimension of the opening of B (mm) × C (mm). While applying a load of 4.9 N to 9.8 N from above, soften and bond the silver powder by heat treatment at 900 °C for 10 minutes in an inert gas. By arranging Y1 blocks vertically and Y2 blocks horizontally, a measurement sample with a height of about 10 mm, a length of about 10 mm, and a width of 2 mm is completed (FIG. 9(d)). Here, when arranging Y1 blocks vertically and Y2 blocks horizontally, the blocks may be bonded with an adhesive member that can withstand heat up to about 800 °C, such as silver brazing foil or a ceramic adhesive. Also, the outer periphery of the block may be fixed by winding it with a stainless steel wire or the like.

[0052] (Measurement of Thermal Conductivity) The evaluation of thermal conductivity is measured by the laser flash method. The thermal diffusivity is measured using a thermal conductivity measurement device (LFA457 MicroFlash manufactured by NETZSCH). The thermal conductivity at room temperature is calculated using the specific heat of the measurement sample obtained from the volume ratio of the constituent materials. The specific heat values used are as follows. Cu: 386 J / kg / K Mo: 251 J / kg / K Ag: 234 J / kg / K (Above, from the 4th Edition of the Metal Data Book, The Japan Institute of Metals (2004)) Carbon fiber: 710 J / kg / K (From Chem. Thermodynamics, 2, 847 (1970)) In the evaluation, a pure copper sample of the same shape was used as a reference and measured under the same conditions, and numerical correction was performed.

[0053] (Measurement of linear expansion coefficient in the plane direction) The linear expansion coefficient in the in-plane direction of the first material 10 when the temperature changes from room temperature to 300 °C is calculated by measuring the expansion displacement in the in-plane direction of the first material 10 when the temperature changes from room temperature to 300 °C using TD5000SA (manufactured by Bruker AXS). When calculating the linear expansion coefficient in the in-plane direction of the first material 10 when the temperature changes from room temperature to 300 °C, the planar shape of the first material 10 is preferably a rectangular shape of tmm × 3mm × (10 to 15)mm. Here, t is the sample thickness. The measured value is the average value of three samples. When the evaluation object is smaller than the above dimensions, the linear expansion coefficient may be calculated using the X-ray diffraction method. The heat dissipation surface of the first material 10 has a total area of 100 mm 2 Rectangles with a side length of 10 mm or more are integrated on the same plane so that the total area is 100 mm². X-rays are irradiated onto the surface of the integrated sample at room temperature and 300 °C, and the diffraction angle (2θ) is derived from the diffraction peak corresponding to Cu(331). By using the following formula from the diffraction angle, the rate of change of the lattice plane spacing can be used as the linear expansion coefficient. When there is anisotropy in the plane of the material, the sample is aligned so that the direction for measuring the linear expansion coefficient of the sample is parallel to the X-ray incident plane. The calculation formula for the linear expansion coefficient when the room temperature is 25 °C is shown. (Linear expansion coefficient) = (1 / sin(θat300 °C) - 1 / sin(θat25 °C)) × sin(θat25 °C) / (300 - 25) Here, θat25 °C is half of the diffraction angle 2θ at the measurement at 25 °C θat300 °C is half of the diffraction angle 2θ at the measurement at 300 °C

[0054] (Evaluation of heat dissipation performance of the laminate) The heat dissipation performance in the plane direction of the laminate prepared above was evaluated. The heat dissipation performance was evaluated as follows using the temperature difference between the central part of the surface and the temperature at the end of the surface as the end temperature difference.

[0055] FIG. 10 is a diagram for explaining a measurement method when evaluating the heat dissipation performance of the laminate. FIG. 10 schematically shows the state of the arrangement described below as viewed from one side surface of the heat dissipation plate 1. The heat dissipation plate 1 is cut into a rectangular shape with a size of 10 mm in length and width as viewed from a direction perpendicular to the surface. Silicone oil (G-751 manufactured by Shin-Etsu Chemical Co., Ltd.) is applied to the upper surface of the aluminum fin 70 at the interface of the heat dissipation plate 1, and adhered with a load of 9.8 N. A heating element 60 with a size of 1 mm in length and width is brought into contact with the center of the surface of the heat dissipation plate 1. The output of the heating element 60 is set to 50 W. Further, the air cooling of the aluminum fin 70 is controlled so that the temperature of the adhesive part between the heat dissipation plate 1 and the aluminum fin 70 becomes 25° C. ±3° C. The ambient temperature as the measurement environment is 25° C. ±5° C. The temperature T1 of the interface between the heating element 60 and the surface of the heat dissipation plate 1 and the temperature T2 of the end part which is the corner of the surface of the heat dissipation plate 1 are measured by a thermocouple. After 30 seconds or more have elapsed since the heating element 60 was brought into contact, the temperature difference T1 - T2 (° C.) in the state where the temperature has reached a steady state is defined as the end part temperature difference. The measurement is performed 10 times, and the average value is adopted as the end part temperature difference. The smaller the temperature difference, the better the in-plane heat conduction is shown. In this case, considering practicality, it was determined that the heat dissipation performance is good when the end part temperature difference is 50° C. or less.

[0056] (Evaluation of the orientation of carbon fibers) Samples for evaluating the orientation of the carbon fibers of the first material were prepared as follows. As an evaluation sample, a flat plate in the state of FIG. 8(b) in the procedure for preparing a measurement sample of the in-plane thermal conductivity was used. Microscopic observation of the cross section orthogonal to the surface of the flat plate was performed with an optical microscope or a scanning electron microscope at a magnification of 200 times. An example of the observed cross section is shown in FIG. 11. The vertical direction in FIG. 11 is the Z direction of the layer thickness, and the horizontal direction is the in-plane direction of the XY plane. The dark gray portions shown in FIG. 11 are carbon fibers 13, and the light gray regions are metal phases 11. In FIG. 11, it was confirmed that groups of carbon fibers 13 are dispersed in the metal phase 11. The cross-sectional shapes of the carbon fiber groups are not the same, and the sizes are also various. For each carbon fiber in the entire field of view, the angle θ was determined by the following procedure.

[0057] Referring to FIG. 4 again, in the cross-sectional shape of each carbon fiber, carbon fiber pieces divided at a length of L0 = 20 μm are obtained. Further, referring to FIG. 5 again, in each carbon fiber piece, the widths L1 and L2 of the line segments in contact with the outer periphery of the carbon fiber piece in two orthogonal directions are obtained. Here, when L1 is obtained such that the value of L1 / L2 becomes maximum, the direction of L1 is defined as the longitudinal direction of the carbon fiber piece. Here, carbon fiber pieces with a small L1 of 5 μm or less when L1 / L2 is maximum are not adopted as evaluation targets because their contribution to orientation is small. The angle θ formed by the longitudinal direction of the carbon fiber piece and the surface within the observed cross-section is obtained. For each carbon fiber piece of each carbon fiber in the entire evaluation target field of view, the angle θ is obtained, and the ratio of the number of carbon fiber pieces with θ within 20 degrees to the number of carbon fiber pieces used as evaluation targets is calculated as the orientation ratio of the carbon fiber. This calculation is performed for 10 or more fields of view, and the average value of the orientation ratios is obtained. The size of the field of view is 500 μm × 500 μm, and 30 or more carbon fibers are used. The angle θ of each carbon fiber piece is calculated from a large number of carbon fiber pieces contained in the carbon fibers.

[0058] (Volume ratio of copper and carbon fiber in the laminate) The volume ratio of copper (Cu) and additive particles in the entire laminate is obtained by the following procedure. First, it is confirmed by X-ray diffraction (XRD) that the additive particle is carbon. Next, using 0.5 g or more of the composite material as a sample, the weight ratio of Cu and carbon in the carbon fiber is obtained by inductively coupled plasma optical emission spectrometry (ICP-OES). From the obtained weight ratio, it is converted to a volume ratio using the density of each substance. The density of each substance used is as follows. Cu: 8.96 g / cm 3 Carbon fiber: 2.24 g / cm 3

[0059] (Evaluation result A) As the first material constituting the first layer, samples with different volume ratios of carbon fibers, orientation ratios of carbon fibers, and thicknesses of the first layer were prepared and measured. As the second material constituting the second layer, a molybdenum (Mo) plate with a predetermined thickness was prepared and measured. The thickness of the completed heat sink, i.e., the laminate, was unified to be 1 mm. The layer structure of the laminate was a three-layer structure of the first layer / the second layer / the first layer. Table 1 shows the composition and measurement results of each sample. For the first layer, the volume ratio of carbon fibers in the first layer, the orientation ratio of carbon fibers, the thermal conductivity (A) in the plane direction of the first layer, the thermal conductivity (B) in the thickness direction of the first layer, the value (A - B) obtained by subtracting the thermal conductivity in the thickness direction of the first layer from the thermal conductivity in the plane direction of the first layer, and the linear expansion coefficient in the plane direction of the first layer are shown in Table 1. For the second layer, the thickness of the second layer, the thermal conductivity in the thickness direction of the second layer, and the linear expansion coefficient in the plane direction of the second layer are shown. For the laminate, the layer structure of the laminate, the number of layers of the laminate, the thickness of the laminate, the Cu ratio of the laminate, the thermal conductivity in the thickness direction of the laminate, the linear expansion coefficient in the plane direction of the laminate, and the end temperature difference are shown.

[0060]

Table 1

[0061] Regarding the performance required for the laminate serving as the heat sink, it was judged to be good based on the criteria that the end temperature difference is 50°C or less and the linear expansion coefficient in the plane direction of the laminate is 8 ppm / K or less. As shown in Table 1, Samples 3 to 5, Sample 7, and Sample 8 were judged to be good.

[0062] Samples 1 to 5 are the measurement results of samples with the thickness of the first layer all being 0.25 mm, but different ratios of carbon fibers and different orientation ratios of carbon fibers. Sample 1 is the measurement result of a sample without carbon fibers in the first layer. Since the first layer does not contain carbon fibers, the end temperature difference did not meet the above criteria. Sample 2 is a sample containing 2.6 Vol% of carbon fibers in the first layer, with an end temperature difference of 52 °C, and the end temperature difference did not meet the above criteria. Samples 3 to 5 are samples containing 6.0 Vol% or more of carbon fibers, and both the end temperature difference and the coefficient of linear expansion in the plane direction of the laminate met the above criteria. At 6.0 Vol%, the end temperature difference is 49 °C. Therefore, considering the volume ratio of carbon fibers and the end temperature difference of these samples, in order for the end temperature difference to be less than 50 °C, it is considered that the volume ratio of carbon fibers in the first layer should be 5 Vol% or less. In addition, when using the method for preparing the samples of the present disclosure, the orientation ratio of carbon fibers is 77.9% or more for any of the samples. Also, from the results in Table 2 and Table 3 described later, the orientation ratio of carbon fibers in each sample is good at 76% or more, and the end temperature difference and the coefficient of linear expansion in the plane direction of the laminate are good.

[0063] Samples 4, 6 to 8 contain 11.3 Vol% of carbon fibers in the first layer. The thickness of the first layer is different among Samples 6 to 8. The thickness of the first layer of Sample 6 is 0.10 mm, but the end temperature difference is 54 °C, and the end temperature difference did not meet the above criteria. On the other hand, the thicknesses of the first layers of Samples 7, 4, and 8 are 0.15 mm, 0.25 mm, and 0.35 mm respectively, and both the end temperature difference and the coefficient of linear expansion in the plane direction of the laminate met the above criteria. From this result, it is considered that the thickness of the first layer is suitable in the range of 0.15 mm or more and 0.35 mm or less.

[0064] Samples 1 to 5 have a thickness such that the thickness of the first layer is equal to 0.25 mm. Sample 1 is the measurement result of a sample that does not contain carbon fiber in the first layer. Since it does not contain carbon fiber, it does not meet the above criteria. For Sample 2, since the value obtained by subtracting the thermal conductivity in the thickness direction of the first layer from the thermal conductivity in the plane direction of the first layer, that is, A - B, was 20 W / m·K, the end temperature difference did not meet the above criteria. For Samples 3 to 5, since A - B is 44 W / m·K or more in all cases, the end temperature difference meets the above criteria. At 44 W / m·K, the end temperature difference is 49°C. Considering the A - B and end temperature difference of these samples, it is considered that at least 40 W / m·K or more is suitable in order for the end temperature difference to be less than 50°C.

[0065] For Samples 3 to 5, Sample 7, and Sample 8, which were judged to be good in Table 1, the thermal conductivity in the thickness direction of the first layer was all 250 W / m·K or more, and the linear expansion coefficient in the plane direction of the first layer when the temperature changed from room temperature to 300°C was all 18.1 ppm / K or less, and they were good. In order to obtain high heat dissipation performance of the entire heat sink, it is preferable that the thermal conductivity in the thickness direction of the first layer is high. Also, considering use at high temperatures, it is preferable that the linear expansion coefficient in the plane direction is below a certain value.

[0066] In all samples in Table 1, the thermal conductivity in the thickness direction of the second layer was 140 W / m·K or more, and the linear expansion coefficient in the plane direction of the second layer when the temperature changed from room temperature to 300°C was 8.0 ppm / K or less, and they were good. The second layer is provided for the purpose of reducing the linear expansion coefficient in the plane direction of the entire heat sink. A heat sink with excellent heat dissipation performance can be obtained with a good balance between thermal conductivity and linear expansion coefficient.

[0067] Incidentally, the larger the proportion of copper in the entire heat sink, the larger the thermal conductivity in the thickness direction, which is preferable for the heat sink.

[0068] (Evaluation Result B) In addition to the first material that constitutes the first layer and the second material that constitutes the second layer used in Evaluation Result A, a pure copper plate with a predetermined thickness was prepared and measured as the third material that constitutes the third layer. After completion, the thickness of the heat sink, that is, the laminate, was unified to be 1 mm. The layer structure of the laminate was a five-layer structure of the first layer / the second layer / the third layer / the second layer / the first layer. Table 2 shows the composition and measurement results of each sample. The items of the first layer and the second layer and the laminate are the same as those in Table 1. Regarding the items of the third layer, the thickness of the third layer, the thermal conductivity in the thickness direction of the third layer, and the linear expansion coefficient in the plane direction of the third layer are also shown together.

[0069]

Table 2

[0070] Regarding the performance required for the laminate to be a heat sink, it was judged to be good based on the criteria that the end temperature difference is 50 °C or less and the linear expansion coefficient in the plane direction of the laminate is 8 ppm / K or less. As shown in Table 2, Samples 13 to 16, Sample 18, and Sample 19 were judged to be good.

[0071] Samples 11 to 15 are the measurement results of samples with the same thickness of 0.25 mm for the first layer but different ratios and orientation ratios of carbon fibers. Sample 11 is the measurement result of a sample without carbon fibers in the first layer. Since it does not contain carbon fibers, it did not meet the above standard for the end temperature difference. Sample 12 has a volume ratio of carbon fibers of 3.1 Vol%, and did not meet the above standard for the end temperature difference. Samples 13 to 15 have a volume ratio of carbon fibers of 11.3 Vol% or more, and both the end temperature difference and the linear expansion coefficient in the plane direction of the laminate met the above standards. Similar to the previous discussion, it is considered that in order for the end temperature difference to be less than 50 °C, the volume ratio of carbon fibers in the first layer should be 5 Vol% or less.

[0072] When the sample preparation method of the present disclosure was used, the orientation ratio of carbon fibers was 76% or more for all samples, and the end temperature difference and the coefficient of linear expansion in the plane direction of the laminate were good. That is, at least samples with an orientation ratio of carbon fibers of 76% or more have good end temperature differences and coefficients of linear expansion in the plane direction of the laminate, so it is considered preferable that the orientation ratio of carbon fibers is 76% or more.

[0073] For Samples 13 to 19, the volume ratio of the carbon fibers in the first layer is 11.3 Vol%. The thickness of the first layer is different among Samples 13, 16 to 19. The thickness of the first layer of Sample 17 is 0.10 mm, but the end temperature difference is 54°C, and the end temperature difference did not meet the above criteria. On the other hand, the thicknesses of the first layers of Samples 16, 13, 18, and 19 are 0.15 mm, 0.25 mm, and 0.35 mm, respectively, and both the end temperature difference and the coefficient of linear expansion in the plane direction of the laminate met the above criteria. From these results, it is considered that a thickness of the first layer of 0.15 mm or more and 0.35 mm or less is suitable.

[0074] For Samples 11 to 15, the thickness of the first layer is equal to 0.25 mm. Sample 11 is the measurement result of a sample that does not contain carbon fibers in the first layer. Since it does not contain carbon fibers, it did not meet the above criteria. For Sample 12, since the value obtained by subtracting the thermal conductivity in the thickness direction of the first layer from the thermal conductivity in the plane direction of the first layer, that is, A - B, was 23 W / m·K, the end temperature difference did not meet the above criteria. For Samples 13 to 15, since A - B was 80 W / m·K or more in all cases, the end temperature difference met the above criteria. From the results of these samples, in order for the end temperature difference to be less than 50°C, considering the A - B and the end temperature difference of these samples, it is considered that at least 40 W / m·K or more is suitable.

[0075] For Samples 13 to 16, Sample 18, and Sample 19, which were judged to be good in Table 2, the thermal conductivity in the thickness direction of the first layer was all 250 W / m·K or more, and the linear expansion coefficient in the plane direction of the first layer when the temperature changed from room temperature to 300 °C was all 18.1 ppm / K or less, which was good. In order to obtain high heat dissipation performance of the entire heat sink, it is preferable that the thermal conductivity in the thickness direction of the first layer is high. Also, considering use at high temperatures, it is preferable that the linear expansion coefficient in the plane direction is below a certain value.

[0076] In all samples in Table 2, the thermal conductivity in the thickness direction of the second layer was 140 W / m·K or more, and the linear expansion coefficient in the plane direction of the second layer when the temperature changed from room temperature to 300 °C was 8.0 ppm / K or less, which was good. The second layer is provided for the purpose of lowering the linear expansion coefficient in the plane direction of the entire heat sink. A heat sink with excellent heat dissipation performance can be obtained with a good balance between thermal conductivity and linear expansion coefficient.

[0077] Note that the higher the proportion of copper in the entire heat sink, the greater the thermal conductivity in the thickness direction, which is preferable for the heat sink. In that regard, the thermal conductivity in the thickness direction is as good as 250 W / m·K or more in any of the samples judged to be preferable above. If the proportion of copper in the laminate is 71 VOl% or more, the thermal conductivity in the thickness direction will be 300 W / m·K or more, which is even better. Also, compared with the results in Table 1 of Evaluation Result A, the results in Table 2 of Evaluation Result B have a higher Cu concentration in the laminate and a higher thermal conductivity in the thickness direction of the laminate, which is advantageous for heat dissipation. That is, compared with the three-layer structure of the first layer / second layer / first layer, the five-layer structure of the first layer / second layer / third layer / second layer / first layer is preferable.

[0078] (Evaluation Result C) In Evaluation Result C, the structure of the sample used in Evaluation Result B was changed so that the thickness of the completed heat sink, that is, the laminate, became 2 mm. Note that the layer configuration of the laminate was the same as in Evaluation Result B, with a five-layer structure of the first layer / second layer / third layer / second layer / first layer. The configurations and measurement results of each sample are shown in Table 3. The items of the first layer, second layer, third layer, and laminate are the same as in Table 2.

[0079]

Table 3

[0080] As a performance requirement for the laminate serving as the heat dissipation plate, it was judged to be good based on the criteria that the end temperature difference is 50°C or less and the linear expansion coefficient in the plane direction of the laminate is 8 ppm / K or less. As shown in Table 3, Samples 23 to 26 and Samples 28 to 30 were judged to be good.

[0081] Samples 21 to 26 are the measurement results of samples with the same thickness of 0.25 mm for the first layer but different ratios and orientation ratios of carbon fibers. Sample 21 is the measurement result of a sample without carbon fibers in the first layer. Since it does not contain carbon fibers, it did not meet the above standard for the end temperature difference. Sample 22 has a volume ratio of carbon fibers of 3.1 Vol% and did not meet the above criterion for the end temperature difference. Samples 23 to 26 have a volume ratio of carbon fibers of 6.0% or more and meet the above criteria for both the end temperature difference and the linear expansion coefficient in the plane direction of the laminate. Similar to the previous discussion, it is considered that in order for the end temperature difference to be less than 50°C, the volume ratio of carbon fibers in the first layer should be 5 Vol% or less. In addition, when using the sample preparation method of the present disclosure, the orientation ratio of carbon fibers in all samples was 76% or more, and the end temperature difference and the linear expansion coefficient in the plane direction of the laminate were good. That is, at least for samples with an orientation ratio of carbon fibers of 76% or more, the end temperature difference and the linear expansion coefficient in the plane direction of the laminate were good, so it is considered preferable that the orientation ratio of carbon fibers is 76% or more.

[0082] For Samples 24 to 30, the volume ratio of the carbon fibers in the first layer is 11.3 Vol%. The thickness of the first layer varies among Samples 24 to 30. The thickness of the first layer of Sample 27 is 0.10 mm, but the end temperature difference is 54 °C, and the end temperature difference did not meet the above criteria. On the other hand, the thicknesses of the first layers of Samples 28, 24, 29, and 30 are 0.15 mm, 0.25 mm, 0.30 mm, and 0.35 mm respectively, and both the end temperature difference and the linear expansion coefficient in the plane direction of the laminate met the above criteria. From these results, it is considered that a thickness of the first layer of 0.15 mm or more and 0.35 mm or less is suitable.

[0083] For Samples 21 to 26, the thickness of the first layer is equal to 0.25 mm. Sample 21 is the measurement result of a sample that does not contain carbon fibers in the first layer. Since it does not contain carbon fibers, it did not meet the above criteria. For Sample 22, since the value obtained by subtracting the thermal conductivity in the thickness direction of the first layer from the thermal conductivity in the plane direction of the first layer, that is, A - B, was 23 W / m·K, the end temperature difference did not meet the above criteria. For Samples 23 to 26, since A - B is 44 W / m·K or more in all cases, the end temperature difference meets the above criteria. From the results of these samples, in order for the end temperature difference to be less than 50 °C, considering A - B and the end temperature difference of these samples, it is considered that at least 40 W / m·K or more is suitable.

[0084] For Samples 23 to 26 and Samples 28 to 30, which were judged to be good in Table 3, the thermal conductivity in the thickness direction of the first layer was all 250 W / m·K or more, and the linear expansion coefficient in the plane direction of the first layer when the temperature changed from room temperature to 300 °C was all 18.1 ppm / K or less, and they were good. In order to obtain high heat dissipation performance of the entire heat sink, it is preferable that the thermal conductivity in the thickness direction of the first layer is high. Also, considering use at high temperatures, it is preferable that the linear expansion coefficient in the plane direction is below a certain value.

[0085] In all the samples of Table 3, the thermal conductivity in the thickness direction of the second layer was 140 W / m·K or more, and the linear expansion coefficient in the plane direction of the second layer when the temperature changed from room temperature to 300 °C was 8.0 ppm / K or less, which was good. The second layer is provided for the purpose of lowering the linear expansion coefficient in the plane direction of the entire heat sink. A heat sink with an excellent heat dissipation performance can be obtained with a good balance between the thermal conductivity and the linear expansion coefficient.

[0086] Incidentally, the higher the proportion of copper in the entire heat sink, the greater the thermal conductivity in the thickness direction, which is preferable for the heat sink. In that regard, the thermal conductivity in the thickness direction was 250 W / m·K or more, which was good, in any of the samples judged to be preferable above. In all the samples prepared this time, the proportion of copper in the laminate was as high as 75 Vol% or more, and the thermal conductivity in the thickness direction was as high as 317 W / m·K or more, which was even better.

[0087] (Evaluation result D) Samples with different layer configurations and thicknesses of the laminate were prepared from the samples used in Evaluation result C. The thickness of the laminate was 1 mm. The layer configuration of the laminate was a seven-layer structure of the first layer / second layer / third layer / second layer / third layer / second layer / first layer. The composition and measurement results of each sample are shown in Table 4. Each item of the first layer, second layer, third layer, and laminate is the same as in Table 3.

[0088]

Table 4

[0089] Based on the criteria that the end temperature difference is 50 °C or less and the linear expansion coefficient in the plane direction of the laminate is 8 ppm / K or less, which are the performances required for the laminate serving as the heat sink, it was judged to be good. As shown in Table 4, Samples 33 to 36, Sample 38, and Sample 39 were judged to be good.

[0090] Samples 32 to 36 are measurement results of samples with the same thickness of 0.25 mm for the first layer but different ratios and orientation ratios of carbon fibers. Sample 32 had a volume ratio of carbon fibers of 3.1 Vol% and did not meet the above criteria for the end temperature difference. Samples 33 to 36 had a volume ratio of carbon fibers of 6.0% or more and met the above criteria for both the end temperature difference and the linear expansion coefficient in the plane direction of the laminate. Similar to the previous discussion, it is considered that in order for the end temperature difference to be less than 50°C, the volume ratio of carbon fibers in the first layer may be set to 5 Vol% or less. In addition, when the sample preparation method of the present disclosure was used, the orientation ratio of carbon fibers was 76% or more for all samples, and the end temperature difference and the linear expansion coefficient in the plane direction of the laminate were good. That is, at least for samples with an orientation ratio of carbon fibers of 76% or more, the end temperature difference and the linear expansion coefficient in the plane direction of the laminate were good, so it is considered preferable that the orientation ratio of carbon fibers is 76% or more.

[0091] Samples 34 and 37 to 39 had a volume ratio of carbon fibers in the first layer of 11.3 Vol%. The thickness of the first layer differed among Samples 34 and 37 to 39. The thickness of the first layer of Sample 37 was 0.10 mm, but the end temperature difference was 54°C and did not meet the above criteria. On the other hand, the thicknesses of the first layers of Samples 38, 34, and 39 were 0.15 mm, 0.25 mm, and 0.30 mm, respectively, and both the end temperature difference and the linear expansion coefficient in the plane direction of the laminate met the above criteria. From this result, it is considered that a thickness of at least 0.15 mm or more is suitable for the first layer.

[0092] Samples 32 to 36 had the same thickness of 0.25 mm for the first layer. For Sample 32, the value obtained by subtracting the thermal conductivity in the thickness direction of the first layer from the thermal conductivity in the plane direction of the first layer, that is, A - B, was 23 W / m·K, so the end temperature difference did not meet the above criteria. For Samples 33 to 36, since A - B was 44 W / m·K or more in all cases, the end temperature difference met the above criteria. From the results of these samples, it is considered that in order for the end temperature difference to be less than 50°C, considering the A-B and end temperature differences of these samples, at least 40 W / m·K or more is suitable.

[0093] For Samples 33 to 36, Sample 38, and Sample 39, which were judged to be good in Table 4, the thermal conductivity in the thickness direction of the first layer was all 250 W / m·K or more, and the linear expansion coefficient in the plane direction of the first layer when the temperature changed from room temperature to 300°C was all 18.1 ppm / K or less, and they were good. In order to obtain high heat dissipation performance of the entire heat sink, it is preferable that the thermal conductivity in the thickness direction of the first layer is high. Also, considering use at high temperatures, it is preferable that the linear expansion coefficient in the plane direction is below a certain value.

[0094] In all the samples in Table 4, the thermal conductivity in the thickness direction of the second layer was 140 W / m·K or more, and the linear expansion coefficient in the plane direction of the second layer when the temperature changed from room temperature to 300°C was 8.0 ppm / K or less, and they were good. The second layer is provided for the purpose of lowering the linear expansion coefficient in the plane direction of the entire heat sink. A heat sink with excellent heat dissipation performance can be obtained with a good balance between thermal conductivity and linear expansion coefficient.

[0095] (Evaluation Result E) Samples were prepared in which the layer structure and thickness of the laminate were changed from the samples used in Evaluation Result C. The thickness of the laminate was 1 mm. The layer structure of the laminate was a nine-layer structure of the first layer / second layer / third layer / second layer / third layer / second layer / third layer / second layer / first layer. The composition and measurement results of each sample are shown in Table 5. Each item of the first layer, second layer, third layer, and laminate is the same as in Table 3.

[0096]

Table 5

[0097] As performance requirements for the laminate serving as a heat dissipation plate, it was judged to be good based on the end temperature difference being 50°C or less and the linear expansion coefficient in the plane direction of the laminate being 8 ppm / K or less. As shown in Table 5, Samples 43 to 46 and Sample 48 were judged to be good.

[0098] Samples 42 to 46 are measurement results of samples where the thickness of the first layer is all 0.25 mm and the ratio of carbon fibers and the orientation ratio of carbon fibers are different. Sample 42 has a volume ratio of carbon fibers of 3.1 Vol% and did not meet the above criteria for the end temperature difference. Samples 43 to 46 have a volume ratio of carbon fibers of 6.0% or more, and both the end temperature difference and the linear expansion coefficient in the plane direction of the laminate met the above criteria. Similar to the previous discussion, it is considered that in order for the end temperature difference to be less than 50°C, the volume ratio of carbon fibers in the first layer may be 5 Vol% or less. In addition, when using the sample preparation method of the present disclosure, the orientation ratio of carbon fibers was 76% or more for all samples, and the end temperature difference and the linear expansion coefficient in the plane direction of the laminate were good. That is, at least samples with an orientation ratio of carbon fibers of 76% or more had good end temperature differences and linear expansion coefficients in the plane direction of the laminate, so it is considered preferable that the orientation ratio of carbon fibers is 76% or more.

[0099] Samples 44, 47, and 48 have a volume ratio of carbon fibers in the first layer of 11.3 Vol%. The thickness of the first layer is different among Samples 44, 47, and 48. The thickness of the first layer of Sample 47 is 0.10 mm, but the end temperature difference is 54°C and the end temperature difference did not meet the above criteria. On the other hand, the thicknesses of the first layers of Samples 48 and 44 are 0.15 mm and 0.25 mm, respectively, and both the end temperature difference and the linear expansion coefficient in the plane direction of the laminate met the above criteria. From this result, it is considered that the thickness of the first layer is preferably at least 0.15 mm or more.

[0100] Samples 42 to 46 have a thickness equal to that of the first layer, which is 0.25 mm. For sample 42, since the value obtained by subtracting the thermal conductivity in the thickness direction of the first layer from the thermal conductivity in the plane direction of the first layer, that is, A - B, was 23 W / m·K, the end temperature difference did not meet the above criteria. For samples 43 to 46, since A - B is 44 W / m·K or more in all cases, the end temperature difference meets the above criteria. From the results of these samples, in order for the end temperature difference to be less than 50°C, considering A - B and the end temperature difference of these samples, it is considered that at least 40 W / m·K or more is suitable.

[0101] For samples 43 to 46 and sample 48, which were judged to be good in Table 5, the thermal conductivity in the thickness direction of the first layer was all 250 W / m·K or more, and the linear expansion coefficient in the plane direction of the first layer when the temperature changed from room temperature to 300°C was all 18.1 ppm / K or less, and they were good. In order to obtain high heat dissipation performance of the entire heat sink, it is preferable that the thermal conductivity in the thickness direction of the first layer is high. Also, considering use at high temperatures, it is preferable that the linear expansion coefficient in the plane direction is below a certain value.

[0102] In all samples in Table 5, the thermal conductivity in the thickness direction of the second layer was 140 W / m·K or more, and the linear expansion coefficient in the plane direction of the second layer when the temperature changed from room temperature to 300°C was 8.0 ppm / K or less, and they were good. The second layer is provided for the purpose of reducing the linear expansion coefficient in the plane direction of the entire heat sink. A heat sink with excellent heat dissipation performance can be obtained with a good balance between thermal conductivity and linear expansion coefficient.

[0103] It should be considered that all the embodiments and examples disclosed this time are illustrative in all respects and not restrictive. The scope of the present invention is shown not by the above-described embodiments but by the claims, and it is intended that all meanings equivalent to the claims and all changes within the scope are included.

Explanation of Reference Numerals

[0104] 1 Heat sink 2 Surface 3 Back surface 10 First material 20 Second material 30 Third material 60 Heating element 70 Aluminum fin 101 First layer 102 Second layer 103 Third layer 104 Fourth layer 105 Fifth layer 11 Metal phase 12 Additive phase 13 Carbon fiber 14 Carbon fiber piece 50 Semiconductor package 51 Terminal 52 Case member 53 Semiconductor element 61 Sample L0 Length L1 Length L2 Length LL1 Major axis length LL2 3 / 4 position LL3 1 / 2 position LL4 1 / 4 position W1 Cross-sectional length 1 W2 Cross-sectional length 2 W3 Cross-sectional length 3 θ Angle

Claims

1. A heat sink having a structure in which three or more layers are laminated, comprising a first layer which is both outermost layers in the thickness direction in the laminated structure, the first layer being made of a first material, the first material being a material containing a plurality of carbon fibers dispersed in a metal phase mainly composed of copper, the volume ratio of the carbon fibers in the entire first material being 5.0% by volume or more and 20.9% by volume or less, the thickness of the first layer being 0.15 mm or more and 0.35 mm or less, the value obtained by subtracting the thermal conductivity in the thickness direction of the first layer from the thermal conductivity in the plane direction orthogonal to the thickness direction of the first layer being 40 W / m·K or more, the plurality of carbon fibers each having an orientation in the plane direction orthogonal to the thickness direction, the orientation rate defined below for the orientation being 76% or more, the second layer in contact with the first layer being made of a second material containing molybdenum or tungsten, Heat sink. Here, the orientation rate is the ratio of the number of carbon fiber pieces in which the angle θ formed with the surface of the first layer is 20 degrees or less when each of the plurality of carbon fibers is divided into carbon fiber pieces of a predetermined length in the cross-sectional observation in the thickness direction of the first layer.

2. The laminated layer is three layers, the second layer being a layer in contact with each of the first layers, The heat sink according to Claim 1.

3. The laminated layer is an odd number of layers of 5 or more, the second layer being a pair of layers in contact with the first layer, the third layer in contact with the surface of the pair of second layers opposite to the surface in contact with the first layer being made of copper or a copper alloy alloy, The heat sink according to Claim 1.

4. The end temperature difference measured by the following method on the surface of the first layer is 50°C or less, The heat sink according to any one of Claims 1 to 3. (Method) Prepare a sample by cutting a heat sink plate into a rectangular piece with a size of 10 mm in length and width as viewed from a direction perpendicular to the surface, and adhering it to an aluminum fin with silicone oil applied to the interface under a load of 9.8 N. A heating element with a size of 1 mm in length and width and an output of 50 W is brought into contact with the center of the surface of the heat sink plate piece of the sample, and in an environment of 25°C ± 5°C, the air cooling of the aluminum fin is controlled so that the temperature of the adhesion part between the heat sink plate piece and the aluminum fin becomes 25°C ± 3°C. After 30 seconds or more have elapsed after the heating element is brought into contact and a steady state is reached, the temperature T1 of the interface between the heating element and the surface of the heat sink plate piece and the temperature T2 of the end part which is the corner part of the surface of the heat sink plate piece are measured 10 times with a thermocouple, and the average value of the temperature difference T1 - T2 is taken as the end part temperature difference.

5. The value obtained by subtracting the thermal conductivity of the first layer in the thickness direction from the thermal conductivity of the first layer in the surface direction is 140 W / m·K or less. The heat sink according to any one of claims 1 to 4.

6. The thermal conductivity of the first layer in the thickness direction is 250 W / m·K or more. The linear expansion coefficient of the first layer in the surface direction when the temperature changes from room temperature to 300°C is 18.1 ppm / K or less. The heat sink according to any one of claims 1 to 5.

7. The thermal conductivity of the second layer in the thickness direction is 140 W / m·K or more.

8. When the temperature changes from room temperature to 300°C, the linear expansion coefficient of the second layer in the surface direction is 8.0 ppm / K or less. The heat sink according to any one of claims 1 to 6.

8. The heat sink according to any one of claims 1 to 7, and a semiconductor element disposed on the surface of the first layer. A semiconductor package comprising the same.

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