Composite material, heat spreader, and semiconductor package

Abstract

This composite material is plate-shaped and comprises at least one first layer and a plurality of second layers. The first layer and the second layers are alternately laminated in the direction along the thickness of the composite material; 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 through the plate in the direction along the thickness of the composite material; the filler is disposed inside the through-holes; and when the composite material is seen through in the direction along the thickness, the through-holes provided in each of the plurality of second layers are deviated from each other.

Description

Composites, Heat Spreaders, and Semiconductor Packages

[0001] The present disclosure relates to a composite material, a heat spreader, and a semiconductor package. This application claims priority to Japanese Patent Application No. 2023-203978 filed on December 1, 2023, the entire contents of which are incorporated herein by reference.

[0002] Patent Document 1 discloses a composite material used in a heat spreader for a semiconductor package. The composite material is plate-shaped. The composite material has a first surface and a second surface. The composite material includes a plurality of first layers and a plurality of second layers. The first layers and second layers are alternately stacked in a direction along the thickness of the composite material. The layer that constitutes the first surface and the second surface is the first layer. The first layer is formed of a metal material whose main component is copper. The second layer includes a molybdenum plate and a copper filler. The molybdenum plate has a plurality of openings that penetrate the molybdenum plate in a direction along the thickness. The copper filler is arranged to fill the interior of the openings.

[0003] International Publication No. 2022 / 030197

[0004] The composite material disclosed herein is a plate-shaped composite material having a first surface and a second surface opposite the first surface. The composite material includes at least one first layer and multiple second layers. The first layers and the second layers are alternately stacked in a thickness direction of the composite material. The layers constituting the first surface and the second surface are the first layer or the second layer. The first layer is a layer made of a first metallic material. Each of the second layers includes a plate made of a second metallic material and a filler made of the first metallic material. The thermal conductivity of the first metallic material is higher than that of the second metallic material. The linear expansion coefficient of the second metallic material is lower than that of the first metallic material. The plate has multiple through holes penetrating the plate in a thickness direction of the composite material. The filler is disposed inside the through holes. When the composite material is viewed through in a thickness direction, the through holes provided in each of the multiple second layers are offset from each other.

[0005] FIG. 1 is a schematic perspective view of a composite material according to an embodiment. FIG. 2 is a partially enlarged view of the II-II cross section of FIG. 1. FIG. 3 is a partially enlarged view of the III-III cross section of FIG. 2. FIG. 4 is a diagram showing the positional relationship of through holes in a second layer in a composite material according to an embodiment. FIG. 5 is a diagram showing another example of the positional relationship of through holes in a second layer in a composite material according to an embodiment. FIG. 6 is a cross-sectional view of a composite material according to Modification 1. FIG. 7 is a manufacturing process diagram of a composite material. FIG. 8 is an exploded perspective view of a semiconductor package according to an embodiment. FIG. 9 is a graph showing the linear expansion coefficient of a sample of Test Example 1. FIG. 10 is a graph showing the thermal conductivity of a sample of Test Example 1.

[0006] [Problem to be Solved by the Present Disclosure] Composite materials are required to have both high thermal conductivity and a low coefficient of linear expansion.

[0007] An object of the present disclosure is to provide a composite material that has high thermal conductivity and can further reduce the linear expansion coefficient.

[0008] [Effects of the Present Disclosure] The composite material of the present disclosure can further reduce the coefficient of linear expansion while having high thermal conductivity.

[0009] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described.

[0010] (1) The composite material disclosed herein is a plate-shaped composite material having a first surface and a second surface opposite the first surface. The composite material includes at least one first layer and multiple second layers. The first layers and the second layers are alternately stacked in a thickness direction of the composite material. The layers constituting the first surface and the second surface are the first layer or the second layer. The first layer is a layer made of a first metallic material. Each of the second layers includes a plate made of a second metallic material and a filler made of the first metallic material. The thermal conductivity of the first metallic material is higher than that of the second metallic material. The linear expansion coefficient of the second metallic material is lower than that of the first metallic material. The plate has multiple through holes penetrating the plate in a thickness direction of the composite material. The filler is disposed inside the through holes. When the composite material is viewed through in a thickness direction, the through holes provided in each of the multiple second layers are offset from each other.

[0011] The composite material (1) above has a high thermal conductivity and a low linear expansion coefficient. This is because it has a structure in which a first layer made of a first metallic material and a second layer having a plate made of a second metallic material and a filler made of the first metallic material are laminated. Here, the term "consisting of" refers to being formed solely of the material in question. In other words, "made of a first metallic material" refers to being formed solely of the first metallic material. Furthermore, the composite material (1) above can maintain a similar thermal conductivity while further reducing the linear expansion coefficient compared to a composite material having the same configuration except that the through holes are not offset, because the through holes provided in each of the multiple second layers are offset from one another.

[0012] (2) In the composite material of (1) above, when the composite material is viewed through in a direction along the thickness, the overlap rate of the through holes provided in each of the multiple second layers may be 80% or less.

[0013] A composite material in which the overlapping rate of the through holes is 80% or less tends to have a lower coefficient of linear expansion.

[0014] (3) In the composite material of (1) or (2) above, the opening ratio of each of the second layers may be 15% or more.

[0015] A composite material in which the opening ratio of the second layer is 15% or more tends to have high thermal conductivity.

[0016] (4) In any of the composite materials (1) to (3) above, when the composite material is viewed through a direction along the thickness, the opening edges of the through holes provided in at least two of the plurality of second layers may partially overlap each other.

[0017] The composite material (4) above tends to have a low coefficient of linear expansion.

[0018] (5) In any of the composite materials (1) to (3) above, when the composite material is viewed through a direction along the thickness, the opening edge of the through hole provided in one of the second layers among the plurality of second layers may include the opening edge of the through hole provided in another of the second layers.

[0019] The composite material (5) above tends to have a low coefficient of linear expansion.

[0020] (6) In the composite material according to any one of (1) to (5) above, the volume ratio of the second metallic material in the composite material may be 15% or more and 45% or less.

[0021] A composite material in which the volume ratio of the second metallic material is 15% or more tends to have a low coefficient of linear expansion, and a composite material in which the volume ratio of the second metallic material is 45% or less tends to have a high thermal conductivity.

[0022] (7) In any of the composite materials (1) to (6) above, the first metal material may be a metal material containing copper as a main component.

[0023] Copper has a high thermal conductivity. When the first metal material is a metal material containing copper as a main component, it is easy to increase the thermal conductivity of the composite material.

[0024] (8) In any of the composite materials (1) to (7) above, the second metallic material may be a metallic material containing molybdenum as a main component.

[0025] Molybdenum has a low coefficient of linear expansion. When the second metal material is a metal material containing molybdenum as a main component, it is easy to reduce the coefficient of linear expansion of the composite material.

[0026] (9) In the composite material of any one 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.

[0027] By setting the thickness of the second layer to 0.05 mm or more, the second layer, which has a relatively low coefficient of linear expansion, has an appropriate thickness. This makes it easy to reduce the coefficient of linear expansion of the composite material. By setting the thickness of the second layer to 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. This makes it easy to increase the thermal conductivity of the composite material.

[0028] (10) In any of the composite materials (1) to (9) above, the value obtained by dividing the average circular equivalent diameter of the through holes 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.

[0029] A composite material having this value of 0.3 or more is likely to have a high thermal conductivity, and a composite material having this value of 5.0 or less is likely to have a low coefficient of linear expansion.

[0030] (11) A heat spreader according to the present disclosure includes the composite material according to any one of (1) to (10), wherein the first surface forms a contact surface with a heat source.

[0031] The heat spreader (11) above is suitable for dissipating heat from semiconductor elements because it comprises a composite material that can achieve both high thermal conductivity and a low coefficient of linear expansion.

[0032] (12) A semiconductor package according to the present disclosure includes the composite material according to any one of (1) to (10) above and a semiconductor element, the semiconductor element being disposed on the first surface.

[0033] The semiconductor package of (12) above tends to reduce the thermal stress generated at the interface between the semiconductor element and the composite material, making it difficult for the semiconductor element to be damaged and facilitating heat dissipation.

[0034] (13) The semiconductor package of (12) may further include a ceramic case member disposed on the first surface so as to surround the semiconductor element.

[0035] The semiconductor package of (13) above is less susceptible to thermal stress occurring at the interface between the case member and the composite material, and therefore is less likely to cause damage to the semiconductor element and the like.

[0036] [Details of the embodiments of the present disclosure] Specific examples of the composite material, heat spreader, and semiconductor package of the present disclosure are described below. The same reference numerals in the figures indicate the same objects. The sizes of components shown in each drawing are expressed for the purpose of clarifying the description and do not necessarily represent actual dimensional relationships. The present invention is not limited to these examples, but is defined by the claims, and all modifications within the meaning and scope equivalent to the claims are intended to be included.

[0037] <<Composite Material>> A composite material 10 according to an embodiment will be described with reference to FIGS. 1 to 4. As shown in FIG. 1, the composite material 10 is plate-shaped. The composite material 10 has a first surface 10a and a second surface 10b. The first surface 10a and the second surface 10b form faces of the composite material 10 that intersect in a direction along the thickness of the composite material 10. The second surface 10b is the opposite face of the first surface 10a. As shown in FIG. 2, the composite material 10 includes at least one first layer 11 and multiple second layers 12. The first layers 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 includes a plate 13 made of a second metal material and a filler 14. As shown in FIGS. 2 and 3, the plate 13 has multiple through holes 13c. The filler 14 is disposed inside the through holes 13c. One of the characteristics of the composite material 10 is that, as shown in Figure 4, when the composite material 10 is viewed through in the thickness direction, the through holes 13c provided in each of the multiple second layers 12 are offset from each other.

[0038] The thickness of the composite material 10 is defined as thickness Tc. The thickness of the first layer 11 is defined as thickness T1. The thickness of the second layer 12 is defined as thickness T2. The direction along the thickness Tc of the composite material 10 is defined as the Z direction. The Z direction is the direction from the first surface 10a to the second surface 10b. In Figure 2, the boundary between the first layer 11 and the second layer 12 is indicated by a two-dot chain line.

[0039] (Laminated Structure) 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 linear expansion coefficient. As shown in FIG. 2, the composite material 10 has a laminated structure in which the first layers 11 and the second layers 12 are alternately laminated. Adjacent first layers 11 and second layers 12 are in contact with each other. This laminated structure allows the composite material 10 to achieve both high thermal conductivity and a low linear expansion coefficient. The layers constituting the first surface 10a and the second surface 10b are the first layer 11 and the second layer 12, respectively. In other words, the layers constituting the first surface 10a and the second surface 10b have the same structure. In the example shown in FIG. 2, the first layer 11 and the second layer 12 are alternately laminated 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 layers 11 and the second layers 12 may be alternately stacked so that the second layers 12 are located on the first surface 10a and the second surface 10b.

[0040] (Number of Layers) The number of first layers 11 is 1 or more. The number of second layers 12 is 2 or more. The total number of stacked layers of the first layers 11 and the second layers 12 is an odd number of 3 or more. The number of first layers 11, the number of second layers 12, and the number of stacked layers in the composite material 10 are not particularly limited and can be selected appropriately. In the example shown in FIG. 2 , the number of first layers 11 is 3, the number of second layers 12 is 2, and the total number of stacked layers is 5.

[0041] (First Layer) The first layer 11 is a layer made of a first metallic material. The thermal conductivity of the first metallic material is higher than that of the second metallic material described below. The thermal conductivity of the first metallic material is, for example, at least twice that of the second metallic material. The thermal conductivity of the first metallic material is, for example, 300 W / m·K or more, and even 350 W / m·K or more. "Thermal conductivity" refers to the thermal conductivity at room temperature. The first metallic material is, for example, a metallic material primarily composed of copper. "A metallic material primarily composed of copper" refers to a metallic material containing 50% by mass or more of copper. In other words, when the total mass of the first layer 11 is 100% by mass, the copper content in the first layer 11 is 50% by mass or more. The copper content may be 70% by mass or more. The first layer 11 is made of, for example, pure copper. "Pure copper" refers to a metallic material containing copper and unavoidable impurities as the remainder. Pure copper has a copper content of 99% by mass or more, particularly 99.9% by mass or more. The thermal conductivity of copper is 398 W / m·K at room temperature. "Room temperature" means 27°C.

[0042] 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. When 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 be high. When 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 be low. 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.

[0043] When the composite material 10 includes a plurality of first layers 11, the thickness T1 of all the first layers 11 may be the same, or the thickness T1 of some of the first layers 11 may be different. In the example shown in Fig. 2 , of the three first layers 11, the thickness T1 of the first layer disposed at the center of the composite material 10 in the Z direction is thicker than the thicknesses T1 of the first layers disposed on the upper and lower sides of the composite material 10. By varying the thickness T1 of any of the first layers 11, it is easy to adjust the thermal conductivity of the composite material 10.

[0044] 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 three or more. The average value of all the measured lengths is the thickness Tc. The thickness T1 of the first layer is determined as follows: A cross section is taken by cutting the composite material 10 in the Z direction with a cutting machine. The length in the Z direction of the first layer 11 is measured in this cross section along the Z direction. The cross section along the Z direction is a plane that is substantially perpendicular to the first surface 10a and the second surface 10b. The number of measurements is three or more. The average value of all the measured lengths is the thickness T1.

[0045] (Second Layer) The second layer 12 includes 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 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 / K (7.0 ppm / K) or less, and even less than 6.0 × 10 ―６ / K (6.0 ppm / K) or less. "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 primarily composed of molybdenum. "Metal material primarily composed of molybdenum" refers to a metal material with a molybdenum content of 50 mass% or more. In other words, when the total mass of the plate 13 is 100 mass%, the molybdenum content in the plate 13 is 50 mass% or more. The molybdenum content may be 70 mass% or more. The plate 13 is made of, for example, pure molybdenum. "Pure molybdenum" refers to a metal material composed of molybdenum and unavoidable impurities constituting the remainder. Pure molybdenum has a molybdenum content 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 .

[0046] 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. When 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. This makes it easy to increase the thermal conductivity of the composite material 10. When the thickness T2 is 0.05 mm or more, the second layer 12, which has a relatively low linear expansion coefficient, has an appropriate thickness. This makes it easy to decrease the linear expansion coefficient of the composite material 10. 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.

[0047] Of the multiple second layers 12, all of the second layers 12 may have the same thickness T2, or some of the second layers 12 may have different thicknesses T2. In the example shown in Fig. 2, the thicknesses T2 of the two second layers 12 are the same. When the thicknesses T2 of all the second layers 12 are the same, warping of the composite material 10 is less likely to occur when the temperature of the composite material 10 increases.

[0048] The thickness T2 of the second layer 12 is determined in the same manner as the thickness T1 of the first layer 11, as follows: The length of the second layer 12 in the Z direction is measured in a cross section of the composite material 10 taken along the Z direction. The length of the second layer 12 in the Z direction is the thickness of the plate 13, i.e., the length in the Z direction between the first surface 13a and the second surface 13b of the plate 13. Measurements are taken at three or more locations. The average value of all the measured lengths is the thickness T2.

[0049] The plate 13 has a first surface 13a and a second surface 13b. The second surface 13b is the surface opposite to the first surface 13a. The first surface 13a and the second surface 13b are planes that intersect with the Z direction. The first surface 13a and the second surface 13b are planes that are substantially parallel to the first surface 10a and the second surface 10b.

[0050] The plurality of through holes 13c formed in the plate 13 penetrates the plate 13 in the Z direction. The plurality of through holes 13c in the plate 13 are independent of one another. 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 arranged in a three-dimensional mesh pattern, but are arranged in a regular pattern. The plurality of through holes 13c in the plate 13 have the same shape and uniform size.

[0051] As shown in Fig. 3, the through hole 13c has a circular shape in a cross section perpendicular to the Z direction. The cross section perpendicular to the Z direction is a plane that is substantially parallel to the first surface 10a and the second surface 10b. In the cross section, the shape of the through hole 13c is not limited to a circular shape. In the cross section, the shape of the through hole 13c may be an ellipse, a polygon, or any other shape.

[0052] In a cross section perpendicular to the Z direction, the plurality of through holes 13c are arranged in a lattice pattern. More specifically, in the cross section, the plurality of through holes 13c are arranged in a square lattice pattern. In the cross section, the plurality of through holes 13c may be arranged in a rectangular lattice pattern. In the cross section, the plurality of through holes 13c may be arranged in an oblique lattice pattern.

[0053] In the second layer 12, 1 mm ２ The number of through holes 13c per mm is, for example, less than 3. ２ If the thickness is less than 1 mm, the linear expansion coefficient of the composite material 10 tends to be low. ２ The number of through holes 13c per 1 mm is calculated by dividing the number of through holes 13c by the area of ​​the second layer 12 in a cross section perpendicular to the Z direction. The area of ​​the second layer 12 is the area of ​​the plate 13 including the through holes 13c. ２ The number of through holes 13c per mm may be less than 2. ２ If it is less than this, the coefficient of linear expansion of the composite material 10 is likely to become lower.

[0054] A cross section of the second layer 12 perpendicular to the Z direction is exposed as follows. The composite material 10 is observed from the side using a digital microscope, and the distance between the first surface 10a and the center of the plate 13 in the Z direction is measured. The first surface 10a is polished using a surface polisher or an automatic rotary polisher. The amount of polishing is set so as to be equal to the distance between the first surface 10a and the center of the plate 13 in the Z direction measured as described above. The cross section of the second layer 12 perpendicular to the Z direction can also be observed using an X-ray CT (Computed Tomography) device.

[0055] The aperture ratio of the second layer 12 is, for example, 15% or more. The aperture ratio is determined as follows: In a cross section passing through the center of the plate 13 in the Z direction and perpendicular to the Z direction, the sum of the aperture areas of all the through holes 13c is measured. The measured sum is divided by the area of ​​the second layer 12 described above. The aperture area is measured using a digital microscope. The aperture area may also be calculated by extracting the through holes 13c from an X-ray CT image. When the aperture ratio is 15% or more, the thermal conductivity of the composite material 10 is likely to be high. The aperture ratio may be 20% or more, 30% or more, or even 35% or more. The aperture ratio is, for example, 70% or less. The aperture ratio may be 60% or less. The aperture ratios of the multiple second layers 12 may be the same or different. In this example, the aperture ratio of the second layer 121 close to the first surface 10a is substantially equal to the aperture ratio of the second layer 122 close to the second surface 10b. The phrase "aperture ratios are substantially equal" means that the difference in aperture ratio between the second layers 12 is within 5%.

[0056] The circle-equivalent diameter of the through hole 13c at any position in the Z direction is defined as the opening diameter D. The opening diameter D can be obtained by dividing the opening area of ​​the through hole 13c at any position in the Z direction by π / 4 and then taking the square root of the value. The opening diameter D is measured on a plane parallel to the first surface 13a.

[0057] In this example, the opening diameter D varies between the first surface 13a and the second surface 13b. That is, the opening diameter D in this example is not constant between the first surface 13a and the second surface 13b. In this example, the opening diameter D decreases from each of the first surface 13a and the second surface 13b toward the midpoint between the first surface 13a and the second surface 13b. That is, the opening diameter D in this example decreases from the first surface 13a toward the midpoint between the first surface 13a and the second surface 13b, and increases from the midpoint between the first surface 13a and the second surface 13b toward the second surface 13b. Unlike this example, the opening diameter D may decrease from the first surface 13a toward the second surface 13b, or from the second surface 13b toward the first surface 13a. Unlike this example, the opening diameter D may be constant across the first surface 13a and the second surface 13b.

[0058] The maximum value of the opening diameter D between the first surface 13a and the second surface 13b of the plate 13 is the opening diameter Dmax. The opening diameter Dmax can be calculated as follows. The shape of the through hole 13c is considered to be similar in the Z direction. When the shape of the through hole 13c on the first surface 13a is a perfect circle, the opening diameter 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 of the through hole 13c in the Z direction parallel to the first surface 13a in a cross section cut in the Z direction through the diameter of the through hole 13c on the first surface 13a. When the shape of the through hole 13c on the first surface 13a is elliptical, the opening diameter Dmax is the maximum value of the equivalent diameter of a circle with an equal area of ​​the through hole 13c. The maximum value of the equivalent circle diameter of the through hole 13c is the diameter of a perfect circle having the same area as the maximum area of ​​the ellipse calculated from the maximum length of the major axis and the maximum length of the minor axis of the through hole 13c in the Z direction parallel to the first surface 13a. The maximum length of the major axis is the maximum width of the through hole 13c in the Z direction parallel to the first surface 13a in a cross section cut in a direction along the thickness through the major axis of the through hole 13c on 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 on 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 equivalent circle diameter. The average 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.

[0059] The value obtained by dividing the average equivalent circular diameter in the second layer 12 by the thickness T2 is, for example, 0.3 or more and 5.0 or less. When the value is 0.3 or more, the thermal conductivity of the composite material 10 is likely to be high. When the value is 5.0 or less, the linear expansion coefficient of the composite material 10 is likely to be low. The value obtained by dividing the average equivalent circular diameter in the second layer 12 by the thickness T2 may be 1.6 or more and less than 5.0. When the value is 1.6 or more, the thermal conductivity of the composite material 10 is likely to be higher. When the value is less than 5.0, the linear expansion coefficient of the composite material 10 is likely to be lower.

[0060] (Positional Relationship of Through Holes in Second Layers) FIG. 4 is a plan view of the composite material 10 seen from the first surface 10a. FIG. 4 shows the positional relationship of the through holes 13c provided in each of the second layers 12 overlapping in the Z direction. As shown in FIG. 4, when the composite material 10 is seen through in the Z direction, the through holes 13c provided in each of the second layers 12 are offset from each other. In FIG. 4, the second layer 121 closer to the first surface 10a is indicated by a solid line, and the second layer 122 closer to the second surface 10b is indicated by a dashed line. In addition, in FIG. 4, to clarify the positional relationship between the second layer 121 and the second layer 122, the second layer 121 is hatched with an upward-to-right angle, and the second layer 122 is hatched with a downward-to-right angle.

[0061] "Through holes are offset from one another" means that the outlines of the through holes 13c provided in each of the multiple second layers 12 do not match, i.e., the openings of the through holes 13c do not overlap. Here, the opening of the through hole 13c in one second layer 12 refers to the narrowest portion of the through hole 13c when viewed through the through hole 13c in the Z direction, i.e., the portion with the smallest opening diameter D. A specific example of the through holes 13c being offset from one another is a configuration in which the opening edges of the through holes 13c partially overlap, as shown in FIG. 4 . In this configuration, it is sufficient that the opening edge of the through hole 13c provided in one second layer 12 among the multiple second layers 12 partially overlaps the opening edge of the through hole 13c provided in another second layer 12. That is, it is sufficient that the edges of the through holes 13c in at least two second layers 12 partially overlap, and it is also acceptable that the edges of the through holes 13c in all of the second layers 12 partially overlap. Another specific example is a configuration in which the edge of a through hole 13c in one second layer 12 is included within the edge of a through hole 13c in another second layer 12, as shown in FIG. 5 . In this configuration, it is sufficient that the edge of a through hole 13c in one second layer 12 is included within the edge of a through hole 13c in another second layer 12, and it is also acceptable that the edges of the through holes 13c in all of the remaining second layers 12 are included. In the example shown in FIG. 4 , the through holes 13c in the second layer 121 and the through holes 13c in the second layer 122 partially overlap. In this example, the shapes and opening diameters Dmax of the through holes 13c in the second layer 121 and the second layer 122 are substantially identical. 5, through holes 13c of second layer 122 are contained within through holes 13c of second layer 121. In this example, the opening diameter Dmax of through holes 13c of second layer 122 is smaller than the opening diameter Dmax of through holes 13c of second layer 121, and the aperture ratio of second layer 122 is smaller than the aperture ratio of second layer 121. Even if through holes 13c do not overlap at all, if the first metal material that is continuous from first surface 10a to second surface 10b can be configured in a stepped pattern, for example, this is included in the category of "through holes that are offset from each other."When the through holes 13c do not overlap at all, the distance between adjacent through holes 13c in one second layer 12 is larger than the opening diameter Dmax of the through holes 13c in another second layer 12. When the through holes 13c are misaligned from each other, the linear expansion coefficient of the composite material 10 is likely to be low.

[0062] Furthermore, when there are three or more second layers 12, it is sufficient that the through holes 13c of one second layer 12 are misaligned with the through holes 13c of any of the remaining second layers 12. Of course, the through holes 13c of all the second layers 12 may be misaligned with each other.

[0063] (Overlapping Ratio of Through Holes) When the composite material 10 is viewed in the Z direction, the overlapping ratio of the through holes 13c is, for example, 80% or less. The "overlapping ratio of through holes" refers to the percentage of overlapping portions of the through holes 13c provided in each of the second layers 12. The overlapping portions of the through holes 13c are the portions through which the through holes 13c of all of the second layers penetrate in the Z direction. The smaller the overlapping ratio of the through holes 13c, the smaller the percentage of overlap between the through holes 13c provided in each of the second layers 12. In other words, the percentage of misalignment between the through holes 13c is greater. When the overlapping ratio is 80% or less, the linear expansion coefficient of the composite material 10 is likely to be low. The overlapping ratio may be 70% or less, or even 60% or less. The smaller the overlapping ratio, the more likely the linear expansion coefficient of the composite material 10 is to be low. The overlapping ratio may be zero. In other words, the through holes 13c do not need to overlap at all. The overlap rate may be 5% or more, 10% or more, or even 15% or more.

[0064] The overlapping ratio is calculated by dividing the aperture ratio of the overlapping portion of the through holes 13c when the composite material 10 is viewed in the Z direction by the average aperture ratio of all the second layers 12. The aperture ratio of the overlapping portion is calculated by dividing the area of ​​the overlapping portion of the through holes 13c by the overlapping area of ​​all the second layers 12. In FIG. 4 , the area of ​​the overlapping portion of the through holes 13c is the area surrounded by a portion of the edge of the through hole 13c in the second layer 121 and a portion of the edge of the through hole 13c in the second layer 122. In this example, the overlapping portion of the through holes 13c is a spindle-shaped region where the through holes 13c in the second layer 121 and the through holes 13c in the second layer 122 overlap. In FIG. 5 , the area of ​​the overlapping portion of the through holes 13c is equal to the area of ​​the through hole 13c in the second layer 122 that is included in the through hole 13c in the second layer 121. The overlapping area of ​​the second layers 12 is the area of ​​the region where the second layers 121 and 122 overlap. The area of ​​the overlapping portion of the through holes 13c and the area of ​​the overlapping second layers 12 can be obtained from an X-ray CT image. When obtaining the area of ​​the overlapping portion of the through holes 13c, some of the through holes 13c that fall outside the area where all of the second layers 12 overlap are ignored. The some of the through holes 13c that fall outside the area where the second layers 12 overlap are, of the through holes 13c in a certain second layer 12, through holes 13c that do not overlap with other second layers. The method for obtaining the aperture ratio of the second layer 12 is as described above.

[0065] (Volume Ratio) The volume ratio of the second metal material in the composite material 10 is, for example, 15% or more and 45% or less. The volume ratio is the proportion of the second metal material when the volume of the composite material 10 is 100% by volume. A composite material 10 having a volume ratio of 15% or more is likely to have a low linear expansion coefficient, which will be described later. A composite material 10 having a volume ratio of 45% or less is likely to have a high thermal conductivity, which will be described later. The volume ratio may be more than 15% and 40% or less, or 17% or more and 35% or less.

[0066] The volume ratio of the second metallic material is determined as follows. The weight ratio of the first metallic material to the second metallic material is determined by inductively coupled plasma optical emission spectroscopy (ICP-OES). The volume ratio is calculated from the obtained weight ratio and the density of each substance. The first metallic material is, for example, copper. The density of copper is 8.96 g / cm ３The second metal material is, for example, molybdenum. The density of molybdenum is 10.2 g / cm ３ is.

[0067] (Linear Expansion Coefficient) 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 a direction perpendicular 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.

[0068] The linear expansion coefficient of the composite material 10 is calculated by measuring the expansion displacement of the composite material 10 in a direction perpendicular to the Z direction in a temperature range from room temperature to 800°C using a TD5000SA manufactured by Bruker AXS. A sample used to measure the linear expansion coefficient of the composite material 10 is cut out from the composite material 10. The planar shape of the sample is rectangular. The size of the planar shape of the sample is 5 mm x 15 mm. The linear expansion coefficient of the composite material 10 is the average value of the linear expansion coefficients of the three samples.

[0069] (Thermal Conductivity) The thermal conductivity of the composite material 10 is, for example, 290 W / m·K or more. The thermal conductivity of the composite material 10 is the thermal conductivity of the composite material 10 in the Z direction at room temperature. The thermal conductivity of the composite material 10 may be 300 W / m·K or more, 320 W / m·K or more, or 350 W / m·K or more.

[0070] The thermal conductivity of the composite material 10 is calculated based on the thermal diffusivity of the composite material 10 and the volume ratio and specific heat of each of the constituent materials of the composite material 10. The thermal diffusivity of the composite material 10 is measured using a laser flash method. A NETZSCH LFA457 MicroFlash is used as the device for measuring the thermal diffusivity of the composite material 10. A sample used to measure the thermal diffusivity of the composite material 10 is cut from the composite material 10. The planar shape of the sample is circular. The planar diameter of the sample is 10 mm. The specific heat of each constituent material of the composite material 10 is determined based on "Metal Data Book, 4th Edition" (2004, Maruzen Publishing), edited by the Japan Institute of Metals. 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 measurement result is used as a reference to correct the measurement result. The thermal conductivity of the composite material 10 is calculated as the average of the thermal conductivities of the three samples. The specific heat of copper is 386 J / (kg·K). The specific heat of molybdenum is 251 J / (kg·K).

[0071] [Modification] A composite material 10 according to a modification will be described with reference to FIG. 6 . Similar to FIG. 2 , FIG. 6 shows a cross section of the composite material 10 cut in the Z direction. In the example shown in FIG. 6 , the number of first layers 11 is four, the number of second layers 12 is three, and the total number of stacked layers is seven. In the example shown in FIG. 6 , all of the first layers 11 have the same thickness. The composite material 10 in the example shown in FIG. 6 has a symmetrical structure with respect to the second layer 123, which is disposed at the center of the composite material 10 in the Z direction. Specifically, the second layers 121 and 122, which are disposed on either side of the second layer 123, have substantially equal aperture ratios. In the example shown in FIG. 6 , the aperture ratio of the second layer 123 is different from the aperture ratios of the second layers 121 and 122. Specifically, the aperture ratio of the second layer 123 is smaller than the aperture ratios of the second layers 121 and 122. With such a symmetrical structure, it is unlikely that a difference in the coefficient of linear expansion will occur between the upper portion closer to the first surface 10a than the second layer 123 and the lower portion closer to the second surface 10b than the second layer 123. Therefore, when the temperature of the composite material 10 rises, the composite material 10 is unlikely to warp.

[0072] <<Manufacturing Method of Composite Material>> The composite material 10 can be manufactured by a manufacturing method of a composite material including a preparation step S1, a drilling step S2, and a joining step S3 shown in FIG.

[0073] In the preparation step S1, at least one first plate material and a plurality of second plate materials are prepared. The first plate material is a plate material made of a first metallic material. The first plate material is, for example, a plate material made of a metallic material mainly composed of copper. The second plate material is a plate material made of a second metallic material. The second plate material is, for example, a plate material made of a metallic material mainly composed of molybdenum. The thicknesses of the first plate material and the second plate material to be prepared are selected appropriately depending on the thickness of the composite material 10 to be produced, the volume ratio of the second metallic material in the composite material 10, and the number of first layers 11 and second layers 12.

[0074] In the drilling process S2, holes are drilled into the second plate to produce a second processed plate having a plurality of through holes 13c penetrating the second plate in a direction along its thickness. After the joining process S3, the second processed plate becomes the plate 13. The drilling process is performed, for example, by etching or laser irradiation. The drilling process may be performed from both the first and second surfaces of the second plate, or from only the first or second surface. By drilling from both the first and second surfaces of the second plate, the through holes 13c shown in FIG. 2 are formed. That is, a second processed plate is produced having through holes 13c formed therein, the opening diameter D of which decreases from each of the first surface 13a and the second surface 13b toward the middle between the first surface 13a and the second surface 13b. By drilling holes from only the first surface or the second surface of the second plate material, a second processed plate material is produced in which a through hole 13c is formed, the opening diameter D of which becomes smaller as it moves from the first surface 13a to the second surface 13b or from the second surface 13b to the first surface 13a, although this is not shown in the figure.

[0075] In the joining step S3, the laminate is heated and pressurized. The laminate is produced by alternately stacking first and second processed plate materials in a mold. The first and second processed plate materials are stacked so that the first plate material is located at the bottom and top of the laminate, respectively, or so that the second processed plate material is located at the bottom and top of the laminate, respectively. The mold is made of, for example, graphite. The heating temperature is below the melting point of the first plate material and at a temperature at which the first plate material 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 flow the first plate material softened by heating. The pressure is, for example, 50 MPa or more. The first and second processed plate materials are joined to each other by the above heating and pressurization. The above-described heating and pressurization causes a portion of the first metallic material constituting the first plate to flow, filling the through holes 13c of the second processed plate to become filler 14. The filler 14 filled in the through holes 13c and the second processed plate form the second layer 12. The remaining portion of the first plate that is not filled in the through holes 13c becomes the first layer 11. Thus, a composite material 10 having the structure shown in FIG. 2 is produced.

[0076] <Semiconductor Package> A semiconductor package according to an embodiment will be described with reference to Fig. 8. The semiconductor package 100 includes a composite material 10, a semiconductor element 30, a case member 40, a lid 41, and terminals 50a and 50b.

[0077] The composite material 10 constitutes a heat spreader of the semiconductor package 100. The semiconductor element 30 is a heat source during operation. The semiconductor element 30 is disposed on the 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.

[0078] The case member 40 is made of, for example, a ceramic material. The ceramic material is, for example, alumina (Al ２ O ３). The case member 40 has a rectangular frame shape. The case member 40 is disposed on the first surface 10a so as to surround the semiconductor element 30. The case member 40 and the first surface 10a are joined together by, for example, brazing. When the case member 40 and the composite material 10 are brazed together, the composite material 10 is exposed to high temperatures. The high temperatures are, 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 that constitutes the case member 40 is small. Therefore, thermal stress generated at the interface between the composite material 10 and the case member 40 is small, making it difficult for the semiconductor element 30 and the like to be damaged. The lid 41 is made of, for example, a ceramic material or a metal material. The lid 41 closes the opening of the case member 40.

[0079] The terminals 50a and 50b are inserted into the case member 40. First ends of the terminals 50a and 50b are located within a space defined by the first surface 10a, the case member 40, and the lid 41. Second ends of the terminals 50a and 50b are located outside the space. The terminals 50a and 50b are made of, for example, a metal material. The metal material is, for example, Kovar.

[0080] Although not shown, first ends of the terminals 50a and 50b are electrically connected to the semiconductor element 30. The semiconductor package 100 is electrically connected to a device or circuit other than the semiconductor package 100 by second ends of the terminals 50a and 50b.

[0081] 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 flow path formed therein through which a refrigerant flows. However, 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.

[0082] Test Example 1 Composite materials No. 1-1 to No. 1-6 were prepared. The composite materials were fabricated as follows. Three first plates made of pure copper were prepared, and two second plates made of pure molybdenum were prepared. The first and second plates were rectangular in shape when viewed from above.

[0083] Each second plate was drilled. A second processed plate was fabricated by drilling, with multiple through holes 13c formed through the thickness of each second plate. The drilling was performed by irradiating the laser from both the first and second surfaces of each second plate. The first and second processed plates were alternately arranged inside a graphite mold. This arrangement produced a stack consisting of the first plate, the second processed plate, the first plate, the second processed plate, and the first plate, arranged in this order from the top to the bottom. Table 1 shows the thickness of each prepared plate. The first to fifth layers in Table 1 correspond to the order in which the plates were stacked, starting from the top layer. For example, the first layer refers to the plate arranged at the top of the stack. The second layer refers to the plate arranged second from the top. The "Material" column in Table 1 indicates the material of the plate constituting each layer of the stack. When the material of the plate is "Cu," it means that the first plate is made of pure copper. When the material of the plate is "Mo," it means that the second plate is made of pure molybdenum. The stack was joined by hot pressing under conditions of a temperature of 1000°C, a time of 60 minutes, and a pressure of 50 MPa. For Sample No. 1-1 to Sample No. 1-6, when the stack was produced, the second processed plate material of the second layer and the second processed plate material of the fourth layer were arranged so as to be shifted from each other in a direction perpendicular to the Z direction.

[0084] As shown in FIG. 2 , the fabricated composite material had first layers 11 and second layers 12 alternately stacked in the Z direction, with the first layers 11 located on the first surface 10a and the second surface 10b. The composite material 10 had a layered structure in which, from the first surface 10a, the first layer 11, the second layer 12, the first layer 11, the second layer 12, and the first layer 11 were arranged. There were three first layers 11 and two second layers 12, for a total of five layers. The thickness of the composite material after bonding was approximately 1 mm. The second layer 12 was composed of a plate 13 with multiple through holes 13c formed therein and fillers 14 disposed inside each through hole 13c. The through holes 13c were circular. The plate 13 was made of pure molybdenum. The fillers 14 were made of pure copper. The first layer 11 was made of pure copper. The planar shape of the composite material 10 was rectangular. 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.

[0085] In the fabricated composite material 10, the second and fourth layers are composed of second layers 12. The second layer 12 corresponds to the second layer 121 shown in FIG. 2. The fourth layer 12 corresponds to the second layer 122 shown in FIG. 2. The opening diameter Dmax of the through holes 13c in each of the second layers 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. Table 2 also shows the overlap ratio of the through holes 13c when the composite material 10 is viewed in the Z direction. The "Opening diameter Dmax" column in Table 2 shows the average opening diameter Dmax of all the through holes 13c. The opening diameter Dmax corresponds to the average circle equivalent diameter described above. The opening diameter Dmax, the opening ratio, and the overlap ratio of the through holes 13c were determined from an X-ray CT image of the composite material 10 viewed in the Z direction.

[0086] 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 ratio of the through holes and the linear expansion coefficient for each sample. The horizontal axis of FIG. 9 represents the overlap ratio, and the vertical axis represents the linear expansion coefficient. The dashed lines in FIG. 9 are approximate straight lines showing the relationship between the overlap ratio and the linear expansion coefficient for Samples No. 1-1 to 1-6. FIG. 10 is a graph showing the relationship between the overlap ratio of the through holes and the thermal conductivity for each sample. The horizontal axis of FIG. 10 represents the overlap ratio, and the vertical axis represents the thermal conductivity.

[0087]

[0088]

[0089]

[0090] As shown in Table 3 and Figure 9, a comparison of Samples No. 1-1 to 1-6 reveals that the smaller the overlap ratio, the lower the linear expansion coefficient. Furthermore, as shown in Table 3 and Figure 10, a comparison of Samples No. 1-1 to 1-6 reveals that there is little correlation between the overlap ratio and thermal conductivity, and that the overlap ratio does not have much effect on thermal conductivity. From the above, it can be seen that when the composite material is viewed in the Z direction, the offset of the through holes provided in each of the overlapping second layers allows for a higher thermal conductivity while still achieving a lower linear expansion coefficient.

[0091] REFERENCE SIGNS LIST 10 Composite material 10a First surface 10b Second surface 11 First layer 12, 121, 122, 123 Second layer 13 Plate 13a First surface 13b Second surface 13c Through hole 14 Filler 30 Semiconductor element 40 Case member 41 Lid 50a, 50b Terminal 60 Heat dissipation member 100 Semiconductor package Tc, T1, T2 Thickness S1 Preparation step S2 Drilling step S3 Bonding step

Claims

1. A plate-shaped composite material having a first surface and a second surface opposite the first surface, the composite material comprising at least one first layer and a plurality of second layers, the first layer and the second layer being alternately stacked in a direction along the thickness of the composite material, each layer constituting the first surface and the second surface being the first layer or the second layer, the first layer being a layer made of a first metallic material, each of the second layers having a plate made of a second metallic material and a filler made of the first metallic material, the thermal conductivity of the first metallic material being higher than the thermal conductivity of the second metallic material, the linear expansion coefficient of the second metallic material being lower than the linear expansion coefficient of the first metallic material, the plate having a plurality of through holes penetrating the plate in a direction along the thickness of the composite material, the filler being disposed inside the through holes, and the through holes provided in each of the plurality of second layers being offset from each other when the composite material is viewed through the thickness direction.

2. The composite material according to claim 1, wherein, when the composite material is viewed through a direction along the thickness, the overlap rate of the through holes provided in each of the plurality of second layers is 80% or less.

3. The composite material according to claim 1 or 2, wherein each of said second layers has an opening rate of 15% or more.

4. A composite material according to any one of claims 1 to 3, wherein, when the composite material is viewed through in a direction along the thickness, the opening edges of the through holes provided in at least two of the second layers partially overlap each other.

5. A composite material according to any one of claims 1 to 3, wherein, when the composite material is viewed through in a direction along the thickness, the edge of an opening of the through hole provided in one of the second layers among the plurality of second layers includes the edge of an opening of the through hole provided in another of the second layers.

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.

7. A composite material according to any one of claims 1 to 6, wherein the first metallic material is a metallic material mainly composed of copper.

8. A composite material according to any one of claims 1 to 7, wherein the second metallic material is a metallic material mainly composed of molybdenum.

9. A composite material according to any one of claims 1 to 8, wherein the thickness of each of the second layers is at least 0.05 mm and not more than 35% of the thickness of the composite material.

10. A composite material described in any one of claims 1 to 9, wherein the value obtained by dividing the average circular equivalent diameter of the through holes 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.

11. A heat spreader comprising the composite material according to any one of claims 1 to 10, wherein the first surface forms a contact surface with a heat source.

12. A semiconductor package comprising: a composite material according to any one of claims 1 to 10; and a semiconductor element, the semiconductor element being disposed on the first surface.

13. The semiconductor package according to claim 12, further comprising a case member made of ceramic, said case member being disposed on said first surface so as to surround said semiconductor element.

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