Power Module

Abstract

The object of the present invention is to improve the heat dissipation of metal wires on a semiconductor chip of a power module. The power module (101) comprises: at least one semiconductor chip mounted on a circuit pattern (6b) of an insulating substrate (7); a plurality of metal wires (10a, 10b) connected to the surface of the semiconductor chip; and a heat conductive sheet in contact with the metal wires (10a, 10b) from above. The metal wires comprise: at least one first metal wire (10a) connecting the surface of the semiconductor chip to the circuit pattern (6a); and at least one second metal wire (10b) connecting two points on the surface of the semiconductor chip and having the same potential as the first metal wire (10a). The heat conductive sheet comprises a graphite sheet (11), and the sheet surface of the heat conductive sheet is in contact with at least one first metal wire (10a) and at least one second metal wire (10b).

Description

Technical Field

[0001] The present invention relates to improving the heat dissipation performance of a power module. Background Art

[0002] Currently, in power modules, wiring on semiconductor chips is performed by bonding using metal wires. If metal wires are used for wiring on semiconductor chips, the size of semiconductor chips or electrode shapes can be changed in the same package to cope with the expansion of types.

[0003] Patent Document 1 discloses a technique for improving the heat dissipation of a joint on the lower side of a semiconductor chip. Patent Document 2 discloses a technique for improving the heat dissipation of a packaging material.

[0004] Patent Document 1: Japanese Patent Application Publication No. 2019-096731

[0005] Patent Document 2: Japanese Patent Application Publication No. 2017-108046 Summary of the invention

[0006] As power modules are becoming larger and smaller, the temperature of the wire wiring increases when the power module is powered on. If the temperature of the wire wiring increases, the life of the semiconductor chip and wire bonding may be reduced due to the temperature cycle of heating and cooling, or the wire wiring itself may melt.

[0007] The present invention is proposed to solve the above-mentioned problem, and its purpose is to improve the heat dissipation of metal wires on the semiconductor chip of the power module.

[0008] The power module of the present invention comprises: a base plate; an insulating substrate, which is arranged on the base plate and has a circuit pattern; at least one semiconductor chip, which is mounted on the circuit pattern of the insulating substrate; a plurality of metal wires, which are connected to the surface of the semiconductor chip; and a heat conductive sheet, which contacts the metal wires from above, the metal wires comprising: at least one first metal wire, which connects the surface of the semiconductor chip to the circuit pattern; and at least one second metal wire, which connects two points on the surface of the semiconductor chip and has the same potential as the first metal wire, the heat conductive sheet comprises a graphite sheet, and the sheet surface of the heat conductive sheet contacts the at least one first metal wire and the at least one second metal wire.

[0009] Effects of the Invention

[0010] In the power module of the present invention, the sheet surface of the heat conductive sheet including the graphite sheet is in contact with at least one first metal wire and at least one second metal wire. Therefore, the heat of the second metal wire is conducted to the first metal wire through the graphite sheet, and the heat is dissipated from the first metal wire to the circuit pattern, thereby preventing the temperature of the second metal wire from rising. In this way, the heat dissipation of the metal wire on the semiconductor chip is improved. The purpose, features, scheme and advantages of the present invention will become clearer through the following detailed description and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a cross-sectional view of the power module according to the first embodiment.

[0012] Figure 2 It is an isometric projection diagram of a power module according to Embodiment 2.

[0013] Figure 3 This is a top view of a power module according to Embodiment 2.

[0014] Figure 4 It is an isometric projection diagram of the power module according to the second embodiment from which the graphite sheet is removed.

[0015] Figure 5 It is a diagram showing the structure of a thermally conductive sheet of a power module according to a third embodiment.

[0016] Figure 6 This is a top view of a power module according to a fourth embodiment. DETAILED DESCRIPTION

[0017] <A. Implementation method 1>

[0018] Figure 1 1 is a cross-sectional view of a power module 101 according to Embodiment 1. The power module 101 includes a base plate 1 , an insulating substrate 7 , a diode chip 81 , transistor chips 9 a 1 , 9 b 1 , metal wires 10 a , 10 b , 10 c , a graphite sheet 11 , a case 12 , and a sealing material 13 .

[0019] An insulating substrate 7 is formed on the upper surface of the base plate 1. The insulating substrate 7 is configured to include an insulating base material 4, a lower surface pattern 2 made of metal and bonded to the lower surface of the insulating base material 4 via a bonding material 3, and circuit patterns 6a, 6b, and 6c made of metal and bonded to the upper surface of the insulating base material 4 via a bonding material 5. The lower surface pattern 2 of the insulating substrate 7 is formed on the upper surface of the base plate 1.

[0020] The diode chip 81 and the transistor chips 9a1 and 9b1 are bonded to the circuit pattern 6b by bonding materials such as solder or sintered materials. The diode chip 81 functions as a freewheeling diode for the transistor chips 9a1 and 9b1. Here, the diode chip 81 and the transistor chips 9a1 and 9b1 are examples of semiconductor chips. Other semiconductor chips may be mounted on the power module 101 instead of these semiconductor chips, or one semiconductor chip may be mounted.

[0021] Wire wiring implemented by metal wires is formed on the upper surface of the semiconductor chip. Among the metal wires connected to the upper surface of the semiconductor chip, the metal wire connecting the diode chip 81 and the circuit pattern 6a is set as a metal wire 10a. The metal wire 10a is also called the first metal wire. In addition, the metal wire connecting two locations on the diode chip 81, connecting the diode chip 81 and the transistor chip 9a1, connecting two locations on the transistor chip 9a1, connecting the transistor chip 9a1 and the transistor chip 9a2, and connecting two locations on the transistor 9a2 is set as a metal wire 10b. The metal wire 10b is also called the second metal wire. In addition, the transistor chip 9a2 is connected to the circuit pattern 6c through the metal wire 10c.

[0022] The metal wire 10c is a gate wire that connects the gate electrode of the transistor chip 9a2 to the circuit pattern 6c, and has the same potential as the gate electrode (hereinafter, also referred to as "gate potential"). In contrast, the metal wires 10a and 10b have the same potential as the emitter electrode of the transistor chip 9a2 (hereinafter, also referred to as "emitter potential").

[0023] The graphite sheet 11 is disposed on the metal wires 10a and 10b connected to the upper surface of the semiconductor chip in such a manner that the sheet surface is in contact with the metal wires 10a and 10b. The graphite sheet 11 is an anisotropic thermally conductive material having a thermal conductivity as low as 1 W / mK in the thickness direction and a thermal conductivity of 500 W / mK or more in the surface direction. Therefore, the heat of the metal wire 10b is conducted to the metal wire 10a through the graphite sheet 11, and then dissipated from the metal wire 10a to the circuit pattern 6a. Thus, the temperature of the metal wire 10b can be reduced. Thus, with respect to the power module 101, the graphite sheet 11 functions as a thermally conductive sheet that conducts the heat of the metal wire 10b in the surface direction. In addition, the graphite sheet 11 is not in contact with the metal wire 10c because the metal wire 10c is at a different potential from the metal wires 10a and 10b.

[0024] The base plate 1 is fitted into the housing 12, and the base plate 1, the insulating substrate 7, the diode chip 81, the transistor chips 9a1, 9b1, the metal wires 10a, 10b, 10c, and the graphite sheet 11 are accommodated by the housing 12. The inside of the housing 12 is filled with a packaging material 13 composed of gel or epoxy resin, and the diode chip 81, the transistor chips 9a1, 9b1, the metal wires 10a, 10b, 10c, and the graphite sheet 11 are packaged by the packaging material 13.

[0025] exist Figure 1 In the embodiment, the graphite sheet 11 contacts all the metal wires 10b, but the above heat dissipation effect can be obtained as long as it contacts the metal wire 10a and at least one metal wire 10b having the same potential as the metal wire 10a. However, the more metal wires 10b the graphite sheet 11 contacts, the more heat from the metal wires 10b can be dissipated to the circuit pattern 6a.

[0026] Conventionally, the heat generated on the semiconductor chip of the power module is conducted to the base plate 1 through the bonding below the semiconductor chip, and is dissipated from the base plate 1 to the cooling fins. However, if the current flowing through the power module increases, the metal wire becomes hot due to heat conduction from the semiconductor chip or heat generated by the current flowing through the metal wire itself. In contrast, in the power module 101 of the first embodiment, the heat of the metal wire 10b is dissipated in a direction parallel to the surface of the base plate 1 through the graphite sheet 11, so the temperature rise of the metal wire 10b is alleviated.

[0027] As described above, the power module 101 of the first embodiment includes: a base plate 1; an insulating substrate 7, which is provided on the base plate 1 and has circuit patterns 6a, 6b, and 6c; a semiconductor chip, namely a diode chip 81 and transistor chips 9a1 and 9b1, which are mounted on the circuit pattern 6b of the insulating substrate 7; a plurality of metal wires, which are connected to the surface of the semiconductor chip; and a heat conductive sheet, which contacts the metal wires from above. The metal wires include: at least one first metal wire, namely a metal wire 10a, which connects the surface of the diode chip 81 to the circuit pattern 6a; and at least one second metal wire, namely a metal wire 10b, which connects two points on the surface of the semiconductor chip and has the same potential as the metal wire 10a. The heat conductive sheet includes a graphite sheet 11, and the sheet surface of the heat conductive sheet contacts at least one metal wire 10a and at least one metal wire 10b. Therefore, the heat of the metal wire 10b is conducted to the metal wire 10a through the graphite sheet 11, and is dissipated from the metal wire 10a to the circuit pattern 6a, thereby preventing the temperature of the metal wire 10b from rising.

[0028] <B. Implementation method 2>

[0029] Figure 2It is an isometric view of the power module 102 according to the second embodiment. Figure 3 is a top view of the power module 102 . Figure 4 It is an isometric projection diagram showing a state of the power module 102 before the graphite sheet 11 is installed.

[0030] In addition to the structure of the power module 101 of the first embodiment, the power module 102 further includes diode chips 82-88 and transistor chips 9a2-9a8, 9b2-9b8. In other words, the power module 102 is equipped with eight semiconductor chip groups consisting of one diode chip 8n and two transistor chips 9an, 9bn in parallel. In addition, n is a natural number from 1 to 8. The connection conditions of the metal wires in each group of semiconductor chips are the same. Figure 3 A transistor chip is arranged in region 14 , and a diode chip is arranged in region 15 .

[0031] exist Figures 2 to 4 In the figure, the metal wires 10a and 10b are shown as ribbon wires, but they may be a single wire. A wire has fewer restrictions on chip size than a ribbon wire, and can also achieve bonding in an oblique direction.

[0032] The diode chip 8n functions as a freewheeling diode for the transistor chips 9an and 9bn. Figure 4 The middle gate wire, namely the metal wire 10c, is connected to each of the transistor chips 9a1-9a8 from the same circuit pattern 6c.

[0033] These multiple semiconductor chips mounted in parallel are connected by metal wires to form an electrical circuit. Figure 4 In the embodiment, transistor chip 9b1 is connected to transistor chip 9b2 through metal wire 10b1, and transistor chip 9b2 is connected to transistor chip 9a3 through metal wire 10b1. These metal wires 10b1 have the same potential as metal wire 10a, and are also called second metal wires like metal wire 10b. In addition, these multiple semiconductor chips mounted in parallel are energized at the same time to achieve a high current for power module 102. However, the bonding point of the metal wire 10b1 is heated due to the simultaneous energization of the semiconductor chips at both ends, and when the metal wire 10b1 itself is energized, the temperature becomes higher than that of the semiconductor chip.

[0034] In this regard, with respect to the power module 102, in addition to the features of embodiment 1, the graphite sheet 11 is formed on the upper portion of the metal wire 10b1 that connects the group of transistor chips 9a1, 9b1, and diode chip 81 to the group of transistor chips 9a2, 9b2, and diode chip 82 in contact with the metal wire 10b1.

[0035] As described above, the power module 102 of the second embodiment includes a plurality of semiconductor chips, namely transistor chips 9b1-9b8, whose control terminals, namely gate terminals, are connected to the same circuit pattern 6a or a circuit pattern of the same potential, and the sheet surface of the heat conductive sheet is in contact with the second metal wire, namely metal wire 10b1, which connects the transistor chips 9b1-9b8. The semiconductor chips 9b1-9b8 at both ends of the metal wire 10b1 are energized at the same time and generate heat, so that sometimes the metal wire 10b1 becomes higher in temperature than the semiconductor chips 9b1-9b8, but the heat of the metal wire 10b1 is conducted to the metal wire 10a through the graphite sheet 11, and the heat is dissipated from the metal wire 10a to the circuit pattern 6a, thereby suppressing the temperature rise of the metal wire 10b1. As a result, the product life of the power module 102 can be extended.

[0036] <C. Implementation method 3>

[0037] In the power modules 101 and 102 of the first and second embodiments, the heat conducting sheet is composed of a single body of the graphite sheet 11. In contrast, in the power module of the third embodiment, Figure 5 As shown in FIG. 1 , the heat conducting sheet is formed by a cladding material composed of a stack of graphite sheets 11 and metal films 16. Figure 5 In the figure, the metal film 16 is shown as the lower layer and the graphite sheet 11 is shown as the upper layer, but the graphite sheet 11 may be the lower layer and the metal film 16 may be the upper layer. The structure of the power module of the third embodiment except the thermal conductive sheet is the same as the power modules 101 and 102 of the first or second embodiment.

[0038] The material of the graphite sheet 11 itself has low strength and is brittle. Therefore, if the heat conductive sheet is formed of the graphite sheet 11 alone, the state will change due to the processing of the shape or the handling during assembly, and there is a concern that the yield rate during product assembly will deteriorate. Therefore, the heat conductive sheet is formed of a cladding material in which the graphite sheet 11 and the metal film 16 are stacked, so that the shape of the heat conductive sheet can be processed or assembled in a state with high strength due to the metal film 16. In addition, the high thermal conductivity in the surface direction of the graphite sheet 11 suppresses the heat generation of the metal wires 10b and 10b1.

[0039] The thickness of the metal film 16 is preferably 100 μm, and the thickness of the graphite sheet 11 is preferably 100 μm or more and 400 μm or less. Thus, the thermally conductive sheet has an appropriate thickness, and thus the shape can be easily changed or arranged to match the wiring material.

[0040] <D. Implementation method 4>

[0041] Figure 6FIG. 1 is a top view of a power module 104 according to a fourth embodiment. The power module 104 according to the fourth embodiment differs from the power module 102 according to the second embodiment in that a hole 15 penetrating the surface of the graphite sheet 11 is formed. Figure 6 Although eight holes 15 are formed therein, it is sufficient that at least one hole 15 is formed.

[0042] When forming the power module 104, as Figure 1 As shown, the housing 12 is filled with a packaging material 13. If bubbles are contained inside the packaging material after hardening, the insulation quality of the power module will be reduced depending on the position where the bubbles are generated. In the case of the power module 104, bubbles generated between the graphite sheet 11 and the semiconductor chip can escape to the top of the graphite sheet 11 through the holes 15 of the graphite sheet 11, and then escape from the packaging material 13. In order to allow the bubbles to escape, the diameter of the hole 15 is preferably greater than or equal to 1.0 mm. In addition, the outer periphery of the hole 15 is preferably away from the position of the graphite sheet 11 that contacts the metal wires 10a and 10b by an amount greater than or equal to 1.0 mm. If the hole 15 is deliberately set at a position where bubbles are likely to remain, the effect of allowing the bubbles to escape can be easily obtained.

[0043] In addition, this embodiment can also be combined with Embodiment 3. That is, in this embodiment, the heat conductive sheet can also be made of a cladding material of the graphite sheet 11 and the metal film 16, and the hole 15 that penetrates the graphite sheet 11 and the metal film 16 is formed on the sheet surface of the heat conductive sheet. In this case, the heat conductive sheet has high strength due to the metal film 16, so it is easy to process the hole 15, and it is possible to reduce the defectiveness of the component itself.

[0044] That is, the power module 104 of the fourth embodiment comprises: a housing 12 which is fitted with the base plate 1 and accommodates the insulating substrate 7, the semiconductor chips 81, 9a1, 9b1, the metal wires 10a, 10b, and the thermally conductive sheet; and a sealing material 13 which is filled in the housing 12 and seals the semiconductor chips, the metal wires 10a, 10b, and the thermally conductive sheet, and a hole 15 which penetrates the sheet surface is formed at a position of the thermally conductive sheet which does not overlap with the metal wires 10a, 10b. Thus, bubbles generated between the graphite sheet 11 and the semiconductor chip and which affect the insulation quality of the power module can be released to the top of the graphite sheet 11 and then released from the sealing material 13.

[0045] In addition, the present invention can freely combine various embodiments within the scope of the present invention, or appropriately modify or omit various embodiments. The present invention has been described in detail, but the above description is illustrative in all aspects, and the present invention is not limited thereto. It can be understood that countless unillustrated variations can be thought of without departing from the scope of the invention.

[0046] Description of the label

[0047] 1 base plate, 2 lower surface pattern, 3, 5 bonding materials, 4 insulating substrate, 6a, 6b, 6c circuit pattern, 7 insulating substrate, 9a1-9a8, 9b1-9b8 transistor chips, 10a, 10b, 10b1, 10c metal wires, 11 graphite sheet, 12 shell, 13 packaging material, 16 metal film, 17 hole, 81-88 diode chip, 101, 102, 104 power module.

Claims

1. A power module, comprising: Base plate; an insulating substrate, which is disposed on the base plate and has a circuit pattern; at least one semiconductor chip mounted on the circuit pattern of the insulating substrate; A plurality of metal wires connected to the surface of the semiconductor chip; as well as a heat conductive sheet, which contacts the metal wire from above, The metal wire has: at least one first metal wire connecting the surface of the semiconductor chip to the circuit pattern; as well as at least one second metal wire, which connects two points on the surface of the semiconductor chip and has the same potential as the first metal wire, The thermally conductive sheet comprises a graphite sheet, The sheet surface of the thermally conductive sheet is in contact with at least one of the first metal wires and at least one of the second metal wires.

2. The power module according to claim 1, wherein: The semiconductor chip includes a plurality of semiconductor chips whose control terminals are connected to the same circuit pattern or the circuit pattern with the same potential, The sheet surface of the thermally conductive sheet is in contact with the second metal wire that connects the plurality of semiconductor chips.

3. The power module according to claim 1 or 2, wherein: The heat conductive sheet is a cladding material formed by laminating a metal film and the graphite sheet.

4. The power module according to claim 3, wherein: The thickness of the metal film is 100 μm. The graphite sheet has a thickness greater than or equal to 100 μm and less than or equal to 400 μm.

5. The power module according to any one of claims 1 to 4, wherein: Also features: A housing, which is engaged with the base plate and houses the insulating substrate, the semiconductor chip, the metal wire, and the heat conducting sheet; as well as The packaging material is filled in the housing to package the semiconductor chip, the metal wire and the heat conducting sheet. A hole penetrating the sheet surface is formed at a position of the thermally conductive sheet that does not overlap with the metal wire.

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