Semiconductor device and semiconductor device manufacturing method

Abstract

To provide a semiconductor device that improves heat dissipation by reducing thermal resistance through a thermal interface material.SOLUTION: A semiconductor device 100 includes: a base plate 15 on which a semiconductor chip 11 is mounted on a first main surface 15a side; and a thermal interface material 21 that is arranged on a second main surface 15b side of the base plate opposite to the surface on which the semiconductor chip is mounted, and that changes in phase at a phase change temperature to change its elastic modulus, in which the base plate has a convex warp on the second main surface side, and the thermal interface material has a phase change temperature of 40°C or higher and 100°C or lower.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a semiconductor device and a method for manufacturing the same. [Background technology]

[0002] A known configuration of a semiconductor device is one in which a semiconductor chip is mounted on an insulating substrate (see, for example, Patent Document 1). The insulating substrate is then placed on a heat sink, which is then placed on a cooler. Thermally conductive grease is applied between the heat sink and the cooler. The heat sink also has a convex curved surface facing the cooler, which improves contact between the heat sink and the cooler and the thermally conductive grease. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-39081 Summary of the Invention [Problem to be solved by the invention]

[0004] In the semiconductor device with the above-described configuration, the heat sink has a convex curved surface, so the gap between the heat sink and the cooler is small at the center of the heat sink, and as a result, the thermal interface material, such as thermally conductive grease, disposed between the heat sink and the cooler is also thinned and deformed at the center of the surface where the heat sink and the cooler are adjacent. On the other hand, some semiconductor devices use thin cooling plates as coolers to reduce the thermal resistance from the semiconductor chip, but when a thin cooling plate is used, the rigidity of the semiconductor device decreases. Furthermore, during actual use or reliability tests such as power cycle tests, a hard (high elastic modulus) thermal interface material may be used to prevent pump-out of the thermal interface material. However, when such a hard thermal interface material is used, the configuration described in Patent Document 1 mentioned above makes it difficult for the thermal interface material to collapse in the center between the heat sink and the cooling plate. In other words, the thermal interface material in the center of the cooling plate becomes thin and does not deform. In this case, the thermal interface material does not deform to fill the gap between the heat sink and the cooling plate, resulting in a gap between the heat sink and the cooling plate. As a result, heat transfer from the heat sink to the cooling plate through the thermal interface material is hindered, thereby reducing the heat dissipation performance of the semiconductor device.

[0005] In order to solve the above-mentioned problems, the present invention provides a semiconductor device that can improve heat dissipation by reducing thermal resistance via a thermal interface material, and a method for manufacturing the semiconductor device.

[0006] The above and other objects of the present invention and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings. [Means for solving the problem]

[0007] The semiconductor device of the present invention comprises a base plate on which a semiconductor chip is mounted on a first main surface side, and a thermal interface material that undergoes a phase change at a phase change temperature and changes its elastic modulus, and that is disposed on a second main surface side of the base plate opposite the surface on which the semiconductor chip is mounted. The base plate has a convex warp on the second main surface side, and the thermal interface material has a phase change temperature of 40°C or higher and 100°C or lower.

[0008] The method for manufacturing a semiconductor device of the present invention includes a step of applying a thermal interface material, which undergoes a phase change and changes its elastic modulus at a phase change temperature of 40° C. to 100° C., to the back surface of a base plate having a convex warp on the side opposite to the mounting surface of a semiconductor chip. The method further includes a step of connecting the surface of the base plate on which the thermal interface material is formed to a heat dissipation member while the temperature of the thermal interface material is heated to the phase change temperature or higher, thereby forming a convex warp on the mounting surface of the base plate on the side on which the semiconductor chip is mounted. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a semiconductor device that can improve heat dissipation by reducing thermal resistance via a thermal interface material, and a method for manufacturing the semiconductor device.

[0010] Problems, configurations, and effects other than those described above will become clear from the following description of the embodiments. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a diagram illustrating a configuration of a semiconductor device according to a first embodiment. [Figure 2] 3 is a diagram showing the configuration of a second main surface side of a base plate of the semiconductor device of the first embodiment. FIG. [Figure 3] FIG. 1 is a diagram showing the relationship between thickness a and surface pressure P when surface pressure is applied to a thermal interface material. [Figure 4] 2 is a diagram showing the configuration of a first main surface side of a base plate of the semiconductor device. FIG. [Figure 5] FIG. 2 is a diagram showing a cross-sectional structure of a semiconductor device connected to a heat sink. [Figure 6] 10 is a diagram showing the configuration of the second main surface side of the base plate after fastening. FIG. [Figure 7] 1 is a diagram showing an example of a cross-sectional structure when a semiconductor device and a heat sink are fastened together at a temperature equal to or lower than the phase change temperature of the thermal interface material; [Figure 8] FIG. 10 is a diagram illustrating a configuration of a semiconductor device according to a second embodiment. [Figure 9] 3 is a diagram showing the configuration of a second main surface side of a base plate of the semiconductor device of the first embodiment. FIG. [Figure 10] FIG. 2 is a diagram showing a cross-sectional structure of a semiconductor device connected to a heat sink. [Figure 11] 10 is a diagram showing the configuration of the second main surface side of the base plate after fastening. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0012] An example of a semiconductor device according to an embodiment of the present invention and a method for manufacturing the semiconductor device will be described below with reference to the drawings. Note that the present invention is not limited to the following example. In the drawings described below, common components are given the same reference numerals. Furthermore, in the drawings used in this specification, identical or corresponding components are given the same reference numerals, and repeated explanations of these components may be omitted.

[0013] 1. First Embodiment of Semiconductor Device A first embodiment of a semiconductor device will be described. FIG. 1 shows a cross-sectional view of the semiconductor device of the first embodiment. In the semiconductor device 100 shown in FIG. 1, a power semiconductor chip (hereinafter simply referred to as "semiconductor chip") 11 is fixed to one main surface (first main surface 13a) of an insulating substrate 13 via under-chip solder 12. The insulating substrate 13 is fixed to a base plate 15, which is an example of a heat sink, via under-substrate solder 14. A plurality of insulating substrates 13 are mounted on the base plate 15. FIG. 1 shows an example in which two insulating substrates 13 are mounted on the base plate 15. A wiring layer pattern (not shown) is formed on the insulating substrate 13.

[0014] Main terminals 17 are connected to the wiring layer patterns on the insulating substrates 13. The main terminals 17 are exposed to the outside of the semiconductor device 100. Furthermore, the insulating substrates 13 mounted on the base plate 15 have their wiring layer patterns connected by wire bonding 18.

[0015] A resin case 16 is formed on the base plate 15. The resin case 16 covers the entire semiconductor chip 11, the under-chip solder 12, the insulating substrate 13, the under-substrate solder 14, the wire bonding 18, and part of the main terminal 17. As shown in FIG. 2, the base plate 15 has base plate fixing holes 15c for screwing to a heat sink 22, which is an example of a cooler.

[0016] As shown in FIG. 1, the base plate 15 has a convex curved surface whose central portion protrudes toward the other main surface (second main surface 15b) opposite the first main surface 15a. The protruding height (warping amount) A of the convex curved surface of the base plate 15 toward the second main surface 15b is, for example, approximately 100 μm. The base plate 15 also has a local height difference, i.e., a distortion 15b of the base plate, on the second main surface 15b on which the thermal interface material 21 is formed. The height C of the distortion 15b is, for example, approximately 30 μm.

[0017] As shown in FIG. 1, the base plate 15 has a thermal interface material 21 formed on the second main surface 15b. As shown in FIG. 2, the thermal interface material 21 is formed in a pattern of hexagons arranged all over the surface when viewed from the second main surface 15b side of the base plate 15. Note that the application pattern in this example is just one example, and other patterns may be used. It is preferable that the thermal interface material 21 is formed in a discontinuous, uniform pattern on the second main surface 15b side of the base plate 15, in which spaces where the thermal interface material 21 is not applied are formed between patterns of a predetermined shape.

[0018] The initial height D0 of the thermal interface material 21 is, for example, 140 μm. The thermal interface material 21 covers the applied area by an occupancy rate ε. For example, the thermal interface material 21 covers the second main surface 15b of the base plate 15 inside the four base plate fixing holes 15c with an occupancy rate ε = 70%. Therefore, the thermal interface material 21 has an average thickness of about 100 μm (D0 × ε ∼ 140 μm × 70%) on the second main surface 15b of the base plate 15 inside the base plate fixing holes 15c.

[0019] The thermal interface material 21 is composed of a material that undergoes a phase change at a predetermined temperature and has a large change in elastic modulus. As an example, the elastic modulus E is obtained by viscoelastic measurement in an oscillation mode. The period for applying strain in the viscoelastic measurement is preferably about 1 second to 1 minute, which is the time for fixing the semiconductor device 100 to the heat sink 22. When the elastic modulus at high temperature (T > T0) where the temperature T is above the phase change temperature T0 is E0 and the elastic modulus at low temperature (T < T0) where the temperature T is below the phase change temperature T0 is E1, it is desirable that the elastic modulus E0 at high temperature is reduced to 1 / 5 or less of the elastic modulus E1 at low temperature.

[0020] Fig. 3 shows the relationship between the thickness D and the surface pressure P when the surface pressure is applied to the thermal interface material 21. When the temperature T of the thermal interface material 21 is at a low temperature (T < T0) below the phase change temperature T0, the thickness D gradually decreases from the initial value D0 with respect to the surface pressure P, and becomes the average coating thickness [D0×ε] at the surface pressure P1. The surface pressure P1 can be expressed as [P1 = E1×(1 - ε)] using the elastic modulus E1. On the other hand, when the temperature T of the thermal interface material 21 is at a high temperature (T > T0) above the phase change temperature T0, the thickness D rapidly decreases from the initial value D0 with respect to the surface pressure P, and becomes the average coating thickness [D0×ε] at the surface pressure P0. The surface pressure P0 can be expressed as [P0 = E0×(1 - ε)] using the elastic modulus E0.

[0021] The temperature at which the thermal interface material 21 undergoes a phase change is, for example, 40°C or higher and 100°C or lower, and more preferably 40°C or higher and 60°C or lower. The working temperature when joining the base plate 15 to the heat sink 22 (Fig. 5) described later is carried out in an environment of about 25°C. Therefore, it is preferable that the phase change temperature of the thermal interface material 21 is 40°C or higher so that the thermal interface material 21 does not undergo a phase change at this working temperature. Also, since it is desirable that the thermal interface material rapidly undergoes a phase change and the elastic modulus decreases due to the temperature rise during the operation of the semiconductor chip 11, it is preferable that the phase change temperature of the thermal interface material 21 is 100°C or lower, and more preferably 60°C or lower.

[0022] Next, Fig. 4 shows the configuration of the base plate 15 of the semiconductor device 100 as viewed from the first main surface 15a side. Four insulating substrates 13 are mounted on the first main surface 15a of the base plate 15. A semiconductor chip 11 is mounted on each insulating substrate 13. Note that Fig. 4 omits wire bonding 18 and wiring on the insulating substrates.

[0023] There are no particular limitations on the materials of the insulating substrate 13 and the base plate 15. For example, the insulating substrate 13 is preferably a ceramic substrate such as AlN or SiN. The base plate 15 is preferably made of a material such as Cu (copper), Al (aluminum), AlSiC, or MgSiC.

[0024] 5 shows a cross-sectional structure of the semiconductor device 100 connected to the heat sink 22. The cross-sectional view shown in Fig. 5 shows a state in which the semiconductor device 100 is pressed against and connected to the heat sink 22 with the thermal interface material 21 heated to a temperature equal to or higher than the phase change temperature. The semiconductor device 100 and the heat sink 22 are fastened together with screws (not shown) in the base plate fixing holes 15c.

[0025] 5, the thermal interface material 21 is present between the semiconductor device 100 and the heat sink 22. The thermal interface material 21 is expanded between the base plate 15 and the heat sink 22 compared to before fastening. Furthermore, the base plate 15 after fastening has a convex curved surface that protrudes toward the first main surface 15a. That is, the base plate 15 has a shape that protrudes in the opposite direction from the semiconductor device 100 (FIG. 1) before fastening. Here, on the second main surface 15b side of the base plate 15, the protrusion amount (warpage amount) of the convex curved surface toward the first main surface 15a is defined as F. The protrusion amount (warpage amount) F has an opposite sign to the protrusion height A of the convex curved surface of the base plate 15 toward the second main surface 15b before fastening. In this embodiment, the protrusion height A is a positive value, and the protrusion amount (warpage amount) F is a negative value.

[0026] The thermal interface material 21 fills the space between the second main surface 15b of the base plate 15 and the heat sink 22. In FIG. 5, the thermal interface material 21 is pressed while heated to a temperature equal to or higher than the phase change temperature, and therefore is pressed while the thermal interface material 21 has a low elastic modulus. As a result, the thermal interface material 21 easily deforms and spreads wet into the space between the base plate 15 and the heat sink 22. Furthermore, because the thermal interface material 21 is pressed at a temperature equal to or higher than the phase change temperature and spreads wet, its thickness after fastening is thinner than before fastening. 6 shows the configuration of the base plate 15 after fastening as viewed from the second main surface 15b side. As shown in Fig. 6, on the second main surface 15b of the base plate 15, the patterns of the thermal interface material 21 that were formed in predetermined island shapes before fastening as shown in Fig. 2 have spread and become integrated after fastening.

[0027] 7 shows an example of a cross-sectional structure when the semiconductor device 100 and the heat sink 22 are fastened together at or below the phase change temperature of the thermal interface material 21. Similar to the semiconductor device 100 shown in FIG. 5, the semiconductor device 100 shown in FIG. 7 has a convex curved surface in which the base plate 15 protrudes toward the first main surface 15a after fastening. However, the thermal interface material 21 does not wet and spread into the space between the second main surface 15b of the base plate 15 and the heat sink 22, and there is a space between the base plate 15 and the heat sink 22 where the thermal interface material 21 is not filled. Specifically, the thermal interface material 21 and the heat sink 22 are in contact at both ends of the base plate 15 near the screw fastening portion. However, the thermal interface material 21 and the heat sink 22 are not in contact in the space near the center generated by deformation of the base plate 15.

[0028] 7, the thermal interface material 21 is pressed at a temperature equal to or lower than the phase change temperature, and therefore the thermal interface material 21 is pressed in a state where the elastic modulus of the thermal interface material 21 is high. Therefore, the thermal interface material 21 does not easily deform between the base plate 15 and the heat sink 22, or the amount of deformation is small. Therefore, the thermal interface material 21 does not wet and spread to the entire space between the base plate 15 and the heat sink 22. In this state, there are areas directly below the semiconductor chip 11 where the thermal interface material 21 is not wet, and air is present in those areas. Therefore, the space between the base plate 15 and the heat sink 22 that is not filled with the thermal interface material 21 inhibits heat transfer from the base plate 15 to the heat sink 22. As a result, the heat dissipation performance of the semiconductor device 100 decreases, and the reliability of the semiconductor device 100 decreases. Therefore, when the semiconductor device 100 is bonded to a cooler such as a heat sink 22, it is necessary to heat the thermal interface material 21 to a temperature equal to or higher than the phase change temperature.

[0029] [Method of manufacturing semiconductor device] An example of a method for manufacturing the semiconductor device 100 according to this embodiment and a method for joining the semiconductor device 100 to the heat sink 22 (cooler) will be described. First, the semiconductor chip 11 is mounted on a die pad or the like of the insulating substrate 13 using under-chip solder 12. Then, the insulating substrate 13 with the semiconductor chip 11 mounted thereon is joined to the base plate 15 using under-substrate solder 14. Furthermore, the main terminals 17 and wire bonding 18 are connected to the wiring of the insulating substrate 13. After this, a resin case 16 is formed to cover the entire semiconductor chip 11, under-chip solder 12, insulating substrate 13, under-substrate solder 14, and wire bonding 18, as well as a portion of the main terminals 17. Finally, an island-shaped pattern of thermal interface material 21 is formed on the second main surface 15b of the base plate 15 using a stencil mask or the like with a thickness equivalent to the thickness of the thermal interface material 21 before fastening. The thermal interface material 21 is then dried in a high-temperature environment, such as a thermostatic oven, to evaporate the solvent contained in the thermal interface material 21, and then returned to room temperature. Through the above steps, a semiconductor device 100 having a thermal interface material 21 made of a phase-change material is fabricated.

[0030] Next, the semiconductor device 100 is transported to a location where it will be used. The base plate 15 of the semiconductor device 100 is heated with a halogen heater or the like to heat the thermal interface material 21 and the base plate 15 to a temperature above the phase change temperature. Furthermore, while the temperature of the thermal interface material 21 is maintained at or above the phase change temperature, the semiconductor device 100 is placed on the heat sink 22, and the base plate fixing holes 15c are fastened with screws. This fixes the semiconductor device 100 to the heat sink 22. The thermal interface material 21 and the base plate 15 are then returned to room temperature. Through these steps, the semiconductor device 100 can be fixed with the thermal interface material 21 in close contact with the heat sink 22. With this configuration, when the semiconductor device 100 is in an operational state, heat generated by the heat generated by the semiconductor chip 11 is dissipated to the heat sink 22 via the thermal interface material 21.

[0031] In the above-described manufacturing process, a method of raising the temperature of the thermal interface material 21 using a halogen heater has been described, but the temperature of the entire semiconductor device 100 may also be raised in a thermostatic bath. Also, the temperature of the heat sink 22 may be raised using a halogen heater, or a high-temperature refrigerant may be circulated to raise the temperature of the thermal interface material 21 when it comes into contact with the heat sink 22.

[0032] In the above manufacturing method, when the semiconductor device 100 and the heat sink 22 come into contact with each other, the base plate 15 protrudes toward the second main surface 15b, so that the vicinity of the center of the base plate 15 first comes into contact with the heat sink 22. At this time, the thermal interface material 21 is at or above the phase change temperature, so the elastic modulus of the thermal interface material 21 at the contact location is reduced, and the thermal interface material 21 at the contact location is easily deformed. As a result, the thermal interface material 21 wets and spreads between the base plate 15 and the heat sink 22. Furthermore, as the semiconductor device 100 is fixed to the heat sink 22, the center of the base plate 15 is pressed from the heat sink 22 side and deformed, deforming in a direction that protrudes toward the semiconductor chip 11 (first main surface 15a). Then, the contact area between the base plate 15 and the heat sink 22 spreads from the center to the periphery. At this time, the thermal interface material 21 is wetted and spread between the base plate 15 and the heat sink 22 while being pushed out from the center toward the periphery. In this way, the thermal interface material 21 can effectively wet the application area between the base plate 15 and the heat sink 22 and fill the gap.

[0033] 7, the gap between the base plate 15 and the heat sink 22 is not filled with the thermal interface material 21, but by heating the thermal interface material 21 to a temperature equal to or higher than the phase change temperature, the gap between the base plate 15 and the heat sink 22 can be filled with the thermal interface material 21. The mechanism by which the gap between the base plate 15 and the heat sink 22 is filled with the thermal interface material 21 will be described below.

[0034] The amount of protrusion (amount of warpage) of the base plate 15 toward the thermal interface material 21 (second main surface 15b) before fastening with the screws is designated as A (FIG. 1). Assuming that the entire thermal interface material 21 is wet and spread after screw fastening, a surface pressure P0 shown in Fig. 3 is applied to the entire thermal interface material 21. The amount of change in warpage toward the first main surface 15a of the base plate 15 when this surface pressure P0 is applied is defined as B. This amount of change in warpage B is expressed as [B = AF], which is the difference between the amount of protrusion A toward the second main surface 15b shown in Fig. 1 and the amount of protrusion F toward the first main surface 15a shown in Fig. 5. Furthermore, this amount of change in warpage B is the amount of change in warpage at the location where the amount of change in warpage B is greatest within the region where the thermal interface material 21 is applied, that is, the amount of change in warpage at the location near the center of the base plate 15. Under the above conditions, the distance G at which the base plate 15 is most distant from the heat sink 22 after fastening can be expressed by the following formula (1). G=B+CA (1)

[0035] On the other hand, the thickness H of the thermal interface material 21 after wetting and spreading at the farthest position between the base plate 15 and the heat sink 22 can be expressed by the following equation (2) using the initial thickness D0 of the thermal interface material 21 and the occupancy rate (opening rate) ε of the thermal interface material 21 at that location. H=D0×ε (2)

[0036] When the thickness H of the thermal interface material 21 after wetting and spreading is greater than the distance G at the farthest point between the base plate 15 and the heat sink 22, the thermal interface material 21 fills the space between the base plate 15 and the heat sink 22, as in the configuration shown in Figure 5 above. Furthermore, when the semiconductor device 100 is in operation and the semiconductor chip 11 reaches a high temperature, the thermal interface material 21 is heated and exceeds the phase change temperature, causing the thermal interface material 21 to soften and spread throughout. This condition also applies to the case where the semiconductor device 100 is fastened to the heat sink 22 at a temperature below the phase change temperature, causing the thermal interface material 21 to spread between the base plate 15 and the heat sink 22. That is, when the semiconductor device 100 is fastened to the heat sink 22 while the thermal interface material 21 is at or above the phase change temperature and while the thermal interface material 21 is heated to or above the phase change temperature by driving the semiconductor chip 11, the condition of the following formula (3) is met. B+CA <D0×ε ···(3)

[0037] In this way, by using a phase change material as the thermal interface material 21, when fastening is performed at or above the phase change temperature, the thermal interface material 21 deforms to satisfy the condition of formula (3) above, and the thermal interface material 21 spreads over the entire application area. Furthermore, even when fastening is performed at or below the phase change temperature, if the thermal interface material 21 is heated to or above the phase change temperature due to heat generated by the semiconductor chip 11, the thermal interface material 21 deforms to satisfy the condition of formula (3) above, and the thermal interface material 21 spreads over the entire application area. Therefore, even at the distance G (= B + CA) where the base plate 15 and the heat sink 22 are furthest apart, the thermal interface material 21 is formed to a filling thickness H (= D0 × ε).

[0038] Furthermore, by using a phase change material as the thermal interface material 21, even if the condition of the above formula (3) is not satisfied, it is possible to fill the gap between the base plate 15 and the heat sink 22 with the thermal interface material 21. That is, even if the distance G at the farthest point between the base plate 15 and the heat sink 22 is larger than the initial thickness D0 of the thermal interface material 21, such that [B+CA>D0×ε], it is possible to fill the gap between the base plate 15 and the heat sink 22 with the thermal interface material 21. The thermal interface material 21 is easily deformed when its temperature reaches or exceeds the phase change temperature. Therefore, the thermal interface material 21 wets and spreads when the central portion of the base plate 15 comes into contact with the heat sink 22, and expands over the entire surface during the fastening process. As a result, the thermal interface material 21 can wet and spread over the entire surface of the gap between the base plate 15 and the heat sink 22 during the fastening process. Therefore, even if the initial thickness D0 of the thermal interface material 21 formed on the second main surface 15b of the base plate 15 is smaller than the change in warpage B of the base plate 15, the thermal interface material 21 can wet and spread over the entire surface of the gap between the base plate 15 and the heat sink 22. Furthermore, due to the above inequality, the base plate 15 and the heat sink 22 can be connected by a thermal interface material 21 that is thinner than conventional materials. In other words, the contact thermal resistance through the thermal interface material 21 can be reduced.

[0039] The preferred value for the elastic modulus of the thermal interface material varies depending on the shape and material of the base plate 15, as well as the initial thickness D0 and occupancy rate ε of the thermal interface material. For example, the base plate 15 has a thickness of 3 mm, with the base plate fixing holes 15c spaced 86 mm apart along the short side and 127 mm apart along the long side. The base plate 15 is made of copper. The initial protrusion amount A and the height C of the distortion 15b of the base plate 15 are both 0 mm. The thermal interface material 21 has an initial thickness D0 of 0.14 mm and an occupancy rate ε of 70% (average thickness D0 × ε = 0.1 mm). When the elastic modulus E0 of the thermal interface material 21 at temperatures higher than the phase change temperature is 100 kPa, the surface pressure P0 required to crush the thermal interface material 21 is 30 kPa, i.e., E0 = E0 × (1 - ε) = 100 kPa × 0.3 = 30 kPa. At this time, the warpage change amount B of the base plate 15 is 0.11 mm, and B + CA = 0.11 mm at temperatures above the phase change temperature. On the other hand, the average thickness D0 × ε of the thermal interface material 21 is 0.1 mm, and by fastening the base plate 15 to the heat sink 22 at a high temperature above the phase change temperature, it becomes possible to wet and spread the thermal interface material 21 over the entire surface of the gap. On the other hand, the elastic modulus E1 of the thermal interface material 21 at low temperatures below the phase change temperature is 500 kPa or more, which is 5 times or more the elastic modulus E0 at high temperatures. At this time, the surface pressure required to crush the thermal interface material 21 also becomes 5 times larger, and the warpage change amount B of the base plate 15 is also 5 times larger, 0.55 mm, which is excessive, so the thermal interface material 21 does not wet and spread over the entire surface of the gap.

[0040] As long as the thermal interface material 21 has the above-mentioned properties, there are no particular limitations on the constituent materials, etc. that can be used as the thermal interface material 21. Commercially available products that can be used as the thermal interface material 21 include LOCTITE TCP 4000 (manufactured by Henkel) and LOCTITE TCP 7000 (manufactured by Henkel).

[0041] In this embodiment, an example in which one semiconductor chip 11 is formed on four insulating substrates 13 has been disclosed, but a different number of insulating substrates may be used, and a different number of semiconductor chips 11 may be used per insulating substrate. Also, although an example in which base plate fixing holes 15c are provided at the four corners has been shown, additional fixing holes may be provided in places other than the four corners.

[0042] 2. Second Embodiment of Semiconductor Device Next, a second embodiment of the semiconductor device will be described. The semiconductor device of the second embodiment differs from the semiconductor device of the first embodiment described above only in the range in which the thermal interface material 21 is formed. Therefore, only the configuration related to the thermal interface material 21 will be described below, and detailed description of the same configuration as the first embodiment described above will be omitted.

[0043] 8 and 9 show the configuration of a semiconductor device according to the second embodiment. In the semiconductor device 100b shown in FIGS. 8 and 9, a thermal interface material 21 is formed only on the second main surface 15b of the base plate 15 directly below the region where the semiconductor chip 11 is mounted. In the semiconductor device 100b, heat generated by the semiconductor chip 11 mounted on the insulating substrate 13 is dissipated to the outside via the base plate 15 and the thermal interface material 21. For this reason, a configuration that enhances heat dissipation is required in the region where the semiconductor chip 11 is mounted. For this reason, in the semiconductor device 100b, the thermal interface material 21 is formed at least on the second main surface 15b of the base plate 15 in the region where the semiconductor chip 11 is mounted.

[0044] Furthermore, by fastening the semiconductor device 100 and the heat sink 22 together in a state in which the thermal interface material 21 is heated to a temperature equal to or higher than the phase change temperature, the thermal interface material 21 spreads between the base plate 15 and the heat sink 22. Even when the semiconductor device 100 and the heat sink 22 are fastened together at a temperature equal to or lower than the phase change temperature of the thermal interface material 21, the thermal interface material 21 spreads between the base plate 15 and the heat sink 22 when the thermal interface material 21 is heated to a temperature equal to or higher than the phase change temperature during actual operation of the semiconductor chip 11. Therefore, as shown in FIGS. 10 and 11, the gap between the base plate 15 and the heat sink 22 can be filled with the thermal interface material 21 in the region where the semiconductor chip 11 is mounted.

[0045] In the semiconductor device 100b of the second embodiment described above, the area where the thermal interface material 21 is formed is smaller than that of the semiconductor device 100 of the first embodiment (FIG. 1). Therefore, when the thermal interface material 21 wets and spreads, the area where the surface pressure is applied to the base plate 15 is reduced. As a result, the change amount B of the warpage of the base plate 15 toward the semiconductor chip 11 (first main surface 15a) side is reduced.

[0046] That is, since the change in warpage B is reduced, the relationship [B+CA>D0×ε] in the above-mentioned formula (3) holds even when the initial thickness D0 or the occupancy rate ε of the thermal interface material 21 is small. Therefore, even when the semiconductor device 100b has a configuration in which the thickness D0 of the thermal interface material 21 is small or the occupancy rate ε is small, it is possible to fill the gap between the base plate 15 and the heat sink 22 directly below the semiconductor chip 11 with the thermal interface material 21. Therefore, the semiconductor device 100b can reduce the thermal resistance (contact thermal resistance) via the thermal interface material 21.

[0047] As described above, according to the semiconductor device of each of the above-mentioned embodiments, the wettability of the thermal interface material is improved, and even a thin thermal interface material can fill the gap between the base plate and the heat sink. As a result, a semiconductor device can be provided that can reduce the thermal resistance via the thermal interface material 21.

[0048] It should be noted that the present invention is not limited to the above-described embodiments and various modifications are possible. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to an embodiment including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment. It is also possible to add the configuration of another embodiment to the configuration of one embodiment. It is also possible to delete part of the configuration of each embodiment, or to add or replace other configurations. [Explanation of symbols]

[0049] 11 semiconductor chip, 12 solder under chip, 13 insulating substrate, 13a, 15a first main surface, 14 solder under substrate, 15 base plate, 15b second main surface, 15c base plate fixing hole, 16 resin case, 17 main terminal, 18 wire bonding, 21 thermal interface material, 22 heat sink, 100 semiconductor device, 100b semiconductor device

Claims

1. a base plate on which a semiconductor chip is mounted on a first main surface side; a thermal interface material that undergoes a phase change at a phase change temperature and changes its elastic modulus, the thermal interface material being disposed on a second main surface of the base plate opposite to the surface on which the semiconductor chip is mounted, the base plate has a convex warp on the second main surface side, The thermal interface material has a phase change temperature of 40°C or higher and 100°C or lower. Semiconductor device.

2. The thermal interface material has an elastic modulus at a high temperature equal to or higher than the phase change temperature that is reduced to 1 / 5 or less of the elastic modulus at a low temperature equal to or lower than the phase change temperature. The semiconductor device according to claim 1 .

3. The thermal interface material is formed on the second main surface side of the base plate in an area where the semiconductor chip is mounted. The semiconductor device according to claim 1 .

4. a heat dissipation member joined to the second main surface side of the base plate via the thermal interface material, When the base plate is joined to the heat dissipation member, the warp of the base plate changes to a convex shape on the mounting surface side of the semiconductor chip. The semiconductor device according to claim 1 .

5. A is the amount of warping of the base plate toward the second main surface before being joined to the heat dissipation member; B is the change in warp of the base plate before and after bonding to the heat dissipation member, C is the local strain on the surface of the second main surface of the base plate; The initial thickness of the thermal interface material formed on the second main surface of the base plate is D ０ , When the occupancy rate of the thermal interface material formed on the second main surface of the base plate is ε, [B+C-A>D ０ × ε] The semiconductor device according to claim 4 .

6. The initial thickness D of the thermal interface material formed on the second main surface of the base plate ０ is smaller than the change in warp B of the base plate The semiconductor device according to claim 5 .

7. The base plate contains at least one material selected from Cu, Al, AlSiC, and MgSiC. The semiconductor device according to claim 1 .

8. a step of applying a thermal interface material, which undergoes a phase change at a phase change temperature of 40° C. to 100° C. and whose elastic modulus changes, to a back surface of a base plate having a convex warp on the side opposite to a mounting surface of the semiconductor chip; and a step of connecting the surface of the base plate on which the thermal interface material is formed to a heat dissipation member while the temperature of the thermal interface material is heated to a temperature equal to or higher than the phase change temperature, and forming a convex warp on the base plate on the mounting surface side of the semiconductor chip. A method for manufacturing a semiconductor device.

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