Semiconductor device

Abstract

The purpose of the present invention is to provide a technology capable of inhibiting deterioration of adhesiveness of a thermal conductive material arranged between the lower surface of a base plate and a cooling fin and preventing the occurrence of a void in a semiconductor device. This semiconductor device is provided with: a base plate; an insulating substrate joined to the upper surface of the base plate; a semiconductor element mounted on the upper surface of the insulating substrate; a case fixed to a peripheral edge portion on the base plate via a screw and surrounding the insulating substrate and the semiconductor element; and an insulating sealing material filled in the case. The case is provided with a first screw hole which extends from the upper surface to the lower surface of the case and into which a threaded part of the screw is screwed. The base plate is provided with a second screw hole which extends from the upper surface of the base plate to an intermediate part so as to communicate with the first screw hole and into which a threaded part of the screw is screwed. In the second screw hole of the base plate, a space is formed below the threaded part in a state where the threaded part of the screw is screwed. The base plate is provided with a pore for discharging gas present in the space of the second screw hole from the space.

Description

Semiconductor Devices

[0001] The present disclosure relates to a semiconductor device.

[0002] Conventionally, a structure has been proposed for suppressing partial discharges that occur in a semiconductor device in which a case is fixed to the periphery of a base plate with screws (see, for example, Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2006-32392

[0004] In the technology described in Patent Document 1, through-holes are provided below the screws fixed to the base plate. Cooling fins are disposed on the underside of the base plate via a thermally conductive material. However, when through-holes are provided below the screws, the gas present in the through-holes repeatedly expands and contracts as the semiconductor device operates, deteriorating the adhesiveness of the thermally conductive material. As a result, the temperature of the semiconductor device rises due to an increase in contact thermal resistance, leading to problems such as the generation of voids within the semiconductor device.

[0005] Therefore, the present disclosure aims to provide a technology that can suppress deterioration of the adhesion of the thermally conductive material placed between the underside of the base plate and the cooling fin, and can suppress the occurrence of voids within the semiconductor device.

[0006] The semiconductor device according to the present disclosure comprises a base plate, an insulating substrate bonded to the upper surface of the base plate, a semiconductor element mounted on the upper surface of the insulating substrate, a case fixed to the peripheral portion of the base plate via screws and enclosing the insulating substrate and the semiconductor element, and an insulating sealing material filled in the case, wherein the case is provided with a first screw hole extending from the upper surface to the lower surface of the case and into which the threaded portion of the screw is screwed, and the base plate is provided with a second screw hole extending from the upper surface of the base plate to a portion thereof so as to communicate with the first screw hole and into which the threaded portion of the screw is screwed, a gap is formed in the second screw hole of the base plate below the threaded portion when the threaded portion of the screw is screwed, and the base plate is provided with a pore for discharging gas present in the gap of the second screw hole from the gap.

[0007] According to the present disclosure, the gas present in the gap of the second screw hole is expelled from the gap to the outside, thereby preventing deterioration of the adhesion of the thermally conductive material placed between the underside of the base plate and the cooling fin and preventing voids from occurring within the semiconductor device.

[0008] The objects, features, aspects, and advantages of the present disclosure will become more apparent from the following detailed description and the accompanying drawings.

[0009] Fig. 1 is an enlarged cross-sectional view of a portion of a semiconductor device according to a first embodiment; Fig. 2 is an enlarged cross-sectional view of a portion of a semiconductor device according to a second embodiment; Fig. 3 is an enlarged cross-sectional view of a portion of a semiconductor device according to a third embodiment; Fig. 4 is an enlarged cross-sectional view of a portion of a semiconductor device according to a related art;

[0010] First Embodiment A first embodiment will be described below with reference to the drawings. Fig. 1 is a partially enlarged cross-sectional view of a semiconductor device 100 according to the first embodiment. Specifically, Fig. 1 is a cross-sectional view simply showing the periphery of a fixing location between a base plate 1 and a case 9 in the semiconductor device 100. Although Fig. 1 shows only one fixing location between the base plate 1 and the case 9, there are multiple fixing locations on the base plate 1, including the four corners.

[0011] As shown in FIG. 1, the semiconductor device 100 includes a base plate 1 , an insulating substrate 3 , a semiconductor element 5 , a case 9 , screws 10 , electrodes 7 , and an insulating sealing material 8 .

[0012] The base plate 1 is a plate made of a metal such as copper or aluminum, or a plate made of an AlSiC composite material.

[0013] The insulating substrate 3 is joined to the upper surface of the base plate 1 via solder 2. The insulating substrate 3 includes an insulating layer 3b, a circuit surface 3c, and a heat dissipation surface 3a. The circuit surface 3c is provided on the upper surface of the insulating layer 3b. The heat dissipation surface 3a is provided on the lower surface of the insulating layer 3b. The insulating layer 3b is made of, for example, resin or ceramic. The circuit surface 3c and the heat dissipation surface 3a are made of, for example, copper.

[0014] The semiconductor element 5 is mounted on the upper surface of the insulating substrate 3 (more specifically, the upper surface of the circuit surface 3c) via solder 4. Although not shown, the semiconductor element 5 is electrically connected to the circuit surface 3c or electrodes 7 via metal wires 6. The semiconductor element 5 is formed of a semiconductor such as Si. The semiconductor element 5 is preferably formed of a wide bandgap semiconductor such as SiC or GaN. The semiconductor element 5 is a power semiconductor element, a control integrated circuit (IC) for controlling the power semiconductor element, or the like. The semiconductor element 5 includes, for example, an insulated gate bipolar transistor (IGBT), a metal oxide semiconductor field effect transistor (MOSFET), a Schottky barrier diode, or the like. Alternatively, the semiconductor element 5 may include a reverse-conducting IGBT (RC-IGBT) in which an IGBT and a freewheeling diode are formed within a single semiconductor chip.

[0015] The case 9 is formed, for example, from resin, into a rectangular frame shape when viewed from above, and surrounds the side surfaces of the insulating substrate 3 and the semiconductor element 5. The case 9 is fixed to the peripheral edge of the base plate 1 via screws 10. More specifically, with a silicone adhesive 11 applied between the base plate 1 and the case 9, the screws 10 are fastened into downwardly recessed recesses 9a formed in the top surface of the case 9. The screws 10 have a head 10a and a threaded portion 10b. The case 9 is provided with a first screw hole 9b that extends from the top surface to the bottom surface of the case 9 and into which the threaded portion 10b of the screw 10 is screwed.

[0016] The base plate 1 is provided with a second screw hole 1c that extends partway from the top surface of the base plate 1 to communicate with the first screw hole 9b and into which the threaded portion 10b of the screw 10 is screwed. When the base plate 1 and the case 9 are fixed together, the threaded portion 10b of the screw 10 is screwed into the second screw hole 1c of the base plate 1 and the first screw hole 9b of the case 9. When the threaded portion 10b of the screw 10 is screwed into the second screw hole 1c of the base plate 1, a gap 1a is formed below the threaded portion 10b (more specifically, the tip of the threaded portion 10b).

[0017] The base plate 1 is also provided with a small hole 1b for discharging gas present in the gap 1a of the second screw hole 1c from the gap 1a. The small hole 1b extends from the gap 1a of the second screw hole 1c to the side surface of the base plate 1. The small hole 1b may extend horizontally or obliquely, regardless of the length of the path. The number of small holes 1b may be one or more.

[0018] The electrodes 7 are bonded to the upper surface of the circuit surface 3c and are electrically connected to the semiconductor element 5 via metal wires 6 (not shown).

[0019] The insulating sealant 8 is filled in the case 9 and seals the insulating substrate 3, the semiconductor element 5, and part of the electrodes 7. The insulating sealant 8 is, for example, a silicone resin or an epoxy resin.

[0020] A cooling fin 13 is fixed to the lower surface of the semiconductor device 100 (more specifically, the lower surface of the base plate 1) via a thermally conductive material 12. The thermally conductive material 12 transfers heat from the semiconductor device 100 to the cooling fin 13. The thermally conductive material 12 is, for example, a TIM (Thermal Interface Material).

[0021] Next, the effects of the first embodiment will be described in comparison with the related art. Fig. 5 is a partially enlarged cross-sectional view of a semiconductor device 101 according to the related art. Specifically, Fig. 5 is a cross-sectional view simply showing the periphery of a fixing point between the base plate 1 and the case 9 in the semiconductor device 101. Although Fig. 5 shows only one fixing point between the base plate 1 and the case 9, there are multiple fixing points on the base plate 1, including the four corners. Note that in the related art, components that are the same as those described in the first embodiment are designated by the same reference numerals, and their description will be omitted.

[0022] First, a description of the related art will be given. As shown in FIG. 5 , in a semiconductor device 101 according to the related art, a second screw hole 1c in a base plate 1 extends from the upper surface to the lower surface of the base plate 1, penetrating the base plate 1. Furthermore, no small holes 1b are provided for discharging gas present in the gap 1a of the second screw hole 1c from the gap 1a. Of the thermally conductive material 12 disposed between the base plate 1 and the cooling fin 13, the portion facing the second screw hole 1c in the base plate 1 is exposed to the gas present in the gap 1a of the second screw hole 1c. Repeated expansion and contraction of the gas present in the gap 1a due to operation of the semiconductor device 101 deteriorates the adhesiveness of the thermally conductive material 12. As a result, the temperature of the semiconductor device 101 increases due to an increase in contact thermal resistance, leading to problems such as the generation of voids 15 within the semiconductor device 101.

[0023] In contrast, as shown in FIG. 1 , in the first embodiment, a semiconductor device 100 includes a base plate 1, an insulating substrate 3 bonded to the upper surface of the base plate 1, a semiconductor element 5 mounted on the upper surface of the insulating substrate 3, a case 9 fixed to the peripheral portion of the base plate 1 via screws 10 and enclosing the insulating substrate 3 and the semiconductor element 5, and an insulating sealing material 8 filled in the case 9. The case 9 is provided with a first screw hole 9b extending from the upper surface to the lower surface of the case 9 and into which a threaded portion 10b of a screw 10 is threaded. The base plate 1 is provided with a second screw hole 1c extending from the upper surface of the base plate 1 to a portion thereof so as to communicate with the first screw hole 9b and into which the threaded portion 10b of the screw 10 is threaded. When the threaded portion 10b of the screw 10 is threadedly engaged in the second screw hole 1c of the base plate 1, a gap 1a is formed below the threaded portion 10b. The base plate 1 is provided with a small hole 1b for discharging gas present in the gap 1a of the second screw hole 1c from the gap 1a. The small hole 1b extends from the gap 1a of the second screw hole 1c to the side surface of the base plate 1.

[0024] Therefore, the gas present in the gap 1a of the second screw hole 1c is discharged to the outside from the gap 1a, which prevents the adhesion of the thermally conductive material 12 disposed between the lower surface of the base plate 1 and the cooling fin 13 from deteriorating and prevents the occurrence of voids 15 (see FIG. 5) in the semiconductor device 100. This makes it possible to prevent the occurrence of partial discharge in the semiconductor device 100.

[0025] Second Embodiment Next, a semiconductor device 100A according to a second embodiment will be described. Fig. 2 is a partially enlarged cross-sectional view of the semiconductor device 100A according to the second embodiment. Specifically, Fig. 2 is a cross-sectional view simply showing the periphery of a fixing location between the base plate 1 and the case 9 in the semiconductor device 100A. Although Fig. 2 shows only one fixing location between the base plate 1 and the case 9, there are multiple fixing locations on the base plate 1, including the four corners. Note that in the second embodiment, the same components as those described in the first embodiment are designated by the same reference numerals, and their description will be omitted.

[0026] In the first embodiment, the hole 1b extends horizontally or obliquely regardless of the length of the path, but in the second embodiment, as shown in Fig. 2, the hole 1b extends horizontally from the gap 1a of the second screw hole 1c to the side surface of the base plate 1 via the shortest path. Note that the hole 1b may extend obliquely as long as it is the shortest path. The number of the hole 1b may be one or more.

[0027] As described above, in the second embodiment, the small hole 1b extends from the gap 1a of the second screw hole 1c to the side surface of the base plate 1 via the shortest path. Therefore, the length of the small hole 1b is shorter than in the first embodiment, making it easier to discharge gas present in the gap 1a of the second screw hole 1c. This makes it possible to further suppress the generation of voids 15 (see FIG. 5) in the semiconductor device 100A and to further suppress the occurrence of partial discharge, compared to the first embodiment.

[0028] Third Embodiment Next, a semiconductor device 100B according to a third embodiment will be described. Fig. 3 is a partially enlarged cross-sectional view of the semiconductor device 100B according to the third embodiment. Specifically, Fig. 3 is a cross-sectional view simply showing the periphery of a fixed location between the base plate 1 and the case 9 in the semiconductor device 100B. Although Fig. 3 shows only one fixed location between the base plate 1 and the case 9, there are multiple fixed locations on the base plate 1, including the four corners. Note that in the third embodiment, the same components as those described in the first and second embodiments are designated by the same reference numerals, and description thereof will be omitted.

[0029] 3, in the third embodiment, unlike the configurations of the first and second embodiments, a through screw 14 is fastened to a recess 9a of a case 9 instead of the screw 10. Also, the small hole 1b is not provided.

[0030] The through-hole screw 14 has a head 14a, a threaded portion 14b, an opening 14c formed in the head 14a, and a through-hole 14d extending from the head 14a to the threaded portion 14b. The opening 14c and the through-hole 14d of the through-hole screw 14 communicate with the gap 1a of the second screw hole 1c. When the insulating sealant 8 is filled into the case 9, the insulating sealant 8 flows from the opening 14c of the through-hole screw 14 and fills the gap 1a of the second screw hole 1c via the through-hole 14d. As a result, there is no gap 1a below the threaded portion 14b in the second screw hole 1c, and no gas is present. Note that the insulating sealant 8 filled in the gap 1a of the second screw hole 1c is not shown in FIG. 3.

[0031] As described above, in the third embodiment, the semiconductor device 100B includes a base plate 1, an insulating substrate 3 bonded to the upper surface of the base plate 1, a semiconductor element 5 mounted on the upper surface of the insulating substrate 3, a case 9 fixed to the peripheral portion of the base plate 1 via through-hole screws 14 and enclosing the insulating substrate 3 and the semiconductor element 5, and an insulating sealing material 8 filled inside the case 9. The case 9 has a first screw hole 9b extending from the upper surface to the lower surface of the case 9 and into which the threaded portion 14b of the through-hole screw 14 is threaded. The base plate 1 has a second screw hole 1c extending from the upper surface of the base plate 1 to a portion thereof so as to communicate with the first screw hole 9b and into which the threaded portion 14b of the through-hole screw 14 is threaded. When the threaded portion 14b of the through-hole screw 14 is threadedly engaged in the second screw hole 1c of the base plate 1, a gap 1a is formed below the threaded portion 14b. The through-hole screw 14 has a through hole 14d extending from the head 14a to the threaded portion 14b. The through hole 14d of the through screw 14 and the gap 1a of the second screw hole 1c are in communication with each other. The gap 1a of the second screw hole 1c is filled with the insulating sealant 8 via the through hole 14d of the through screw 14.

[0032] Therefore, since no gas is present in the gap 1a of the second screw hole 1c, deterioration of the adhesion of the thermally conductive material 12 disposed between the underside of the base plate 1 and the cooling fin 13 is suppressed, and the occurrence of voids 15 (see FIG. 5) in the semiconductor device 100B can be suppressed. This makes it possible to suppress the occurrence of partial discharge in the semiconductor device 100B.

[0033] Furthermore, since the fine holes 1b are not required, the manufacturing process of the semiconductor device 100B is simplified and made easier than in the first and second embodiments.

[0034] Fourth Embodiment Next, a semiconductor device 100C according to a fourth embodiment will be described. FIG. 4 is a partially enlarged cross-sectional view of the semiconductor device 100C according to the fourth embodiment. Specifically, FIG. 4 is a cross-sectional view simply showing the periphery of a fixed location between the base plate 1 and the case 9 in the semiconductor device 100C. Although FIG. 4 shows only one fixed location between the base plate 1 and the case 9, there are multiple fixed locations on the base plate 1, including the four corners. Note that in the fourth embodiment, the same components as those described in the first to third embodiments are designated by the same reference numerals, and description thereof will be omitted.

[0035] As shown in FIG. 4, in the fourth embodiment, the screws 10 or the through screws 14 are not provided, unlike the configurations of the first to third embodiments.

[0036] The case 9 is provided with a first hole 9c extending from the top surface to the bottom surface of the case 9. The base plate 1 is provided with a second hole 1d extending from the top surface to partway through the base plate 1 so as to communicate with the first hole 9c. The first hole 9c of the case 9 and the second hole 1d of the base plate 1 are filled with an insulating sealant 8. Therefore, no gas is present in the first hole 9c of the case 9 or the second hole 1d of the base plate 1. Furthermore, by filling the first hole 9c of the case 9 and the second hole 1d of the base plate 1 with the insulating sealant 8, the base plate 1 and the case 9 can be fixed together.

[0037] As described above, in the fourth embodiment, the semiconductor device 100C includes the base plate 1, the insulating substrate 3 bonded to the upper surface of the base plate 1, the semiconductor element 5 mounted on the upper surface of the insulating substrate 3, the case 9 fixed to the peripheral portion of the base plate 1 and enclosing the insulating substrate 3 and the semiconductor element 5, and the insulating sealant 8 filled inside the case 9. The case 9 is provided with a first hole 9c extending from the upper surface to the lower surface of the case 9. The base plate 1 is provided with a second hole 1d extending from the upper surface to a portion of the base plate 1 so as to communicate with the first hole 9c. The first hole 9c of the case 9 and the second hole 1d of the base plate 1 are filled with the insulating sealant 8.

[0038] Therefore, since no gas is present in the first hole 9c of the case 9 and the second hole 1d of the base plate 1, deterioration of the adhesion of the thermally conductive material 12 disposed between the underside of the base plate 1 and the cooling fin 13 is suppressed, and the occurrence of voids 15 (see FIG. 5) in the semiconductor device 100C can be suppressed. This makes it possible to suppress the occurrence of partial discharge in the semiconductor device 100C.

[0039] Moreover, since the fine holes 1b are no longer necessary, the manufacturing process of the semiconductor device 100C is simplified and made easier than in the cases of the first and second embodiments. Furthermore, since the screws 10 or the through screws 14 are no longer necessary, the manufacturing cost is reduced compared to the cases of the first to third embodiments.

[0040] Although this disclosure has been described in detail, the above description is illustrative in all respects and is not restrictive. It is understood that countless variations not illustrated can be envisioned.

[0041] It should be noted that the embodiments can be freely combined, and each embodiment can be modified or omitted as appropriate.

[0042] 1 base plate, 1a gap, 1b small hole, 1c second screw hole, 1d second hole, 3 insulating substrate, 5 semiconductor element, 8 insulating sealing material, 9 case, 9b first screw hole, 9c first hole, 10 screw, 10b screw portion, 14 through screw, 14a head, 14b screw portion, 14d through hole, 100, 100A, 100B, 100C semiconductor device.

Claims

1. A semiconductor device comprising: a base plate; an insulating substrate bonded to the upper surface of the base plate; a semiconductor element mounted on the upper surface of the insulating substrate; a case fixed to the peripheral edge of the base plate via screws and enclosing the insulating substrate and the semiconductor element; and an insulating sealing material filled inside the case, wherein the case is provided with a first screw hole extending from the upper surface to the lower surface of the case and into which the threaded portion of the screw is screwed; the base plate is provided with a second screw hole extending from the upper surface to a portion of the base plate so as to communicate with the first screw hole and into which the threaded portion of the screw is screwed; a gap is formed in the second screw hole of the base plate below the threaded portion when the threaded portion of the screw is screwed; and the base plate is provided with a small hole for discharging gas present in the gap of the second screw hole from the gap.

2. The semiconductor device according to claim 1, wherein said small hole extends from said gap of said second screw hole to a side surface of said base plate.

3. The semiconductor device according to claim 1, wherein said small hole extends from said gap of said second screw hole to the side surface of said base plate via the shortest path.

4. A semiconductor device comprising: a base plate; an insulating substrate bonded to an upper surface of the base plate; a semiconductor element mounted on an upper surface of the insulating substrate; a case fixed to the peripheral edge of the base plate via screws and enclosing the insulating substrate and the semiconductor element; and an insulating sealant filled into the case, wherein the case has a first screw hole extending from the upper surface to the lower surface of the case and into which the threaded portion of the screw is screwed; the base plate has a second screw hole extending from the upper surface of the base plate to a portion thereof so as to communicate with the first screw hole and into which the threaded portion of the screw is screwed; a void is formed in the second screw hole of the base plate below the threaded portion of the screw when the threaded portion of the screw is screwed; the screw is a through screw having a through hole extending from its head to the threaded portion; the through hole of the through screw and the void of the second screw hole are communicated; and the void of the second screw hole is filled with the insulating sealant via the through hole of the through screw.

5. A semiconductor device comprising: a base plate; an insulating substrate bonded to the upper surface of the base plate; a semiconductor element mounted on the upper surface of the insulating substrate; a case fixed to the peripheral portion of the base plate and enclosing the insulating substrate and the semiconductor element; and an insulating sealant filled inside the case, wherein the case has a first hole extending from the upper surface to the lower surface of the case; and the base plate has a second hole extending from the upper surface to a portion of the base plate so as to communicate with the first hole, and the first hole in the case and the second hole in the base plate are filled with the insulating sealant.

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