JP2003218291A - Semiconductor device and method of manufacturing the same - Google Patents

Abstract

(57) [Problem] To provide a method of manufacturing a semiconductor device having excellent heat dissipation performance in a semiconductor device in which a semiconductor element is mounted on a bus bar integrated by a mold member. SOLUTION: First, a plurality of bus bars 11 to 13 are molded resin 1 so that their front and back surfaces are exposed.
And integrated. Secondly, a heat radiation resin 8 having high thermal conductivity is applied to the entire back surfaces of the integrated bus bars 11 to 13 and the mold member 1 and cured. Third, the heating surface 15a of the heater 15 is provided on the surface 8a of the heat dissipation resin 8.
a is brought into contact with the heat-dissipating resin 8 to make it uniform by heat treatment.
Thereby, the bus bars 11 to 13 and the mold member 1
The adhesion between the back surface of the heat dissipation resin 8 and the heat dissipation resin 8 is improved, and the front surface 8a of the heat dissipation resin 8 is flattened by the heating surface 15a. After that, the semiconductor element 22 is mounted on the bus bar 12 and fixed to the cooling surface of the heat sink.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device in which a semiconductor element is mounted on a bus bar integrated by a molding member, and a manufacturing method thereof.

[0002]

2. Description of the Related Art A semiconductor device in which a semiconductor element is mounted on a bus bar and the bus bar is molded with a resin is disclosed in Japanese Patent Application Laid-Open No. 2-212058
The one disclosed in Japanese Patent Application Laid-Open No. 001-110985 is known. The plurality of bus bars are integrated by resin molding to form one module. The front and back surfaces of each bus bar are exposed, a semiconductor element is joined to the front surface of the bus bar by soldering, and the back surface side is fixed to a cooling surface such as a heat sink. An electrically insulating heat dissipation sheet is provided between the bus bar and the cooling surface.

[0003]

By the way, each bus bar is molded such that the back surface of the bus bar projects beyond the molding member so that the contact between the bus bar and the heat dissipation sheet is ensured. Therefore, the back surface of the module is not flat but has an uneven shape. As a result, there is a drawback in that the adhesion between the heat dissipation sheet and the bus bar is impaired and an air layer is generated between the bus bar and the heat dissipation sheet. Further, the contact surfaces of the bus bar, the heat dissipation sheet, and the heat sink are not smooth when viewed microscopically, but are uneven surfaces, and the contact state can be regarded as substantially consisting of many point contact portions.

As a result, the actual contact area becomes smaller than it appears, and the air layer also intervenes in the gap between the microscopically uneven surfaces. Since the thermal conductivity of air is much smaller than that of a heat dissipation sheet, it may not be possible to efficiently transfer heat from the bus bar to the heat sink, and sufficient heat dissipation performance may not be obtained for the heat generated by the semiconductor element. It was

An object of the present invention is to provide a semiconductor device having excellent heat dissipation performance and a manufacturing method thereof.

[0006]

An embodiment of the invention will be described with reference to FIGS. (1) Describing in association with FIG. 3, the semiconductor device according to the invention of claim 1 is a semiconductor mounting in which a plurality of bus bars 11 to 13 are molded by a molding member so that their front and back surfaces are exposed and integrated. Part 10 and bus bar 12
The semiconductor element 22 mounted on the surface of the
No. 0 busbars 11 to 13 and a heat-dissipating resin 8 having high thermal conductivity that covers the entire back surface of the molding member 1, and a cooling device in which the semiconductor mounting portion 10 is mounted so that the surface of the heat-dissipating resin 8 contacts the cooling surface 2b. And 2 to achieve the above-mentioned object. (2) When it is described in association with FIG. 8, the invention of claim 2 is the semiconductor device according to claim 1, wherein the back surface 1e of the mold member 1 is provided with irregularities. (3) Describing in association with FIG. 10, the invention according to claim 3 is the semiconductor device according to claim 1 or 2, wherein the heat dissipation resin 8 has a thickness such that other parts are thinner than the middle part. It is a convex surface. (4) Describing in association with FIG. 9, the invention of claim 4 is, in the semiconductor device according to any one of claims 1 to 3, sandwiched between the surface 8a of the heat dissipation resin 8 and the cooling surface 2b. Thus, the foil 17 of the heat conductive material is provided. (5) When it is described in association with FIGS.
The method for manufacturing a semiconductor device according to the invention comprises a first step (FIG. 4A) in which a plurality of bus bars 11 to 13 are molded and integrated with a molding member 1 so that their front and back surfaces are exposed, A second step (FIG. 4B) of covering the entire back surfaces of the integrated bus bars 11 to 13 and the molding member 1 with the heat-dissipating resin 8 having high thermal conductivity, and the heat-dissipating resin 8
Third step of heating the heat radiation resin 8 by bringing the heating surface 15a of the heating device 15 into contact with the front surface 8a of the heating device 15 (FIG. 4C)
And a fourth step of mounting the semiconductor element 22 on the surface of the bus bar 12 (FIG. 4C), and a fifth step of fixing the cooling surface 2b of the cooling device 2 to the surface 8a of the heat dissipation resin 8. To achieve the above object.

[0007]

(1) According to the invention of claim 1, the heat radiation resin adheres to the entire back surface of the bus bar and the molding member, so that the heat transfer performance from the semiconductor mounting portion to the heat radiation resin is improved. (2) In the invention of claim 2, in addition to the effect of the invention of claim 1, the contact area between the mold member and the heat dissipation resin is increased, and the heat transfer performance to the heat dissipation member via the mold member is further improved. improves. (3) In the invention of claim 3, in addition to the effects of the inventions of claims 1 and 2, it is possible to prevent air from remaining between the heat-dissipating resin and the cooling surface. Heat transfer performance is improved. (4) In the invention of claim 4, in addition to the effects of the inventions of claims 1 to 3, the foil serves as a cushioning agent against the entrapment of foreign matter or the like, so that an electrical short circuit occurs between the bus bar and the cooling device. Can be prevented. (5) According to the invention of claim 5, the heat treatment of the heat dissipation resin improves the adhesion between the heat dissipation resin covering the entire back surface of the bus bar and the mold member and the bus bar and the mold member. Further, the surface of the heat dissipation resin can be flattened by the heating surface, and the adhesion with the cooling surface can be improved. As a result, the heat radiation effect from the semiconductor mounting part to the cooling device can be improved.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a part of a power converter circuit of an inverter that converts direct current P, N into alternating current U, V, W by using semiconductor elements 21, 22. It shows a portion related to a phase component, for example, a U phase. In the example shown in FIG. 1, the semiconductor elements 21 and 22 are
MOSFET is used. 11 is a bus bar for P pole, 1
2 is a bus bar for inverter output, and 13 is a bus bar for N pole. Further, 51 and 52 are semiconductor elements 21 and 2.
2 is a gate terminal for applying a driving signal to each of the gates G of 2.

FIG. 2 is a perspective view showing a mounting structure of a portion corresponding to the circuit shown in FIG. The semiconductor element 21 is mounted on the upper surface of the P pole bus bar 11, and the semiconductor element 22 is mounted on the upper surface of the inverter output bus bar 12.
The busbars 11 to 13 are integrated by the molding resin 1 which is a molding member, and the module case 10 which is a semiconductor mounting portion is formed. Since the bus bars 11 to 13 have different potentials, they are arranged at intervals so that they do not contact each other. The mold resin 1 also has a function of electrically insulating between the bus bars 11 to 13. Bus bars 11-1
It is preferable that the material of 3 has a high thermal conductivity and a low volume resistivity. For example, copper (Cu), aluminum (Al), or an alloy containing these is used.

The semiconductor elements 21 and 22 are surface-bonded on the bus bars 11 and 12 by solders 31 and 32 which are bonding materials, and the drains D formed on the back surfaces of the semiconductor elements 21 and 22 are solder 31 respectively. , 32 are electrically connected to the bus bars 11, 12. Solder 32
Has a function of transmitting heat of the semiconductor element 22 to the bus bar 12 as well as electrical connection, and a conductive paste containing a silver filler may be used instead of the solder.

A source S and a gate G are formed on the upper surfaces of the semiconductor elements 21 and 22. The source S of the semiconductor element 21 is connected to the upper surface of the bus bar 12 by the metal wire 41, and the gate G is connected to the gate terminal 51 by the metal wire 61. On the other hand, the source S of the semiconductor element 22 is connected to the upper surface of the N pole bus bar 13 by the metal wire 42, and the gate G is connected to the gate terminal 52 by the metal wire 62. In this way, the semiconductor element 21,
The module M for one phase is formed by mounting 22.

A heat radiation resin 8 is provided on the back surface side of the module M, and the module M is fixed to the heat sink 2 so as to sandwich the heat radiation resin 8. A flow path 2a through which a coolant such as cooling water flows is formed in the heat sink 2. The heat generated in the semiconductor elements 21 and 22 is transferred to the heat sink 2 via the bus bars 11 and 12 and the heat radiation resin 8 and is radiated to the refrigerant flowing in the flow path 2a.

FIG. 3 is a sectional view taken along the line AA of FIG. 2, in which the module M and the heat sink 2 are shown separated for easy understanding. A plurality of through holes 1b for mounting bolts are formed in the flange portion 1a formed in the peripheral portion of the mold resin 1. The bus bars 11 to 13 integrated with the mold resin 1 are cooled by the bolts 9 on the cooling surface of the heat sink 2. Two
fixed to b. Reference numeral 2c is a mounting screw hole formed in the heat sink 2. The element space formed by the mold resin 1 is filled with a gel member 4 containing silicone as a main component, and the semiconductor elements 21, 22 and the metal wires 41, 42, 61, 62 shown in FIG. It has been stopped. The gel member 4 is not shown in FIG.

The back surfaces of the bus bars 11 to 13 project more than the back surface of the mold resin 1. In this embodiment, a layer of the heat dissipation resin 8 is formed so as to cover the bus bars 11 to 13 and the back surfaces of the mold resin 1. . The heat dissipation resin 8 is mainly composed of a resin having a high heat resistance such as epoxy, and the resin contains ceramics such as alumina (Al ₂ O ₃ ), aluminum nitride (AlN) or a filler of glass. By including these fillers, the thermal conductivity of the heat dissipation resin 8 can be made higher than that of the resin alone.
Further, the thickness of the heat dissipation resin 8 is preferably thin from the viewpoint of heat dissipation, but is preferably thick from the viewpoint of insulation. In the present embodiment, heat resistance, heat dissipation and insulation are secured by setting the thickness to about 0.05 mm to 0.5 mm.

Next, the procedure for manufacturing the semiconductor device will be described with reference to FIG. In the step shown in FIG. 4A, the module case 10 including the bus bars 11 to 13 and the molding resin 1 is formed by injection molding. That is, the integrated module case 10 is formed by inserting the bus bars 11 to 13 into the resin molding die and injecting the molding resin. At this time, molding is performed so that the back surface of the bus bar (the surface on the upper side in the drawing) projects beyond the molding resin 1.

In the step shown in FIG. 4B, a layer of heat dissipation resin 8 is formed on the back surface of the module case 10. When the layer of the heat dissipation resin 8 is formed, it is obtained by printing the heat dissipation resin 8 in a paste form by a metal mask or silk printing and then curing it. The thickness of the heat dissipation resin 8 at this time is controlled by controlling the thickness of the metal mask or silk. As another method of forming the heat dissipation resin 8,
A sheet-shaped uncured heat dissipation resin having a predetermined thickness may be formed in advance, and the sheet-shaped uncured heat dissipation resin may be attached to the back surface of the module case 10 and then cured. In this way, the uncured heat dissipation resin 8 can be used for the module case 10
Since the entire back surface of the heat radiation resin 8 is covered, the adhesion between the heat radiation resin 8 and the respective back surfaces of the bus bars 11 to 13 and the molding resin 1 is improved as compared with the case of using the conventional heat radiation sheet.

In the process shown in FIG. 4C, the bus bar 12
The solder 32 and the semiconductor element 22 are placed in this order on top, and the surface 8a of the heat dissipation resin 8 is brought into contact with the heating surface 15a of the heater 15 to heat it. This heating melts the solder 32,
The semiconductor element 22 and the bus bar 12 are joined. At the same time, the surface of the heat-dissipating resin 8 becomes flat by following the heater surface by heating, and the adhesion to the back surface side of the module case 10 is further improved. That is, the heat radiation resin 8 is slightly softened by heating, and acts to fill the gap. Thereafter, wire bonding and filling of the gel member 4 are performed to form a module M as shown in FIG. Since the surface 8a of the heat dissipation resin 8 is flattened, when the module M is fixed to the heat sink 2 with the bolt 9 as shown in FIG. 3, the surface 8a of the heat dissipation resin 8 and the cooling surface 2b of the heat sink 2 come into close contact with each other.

FIG. 5 is a diagram qualitatively showing the flow of heat from the bus bars 11 and 12 and the mold resin 1 to the heat sink 2. The heat-dissipating resin 8 adheres to the minute recesses of the bus bars 11 and 12, and the heat-dissipating resin 8 also enters the recesses of the back surface of the mold resin 1 and adheres to the back surface of the mold resin 1. Further, since the surface 8a of the heat dissipation resin 8 is also flattened following the heating surface 15a during heating, heat dissipation from the heat dissipation resin 8 to the heat sink 2 is efficiently performed. In addition, since the heat radiation resin 8 is in close contact with the end faces 11a, 12a of the bus bars 11, 12, heat is also radiated from the end faces 11a, 12a to the heat sink 2 as shown in the heat transfer path 16, which improves the heat radiation efficiency. Planned.

When heating the semiconductor elements,
Since the heaters are brought into direct contact with the back surfaces of the bus bars 11 to 13, it is necessary to adjust the flatness of the bus bars during molding with high accuracy. However, in the present embodiment, as described above, the heat radiation resin 8 is in contact with the heater 15, and the heat radiation resin 8 has its contact surface flattened by heating. Therefore, the accuracy required for the flatness of the bus bars can be relaxed, and the heating efficiency can be improved and the heating time can be shortened. As a result, it is possible to avoid variations in the mounting time for each module and reduce the mounting time.

Further, even if the gel member 4 leaks from the boundary surface between the bus bars 11 and 12 and the molding resin 1, the gel member 4 is formed by the heat dissipation resin 8 formed on the back surface side of the module case 10. Can be prevented from leaking out of the module case 10. Further, since the heat dissipation resin 8 is formed so as to fill the irregularities on the back surface side of the module case 10, it is possible to make the pressure distribution uniform when the module M is fixed to the heat sink 2. As a result, the reliability of the insulating layer against pressure is improved.

In consideration of the heat radiation from the end surface of the bus bar as described above, it is better to increase the area of the end surface exposed on the back surface side of the resin mold 1, that is, the protruding dimension t in FIG. That is, the busbars 11 to 13 are made thicker to increase the protrusion dimension t. As a result, the rigidity of the bus bar itself can be increased in addition to the improvement of heat dissipation performance. For example, if the plate thickness is thin, the bus bar may warp during molding, and the bus bar may go around the mounting surface of the bus bar or the contact surface with the heat sink 2. Such a problem can be avoided by increasing the plate thickness. When using a copper-based material for the bus bars 11 to 13, it is desirable that the plate thickness be 0.5 mm or more. Further, the thicker the plate, the larger the heat capacity of the bus bar, and the lower the temperature when the semiconductor element operates. As a result, it is possible to omit the heat spreader, which is conventionally arranged separately under the semiconductor element. Furthermore, since the bus bar cross-sectional area increases, the resistance value in the current path decreases, and the loss due to heat generation of the bus bar itself can be suppressed.

On the other hand, when the module M is attached to the heat sink via the heat dissipation sheet as in the conventional semiconductor device, there is a problem in heat dissipation performance as described below. FIG. 6 is a sectional view when the heat dissipation sheet 3 is used,
It is a figure similar to FIG. Similar to the case of the heat dissipation resin 8, the heat dissipation sheet 3 includes the semiconductor elements 21, 22 to the bus bar 11,
It plays a role of transferring the heat transferred to the heat sink 2 to the heat sink 2 and ensuring electrical insulation between the bus bars 11 and 12 and the heat sink 2.

FIG. 7 is an enlarged view of a portion indicated by reference symbol B in FIG. 6, and schematically shows the contact states of the bus bars 11 and 12, the heat radiation sheet 3 and the heat sink 2 with each other. Since the back surface of the module M is not flat but has an uneven shape, the air layer 5 is formed on the back surface side of the molding resin 1, and the end surfaces 11a of the bus bars 11, 12 are
The heat radiation from 12a could not be expected.

Further, the contact surfaces of the bus bars 11 and 12, the heat radiation sheet 3 and the heat sink 2 are not smooth when viewed microscopically but are uneven surfaces, and the contact state is substantially from a number of point contact portions. Can be considered to consist of Therefore, the actual contact area becomes smaller than it appears, and the air layer 5 also intervenes in the gap between the microscopically uneven surfaces. As a result, the heat of the busbars 11 and 12 is transferred from the point contact portion between the busbar 11 and the heat dissipation sheet to the point contact portion between the heat dissipation sheet 3 and the heatsink 2 as shown by the heat transfer path 6 in FIG. As a result, the heat dissipation performance is deteriorated.

[First Modification] FIG. 8 is a view showing a first modification of the above-described embodiment, and is a sectional view showing a portion similar to that of FIG. In the first modified example, the lower surface 1e of the mold resin 1, that is, the contact surface with the heat dissipation resin 8 has an uneven shape. For example, the surface 1e can be formed into an uneven shape by forming unevenness in the molding die used when molding the module case 10. As a result, the contact area between the mold resin 1 and the heat dissipation resin 8 increases, and the bus bar → mold resin 1 →
The heat radiation through the path from the heat radiation resin 8 to the heat sink 2 increases.

Further, this causes a van der Waals force and an anchor effect between the mold resin 1 and the heat dissipation resin 8. Therefore, for example, polyphenylene sulfide (PPS) is used for the mold resin 1 and epoxy is used for the heat dissipation resin 8. As in the case described above, even if the resins that are difficult to join are used in combination, the contact state on the contact surface can be maintained and peeling or the like can be prevented.

[Second Modification] FIG. 9 is a view showing a second modification and is a sectional view similar to FIG. In the second modification, the foil 17 is added to the surface of the heat dissipation resin 8 that contacts the heat sink 2. The foil 17 is preferably made of a relatively soft material and has a high thermal conductivity, and is preferably easily available. For example, aluminum (Al), copper (Cu), or an alloy foil containing these as main components is preferable. By providing such a foil 17, even when a fine foreign substance (particularly a conductive foreign substance) is caught when the module 4 is mounted on the heat sink 2, the foil 17 is plastically deformed to cause the module case 10 to be inserted. The bottom surface of the can be closely attached to the surface of the heat sink 2. Also, the foil 17
Since it serves as a cushioning material, there is no possibility that stress concentrates on the portion where the foreign matter is sandwiched and the heat dissipation resin 8 is cracked. Therefore, even if a conductive foreign matter is sandwiched, there is no possibility that an electrical short circuit will occur between the module M and the heat sink 2.

[Third Modification] FIG. 10 is a sectional view showing a third modification. In the third modified example, the shape of the heat dissipation resin 18 is different from that of the heat dissipation resin 8 described above. In the case of the heat dissipation resin 18, the shape of the surface 18a that contacts the heat sink 2 is a convex surface such that the central portion of the module case 10 is thickest. When the heat dissipation resin 18 is manufactured using a metal mask or silk printing, such a convex surface can be obtained by changing the thickness of the mask. Further, when the sheet-shaped heat dissipation resin 18 is separately manufactured, a molding die processed so as to be convex toward the central portion of the module may be used.

When the semiconductor element is mounted on the bus bar, a concave-shaped special jig that is in close contact with the convex surface 18a of the heat dissipation resin 18 is mounted on the module M, and the special jig is heated by a heater to form a semiconductor. It suffices to bond the element to the bus bar. The dedicated jig is formed of carbon, copper (Cu) having a high thermal conductivity, or the like.

When fixing the module M to the heat sink 2, the bolt 9 is tightened to dissipate the heat radiation resin 18.
Is deformed and the surface 18a becomes flat, and the air in the gap between the module M and the heat sink 2 is pushed out from the central portion of the module to the peripheral portion. Therefore, module M
Air can be prevented from remaining between the heat sink 2 and the heat sink 2, and the heat dissipation performance can be improved. When fixing the module M to the heat sink 2, the bolt 9 is urged while biasing the module M toward the heat sink 2.
May be tightened.

In the above-described embodiment, the inverter 1
Although the circuit for the phase has been described as an example, the present invention can be applied to any structure in which a plurality of bus bars are integrally molded by resin molding and the bus bars are cooled by a cooling device.

[Brief description of drawings]

FIG. 1 is a diagram showing a circuit for one phase in an inverter.

FIG. 2 is a perspective view showing a mounting structure of a portion corresponding to the circuit shown in FIG.

FIG. 3 is a cross-sectional view of the semiconductor device shown in FIG.

FIG. 4 is a diagram illustrating a manufacturing procedure of the semiconductor device,
Each step is shown in (a) to (c).

FIG. 5 is a diagram qualitatively showing heat flows from the bus bars 11 and 12 and the mold resin 1 to the heat sink 2.

FIG. 6 is a cross-sectional view when a heat dissipation sheet 3 is used.

FIG. 7 is an enlarged view of a portion indicated by reference numeral B in FIG.

FIG. 8 is a sectional view showing a first modified example.

FIG. 9 is a sectional view showing a second modification.

FIG. 10 is a sectional view showing a third modification.

[Explanation of symbols]

1 Mold resin 2 heat sink 2b Cooling surface 3 heat dissipation sheet 4 Gel member 5 air layer 8,18 Heat dissipation resin 10 module case 11-13 Busbar 15 heater 17 foil 21,22 Semiconductor element M module

Claims (5)

[Claims] 1. A semiconductor mounting part in which a plurality of bus bars are molded and integrated with a molding member so that their front and back surfaces are exposed, a semiconductor element mounted on the surface of the bus bar, and a semiconductor mounting part of the semiconductor mounting part. A semiconductor device comprising: a heat-dissipating resin having a high thermal conductivity, which covers the entire back surface of a bus bar and a molding member; and a cooling device in which the semiconductor mounting portion is mounted so that a surface of the heat-dissipating resin contacts a cooling surface. 2. The semiconductor device according to claim 1, wherein unevenness is formed on the back surface of the mold member. 3. The semiconductor device according to claim 1, wherein the thickness of the heat dissipation resin is a convex surface such that other portions are thinner than the middle portion. 4. The semiconductor device according to claim 1, wherein a foil of a heat conductive material is provided so as to be sandwiched between the surface of the heat dissipation resin and the cooling surface. Semiconductor device. 5. A first step of molding a plurality of bus bars with a molding member so as to expose the front surface and the back surface of the bus bars, and integrating the bus bars and the back surfaces of the integrated bus bar and the molding member with high thermal conductivity. A second step of covering with a conductive heat-dissipating resin, a third step of heating the heat-dissipating resin by bringing a heating surface of a heating device into contact with the surface of the heat-dissipating resin, and a semiconductor on the surface of the bus bar. A method of manufacturing a semiconductor device, comprising: a fourth step of mounting an element; and a fifth step of fixing a cooling surface of a cooling device to the surface of the heat dissipation resin.