JP2002237556A - Power semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reliable power semiconductor device which has reduced thermal stress and thermal strain caused by the difference in the coefficient of linear expansion between members and which can dissipate efficiently and stably heat generated by a power semiconductor element through effective conduction of heat. SOLUTION: The bottom surface of an insulation substrate 11, having a small coefficient of linear expansion which is mounted with the power semiconductor element 10, and a metal base plate 15 having a large coefficient of linear expansion which will become a heat dissipation plate are bonded to each other via a heat-conductivity type porous metal plate 22, having through-holes into which columnar heat conductors 24 are inserted. By separating each columnar heat conductor 24 from the sidewall of each through-hole 23 by a very small gap 23a, thermal stress is lowered while at the same time the thermal conductivity is maintained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power semiconductor device used for power conversion, motor drive, and the like, and more particularly to a power semiconductor device having a plurality of semiconductor elements mounted thereon and having a cooling mechanism.

[0002]

2. Description of the Related Art As an example of a conventional power semiconductor device,
General-purpose IGBT (Insulated Gate Bipolar Transisto)
r) A cross-sectional view of a power semiconductor device using a module is shown in FIG. In FIG. 6, reference numeral 1 denotes an IGBT module which is one of power modules, 2 denotes an IGBT element which is one of power semiconductor elements, and 3 denotes an IGBT element made of alumina, aluminum nitride, or the like having a metal foil such as copper bonded to both surfaces. An insulating substrate,
Reference numeral 4 denotes a heat-dissipating metal base plate made of molybdenum, tungsten, or the like, 5 denotes cooling means such as a heat sink, 6 and 7 denote solder, and 8 denotes a compound such as heat conductive grease. As shown in the figure, a plurality of IGBT elements 2 are mounted on a heat-dissipating metal base plate 4 via an insulating substrate 3 and are covered with a resin (not shown) to constitute an IGBT module 1. Further, the IGBT element 2 is bonded on the insulating substrate 3, and the insulating substrate 3 is bonded on the metal base plate 4 for heat radiation with solders 6 and 7, and the metal base plate 4 for heat radiation is pressed against the cooling means 5 via the compound 8. Have been. During operation of the IGBT module 1, heat generated in the IGBT element 2 is conducted to the cooling means 5 via the insulating substrate 3 and the metal base plate 4 for heat dissipation, and is cooled. Also, as another structure of the power module,
There is a press-contact stack type in which cooling means such as a heat sink is attached to both sides of a power module such as a GTO (Gate Turn-Off Thyristor) and each connection portion is connected by external pressure.

[0003]

SUMMARY OF THE INVENTION These IGBT modules
In the internal structure of the tool 1, the joints due to temperature changes during operation
In order to reduce the thermal stress of
Uses a material that is close to the rate. I of IGBT module 1
The linear expansion coefficient of the GBT element 2 is about 3 × 10 ^-6/
K, the coefficient of linear expansion of the insulating substrate 3 is about 4 × 10
^-6/ K, the coefficient of linear expansion of the metal base plate 4 for heat radiation is molybdenum
About 4.9 × 10^-6/ K, about 4.6 for tungsten
× 10^-6/ K. In addition, cooling hand such as heat sink
Step 5 is made of metal with high thermal conductivity, such as copper or aluminum
However, metals with high thermal conductivity generally have a high coefficient of linear expansion.
And the coefficient of linear expansion is about 17.1 × 10^-6/ K, A
About 24.4 × 10 in Lumi^-6/ K and IGBT module
The difference from the coefficient of linear expansion of 1 is very large. Thus IGB
The parts used between the T module 1 and the cooling means 5
The difference in the coefficient of linear expansion of the material is large, and heat changes due to temperature changes during operation.
A difference in elongation occurs. Therefore, the IGBT module 1
Use no compound between the cooling means 5 and the compound.
Pressure contact through the metal 8 reduces thermal stress and thermal strain.
It was sum.

However, the compound 8, which is interposed between the IGBT module 1 and the cooling means 5 and thermally connects the two, has a low thermal conductivity of about 1 to several Watt / m · K and a low cooling performance. . Further, the dimensions between the IGBT module 1 and the cooling means 5 change due to thermal deformation, and the cooling performance is not stable. This tendency is due to high voltage
The amount of heat generated from the semiconductor element has increased with the increase in capacity such as the increase in current and cycle, and the number of heat cycles has also increased in recent years, from the viewpoint of long-term reliability.
It has been difficult to stably and efficiently release the heat generated by the IGBT module 1 to the outside.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and it is intended to reduce thermal stress and thermal strain caused by a difference in linear expansion coefficient between members and to generate heat of a power semiconductor element. It is an object of the present invention to obtain a highly reliable power semiconductor device capable of stably and efficiently dissipating heat by good heat conduction.

[0006]

Means for Solving the Problems Claim 1 according to the present invention.
In the power semiconductor device described above, the lower surface of the insulating substrate on which the power semiconductor element is mounted and the heat conductive metal radiator plate are interposed with a heat conductive porous metal plate having a hole occupancy of 30 to 80%. They are joined.

According to a second aspect of the present invention, there is provided the power semiconductor device according to the first aspect, wherein the hole of the heat conductive porous metal plate is spherical or extends substantially perpendicular to the surface of the porous metal plate. It is a cavity of a shape.

According to a third aspect of the present invention, there is provided a power semiconductor device, wherein a lower surface of an insulating substrate on which a power semiconductor element is mounted and a heat conductive metal radiating plate are joined via a heat conductive porous metal plate. The porous metal plate includes a cavity penetrating in a direction substantially perpendicular to a surface of the porous metal plate, and a columnar heat conductive metal penetrating from one surface of the porous metal plate to another surface is formed in the cavity. It is disposed apart from the side wall by a minute gap.

A power semiconductor device according to a fourth aspect of the present invention is the power semiconductor device according to the third aspect, wherein the power semiconductor device is provided between the heat conductive metal in the cavity and the side wall of the cavity in a range from room temperature to the operating temperature of the power semiconductor element. Thus, the gap is secured and the separated state continues.

According to a fifth aspect of the present invention, in the power semiconductor device according to the fourth aspect, the heat conductive metal in the cavity has a lower melting point and a higher linear expansion coefficient than the metal material of the porous metal plate. It is made of a material, and is formed by filling the above cavity by a melt impregnation method.

According to a sixth aspect of the present invention, there is provided the power semiconductor device according to any one of the first to fifth aspects, wherein the aperture ratio of the hole (cavity) of the porous metal plate is more outer than the center of the metal plate. It is big in part.

A power semiconductor device according to a seventh aspect of the present invention is the power semiconductor device according to any one of the first to sixth aspects, wherein a buffer plate made of molybdenum or tungsten is joined to the insulating substrate side of the porous metal plate. It is.

According to an eighth aspect of the present invention, in the power semiconductor device according to the seventh aspect, the bonding between the porous metal plate and the buffer plate is performed by cladding.

According to a ninth aspect of the present invention, there is provided the power semiconductor device, wherein the lower surface of the insulating substrate on which the power semiconductor element is mounted and the heat conductive metal radiating plate are formed by forming a large number of columnar heat conductive metals with fine gaps. The insulating substrate is joined to the insulating substrate via a layer that is vertically separated from the insulating substrate.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view of a power semiconductor device according to Embodiment 1 of the present invention.
In FIG. 1, reference numeral 9 denotes an IG which is one of the power modules.
BT module, 10 is IG as power semiconductor element
The BT element 11 has a metal foil such as copper adhered to both sides thereof,
An insulating substrate made of alumina or aluminum nitride, 12 a buffer plate made of molybdenum or tungsten, 13 a heat conductive porous metal plate made of copper or aluminum, 14
Is a through hole as a cavity provided in the porous metal plate 13 and penetrates in a direction from the surface of the porous metal plate 13 to the back surface. Reference numeral 15 denotes a metal base plate as a heat conductive metal radiating plate made of a copper plate or an aluminum plate, and 16 denotes a cooling means such as a heat sink made of copper or aluminum. 17 to 20 are solder for joining, 2
Reference numeral 1 denotes a clad joint between the buffer plate 12 and the porous metal plate 13.

As shown in the drawing, a plurality of IGBT elements 10
Is mounted on the metal base plate 15 via the insulating substrate 11. The insulating substrate 11 and the metal base plate 15
2 and a thermally conductive porous metal plate 13 having through holes 14 with a predetermined in-plane occupancy. The structure on the metal base plate 15 is covered with a resin (not shown) to form the IGBT module 9. Also, IGBT
The element 10 is on the insulating substrate 11, and the insulating substrate 11 is
2 are joined by solders 17 and 18, respectively,
The metal plate 2 and the porous metal plate 13 are joined by a clad joint 21 which strongly joins metals of different materials by pressure at the interface. Further, the porous metal plate 13 is a metal base plate 15.
The metal base plate 15 is joined to the cooling means 16 by solder 20.

In the power semiconductor device configured as described above, the heat generated in the power semiconductor element 10 during operation passes through the insulating substrate 11, the buffer plate 12, the porous metal plate 13, and the metal base plate 15 by heat conduction in order, and the cooling means. It is conducted to 16 and cooled. In this heat conduction path, as described above, the power semiconductor element 10 made of silicon or the like and the insulating substrate 11 made of aluminum nitride or the like have a small coefficient of linear expansion, and the cooling means 16 made of copper or aluminum has a large coefficient of linear expansion. . In this embodiment, the metal base plate 15 on the cooling means 16 is made of a thermally conductive metal having a large linear expansion coefficient such as copper or aluminum. The buffer plate 12 and the porous metal plate 13 were inserted between the insulating substrate 11.

The porous metal plate 13 is made of a heat conductive metal having a high thermal conductivity and a high coefficient of linear expansion, such as copper and aluminum, and is substantially perpendicular to the surface of the porous metal plate 13 as shown in FIG. It has a through hole 14 that penetrates. The diameter of the through hole 14 is about 1 μm to 5 mm and the in-plane occupancy is about 30 to 80%. The porous metal plate 13 has rigidity because of the through hole 14 having the relatively large in-plane occupancy. It is low and easy to bend. For this reason, as shown in FIG. 3 due to a temperature change during operation, the difference in thermal expansion between the metal base plate 15 having a large linear expansion coefficient and the insulating substrate 11 having a small linear expansion coefficient can be absorbed, and the stress can be reduced. Further, a buffer plate 12 inserted into the insulating substrate 11 side of the porous metal plate 13 is provided.
Is made of a material having a low linear expansion coefficient and high rigidity such as molybdenum and tungsten, so that the effect of thermal stress on the insulating substrate 11 can be further reduced, and the bonding between the buffer plate 12 and the insulating substrate 11 by soldering The thermal stress generated in the part is reduced to improve long-term reliability. The material of the buffer plate 12 has good thermal conductivity (molybdenum thermal conductivity; 138 Watt / mK). Furthermore, since the buffer plate 12 is firmly bonded at the interface with the porous metal plate 13 and the clad, the reliability of the bonding portion 21 is high, and the buffer plate 12 and the porous metal plate 13 are stable and good. High thermal conductivity is obtained.

As described above, the buffer plate 12 and the porous metal plate 13 can alleviate the thermal stress caused by the difference in the coefficient of linear expansion between the metal base plate 15 and the insulating substrate 11, and can reduce the IG.
The heat generated by the BT element 10 can be stably and efficiently radiated by good heat conduction.

By the way, the porous metal plate as described above is made of a material in which the solubility of gas atoms is large in a liquid metal and which solidifies when transformed into a solid and has a low solid solubility of gas atoms, in a high-pressure gas (hydrogen or oxygen) atmosphere. It is formed by dissolving and coagulating in a pore.
５5 mm, and the in-plane occupancy is about 30-80%.
In addition, when the molten metal poured into the mold at the time of forming is unidirectionally solidified, for example, from below or from the side, the growth direction of the pores (holes) can be freely controlled. Further, by controlling control parameters such as melting temperature, solidification cooling rate, and gas pressure, the pore size and the in-plane occupancy can be controlled. The porous metal plate thus formed has relatively high mechanical strength and a large in-plane occupancy (30 to 80%).
) Pores are formed and are easily flexible while maintaining mechanical properties, so that thermal stress can be effectively reduced as described above. In addition, since it is configured using a heat conductive metal, the heat conductivity is also excellent. Some porous metals formed by a casting method, a plating method, or the like have pores having an in-plane occupancy of more than 80%. However, the mechanical strength is low, and the formation of pores cannot be sufficiently controlled. It is not suitable because the in-plane occupancy is too large and the thermal conductivity deteriorates.

In the above embodiment, the porous metal plate 13 having the through-holes 14 is used, but the pores do not have to penetrate, and the porous metal plate 13 extends in a direction substantially perpendicular to the surface of the porous metal plate 13. Or a spherical hole. Thereby, stress due to a difference in thermal expansion in the plane direction generated between the metal base plate 15 and the insulating substrate 11 can be effectively reduced. When the aperture ratio of the porous metal plate 13 due to the pores is larger at the outer peripheral portion than at the central portion, the flexibility at the outer peripheral portion is increased and the deflection can be generated effectively, and the heat conduction amount at the central portion can be increased. And the heat radiation effect can be improved.

In the above embodiment, the cushioning plate 12 is joined to the porous metal plate 13 by cladding. However, it is inferior in terms of thermal conductivity and strength, but may be joined by soldering. Further, only the porous metal plate 13 may be interposed between the metal base plate 15 and the insulating substrate 11 without providing the buffer plate 12, and an effect of reducing thermal stress can be obtained.

Furthermore, without providing the metal base plate 15,
The cooling means 16 serving as a heat conductive heat radiating plate may be used as the base plate of the IGBT module 9 and the porous metal plate 13 may be directly bonded to the base plate.

Embodiment 2 FIG. Next, a second embodiment of the present invention will be described with reference to FIG. In the first embodiment, the porous metal plate 13 having the through holes 14 is used. In the second embodiment, however, as shown in FIG. In this case, a columnar heat conductor 24 as a columnar heat conductive metal is inserted. The base material of the heat conductive porous metal plate 22 is made of, for example, copper, and a columnar heat conductor 24 made of, for example, aluminum, which is a metal material having a lower melting point and a higher linear expansion coefficient than copper, is formed in the through hole 23. It is inserted away from the side wall of the through hole 23 by a minute gap 23a. The configuration other than the porous metal plate 22 is the same as that of the first embodiment.

The porous metal plate 22 forms a porous metal plate 22 having a through hole 23 in the same manner as in the first embodiment, and thereafter, the melting point of the columnar heat conductor 24 and the base material 21 of the porous metal plate are formed. Is manufactured by a so-called melt impregnation method in which the through-holes 23 of the porous metal plate 22 are impregnated with the molten columnar heat conductor 24 by heating to a temperature between the melting points of the porous metal plates 22. As described above, for example, copper having a melting point of 1357.6 K can be used for the base material of the porous metal plate 22, and aluminum having a melting point of 933.5 K can be used for the columnar heat conductor 24. Since it is larger than the linear expansion coefficient of copper, when it is cooled to an operating temperature close to room temperature, a minute gap 23 a is formed between the side wall of the through hole 23 and the columnar heat conductor 24.
Can be. The space 23a is secured in a range from room temperature to the operating temperature of the power semiconductor device, and the through hole 2a is formed.
The side wall 3 and the columnar heat conductor 24 are surely separated from each other.

In the second embodiment, since the columnar heat conductor 24 is inserted into the through hole 23, heat is conducted not only by the base material of the porous metal plate 22 but also by the columnar heat conductor 24, and the heat conduction is performed. High performance. Further, since the gap 23a between the side wall of the through hole 23 and the columnar heat conductor 24 is secured in the range from room temperature to the operating temperature of the power semiconductor device, when the porous metal plate 24 bends, Does not interfere with each other, and does not hinder the effect of bending. Therefore, the metal base plate 15 having a large linear expansion coefficient and the insulating substrate 1 having a small linear expansion coefficient are bent as shown in FIG.
In addition to absorbing the difference in thermal elongation from the first embodiment and having the same thermal stress relaxation effect as in the first embodiment, the thermal conductivity is further improved, so that the heat radiation effect is improved.

Note that the columnar heat conductor 24 may be manufactured to be slightly smaller than the through hole 23 by machining and inserted. In this case, the material of the columnar heat conductor 24 is changed to the base material of the porous metal plate 22. It is not necessary to use a material having a lower melting point and a higher coefficient of linear expansion than the material.
It is sufficient that a gap 23a between the side wall and the columnar heat conductor 24 can be secured.

In the second embodiment, the porous metal plate 22 has no base material, that is, a layer in which a number of columnar heat conductors 24 are spaced apart from each other by fine voids. When used in place of 22, the effect of reducing thermal stress is further improved. In this case, the support plate for supporting the large number of columnar heat conductors 24 is replaced with the lower metal base plate 15.
It may be provided on the side, or both upper and lower sides.

[0029]

As described above, the first aspect of the present invention is as follows.
In the power semiconductor device described above, the lower surface of the insulating substrate on which the power semiconductor element is mounted and the heat conductive metal radiator plate are interposed with a heat conductive porous metal plate having a hole occupancy of 30 to 80%. Because of the bonding, thermal stress and thermal distortion between the insulating substrate and the heat conductive metal heat radiating plate can be reduced, and the heat generated by the power semiconductor element can be stably and efficiently radiated by good heat conduction.

According to a second aspect of the present invention, there is provided the power semiconductor device according to the first aspect, wherein the hole of the heat conductive porous metal plate is spherical or extends substantially perpendicular to the surface of the porous metal plate. Due to the shape of the cavity, the stress caused by the difference in thermal expansion in the plane direction generated between the insulating substrate and the heat conductive metal radiating plate can be effectively reduced.

According to a third aspect of the present invention, in the power semiconductor device, the lower surface of the insulating substrate on which the power semiconductor element is mounted and the heat conductive metal radiating plate are joined via the heat conductive porous metal plate. The porous metal plate includes a cavity penetrating in a direction substantially perpendicular to a surface of the porous metal plate, and a columnar heat conductive metal penetrating from one surface of the porous metal plate to another surface is formed in the cavity. Since it is arranged apart from the side wall with a minute gap, thermal stress and thermal distortion between the insulating substrate and the heat conductive metal heat sink are reduced, and the heat generation of the power semiconductor element is further improved by better heat conduction. Heat can be dissipated more efficiently.

According to a fourth aspect of the present invention, there is provided the power semiconductor device according to the third aspect, wherein the power semiconductor device is provided between the heat conductive metal in the cavity and the side wall of the cavity in a range from room temperature to the operating temperature of the power semiconductor element. As a result, the gap is secured and the separated state continues, so that stable and reliable heat radiation performance can be obtained.

According to a fifth aspect of the present invention, in the power semiconductor device according to the fourth aspect, the heat conductive metal in the cavity has a lower melting point and a higher linear expansion coefficient than the metal material of the porous metal plate. It is made of a material and formed by filling the cavity by the melt impregnation method, so that a fine gap can be easily secured with good controllability between the heat conductive metal in the cavity and the side wall of the cavity, and the reliability is stable. High heat dissipation performance can be easily obtained.

According to a sixth aspect of the present invention, there is provided the power semiconductor device according to any one of the first to fifth aspects, wherein the aperture ratio of the hole (cavity) of the porous metal plate is more outer than the center of the metal plate. Since it is large in the portion, the thermal stress can be effectively reduced and the heat radiation effect can be improved.

According to a seventh aspect of the present invention, in the power semiconductor device according to any one of the first to sixth aspects, a buffer plate made of molybdenum or tungsten is joined to an insulating substrate side of the porous metal plate. The influence of thermal stress on the insulating substrate and the power semiconductor element can be further reduced.

In the power semiconductor device according to the present invention, since the bonding between the porous metal plate and the buffer plate is performed by cladding, the power semiconductor device is strong, has high reliability, and has high thermal conductivity. A junction having good conductivity can be formed.

According to a ninth aspect of the present invention, in the power semiconductor device, the lower surface of the insulating substrate on which the power semiconductor element is mounted and the heat conductive metal radiating plate are formed by forming a large number of columnar heat conductive metals with fine gaps. Since the layers are vertically separated from the insulating substrate and are bonded to each other with an interval therebetween, thermal stress and thermal distortion between the insulating substrate and the heat conductive metal radiating plate can be further reduced, and the power The heat generated by the semiconductor element can be stably and efficiently radiated by good heat conduction.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a structure of a power semiconductor device according to a first embodiment of the present invention.

FIG. 2 is a perspective view showing a porous metal plate according to Embodiment 1 of the present invention.

FIG. 3 is a diagram for explaining deflection of the porous metal plate during operation according to the first embodiment of the present invention.

FIG. 4 is a sectional view showing a structure of a power semiconductor device according to a second embodiment of the present invention;

FIG. 5 is a diagram for explaining deflection of the porous metal plate during operation according to the second embodiment of the present invention.

FIG. 6 is a cross-sectional view showing a structure of a conventional power semiconductor device.

[Explanation of symbols]

10 IGBT element as power semiconductor element, 11
Insulating substrate, 12 buffer plate, 13 heat conductive porous metal plate, 14 through hole as cavity, 15 metal base plate as heat sink, 16 cooling means as heat sink, 21
Clad joint, 22 heat conductive porous metal plate, 23
Through holes as cavities, 23a voids, 24 columnar heat conductors as columnar heat conductive metals.

Claims (9)

[Claims] 1. The method according to claim 1, wherein the lower surface of the insulating substrate on which the power semiconductor element is mounted and the heat conductive metal radiating plate have a hole occupancy of 30%.
A power semiconductor device characterized by being joined by interposing a thermally conductive porous metal plate of up to 80%. 2. The power semiconductor device according to claim 1, wherein the hole of the heat conductive porous metal plate is a cavity having a spherical shape or a shape extending substantially perpendicular to the surface of the porous metal plate. . 3. A lower surface of an insulating substrate on which a power semiconductor element is mounted and a heat conductive metal radiator plate are joined with a heat conductive porous metal plate interposed therebetween, and the porous metal plate is connected to a surface of the porous metal plate. A hollow which penetrates the porous metal plate from one side to the other side is provided in the cavity, and a columnar heat conductive metal is arranged in the cavity so as to be separated from the side wall of the hollow by a minute gap. Power semiconductor device characterized by the above-mentioned. 4. A space is maintained between the heat conductive metal in the cavity and the side wall of the cavity in a range from room temperature to the operating temperature of the power semiconductor element, and the separated state is continued. Item 4. The power semiconductor device according to Item 3. 5. The heat conductive metal in the cavity is made of a material having a lower melting point and a higher linear expansion coefficient than the metal material of the porous metal plate, and is formed by filling the cavity by a melt impregnation method. The power semiconductor device according to claim 4, wherein: 6. The power semiconductor device according to claim 1, wherein an aperture ratio of the porous metal plate due to a hole (cavity) is larger at an outer peripheral portion than at a central portion of the metal plate. 7. The power semiconductor device according to claim 1, wherein a buffer plate made of molybdenum or tungsten is bonded to an insulating substrate side of the porous metal plate. 8. The power semiconductor device according to claim 7, wherein the bonding between the porous metal plate and the buffer plate is performed by cladding. 9. A lower surface of an insulating substrate on which a power semiconductor element is mounted and a heat conductive metal radiator are separated from each other by a plurality of columnar heat conductive metals with minute gaps so as to be perpendicular to the insulating substrate. A power semiconductor device, wherein the power semiconductor device is joined with an interposed layer.