Semiconductor device and method for manufacturing semiconductor device

Abstract

This semiconductor device includes: a base plate on which a semiconductor chip is mounted on a first principal surface side; and a thermal interface material which is arranged on a second principal surface side opposite to the semiconductor chip mounting surface of the base plate, and the elastic modulus of which changes due to a phase change at a phase change temperature. The base plate has a convex warpage on the second principal surface side, and the thermal interface material has a phase change temperature of 40°C-100°C inclusive.

Description

Semiconductor device and method for manufacturing the same

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

[0002] A known semiconductor device has a structure in which a semiconductor chip is mounted on an insulating substrate (see, for example, Patent Document 1). In this semiconductor device, the insulating substrate is placed on a heat sink, which is placed on a cooler. Thermally conductive grease is applied between the heat sink and the cooler. In addition, the heat sink has a convex curved surface facing the cooler, which improves contact between the heat sink and the cooler and the thermally conductive grease.

[0003] Japanese Patent Application Laid-Open No. 2005-39081

[0004] In the semiconductor device with the above-described configuration, the heat sink has a convex curved surface, resulting in a smaller gap between the heat sink and the cooler at the center of the heat sink. As a result, the thermal interface material, such as thermally conductive grease, disposed between the heat sink and the cooler also thins and deforms at the center of the surface adjacent to the heat sink and the cooler. Meanwhile, semiconductor devices are known to use thin cooling plates as coolers to reduce thermal resistance from the semiconductor chip. Semiconductor devices using such thin cooling plates are prone to reduced rigidity. Furthermore, during actual use and reliability tests such as power cycle tests, a hard (high-elasticity) thermal interface material is sometimes used to suppress pump-out of the thermal interface material. However, when such a hard thermal interface material is used, the configuration described in the aforementioned Patent Document 1 is less likely to collapse at the center between the heat sink and the cooler. In other words, the thermal interface material at the center of the cooler does not thin and deform. In this case, the thermal interface material does not deform to fill the gap between the heat sink and the cooler, resulting in a gap between the heat sink and the cooler. As a result, heat transfer from the heat sink to the cooling plate through the thermal interface material is hindered, and the heat dissipation performance of the semiconductor device is reduced.

[0005] In order to solve the above-mentioned problems, the present invention provides a semiconductor device capable of improving 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.

[0007] The semiconductor device of the present invention includes a base plate having a first main surface on which a semiconductor chip is mounted, and a thermal interface material that undergoes a phase change at a phase change temperature and whose elastic modulus changes, and that is disposed on a second main surface 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.

[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.

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

[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 the semiconductor device will be described. FIG. 1 shows a cross-sectional view of a semiconductor device according to the first embodiment. In the semiconductor device 100 shown in FIG. 1, a power semiconductor chip (hereinafter simply referred to as a "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 wiring layer patterns of the insulating substrates 13 mounted on the base plate 15 are 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, under-chip solder 12, insulating substrate 13, under-substrate solder 14, and wire bonding 18, as well as part of the main terminals 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 protrusion height (warpage) 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 base plate distortion 15b, 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 15 b. As shown in FIG. 2 , the thermal interface material 21 is formed in a pattern of hexagonal shapes arranged all over the surface when viewed from the second main surface 15 b side of the base plate 15. Note that the application pattern in this example is just an 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 15 b side of the base plate 15, with spaces between the patterns of a predetermined shape where the thermal interface material 21 is not applied.

[0018] In the semiconductor device shown in FIG. 1, the height of the thermal interface material 21 is indicated by D. The initial height D of the thermal interface material 21 ０is, for example, 140 μm. The thermal interface material 21 covers the application area at 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 at an occupancy rate ε=70%. Therefore, the thermal interface material 21 covers an average of 100 μm (D ０ ×ε ~ 140 μm × 70%).

[0019] The thermal interface material 21 is made of a material that undergoes a phase change at a predetermined temperature and exhibits a large change in elastic modulus. As an example, the elastic modulus E can be determined by viscoelasticity measurement in an oscillation mode. The period for applying strain in the viscoelasticity measurement is preferably about 1 second to 1 minute, which is the time it takes for the semiconductor device 100 to be fixed to the heat sink 22. The thermal interface material 21 is made of a material that undergoes a phase change temperature T ０ High temperature (T > T ０ ) is the elastic modulus in the case of E ０ , temperature T is phase change temperature T ０ The following low temperatures (T<T ０ ) is the elastic modulus in the case of E １ When this is the case, the elastic modulus at high temperature E ０ is the elastic modulus at low temperature E １ It is desirable to reduce it to 1 / 5 or less.

[0020] 3 shows the relationship between the thickness D and the surface pressure P when a surface pressure is applied to the thermal interface material 21. The thermal interface material 21 is heated when the temperature T is equal to or exceeds the phase change temperature T ０ The following low temperatures (T<T ０ ) In the case where the thickness D is the initial value D for the surface pressure P ０ The surface pressure P １ The average coating thickness [D ０ × ε]. １ is the elastic modulus E １ Using [P １ = E １ On the other hand, the thermal interface material 21 can be expressed as follows: ０ High temperature (T > T ０ ) In the case where the thickness D is the initial value D for the surface pressure P ０ The surface pressure P ０ The average coating thickness [D０ × ε]. ０ is the elastic modulus E ０ Using [P ０ = E ０ ×(1-ε)].

[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 a heat sink 22 (FIG. 5) described below is performed in an environment of about 25°C. Therefore, the phase change temperature of the thermal interface material 21 is preferably 40°C or higher so that the thermal interface material 21 does not undergo a phase change at this working temperature. Furthermore, since it is desirable for the thermal interface material 21 to undergo a rapid phase change and a decrease in elastic modulus due to a temperature increase during operation of the semiconductor chip 11, the phase change temperature of the thermal interface material 21 is preferably 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 of Fig. 5 shows the semiconductor device 100 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] As shown in FIG. 5 , a 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, after fastening, the base plate 15 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 above the phase change temperature, so the thermal interface material 21 is pressed while its elastic modulus is low. As a result, the thermal interface material 21 easily deforms and spreads throughout the space between the base plate 15 and the heat sink 22. Furthermore, because the thermal interface material 21 is pressed at a temperature above the phase change temperature and spreads, its thickness after fastening is thinner than before fastening. FIG. 6 shows the configuration of the base plate 15 viewed from the second main surface 15b after fastening. As shown in FIG. 6, the island-shaped pattern of the thermal interface material 21 (FIG. 2) before fastening has spread and become integrated on the second main surface 15b of the base plate 15 after fastening.

[0027] On the other hand, FIG. 7 shows an example of the cross-sectional structure of a semiconductor device 100 when fastened to a heat sink 22 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 created by deformation of the base plate 15.

[0028] The example shown in FIG. 7 shows a structure in which the thermal interface material 21 is pressed below its phase change temperature, with the thermal interface material 21 being pressed while its elastic modulus 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 throughout 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 that are not wetted by the thermal interface material 21, and air is present in these 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 is reduced, and the reliability of the semiconductor device 100 is reduced. Therefore, when the semiconductor device 100 is bonded to a cooler such as a heat sink 22, the thermal interface material 21 must be heated above its phase change temperature.

[0029] [Method of Manufacturing Semiconductor Device] An example of a method of manufacturing the semiconductor device 100 according to this embodiment and a method of bonding the semiconductor device 100 to a heat sink 22 (cooler) will be described. First, the semiconductor chip 11 is mounted on a die pad or the like of an insulating substrate 13 using under-chip solder 12. Then, the insulating substrate 13 on which the semiconductor chip 11 is mounted is bonded to a 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. Next, 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 that of the thermal interface material 21 before fastening. Finally, the solvent contained in the thermal interface material 21 is removed in a high-temperature environment such as a thermostatic oven, and then the temperature is returned to room temperature. Through the above steps, the semiconductor device 100 having the 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 then 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 of the thermal interface material 21. Furthermore, while the temperature of the thermal interface material 21 is maintained 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 operation, 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, the base plate 15 protrudes toward the second main surface 15b, so initially, the center of the base plate 15 comes into contact with the heat sink 22. At this time, the thermal interface material 21 is at or above its phase change temperature. Therefore, 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 easily deforms. As a result, the thermal interface material 21 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 deforms, 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 pushed out from the center toward the periphery between the base plate 15 and the heat sink 22 and spreads. 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 described above, where the gap between the base plate 15 and the heat sink 22 is not filled with the thermal interface material 21, can be changed to the structure shown in Fig. 5 in which the gap between the base plate 15 and the heat sink 22 is filled with the thermal interface material 21 by heating the thermal interface material 21 to a temperature equal to or higher than the phase change temperature. 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 (warpage) of the base plate 15 toward the thermal interface material 21 (second main surface 15b) before the screw fastening is defined as protrusion amount A (FIG. 1). Assuming that the entire thermal interface material 21 is wet and spread after the screw fastening, the entire thermal interface material 21 is subjected to a surface pressure P ０This surface pressure P ０ The amount of change in warpage of the base plate 15 toward the first main surface 15a when the applied voltage is defined as change B. This amount of change in warpage B is expressed as the difference [B=A-F] 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 warpage change is greatest among the areas where the thermal interface material 21 is applied, that is, the amount of warpage change at the location near the center of the base plate 15. Under the above conditions, the distance G at the location where the base plate 15 is farthest from the heat sink 22 after fastening can be expressed by the following equation (1): G=B+C-A (1)

[0035] On the other hand, the thickness H of the thermal interface material 21 after spreading at the farthest position between the base plate 15 and the heat sink 22 is the initial thickness D of the thermal interface material 21. ０ , can be expressed by the following equation (2) using the occupancy rate (aperture rate) ε of the thermal interface material 21 at that location: H=D ０ × 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 furthest point between the base plate 15 and the heat sink 22, the thermal interface material 21 fills the gap 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 heats up and exceeds the phase change temperature, softening the thermal interface material 21 and spreading throughout. This is also a condition for the thermal interface material 21 to spread between the base plate 15 and the heat sink 22 when the semiconductor device 100 is fastened to the heat sink 22 below the phase change temperature. In other words, when the semiconductor device 100 is fastened to the heat sink 22 in a state where the thermal interface material 21 is above the phase change temperature and in a state where the thermal interface material 21 is heated above the phase change temperature by the operation of the semiconductor chip 11, the condition of the following equation (3) is met: B + C - A < D ０ × ε (3)

[0037] In this way, by using a phase change material as the thermal interface material 21, when fastening is performed at a temperature equal to or higher than the phase change temperature, the deformation of the thermal interface material 21 satisfies the condition of the above formula (3), and the thermal interface material 21 spreads over the entire application area. Furthermore, even when fastening is performed at a temperature equal to or lower than the phase change temperature, when the thermal interface material 21 is heated to a temperature equal to or higher than the phase change temperature due to heat generated by the semiconductor chip 11, the deformation of the thermal interface material 21 satisfies the condition of the above formula (3), and the thermal interface material 21 spreads over the entire application area. Furthermore, even at the distance G (= B + C - A) where the base plate 15 and the heat sink 22 are furthest apart, the thickness H (= D ０ × ε).

[0038] Furthermore, by using a phase change material as the thermal interface material 21, it is possible to fill the gap between the base plate 15 and the heat sink 22 with the thermal interface material 21 even when the condition of the above formula (3) is not satisfied. That is, the distance G between the farthest point of the base plate 15 and the heat sink 22 is less than the initial thickness D of the thermal interface material 21. ０ is greater than [B+C-A>D ０ ×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 it reaches or exceeds its phase change temperature. Therefore, the thermal interface material 21 spreads wet when the vicinity of the center 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 spread wet over the entire surface of the gap between the base plate 15 and the heat sink 22 during the fastening process. Therefore, the initial thickness D of the thermal interface material 21 formed on the second main surface 15b of the base plate 15 ０ 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 via the thermal interface material 21 can be reduced.

[0039] The preferred value of the elastic modulus of the thermal interface material depends on the shape and material of the base plate 15 and the initial thickness D of the thermal interface material. ０ and the size of the occupancy rate ε. For example, the base plate 15 has a base plate fixing hole 15c with a spacing of 86 mm in the short side direction and 127 mm in the long side direction, and a thickness of 3 mm. The base plate 15 is made of copper. Furthermore, the base plate 15 has an initial protrusion amount A and a height C of the distortion 15b of the base plate 15, both of which are 0 mm. The thermal interface material 21 has an initial thickness D ０ is 0.14 mm and the occupancy rate ε is 70% (average thickness D ０ The thermal interface material 21 has an elastic modulus E ０ When the pressure P is 100 kPa, the surface pressure P required to crush the thermal interface material 21 is ０ is [P ０ = E ０ × (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 above the phase change temperature, B + C - A = 0.11 mm. On the other hand, the average thickness D of the thermal interface material ０ ×ε is 0.1 mm, and by fastening the base plate 15 to the heat sink 22 at a high temperature equal to or higher than the phase change temperature, it is possible to wet and spread the thermal interface material 21 over the entire surface of the gap. On the other hand, the thermal interface material 21 has an elastic modulus E １ is the modulus of elasticity at high temperatures E ０ At this time, the surface pressure required to crush the thermal interface material 21 also increases by five times, and the warpage change amount B of the base plate 15 also increases by five times to 0.55 mm, which is excessively large, and therefore 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-described properties, there are no particular limitations on the constituent materials, etc. that can be used for the thermal interface material 21. Commercially available products that can be used for 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 provided 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. Note that 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. Therefore, a configuration that enhances heat dissipation is required in the region where the semiconductor chip 11 is mounted. Therefore, 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 while the thermal interface material 21 is heated to or above 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 or below the phase change temperature of the thermal interface material 21, if the thermal interface material 21 is heated to or above the phase change temperature during actual operation of the semiconductor chip 11, the thermal interface material 21 will spread between the base plate 15 and the heat sink 22. Therefore, as shown in Figures 10 and 11, the gap between the base plate 15 and the heat sink 22 in the region where the semiconductor chip 11 is mounted can be filled with the thermal interface material 21.

[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 in warpage B of the base plate 15 toward the semiconductor chip 11 (first main surface 15a) side is reduced.

[0046] That is, since the change amount B of the warp is reduced, the initial thickness D of the thermal interface material 21 is reduced. ０ Even if the occupancy rate ε is small, the above-mentioned formula (3) [B+C-A>D ０ ×ε] relationship holds. ０ Even in a configuration in which the area ratio ε 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 embodiments that include 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.

[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 semiconductor device comprising: a base plate on which a semiconductor chip is mounted on a first main surface side; and a thermal interface material that changes phase at a phase change temperature and changes its elastic modulus, the thermal interface material being arranged on a second main surface side of the base plate opposite the surface on which the semiconductor chip is mounted, wherein the base plate has a convex warp on the second main surface side, and the phase change temperature of the thermal interface material is between 40°C and 100°C.

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

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

4. The semiconductor device according to claim 1, further comprising a heat dissipation member joined to the second main surface side of the base plate via the thermal interface material, wherein the base plate has a convex warp toward the first main surface side when joined to the heat dissipation member.

5. A is the amount of warping of the base plate toward the second main surface before bonding to the heat dissipation member, B is the amount of change in warping of the base plate before and after bonding to the heat dissipation member, C is the local distortion on the surface of the second main surface of the base plate, and D is the initial thickness of the thermal interface material formed on the second main surface of the base plate. 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 5. The semiconductor device according to claim 4, wherein the relationship of [(x, y) / ( ...)] is satisfied.

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

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

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

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