Composite materials, heat spreaders, and semiconductor packages

Abstract

A composite material in the shape of a plate, wherein the composite material comprises at least one first layer and a plurality of second layers, wherein the first layer and the second layers are alternately stacked in a direction along the thickness of the composite material, wherein the first layer is a layer made of a first metal material, and each of the second layers has a plate made of a second metal material and a filler made of the first metal material, wherein the thermal conductivity of the first metal material is higher than the thermal conductivity of the second metal material, and the linear expansion coefficient of the second metal material is lower than the linear expansion coefficient of the first metal material, wherein the plate has a plurality of through holes penetrating the plate in a direction along the thickness of the composite material, and the filler is disposed inside the through holes, and wherein, when the composite material is viewed in a direction along the thickness, the through holes formed in each of the plurality of second layers are offset from each other.

Description

Technology Field

[0001] The present disclosure relates to a composite material, a heat spreader, and a semiconductor package.

[0002] The present application claims priority based on Japanese application No. 2023-203978 filed on December 1, 2023, and all contents of said Japanese application are incorporated herein by reference. Background Technology

[0003] Patent Document 1 discloses a composite material used in a heat spreader of a semiconductor package. The composite material has a plate shape. The composite material has a first surface and a second surface. The composite material has a plurality of first layers and a plurality of second layers. The first layers and the second layers are alternately stacked in a direction along the thickness of the composite material. The layer constituting the first surface and the second surface is the first layer. The first layer is formed of a metal material having copper as the main component. The second layer has a molybdenum plate and a copper filler. The molybdenum plate has a plurality of openings penetrating the molybdenum plate in a direction along the thickness. The copper filler is arranged to fill the interior of the openings. Prior art literature

[0004] International Publication No. 2022 / 030197

[0005] (Summary of the Invention)

[0006] The composite material of the present disclosure is a plate-shaped composite material having a first surface and a second surface opposite to the first surface. The composite material comprises at least one first layer and a plurality of second layers. The first layer and the second layers are alternately stacked in a direction along the thickness of the composite material. Each layer constituting the first surface and the second surface is either the first layer or the second layer. The first layer is a layer made of a first metal material. Each of the second layers has a plate made of a second metal material and a filler made of the first metal material. The thermal conductivity of the first metal material is higher than the thermal conductivity of the second metal material. The linear expansion coefficient of the second metal material is lower than the linear expansion coefficient of the first metal material. The plate has a plurality of through holes penetrating the plate in a direction along the thickness of the composite material. The filler is disposed inside the through holes. When the above composite material is viewed in the direction along the thickness, the through holes formed in each of the plurality of the second layers are offset from each other. Brief explanation of the drawing

[0007] FIG. 1 is a schematic perspective view of a composite material according to an embodiment. Figure 2 is a partial enlarged view of the section II-II of Figure 1. Figure 3 is a partial enlarged view of the III-III section of Figure 2. FIG. 4 is a diagram showing the positional relationship of the through holes of the second layer in a composite material according to an embodiment. FIG. 5 is a drawing showing another example of the positional relationship of the through holes of the second layer in a composite material according to an embodiment. FIG. 6 is a cross-sectional view of a composite material according to deformation example 1. Figure 7 is a manufacturing process diagram of a composite material. FIG. 8 is an exploded perspective view of a semiconductor package of an embodiment. Figure 9 is a graph showing the linear expansion coefficient of the sample of Test Example 1. Figure 10 is a graph showing the thermal conductivity of the sample of Test Example 1. Specific details for implementing the invention

[0008] [Problems to be solved by the present disclosure]

[0009] Composite materials are required to have both high thermal conductivity and a low coefficient of linear expansion.

[0010] One of the objectives of the present disclosure is to provide a composite material that has high thermal conductivity and can further reduce the coefficient of linear expansion.

[0011] [Effects of the present disclosure]

[0012] The composite material of the present disclosure can further reduce the coefficient of linear expansion while having high thermal conductivity.

[0013] [Description of embodiments of the present disclosure]

[0014] First, an embodiment of the present disclosure is described.

[0015] (1) The composite material of the present disclosure is a plate-shaped composite material having a first surface and a second surface opposite to the first surface. The composite material has at least one first layer and a plurality of second layers. The first layer and the second layers are alternately stacked in a direction along the thickness of the composite material. Each layer constituting the first surface and the second surface is either the first layer or the second layer. The first layer is a layer made of a first metal material. Each of the second layers has a plate made of a second metal material and a filler made of the first metal material. The thermal conductivity of the first metal material is higher than the thermal conductivity of the second metal material. The linear expansion coefficient of the second metal material is lower than the linear expansion coefficient of the first metal material. The plate has a plurality of through holes penetrating the plate in a direction along the thickness of the composite material. The filler is disposed inside the through holes. When the above composite material is viewed in the direction along the thickness, the through holes formed in each of the plurality of the second layers are offset from each other.

[0016] The composite material of (1) above has high thermal conductivity and a low coefficient of linear expansion. This is because it has a structure in which a first layer made of a first metal material and a second layer having a plate made of a second metal material and a filler made of the first metal material are laminated. Here, the phrase “made of” means that it is formed solely of the said material. That is, “made of the first metal material” means that it is formed solely of the first metal material. Furthermore, the composite material of (1) above can further reduce the coefficient of linear expansion while maintaining the same thermal conductivity as a composite material with the same composition except that the through holes formed in each of the multiple second layers are offset from each other.

[0017] (2) In the composite material of (1) above, when the composite material is viewed in the direction along the thickness, the overlap rate of the through holes formed in each of the plurality of second layers may be 80% or less.

[0018] Composite materials with a through-hole overlap rate of 80% or less tend to have a lower coefficient of linear expansion.

[0019] (3) In the composite material of (1) or (2) above, the opening ratio of each of the second layers may be 15% or more.

[0020] Composite materials with an opening ratio of 15% or more in the second layer are prone to high thermal conductivity.

[0021] (4) In any of the composite materials of (1) to (3) above, when the composite material is viewed in the direction along the thickness, the opening edges of the through holes formed in each of at least two of the plurality of second layers may partially overlap.

[0022] The composite material of (4) above is prone to having a low linear expansion coefficient.

[0023] (5) In any of the composite materials of (1) to (3) above, when the composite material is viewed in the direction along the thickness, the opening of the through hole formed in one of the second layers may be included within the opening of the through hole formed in another second layer.

[0024] The composite material of (5) above is prone to having a low linear expansion coefficient.

[0025] (6) In any of the composite materials of (1) to (5) above, the volume ratio of the second metal material in the composite material may be 15% or more and 45% or less.

[0026] Composite materials in which the volume ratio of the second metal material is 15% or more tend to have a lower coefficient of linear expansion. Composite materials in which the volume ratio of the second metal material is 45% or less tend to have a higher thermal conductivity.

[0027] (7) In any of the composite materials of (1) to (6) above, the first metal material may be a metal material having copper as the main component.

[0028] Copper has high thermal conductivity. When the primary metal material is a metal material with copper as the main component, it is easy to increase the thermal conductivity of the composite material.

[0029] (8) In any of the composite materials of (1) to (7) above, the second metal material may be a metal material having molybdenum as the main component.

[0030] Molybdenum has a low coefficient of linear expansion. When the second metal material is a metal material with molybdenum as the main component, it is easy to lower the coefficient of linear expansion of the composite material.

[0031] (9) In any of the composite materials of (1) to (8) above, the thickness of each of the second layers may be 0.05 mm or more and 35% or less of the thickness of the composite material.

[0032] Since the thickness of the second layer is 0.05 mm or more, the second layer, which has a relatively low coefficient of linear expansion, has an appropriate thickness. Therefore, the coefficient of linear expansion of the composite material is likely to decrease. Since the thickness of the second layer is 35% or less of the thickness of the composite material, the second layer, which has a relatively low thermal conductivity, does not become excessively thick. Therefore, the thermal conductivity of the composite material is likely to increase.

[0033] (10) In any of the composite materials of (1) to (9) above, the value obtained by dividing the average equivalent circle diameter of the through hole in each of the second layers by the thickness of each of the second layers may be 0.3 or more and 5.0 or less.

[0034] Composite materials with a value of 0.3 or higher tend to have high thermal conductivity. Composite materials with a value of 5.0 or lower tend to have a low coefficient of linear expansion.

[0035] (11) The heat spreader of the present disclosure comprises a composite material of any one of (1) to (10). The first surface forms a contact surface with a heat source.

[0036] The heat spreader of the above (11) is suitable for heat dissipation of semiconductor devices because it is equipped with a composite material that can achieve both high thermal conductivity and a low linear expansion coefficient.

[0037] (12) The semiconductor package of the present disclosure comprises a composite material of any one of (1) to (10) and a semiconductor element. The semiconductor element is disposed on the first surface.

[0038] The semiconductor package of (12) above is easy to reduce thermal stress occurring at the interface between the semiconductor device and the composite material, so it is difficult to damage the semiconductor device and easy to dissipate heat.

[0039] (13) The semiconductor package of (12) above may additionally be provided with a ceramic case member. The case member is disposed on the first surface to surround the semiconductor element.

[0040] The semiconductor package of (13) above is easy to reduce thermal stress occurring at the interface between the case member and the composite material, so it is difficult for the semiconductor device to be damaged.

[0041] [Details of embodiments of the present disclosure]

[0042] Specific examples of the composite material, heat spreader, and semiconductor package of the present disclosure are described below. Identical reference numerals in the drawings indicate identical names. The dimensions, etc., of the components shown in each drawing are depicted for the purpose of clarifying the explanation and do not necessarily represent actual dimensional relationships.

[0043] Furthermore, the present invention is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope of equivalents to the claims.

[0044] Composite Materials

[0045] With reference to FIGS. 1 to 4, a composite material (10) according to an embodiment is described. As shown in FIG. 1, the composite material (10) is in the shape of a plate. The composite material (10) has a first surface (10a) and a second surface (10b). The first surface (10a) and the second surface (10b) form a surface of the composite material (10) that intersects in a direction along the thickness of the composite material (10). The second surface (10b) is the opposite side of the first surface (10a). As shown in FIG. 2, the composite material (10) has at least one first layer (11) and a plurality of second layers (12). The first layer (11) and the second layers (12) are alternately stacked in a direction along the thickness of the composite material (10). The first layer (11) is made of a first metal material. The second layer (12) has a plate (13) made of a second metal material and a filler (14). As shown in FIGS. 2 and 3, the plate (13) has a plurality of through holes (13c). The filler (14) is disposed inside the through holes (13c). One of the features of the composite material (10) is that, as shown in FIG. 4, when the composite material (10) is viewed along the thickness direction, the through holes (13c) formed in each of the plurality of second layers (12) are offset from each other.

[0046] The thickness of the composite material (10) is denoted as thickness (Tc). The thickness of the first layer (11) is denoted as thickness (T1). The thickness of the second layer (12) is denoted as thickness (T2). The direction along the thickness (Tc) of the composite material (10) is denoted as the Z direction. The Z direction is the direction from the first surface (10a) toward the second surface (10b). In FIG. 2, the boundary between the first layer (11) and the second layer (12) is indicated by a dotted line.

[0047] (Laminated structure)

[0048] The first metal material constituting the first layer (11) has high thermal conductivity. The second metal material constituting the plate (13) of the second layer (12) has a low coefficient of linear expansion. As shown in FIG. 2, the composite material (10) has a laminated structure in which the first layer (11) and the second layer (12) are alternately stacked. The first layer (11) and the second layer (12) adjacent to each other are in contact. Due to this laminated structure, the composite material (10) can achieve both high thermal conductivity and a low coefficient of linear expansion. Each layer constituting the first surface (10a) and the second surface (10b) is the first layer (11) or the second layer (12). That is, the layer constituting the first surface (10a) and the layer constituting the second surface (10b) are layers of the same composition. In the example shown in FIG. 2, the first layer (11) and the second layer (12) are alternately stacked so that the first layer (11) is located on the first surface (10a) and the second surface (10b). Unlike the example shown in FIG. 2, the first layer (11) and the second layer (12) may be alternately stacked so that the second layer (12) is located on the first surface (10a) and the second surface (10b).

[0049] (Floor number)

[0050] The number of the first layer (11) is 1 or more. The number of the second layer (12) is 2 or more. The total number of layers of the first layer (11) and the second layer (12) is an odd number of 3 or more. The number of the first layer (11), the number of the second layer (12), and the number of layers in the composite material (10) are not particularly limited and can be appropriately selected. In the example shown in FIG. 2, the number of the first layer (11) is 3, the number of the second layer (12) is 2, and the total number of layers is 5.

[0051] (1st floor)

[0052] The first layer (11) is a layer made of a first metal material. The thermal conductivity of the first metal material is higher than the thermal conductivity of the second metal material described later. For example, the thermal conductivity of the first metal material is at least twice the thermal conductivity of the second metal material. For example, the thermal conductivity of the first metal material is 300 W / m·K or higher, and also 350 W / m·K or higher. "Thermal conductivity" refers to the thermal conductivity at room temperature. The first metal material is, for example, a metal material with copper as its main component. "Metal material with copper as its main component" refers to a metal material having a copper content ratio of 50 mass% or more. That is, when the total mass of the first layer (11) is 100 mass%, the copper content ratio in the first layer (11) is 50 mass% or more. The copper content ratio may be 70 mass% or more. The first layer (11) is, for example, made of pure copper. "Pure copper" is a metallic material composed of copper and unavoidable impurities constituting the remainder. Pure copper has a copper content of 99 mass% or more, specifically 99.9 mass% or more. The thermal conductivity of copper is 398 W / m·K at room temperature. "Room temperature" means 27°C.

[0053] The thickness (T1) of the first layer (11) is, for example, 0.025 mm or more and 30% or less of the thickness (Tc) of the composite material (10). Since the thickness (T1) is 0.025 mm or more, the first layer (11), which has a relatively high thermal conductivity, has an appropriate thickness. Therefore, the thermal conductivity of the composite material (10) is likely to increase. Since the thickness (T1) is 30% or less of the thickness (Tc), the first layer (11), which has a relatively high linear expansion coefficient, does not become excessively thick. Therefore, the linear expansion coefficient of the composite material (10) is likely to decrease. The thickness (T1) may be 0.035 mm or more and less than 30% of the thickness (Tc), or 0.045 mm or more and less than 30% of the thickness (Tc).

[0054] When the composite material (10) has a plurality of first layers (11), the thickness (T1) of all first layers (11) may be the same, or the thickness (T1) of some first layers (11) may be different. In the example shown in FIG. 2, among the three first layers (11), the thickness (T1) of the first layer positioned in the center in the Z direction of the composite material (10) is thicker than the thickness (T1) of the first layers positioned on the upper and lower sides of the composite material (10), respectively. By having different thicknesses (T1) of the first layers (11), it is easy to adjust the thermal conductivity of the composite material (10).

[0055] The thickness (Tc) of the composite material (10) is determined as follows: The length in the Z direction between the first surface (10a) and the second surface (10b) is measured. The number of measurements is at least three. The average value of all measured lengths is the thickness (Tc). The thickness (T1) of the first layer is determined as follows: A cross-section is obtained by cutting the composite material (10) in the Z direction with a cutter. In this cross-section along the Z direction, the length in the Z direction of the first layer (11) is measured. The cross-section along the Z direction is a plane substantially orthogonal to the first surface (10a) and the second surface (10b). The number of measurements is at least three. The average value of all measured lengths is the thickness (T1).

[0056] (2nd floor)

[0057] The second layer (12) has a plate (13) made of a second metal material and a filler (14). The linear expansion coefficient of the second metal material is lower than the linear expansion coefficient of the first metal material constituting the first layer (11). The linear expansion coefficient of the second metal material is, for example, 0.5 times or less of the linear expansion coefficient of the first metal material. The linear expansion coefficient of the second metal material is, for example, 7.0 × 10⁻⁶ ―6 / K (7.0 ppm / K) or less, also 6.0 × 10⁻⁶ ―6 It is less than / K (6.0 ppm / K). "Linear expansion coefficient" refers to the linear expansion coefficient in the temperature range from room temperature to 800°C. The second metal material is, for example, a metal material with molybdenum as the main component. "Metal material with molybdenum as the main component" refers to a metal material having a molybdenum content ratio of 50 mass% or more. That is, when the total mass of the plate (13) is 100 mass%, the molybdenum content ratio in the plate (13) is 50 mass% or more. The molybdenum content ratio may be 70 mass% or more. The plate (13) is, for example, made of pure molybdenum. "Pure molybdenum" refers to a metal material composed of molybdenum and unavoidable impurities constituting the remainder. Pure molybdenum has a molybdenum content ratio of 99 mass% or more, particularly 99.9 mass% or more. The linear expansion coefficient of molybdenum is 5.7 ppm / K. The filler (14) is made of the first metal material. That is, the filler (14) is made of the same material as the first layer (11).

[0058] The thickness (T2) of the second layer (12) is, for example, 0.05 mm or more and 35% or less of the thickness (Tc) of the composite material (10). Since the thickness (T2) is 35% or less of the thickness (Tc), the second layer (12), which has a relatively low thermal conductivity, does not become excessively thick. Therefore, the thermal conductivity of the composite material (10) is likely to increase. Since the thickness (T2) is 0.05 mm or more, the second layer (12), which has a relatively low coefficient of linear expansion, has an appropriate thickness. Therefore, the coefficient of linear expansion of the composite material (10) is likely to decrease. The thickness (T2) may be 0.10 mm or more and 35% or less of the thickness (Tc), or 0.15 mm or more and 30% or less of the thickness (Tc).

[0059] Among the plurality of second layers (12), the thickness (T2) of all second layers (12) may be the same, or the thickness (T2) of some second layers (12) may be different. In the example shown in FIG. 2, the thickness (T2) of each of the two second layers (12) is the same. When the thickness (T2) of all second layers (12) is the same, it is difficult for the composite material (10) to bend when the temperature of the composite material (10) rises.

[0060] The thickness (T2) of the second layer (12) is determined as follows, just like the thickness (T1) of the first layer (11). In a cross-section along the Z direction of the composite material (10), the length in the Z direction of the second layer (12) is measured. The length in the Z direction of the second layer (12) is the thickness of the plate (13), that is, the length in the Z direction between the first surface (13a) and the second surface (13b) of the plate (13). The number of measurements is three or more. The average value of all measured lengths is the thickness (T2).

[0061] The plate (13) has a first surface (13a) and a second surface (13b). The second surface (13b) is the opposite side of the first surface (13a). The first surface (13a) and the second surface (13b) are surfaces that intersect in the Z direction. The first surface (13a) and the second surface (13b) are surfaces substantially parallel to the first surface (10a) and the second surface (10b).

[0062] A plurality of through holes (13c) formed in the plate (13) penetrate the plate (13) in the Z direction. The plurality of through holes (13c) in the plate (13) are independent of each other. That is, adjacent through holes (13c) in the plate (13) are not connected to each other. The plurality of through holes (13c) in the plate (13) are not configured in a three-dimensional mesh shape, but are configured regularly. The shape of the plurality of through holes (13c) in the plate (13) is identical, and the size is uniform.

[0063] As shown in FIG. 3, in a cross-section orthogonal to the Z direction, the through hole (13c) has a circular shape. The cross-section orthogonal to the Z direction is a plane substantially parallel to the first surface (10a) and the second surface (10b). When viewed from the cross-section, the shape of the through hole (13c) is not limited to a circular shape. When viewed from the cross-section, the shape of the through hole (13c) may be an elliptical shape, a polygonal shape, or any other shape.

[0064] In a cross-section orthogonal to the Z direction, a plurality of through holes (13c) are arranged to form a grid arrangement. More specifically, in the cross-section, a plurality of through holes (13c) are arranged in a square grid shape. In the cross-section, a plurality of through holes (13c) may be arranged in a rectangular grid shape. In the cross-section, a plurality of through holes (13c) may be arranged in a four-sided grid shape.

[0065] In the second layer (12), the number of through holes (13c) per 1 mm² is, for example, less than 3. If the number of through holes (13c) is less than 3 / mm², the linear expansion coefficient of the composite material (10) is likely to decrease. The number of through holes (13c) per 1 mm² is obtained by dividing the number of through holes (13c) in a cross-section orthogonal to the Z direction by the area of ​​the second layer (12). The area of ​​the second layer (12) is the area of ​​the plate (13) containing the through holes (13c). The number of through holes (13c) per 1 mm² may be less than 2. If the number of through holes (13c) is less than 2 / mm², the linear expansion coefficient of the composite material (10) is likely to decrease further.

[0066] A cross-section perpendicular to the Z direction of the second layer (12) is exposed as follows. By observing the composite material (10) from the side using a digital microscope, the distance between the first surface (10a) and the center of the plate (13) in the Z direction is measured. Polishing of the first surface (10a) is performed using a flat polisher or an automatic rotary polisher. At this time, the amount of polishing is set to be equal to the distance between the first surface (10a) and the center of the plate (13) in the Z direction measured as above. It is also possible to observe a cross-section perpendicular to the Z direction of the second layer (12) using an X-ray CT (Computed Tomography) device.

[0067] The opening ratio of the second layer (12) is, for example, 15% or more. The opening ratio is calculated as follows: The sum of the opening areas of all through holes (13c) is measured in a cross-section that passes through the center in the Z direction of the plate (13) and is also orthogonal to the Z direction. The measured sum is divided by the area of ​​the second layer (12) described above. The opening area is measured using a digital microscope. The opening area may also be calculated by extracting the through holes (13c) from an X-ray CT image. If the opening ratio is 15% or more, the thermal conductivity of the composite material (10) is likely to increase. The opening ratio may be 20% or more, 30% or more, or 35% or more. The opening ratio is, for example, 70% or less. The opening ratio may be 60% or less. The opening ratio of each of the multiple second layers (12) may be the same or different. In this example, the opening ratio of the second layer (121) near the first surface (10a) and the opening ratio of the second layer (122) near the second surface (10b) are substantially the same. "The opening ratios are substantially the same" means that the difference between the opening ratios of each of the second layers (12) is within 5%.

[0068] The original diameter of the through hole (13c) at any position in the Z direction is defined as the opening diameter D. The opening diameter D is obtained by calculating the square root of the value obtained by dividing the opening area of ​​the through hole (13c) at any position in the Z direction by π / 4. The opening diameter D is measured on a plane parallel to the first plane (13a).

[0069] The aperture D of this example changes between the first surface (13a) and the second surface (13b). That is, the aperture D of this example is not constant across the first surface (13a) and the second surface (13b). The aperture D of this example decreases as it moves from each of the first surface (13a) and the second surface (13b) toward the middle of the first surface (13a) and the second surface (13b). That is, the aperture D of this example decreases as it moves from the first surface (13a) toward the middle of the first surface (13a) and the second surface (13b), and increases as it moves from the middle of the first surface (13a) and the second surface (13b) toward the second surface (13b). Unlike the present example, the aperture D may decrease as it moves from the first surface (13a) toward the second surface (13b), or it may decrease as it moves from the second surface (13b) toward the first surface (13a). Unlike the present example, the aperture D may remain constant between the first surface (13a) and the second surface (13b).

[0070] The maximum value of the opening D between the first surface (13a) and the second surface (13b) of the plate (13) is the opening Dmax. The opening Dmax is calculated as follows. The shape of the through hole (13c) is assumed to be similar in the Z direction. When the shape of the through hole (13c) in the first surface (13a) is a circular shape, the opening Dmax is the maximum value of the diameter of the through hole (13c). The maximum value of the diameter of the through hole (13c) is the maximum width parallel to the first surface (13a) in the Z direction of the through hole (13c) in the cross-section cut in the Z direction through the diameter of the through hole (13c) in the first surface (13a). When the shape of the through hole (13c) in the first surface (13a) is elliptical, the opening diameter Dmax is the maximum value of the equal area equivalent diameter of the through hole (13c). The maximum value of the equal area equivalent diameter of the through hole (13c) is the diameter of a circle having an area equal to the maximum area of ​​the elliptical shape obtained from the maximum length of the major axis and the maximum length of the minor axis parallel to the first surface (13a) in the Z direction of the through hole (13c). The maximum length of the major axis is the maximum width parallel to the first surface (13a) in the Z direction of the through hole (13c) in the cross-section cut along the thickness through the major axis of the through hole (13c) in the first surface (13a). The maximum length of the minor axis is calculated from the ratio of the major axis to the minor axis of the through hole (13c) in the first surface (13a) and the maximum length of the major axis. The average value of the opening diameter Dmax is defined as the average circular equivalent diameter. The average value of the opening diameter Dmax is the sum of the opening diameters Dmax of all through holes (13c) divided by the total number of through holes (13c).

[0071] The value obtained by dividing the average equivalent diameter of the second layer (12) by the thickness (T2) is, for example, 0.3 or more and 5.0 or less. If the value is 0.3 or more, the thermal conductivity of the composite material (10) is likely to increase. If the value is 5.0 or less, the linear expansion coefficient of the composite material (10) is likely to decrease. The value obtained by dividing the average equivalent diameter of the second layer (12) by the thickness (T2) may be 1.6 or more and less than 5.0. If the value is 1.6 or more, the thermal conductivity of the composite material (10) is likely to increase further. If the value is less than 5.0, the linear expansion coefficient of the composite material (10) is likely to decrease further.

[0072] (Positional relationship of the penetration hole in the second floor)

[0073] FIG. 4 is a plan view of the composite material (10) viewed from the first surface (10a). FIG. 4 shows the positional relationship of the through holes (13c) formed in each of the second layers (12) that overlap each other in the Z direction. As shown in FIG. 4, when the composite material (10) is viewed in the Z direction, the through holes (13c) formed in each of the second layers (12) are misaligned from each other. FIG. 4 shows the second layer (121) near the first surface (10a) as a solid line, and the second layer (122) near the second surface (10b) as a dashed line. In addition, FIG. 4 shows that to clarify the positional relationship between the second layer (121) and the second layer (122), the second layer (121) is given a right-up hatching and the second layer (122) is given a right-down hatching.

[0074] "The through holes are misaligned" means that the outlines of the through holes (13c) formed in each of the plurality of second layers (12) do not match, that is, the openings of each through hole (13c) do not overlap. The opening of the through hole (13c) in one of the second layers (12) referred to here is the narrowest part of the through hole (13c) when viewed in the Z direction, that is, the part where the opening diameter D is smallest. A specific example of the state in which the through holes (13c) are misaligned is a form in which the opening edges of the through holes (13c) partially overlap, as shown in FIG. 4. In this form, it is preferable that the opening edge of the through hole (13c) formed in one of the plurality of second layers (12) partially overlaps with the opening edge of the through hole (13c) formed in another second layer (12). That is, the openings of the through holes (13c) formed in each of at least two second layers (12) may partially overlap, and the openings of the through holes (13c) formed in each of all second layers (12) may partially overlap. Another embodiment is a form in which the opening of the through hole (13c) of another second layer (12) is included within the opening of the through hole (13c) of one second layer (12), as shown in FIG. 5. In this form, the opening of the through hole (13c) formed in one second layer (12) may be included within the opening of the through hole (13c) formed in another second layer (12), and the opening of the through hole (13c) formed in each of all remaining second layers (12) may also be included. In the example shown in FIG. 4, the through hole (13c) of the second layer (121) and the through hole (13c) of the second layer (122) have a partially overlapping portion. In this example, the shape and opening diameter Dmax of the respective through holes (13c) of the second layer (121) and the second layer (122) are substantially the same. In the example shown in FIG. 5, the through hole (13c) of the second layer (122) is contained within the through hole (13c) of the second layer (121).In this example, the opening diameter Dmax of the through hole (13c) of the second layer (122) is smaller than the opening diameter Dmax of the through hole (13c) of the second layer (121), and the opening ratio of the second layer (122) is smaller than the opening ratio of the second layer (121). Even if the through holes (13c) do not overlap at all, if the first metal material that is continuous from the first surface (10a) to the second surface (10b) can be configured, for example, in a stepped shape, it is included in the case where "the through holes are offset from each other." In the case where the through holes (13c) do not overlap at all, the spacing between adjacent through holes (13c) of one second layer (12) is larger than the opening diameter Dmax of the through hole (13c) of the other second layer (12). If the through holes (13c) are offset from each other, the linear expansion coefficient of the composite material (10) is likely to decrease.

[0075] In addition, if there are three or more second layers (12), it is preferable that the through hole (13c) of one second layer (12) and the through hole (13c) of any other second layer are misaligned with each other. Of course, it is also preferable that the through holes (13c) of each second layer (12) are misaligned with each other.

[0076] (Overlap rate of penetration holes)

[0077] When the composite material (10) is viewed in the Z direction, the overlap rate of the through holes (13c) is, for example, 80% or less. "Overlap rate of through holes" refers to the ratio of the portion where the through holes (13c) formed in each of the second layer (12) overlap each other. The portion where the through holes (13c) overlap is the portion where all through holes (13c) of the second layer penetrate in the Z direction. The smaller the overlap rate of the through holes (13c), the smaller the ratio of the through holes (13c) formed in each of the second layer (12) overlapping each other. In other words, the ratio of the through holes (13c) being misaligned from each other is large. If the overlap rate is 80% or less, the linear expansion coefficient of the composite material (10) is likely to decrease. The overlap rate may be 70% or less, or 60% or less. The smaller the overlap rate, the more likely the linear expansion coefficient of the composite material (10) is to decrease. The overlap rate may be zero. That is, the through holes (13c) may not overlap at all. The above overlap rate may be 5% or more, 10% or more, and also 15% or more.

[0078] The overlap ratio is obtained by dividing the opening ratio of the overlapping portion of the through hole (13c) when the composite material (10) is viewed in the Z direction by the average value of the opening ratios of all second layers (12). The opening ratio of the overlapping portion is obtained by dividing the area of ​​the overlapping portion of the through hole (13c) by the area of ​​all second layers (12) overlapping. In FIG. 4, the area of ​​the overlapping portion of the through hole (13c) is an area enclosed by a part of the opening edge of the through hole (13c) of the second layer (121) and a part of the opening edge of the through hole (13c) of the second layer (122). In the present example, the overlapping portion of the through hole (13c) is a spindle-shaped area where the through hole (13c) of the second layer (121) and the through hole (13c) of the second layer (122) overlap. In FIG. 5, the area of ​​the overlapping portion of the through hole (13c) is the same as the area of ​​the through hole (13c) of the second layer (122) that is included within the through hole (13c) of the second layer (121). The area of ​​the overlapping portion of the second layer (12) is the area of ​​the region where the second layer (121) and the second layer (122) overlap each other. The area of ​​the overlapping portion of the through hole (13c) and the area of ​​the overlapping portion of the second layer (12) can be obtained from X-ray CT. When calculating the area of ​​the overlapping portion of the through hole (13c), some of the through holes (13c) that fall outside the range where all of the second layer (12) overlap are ignored. Some of the through holes (13c) that are outside the overlapping range of the second layer (12) are through holes (13c) of a second layer (12) that do not overlap with other second layers. The method for determining the opening ratio of the second layer (12) is as described above.

[0079] (Volume ratio)

[0080] The volume ratio of the second metal material in the composite material (10) is, for example, 15% or more and 45% or less. The above volume ratio is the ratio of the second metal material when the volume of the composite material (10) is 100%. A composite material (10) with a volume ratio of 15% or more is prone to having a lower linear expansion coefficient, which will be described later. A composite material (10) with a volume ratio of 45% or less is prone to having a higher thermal conductivity, which will be described later. The above volume ratio may be greater than 15% and less than or equal to 40%, or greater than or equal to 17% and less than or equal to 35%.

[0081] The volume ratio of the second metal material is obtained as follows. The weight ratio of the first metal material and the second metal material is obtained by inductively coupled plasma emission spectroscopy (ICP-OES). The volume ratio is calculated from the obtained weight ratio and the density of each material. The first metal material is, for example, copper. The density of copper is 8.96 g / cm³. The second metal material is, for example, molybdenum. The density of molybdenum is 10.2 g / cm³.

[0082] (Linear expansion coefficient)

[0083] The linear expansion coefficient of the composite material (10) is, for example, 9.0 ppm / K or less. The linear expansion coefficient of the composite material (10) is the linear expansion coefficient in the direction orthogonal to the Z direction when the temperature changes from room temperature to 800°C. The linear expansion coefficient of the composite material (10) may be 8.8 ppm / K or less, or 8.6 ppm / K or less.

[0084] The linear expansion coefficient of the composite material (10) is calculated by measuring the expansion displacement in a direction orthogonal to the Z direction of the composite material (10) in a temperature range from room temperature to 800°C using a TD5000SA manufactured by Bruker AXS. The sample used to measure the linear expansion coefficient of the composite material (10) is cut from the composite material (10). The planar shape of the sample is a rectangular shape. The size of the planar shape of the sample is 5 mm × 15 mm. The linear expansion coefficient of the composite material (10) is the average value of the linear expansion coefficients of three samples.

[0085] (Thermal conductivity)

[0086] The thermal conductivity of the composite material (10) is, for example, 290 W / m·K or higher. The thermal conductivity of the composite material (10) is the thermal conductivity in the Z direction of the composite material (10) at room temperature. The thermal conductivity of the composite material (10) may be 300 W / m·K or higher, 320 W / m·K or higher, or 350 W / m·K or higher.

[0087] The thermal conductivity of the composite material (10) is calculated based on the thermal diffusivity of the composite material (10), the volume ratio of each constituent material of the composite material (10), and the specific heat. The thermal diffusivity of the composite material (10) is measured using a laser flash method. An LFA457 MicroFlash manufactured by NETZSCH is used as the measuring device for the thermal diffusivity of the composite material (10). The sample used for measuring the thermal diffusivity of the composite material (10) is cut from the composite material (10). The planar shape of the sample is circular. The diameter of the planar shape of the sample is 10 mm. The specific heat of each constituent material of the composite material (10) is determined based on the "Metal Data Book 4th Edition" (2004, Maruzen Publishing) edited by the Institute of Metallurgy of Japan. Prior to measuring the thermal conductivity of the composite material (10), the thermal conductivity of a pure copper sample of the same shape is measured under the same conditions, and the result is used as a reference to correct the measurement result. The thermal conductivity of the composite material (10) is the average value of the thermal conductivity of the three samples. The specific heat of copper is 386 J / (kg·K). The specific heat of molybdenum is 251 J / (kg·K).

[0088] [Variation Example]

[0089] Referring to FIG. 6, a composite material (10) according to a modified example is described. FIG. 6 shows a cross-section of the composite material (10) cut in the Z direction, similar to FIG. 2. In the example shown in FIG. 6, the number of first layers (11) is 4, the number of second layers (12) is 3, and the total number of layers is 7. In the example shown in FIG. 6, the thickness of all first layers (11) is the same. The composite material (10) of the example shown in FIG. 6 has a symmetrical structure with a second layer (123) positioned in the center of the composite material (10) in the Z direction. Specifically, the opening ratios of the second layer (121) and the second layer (122) positioned with the second layer (123) in between are substantially the same. In the example shown in FIG. 6, the opening ratio of the second layer (123) is different from the respective opening ratios of the second layer (121) and the second layer (122). Specifically, the opening ratio of the second layer (123) is smaller than the respective opening ratios of the second layer (121) and the second layer (122). In such a symmetrical structure, it is difficult for a difference in the linear expansion coefficient to occur between the upper part closer to the first surface (10a) than the second layer (123) and the lower part closer to the second surface (10b) than the second layer (123). Therefore, when the temperature of the composite material (10) rises, it is difficult for the composite material (10) to bend.

[0090] Method for manufacturing composite materials

[0091] The composite material (10) can be manufactured by a method for manufacturing a composite material comprising a preparation process S1, a drilling process S2, and a bonding process S3 as shown in FIG. 7.

[0092] In preparation process S1, at least one first plate and a plurality of second plates are prepared. The first plate is a plate made of a first metal material. The first plate is a plate made of a metal material with copper as the main component, for example. The second plate is a plate made of a second metal material. The second plate is a plate made of a metal material with molybdenum as the main component, for example. The respective thicknesses of the first plate and the second plate are appropriately selected according to the thickness of the composite material (10) being produced, the volume ratio of the second metal material in the composite material (10), and the respective number of the first layer (11) and the second layer (12).

[0093] In the perforation process S2, a second processed plate is produced by perforating the second plate to form a plurality of through holes (13c) that penetrate along the thickness of the second plate. After undergoing the bonding process S3, the second processed plate becomes a plate (13). The perforation is performed, for example, by etching or laser irradiation. The perforation may be performed from both the first and second surfaces of the second plate, or from only the first or second surface. By perforating from both the first and second surfaces of the second plate, through holes (13c) as shown in FIG. 2 are formed. That is, a second processed plate is produced in which through holes (13c) are formed such that the opening diameter D decreases from each of the first surface (13a) and the second surface (13b) toward the middle of the first surface (13a) and the second surface (13b). A second processed plate is produced by perforating only the first or second surface of the second plate, and although the city is omitted, a through hole (13c) is formed in which the opening D decreases as it moves from the first surface (13a) to the second surface (13b) or from the second surface (13b) to the first surface (13a).

[0094] In the bonding process S3, the laminate is heated and pressurized. The laminate is manufactured by alternately stacking a first plate and a second processed plate in sequence inside a mold. The stacking of the first plate and the second processed plate is performed such that the first plate is placed on the bottom and top layers of the laminate, respectively, or the second processed plate is placed on the bottom and top layers of the laminate, respectively. The mold is formed of, for example, graphite. The heating temperature is below the melting point of the first plate and is a temperature at which the first plate is sufficiently softened. The heating temperature is, for example, 1000°C. Pressurization is performed in a direction along the thickness of the laminate. Pressurization is performed at a pressure necessary to make the first plate, softened by heating, flow. The pressure is, for example, 50 MPa or more. Through the above heating and pressurization, the first plate and the second processed plate are bonded together. Due to the heating and pressurization described above, a portion of the first metal material constituting the first plate material flows, and said portion is filled into the through hole (13c) of the second processed plate material to become a filler (14). The filler (14) filled into the through hole (13c) and the second processed plate material become the second layer (12). The remainder of the first plate material that was not filled into the through hole (13c) becomes the first layer (11). Thus, a composite material (10) with the structure shown in FIG. 2 is manufactured.

[0095] Semiconductor Package

[0096] A semiconductor package of an embodiment is described with reference to FIG. 8. The semiconductor package (100) comprises a composite material (10), a semiconductor element (30), a case member (40), a cover (41), and terminals (50a) and (50b).

[0097] The composite material (10) constitutes a heat spreader of a semiconductor package (100). The semiconductor element (30) serves as a heat source during operation. The semiconductor element (30) is disposed on a first surface (10a). A heat transfer member may be interposed between the semiconductor element (30) and the first surface (10a). The heat transfer member is, for example, a bonding material such as solder or nano silver paste.

[0098] The case member (40) is composed of, for example, a ceramic material. The ceramic material is, for example, alumina (Al2O3). The shape of the case member (40) is a rectangular frame shape. The case member (40) is placed on a first surface (10a) to surround the semiconductor device (30). The case member (40) and the first surface (10a) are joined, for example, by soldering. When the case member (40) and the composite material (10) are soldered together, the composite material (10) is exposed to a high temperature. The high temperature is, for example, about 800°C. The difference between the linear expansion coefficient of the composite material (10) itself and the linear expansion coefficient of the alumina constituting the case member (40) is small. Therefore, the thermal stress generated at the interface between the composite material (10) and the case member (40) is small, and it is difficult for the semiconductor device (30), etc., to be damaged. The cover (41) is made of, for example, a ceramic material or a metal material. The cover (41) closes the opening of the case member (40).

[0099] Terminals (50a) and (50b) are inserted into the case member (40). The first end of terminals (50a) and (50b) is located within a space partitioned by the first surface (10a), the case member (40), and the cover (41). The second end of terminals (50a) and (50b) is located outside the space. Terminals (50a) and (50b) are composed of, for example, a metal material. The metal material is, for example, Covar.

[0100] Although not illustrated, the first end of terminal (50a) and terminal (50b) is electrically connected to the semiconductor device (30). The semiconductor package (100) is electrically connected to a device or circuit different from the semiconductor package (100) by the second end of terminal (50a) and terminal (50b).

[0101] A heat dissipation member (60) is attached to the second surface (10b). The heat dissipation member (60) is, for example, a metal plate having a channel formed therein for refrigerant to flow. The heat dissipation member (60) is not limited to this. The heat dissipation member (60) may be, for example, a cooling fin. A heat transfer member not shown may be interposed between the heat dissipation member (60) and the second surface (10b).

[0102] [Test Example 1]

[0103] Composite materials of samples No. 1-1 to No. 1-6 were prepared. The composite materials were manufactured as follows. Three first plates made of pure copper were prepared, and two second plates made of pure molybdenum were prepared. The first plates and the second plates have a rectangular shape when viewed from a planar perspective.

[0104] Each second plate was perforated. By perforating, a second processed plate was produced in which a plurality of through holes (13c) were formed penetrating in the direction along the thickness of each second plate. The perforation was performed by laser irradiation from both the first and second surfaces of each second plate. The first plate and the second processed plate were alternately arranged in order inside a graphite mold. By this arrangement, a laminate was produced in which the first plate, the second processed plate, the first plate, the second processed plate, and the first plate were arranged in order from the top layer to the bottom layer. Table 1 shows the thickness of each prepared plate. The first to fifth layers in Table 1 correspond to the order in which they are stacked in order from the top layer. For example, the first layer represents the plate placed at the very top of the laminate. The second layer represents the plate placed second from the top layer. The "Material" column of Table 1 indicates the material of the plate constituting each layer of the laminate. If the material of the plate is "Cu," it means that the first plate is made of pure copper. If the material of the plate is "Mo," it means that the second plate is made of pure molybdenum. The laminate was joined by a hot press under conditions of a temperature of 1000°C, a time of 60 minutes, and a pressure of 50 MPa. For samples No. 1-1 to No. 1-6, when manufacturing the laminate, the second processed plate of the second layer and the second processed plate of the fourth layer were arranged so as to be offset from each other in a direction perpendicular to the Z direction.

[0105] As shown in FIG. 2, the fabricated composite material had the first layer (11) and the second layer (12) alternately stacked in the Z direction such that the first layer (11) is located on the first surface (10a) and the second surface (10b). The composite material (10) has a stacked structure in which the first layer (11), the second layer (12), the first layer (11), the second layer (12), and the first layer (11) are arranged in order from the first surface (10a). The number of the first layer (11) is 3, the number of the second layer (12) is 2, and the total number of stacked layers is 5. The thickness of the composite material after bonding was about 1 mm. The second layer (12) consisted of a plate (13) having a plurality of through holes (13c) formed therein and a filler (14) placed inside each through hole (13c). The shape of the through hole (13c) was circular. The plate (13) was a plate made of pure molybdenum. The filler (14) was formed of pure copper. The first layer (11) was formed of pure copper. The planar shape of the composite material (10) was a rectangular shape. The number of layers of the composite material (10), the thickness of the composite material (10), and the volume ratio of molybdenum in the composite material (10) are shown in Table 1.

[0106] The fabricated composite material (10) is composed of a second layer and a fourth layer made of a second layer (12). The second layer (12) of the second layer corresponds to the second layer (121) shown in FIG. 2. The second layer (12) of the fourth layer corresponds to the second layer (122) shown in FIG. 2. The opening diameter Dmax of the through hole (13c) in each second layer (12) constituting the second and fourth layers, the opening ratio of each second layer (12), and the thickness of each second layer (12) are shown in Table 2. In addition, the overlap ratio of the through hole (13c) when the composite material (10) is viewed in the Z direction is shown in Table 2. The column "Opening Diameter Dmax" in Table 2 indicates the average value of the opening diameter Dmax of all through holes (13c). The aperture Dmax corresponds to the aforementioned average circular equivalent diameter. The aperture Dmax, the aperture ratio, and the overlap ratio of the through hole (13c) were obtained from an X-ray CT image projected in the Z direction of the composite material (10).

[0107] The linear expansion coefficient (ppm / K) and thermal conductivity (W / m·K) of the composite material (10) of each sample are shown in Table 3. FIG. 9 is a graph showing the relationship between the overlap rate of through holes and the linear expansion coefficient for each sample. The horizontal axis of FIG. 9 represents the overlap rate, and the vertical axis represents the linear expansion coefficient. The dashed line in FIG. 9 is an approximate straight line showing the relationship between the overlap rate and the linear expansion coefficient of samples No. 1-1 to No. 1-6. FIG. 10 is a graph showing the relationship between the overlap rate of through holes and the thermal conductivity for each sample. The horizontal axis of FIG. 10 represents the overlap rate, and the vertical axis represents the thermal conductivity.

[0108]

[0109]

[0110]

[0111] As shown in Table 3 and Figure 9, from a comparison of samples No. 1-1 to No. 1-6, it can be seen that the coefficient of linear expansion decreases as the overlap ratio decreases. In addition, as shown in Table 3 and Figure 10, from a comparison of samples No. 1-1 to No. 1-6, it can be seen that there is little correlation between the overlap ratio and thermal conductivity, and that the overlap ratio does not significantly affect thermal conductivity. From the above, it can be seen that when the composite material is viewed in the Z direction, the through holes formed in each of the overlapping second layers are offset from each other, thereby allowing for a higher thermal conductivity while further reducing the coefficient of linear expansion. Explanation of the symbols

[0112] 10: Composite materials 10a: First surface 10b : Second surface 11 : 1st floor 12, 121, 122, 123: 2nd layer 13 : Plate 13a : 1st side 13b : 2nd side 13c : Through hole 14 : Filler 30 : Semiconductor device 40 : Case absence 41 : Cover 50a, 50b: Terminals 60: Heat dissipation component 100 : Semiconductor package Tc, T1, T2: Thickness S1: Preparation Process S2: Drilling process S3: Bonding process

Claims

Claim 1 A plate-shaped composite material having a first surface and a second surface opposite to the first surface, wherein the composite material comprises at least one first layer and a plurality of second layers, wherein the first layer and the second layers are alternately stacked in a direction along the thickness of the composite material, wherein each layer constituting the first surface and the second surface is the first layer or the second layer, wherein the first layer is a layer made of a first metal material, and each of the second layers has a plate made of a second metal material and a filler made of the first metal material, wherein the thermal conductivity of the first metal material is higher than the thermal conductivity of the second metal material, and the linear expansion coefficient of the second metal material is lower than the linear expansion coefficient of the first metal material, wherein the plate has a plurality of through holes penetrating the plate in a direction along the thickness of the composite material, and the filler is disposed inside the through holes, and wherein, when the composite material is viewed in a direction along the thickness, the Composite material with through holes that are offset from each other. Claim 2 A composite material according to claim 1, wherein when the composite material is viewed in the direction along the thickness, the overlap rate of the through holes formed in each of the plurality of second layers is 80% or less. Claim 3 A composite material according to claim 1 or 2, wherein the opening ratio of each of the second layers is 15% or more. Claim 4 A composite material according to any one of claims 1 to 3, wherein when the composite material is viewed in the direction along the thickness, the opening edges of the through holes formed in each of at least two of the plurality of second layers partially overlap. Claim 5 A composite material according to any one of claims 1 to 3, wherein, when the composite material is viewed in the direction along the thickness, the opening of the through hole formed in one of the plurality of second layers is included within the opening of the through hole formed in another second layer. Claim 6 A composite material according to any one of claims 1 to 5, wherein the volume ratio of the second metal material in the composite material is 15% or more and 45% or less. Claim 7 A composite material according to any one of claims 1 to 6, wherein the first metal material is a metal material having copper as the main component. Claim 8 A composite material according to any one of claims 1 to 7, wherein the second metal material is a metal material having molybdenum as its main component. Claim 9 A composite material according to any one of claims 1 to 8, wherein the thickness of each of the second layers is 0.05 mm or more and 35% or less of the thickness of the composite material. Claim 10 A composite material according to any one of claims 1 to 9, wherein the value obtained by dividing the average equivalent circle diameter of the through hole in each of the second layers by the thickness of each of the second layers is 0.3 or more and 5.0 or less. Claim 11 A heat spreader having a composite material described in any one of claims 1 to 10, wherein the first surface forms a contact surface with a heat source. Claim 12 A semiconductor package comprising a composite material described in any one of claims 1 to 10 and a semiconductor element, wherein the semiconductor element is disposed on the first surface. Claim 13 A semiconductor package according to claim 12, further comprising a case member made of ceramics, wherein the case member is disposed on the first surface to surround the semiconductor element.

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