JPH11297869A - Power semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power semiconductor device which is high in long-term reliability and restrained from deteriorating in withstand voltage performance particularly after it is subjected to a heat cycle test by a method wherein an insulating substrate is enhanced in withstand voltage characteristics. SOLUTION: A coating film 4 is made to contain inorganic particles so as to be lessened in thermal expansion coefficient, whereby the coating film 4 is lessened from varying in volume in a heat cycle. At the same time the relative dielectric constant of the coating films4 is set close to that of an insulating board 1, or silicon carbide which shows non-linear resistance is used as the inorganic particles so as to relax an electric field around an electrode. By this setup, a power semiconductor device excellent in withstand voltage characteristics can be provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device, and more particularly to a power semiconductor device (hereinafter, referred to as a power module) in which a power semiconductor element having an insulating substrate with a high withstand voltage is accommodated.

[0002]

2. Description of the Related Art A power module is an IGBT (Insu).
rating Gate Bipolar Trans
Semiconductor devices such as isolators have been used, and high-voltage high-speed switching has become possible. An inverter device using a power module is an SVC (Stat) for controlling a train motor, a rolling mill motor for steel, and a power phase control.
ic Var Compensator). As disclosed in, for example, Japanese Patent Application Laid-Open No. 60-103649, a power module has a structure in which an insulating substrate is provided on a metal heat dissipation base plate for transmitting heat generated from a semiconductor element to the outside and an upper portion thereof. The semiconductor element is joined, and the periphery is covered with a plastic case. Since a high switching voltage is applied to the insulating substrate during operation in a one-minute AC withstanding voltage test in a power module shipping test, the reliability of the insulating substrate is important. Therefore, insulation treatment is performed by enclosing silicone gel or the like inside the case. Furthermore, various measures have been devised to improve the withstand voltage performance of the insulating substrate. For example, Japanese Patent Application Laid-Open No. 8-511
70, JP-B-3-51119, and the like.

FIG. 6 shows a conventional example described in Japanese Patent Application Laid-Open No. 8-51170, and shows a schematic view of a cross-sectional structure of a conventional insulating substrate for a power module. In FIG. 6, 10
Reference numeral 1 denotes an insulating substrate made of ceramic having excellent thermal conductivity for electrically insulating a metal base plate (not shown) for heat dissipation from a semiconductor element, and is made of alumina, aluminum nitride, silicon nitride, or the like. I have. 102 is an IGBT
A conductor pattern 103 for mounting a semiconductor element having a high voltage and a large current, such as a high voltage and a large current, is a conductor pattern formed for bonding to a metal heat dissipation base plate and usually has a ground potential. Reference numeral 104 denotes an insulator that covers an end of the conductor pattern 3 on which a semiconductor element to which a high voltage is applied is mounted. In recent years, power modules using the IGBT have been developed in the class of 3.3 KV to 4.5 KV, and accordingly, 1.5 to 2.5 KV.
Used for V high voltage circuits. The withstand voltage test voltage of the power module is determined by the circuit voltage used and is 6 KV.
AC voltage is imposed for one minute. Therefore, between the conductor pattern 102 and the conductor pattern 103 on the ground side, 6
KV. It is required to withstand a withstand voltage of 1 minute. Since the end of the conductor pattern 102 has a very high electric field, a measure to improve the withstand voltage performance and the partial discharge performance by covering the conductor end with an insulator 104 has been considered. In this conventional example,
A method of applying an epoxy resin, a phenol resin, a fluorine resin, a silicon resin, or the like as the insulator 104 is disclosed.

[0004]

As described above, the conductor pattern 102, the ground-side conductor pattern 103, the insulator 104
Are mounted on a metal base plate for heat dissipation, are surrounded by a plastic case, and are used as a power module in which the inside of the case is sealed with silicone gel. As the performance of the power module, it is required to withstand heat generation of the power semiconductor element and long-term reliability due to a change in ambient temperature, that is, a so-called heat cycle test (−40 ° C. to 125 ° C., 1000 cycles). In the heat cycle test, the insulator 10
At the interface between the substrate 4 and the insulating substrate 101, peeling occurs, and a partial discharge occurs inside the gap, which further impairs the withstand voltage performance.

[0005] The present invention has been made to solve the above problems, and has as its object to provide a power module having improved withstand voltage characteristics.

[0006]

SUMMARY OF THE INVENTION The present invention has been completed by finding that the withstand voltage characteristics of an insulating substrate can be improved by coating the periphery of an electrode with a coating film containing inorganic particles. An insulating substrate having an electrically independent electrode, mounted on a heat dissipation base plate via a lower electrode, and further having a power semiconductor element bonded to an upper electrode is housed in a case, and the inside of the case is silicone gel. In the power semiconductor device sealed by the above, at least the peripheral portion of the upper electrode is coated with a coating film containing inorganic particles imparting low thermal expansion, thereby suppressing the thermal expansion of the coating film. And By reducing the thermal expansion coefficient of the coating film, the expansion and contraction of the volume of the coating film due to the heat cycle test is suppressed.
Furthermore, by bringing the coefficient of thermal expansion of the coating film closer to the coefficient of thermal expansion of the electrode and the insulating substrate, the inconsistency of the volume change with the insulating substrate and the electrode can be reduced. Peeling can be suppressed,
A power module that does not deteriorate in withstand voltage characteristics even by a heat cycle test can be obtained.

The coating film is made of one of a thermosetting epoxy resin, a polyimide resin and a silicone resin, and silica (SiO ₂ ) or alumina (Al ₂ O ₃ ) for imparting dielectric properties. It is preferable to include any of the inorganic particles. Since the coefficient of thermal expansion of the coating film can be reduced and the relative dielectric constant can be increased, the electric field at the peripheral portion of the electrode can be reduced, and a power module having a high withstand voltage can be obtained.

Further, it is preferable that the coating film contains silicon carbide (SiC) powder as the inorganic particles. Not only is the coefficient of thermal expansion of the coating film reduced, but also non-linear resistance is imparted, so that the electric field at the peripheral edge of the electrode can be reduced and a power module with high withstand voltage can be obtained.

The average particle size of the SiC particles is as follows:
0. The thickness is preferably in the range of 1 to 2 μm. In this range, the non-linear resistance can be more effectively imparted to the coating film, so that the withstand voltage can be further improved.

The coating film preferably contains the inorganic particles in an amount of 5 to 60% by volume. When the content of the inorganic particles is within the above range, a thermal expansion coefficient and a dielectric constant close to those of the insulating substrate, or non-linear resistance is imparted, and the withstand voltage characteristics are not reduced even by the heat cycle test, and the high withstand voltage is also high. A power module having a voltage is obtained.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. <First Embodiment> FIG. 1 is a schematic plan view of an insulating substrate used for a power module according to a first embodiment of the present invention. FIG. 2A is a schematic sectional view of an insulating substrate used in the power module according to the first embodiment of the present invention, and FIG. 2B is an enlarged schematic sectional view of an electrode end. 1 and 2, an insulating substrate 1 is composed of a heat dissipation base plate (not shown) made of metal and a semiconductor element (not shown).
Made of ceramics having excellent thermal conductivity to electrically insulate ceramics. The collector electrode 2 is an electrode formed to be soldered to a high-voltage large-current semiconductor element such as an IGBT, and is formed by brazing a copper plate to the insulating substrate 1. The ground electrode 3 is an electrode formed for bonding to a heat dissipation base plate made of a metal, and usually has a ground potential. Then, a coating film 4 is formed so as to cover the peripheral portion of the collector electrode 2 where the electric field is concentrated and the front and back edges of the insulating substrate.

Here, the insulating substrate used in the power module of the first embodiment is electrically insulating.
As long as the material has excellent thermal conductivity, any conventionally known material can be used, and examples thereof include oxide ceramics such as alumina and nitride ceramics such as aluminum nitride and silicon nitride.

The resin used for the coating film of the power module according to the first embodiment includes an epoxy resin, a silicone resin, a polyimide resin and a fluororesin.

The inorganic particles used in the coating film of the power module of the first embodiment include silica, alumina, calcium carbonate, dolomite, talc, and the like.
Examples include aluminum fluoride and calcium fluoride. The average particle size of the inorganic particles is preferably in the range of 10 to 20 μm. Further, when the content of the inorganic particles is too small, a sufficient withstand voltage cannot be obtained, and when the content is too large, the film formability of the coating film is reduced.
% By volume is preferred.

As described above, in the first embodiment of the present invention, at least the collector electrode 2 where the electric field is concentrated.
When the coating film 4 containing the inorganic particles is formed so as to cover the peripheral portion, the difference between the thermal expansion coefficient of the coating film 4 and the thermal expansion coefficient of the insulating substrate 1 and the electrodes 2 and 3 becomes small. In this case, peeling of the interface between the coating film 5 and the insulating substrate 1 and the electrodes 2 and 3 can be prevented.

<Second Embodiment> A second embodiment of the present invention has the same configuration as the first embodiment except that silica or alumina for increasing the relative dielectric constant of the coating film is used as the inorganic particles. Is done.

In the power module of the second embodiment configured as described above, the relative permittivity of the coating film 4 is increased, and the difference in the relative permittivity between the insulating substrate and the coating film is reduced, so that the electric field of the electric field is reduced. Since the concentrated electric field at the periphery of the collector electrode can be reduced, the withstand voltage can be increased.

<Third Embodiment> In a third embodiment of the present invention, silicon carbide (SiC) which gives a non-linear resistance characteristic to a coating film is used as the inorganic particles, and the average particle diameter of the silicon carbide is set to 0.1. The configuration is the same as that of the first embodiment except that the thickness is set to 1 to 2 μm.

In the power module of the third embodiment configured as described above, the coating film 4 is provided with a non-linear resistance whose resistance is reduced by a high electric field, so that the peripheral portion of the collector electrode where the electric field is concentrated is provided. Since the resistance can be reduced and the electric field can be reduced, the withstand voltage can be increased.

[0020]

Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.

EXAMPLE 1 A 0.635 mm thick aluminum nitride plate having good thermal conductivity was used as an insulating substrate, and both surfaces were formed to a thickness of 0.035 mm.
A 2 mm steel plate brazed was used. The creepage distance from the end of the electrode to the end of the insulating substrate was 2 mm. As a reference sample, one without coating (Comparative Example 1: Sample A), as a coating material shown in FIG. 1, one coated with a polyimide resin (Hitachi Chemical: PIQ-4400) (Comparative Example 2: Sample B), and A coating of a polyimide resin (PIQ-4400, manufactured by Hitachi Chemical Co., Ltd.) containing 20% by weight of silica particles (Hysurex RD-8, manufactured by Tatsumori) as inorganic particles (Example 1: Sample C) was applied to each of 350 samples.
The composition was cured by heating at 15 ° C. for 15 minutes. This is set in a case and the whole is silicone gel (SE1885A manufactured by Toray)
/ B) and cured by heating at 70 ° C. for 2 hours.

An AC voltage was applied to the collector electrode 2 and the ground electrode 3 to determine a dielectric breakdown voltage. Figure 2 shows an example of the results.
This is compared with the case without the coating film (sample A).
The breakdown voltage of the coated insulating substrate (Sample B) including the present invention (Sample C) is high and the variation is small. On the other hand, the breakdown voltage of the uncoated insulating substrate (sample A) has large variations. When used as a power module, since a large number of insulating substrates are used, the withstand voltage performance of the entire module is determined by the minimum breakdown voltage that varies, so that characteristics such as sample A do not have sufficient withstand voltage reliability. You can see that.

FIG. 3 shows the dielectric breakdown voltage of each of the insulating substrates A, B, and C after 1000 repetitive heat cycle tests at -40.degree. C. to 125.degree. The breakdown voltage of sample A is often low. In addition, the sample B with the conventional coating
Some have a low breakdown voltage. This is because the difference between the thermal expansion coefficients of the coating film and the insulating substrate is large, so that the interface between the coating film and the insulating substrate is peeled off by the heat cycle, and a defect that lowers the breakdown voltage occurs. On the other hand, although the breakdown voltage of Sample C of the present invention is slightly lower than the initial value (FIG. 2), there is no large variation indicating a low breakdown voltage. Addition of silica has the effect of reducing the thermal expansion coefficient of the coating film.

Example 2 A 0.635 mm thick aluminum nitride (AlN) plate having good thermal conductivity was used as an insulating substrate, and a 0.2 mm thick steel plate was brazed on both sides.
The creepage distance from the electrode end face to the insulating substrate end face was 2 mm. As a coating material shown in FIG. 1, an epoxy resin (manufactured by Chise Nagase: CY205 / HY-905) to which a silica filler (RD-8 manufactured by Tatsumori) was added (Example 1:
Sample C1) and a mixture of alumina filler (Fujimi abrasive: Maloxite-2) at 50% by volume with respect to the epoxy resin (Example 2: Sample D) were applied and heat-cured at 130 ° C. for 2 hours. . These were set in a case, the whole was sealed with silicone gel (SE1885A / B, manufactured by Toray Industries, Inc.), and cured by heating at 70 ° C. for 2 hours.

An AC voltage was applied to the collector electrode 2 and the ground electrode 3 to determine a dielectric breakdown voltage. FIG. 4 shows an example of the result.
Characteristics of coating film made of epoxy resin only (Comparative Example 2:
It is compared with the sample B1). The relative permittivity of only epoxy resin is about 3, that of silica-filled epoxy resin is about 4.5, and that of alumina-filled epoxy resin is about 6.
2. An insulating substrate having an epoxy resin coating film to which a filler has been added tends to have a higher breakdown voltage as its relative dielectric constant increases.

Example 3 A 0.635 mm thick aluminum nitride plate having good thermal conductivity was used for the insulating substrate, and the thickness of the aluminum nitride plate was 0.1 mm on both sides.
A 2 mm steel plate brazed was used. The creepage distance from the electrode end face to the insulating substrate end face was 2 mm. As the coating material shown in FIG. 1, three types of SiC particles (Fujimi: # 1000, # 10000, # 3000) are applied to an epoxy resin (CY205 / HY-905, manufactured by Chise Nagase).
A mixture of 0) and 50% by volume with respect to the epoxy resin was respectively applied, and was cured by heating at 130 ° C. for 2 hours. These are set in a case, the whole is sealed with silicone gel (manufactured by Toray: SE1885A / B),
Heat cured for hours.

An AC voltage was applied to the collector electrode 2 and the ground electrode 3 to determine a dielectric breakdown voltage. FIG. 5 shows an example of the result.
It is a comparison of breakdown voltages of epoxy resins to which three types of SiC are added. Since the resistance value of # 1000 having a coarse particle diameter decreases at a low voltage, thermal destruction of the SiC-added epoxy resin occurred, and as a result, the resin was broken at a low voltage. Particle size 2μm
In the following # 10000 and # 30000, relaxation of the electric field at the peripheral portion of the collector electrode 2 is effectively working.

[0028]

As described above, in the power semiconductor device according to the present invention, since the periphery of the collector electrode is covered with the coating film containing inorganic particles, the coefficient of thermal expansion of the coating film is reduced and the thermal expansion is suppressed. In addition, the difference in the coefficient of thermal expansion between the insulating substrate and the coating film can be reduced, and peeling of the coating film from the insulating substrate, which causes a decrease in withstand voltage in a heat cycle test, can be prevented.
A power semiconductor device having excellent long-term reliability can be provided.

Further, in the power semiconductor device of the present invention, silica (SiO ₂ ), alumina (Al ₂
By using any one of O ₃ ), the thermal expansion coefficient of the coating film can be reduced and the relative dielectric constant of the coating film can be increased, so that the relative dielectric constant of the insulating substrate having high thermal conductivity (about 9) can be obtained. As a result, the effect of reducing the electric field at the periphery of the collector electrode can be obtained. As a result, it is possible to provide a highly reliable power semiconductor device capable of improving the breakdown voltage.

Further, in the power semiconductor device of the present invention, the inorganic particles may be made of silicon carbide (Si) having nonlinear resistance.
C) By using particles, an effect of alleviating the electric field at the periphery of the collector electrode is obtained, and a power semiconductor device with a high breakdown voltage can be provided.

Further, in the power semiconductor device of the present invention, as the inorganic particles, silicon carbide having non-linear resistance (S
iC) In the particles, the particle size range is from 0.1 μm to 2 μm.
By using such a power semiconductor device, it is possible to provide a power semiconductor device having a particularly high breakdown voltage, which is effective for alleviating the electric field at the peripheral portion of the collector electrode.

In the power semiconductor device according to the present invention, since the coating film contains 5 to 60% by volume of the inorganic particles, the power semiconductor device is effective in alleviating the electric field at the periphery of the collector electrode.
In particular, a power semiconductor device having a high breakdown voltage can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic plan view (a) and a schematic cross-sectional view (b) showing an insulating substrate structure of a power semiconductor device according to a first embodiment of the present invention.
And an enlarged schematic sectional view (c).

FIG. 2 is a diagram showing a test result of a dielectric breakdown voltage obtained by examining an effect of the first embodiment of the present invention.

FIG. 3 is a diagram showing a test result of a dielectric breakdown voltage obtained by examining the effect of the first embodiment of the present invention.

FIG. 4 is a diagram showing a test result of a dielectric breakdown voltage obtained by examining an effect of the second embodiment of the present invention.

FIG. 5 is a diagram showing a test result of a dielectric breakdown voltage obtained by examining an effect of the third embodiment of the present invention.

FIG. 6 is a schematic sectional view showing a conventional insulating substrate structure.

[Explanation of symbols]

1 insulating substrate, 2 conductor pattern (collector electrode),
3 Conductor pattern (ground electrode) 4 Coating film

Claims (5)

[Claims] Claims: 1. An electrode having electrically independent electrodes on the front and back surfaces,
In a power semiconductor device, which is mounted on a heat dissipation base plate via a lower electrode and further accommodates an insulating substrate in which a power semiconductor element is joined to an upper electrode in a case, and the inside of the case is sealed with silicone gel, A power semiconductor device, wherein at least a peripheral portion of the upper electrode is coated with a coating film containing inorganic particles imparting low thermal expansion properties to suppress thermal expansion of the coating film. 2. The method according to claim 1, wherein the coating film includes at least one resin selected from a thermosetting epoxy resin, a polyimide resin, and a silicone resin, and at least one of inorganic particles such as silica or alumina particles. The power semiconductor device according to claim 1. 3. The coating film according to claim 1, wherein the coating film includes at least one resin selected from a thermosetting epoxy resin, a polyimide resin, and a silicone resin, and silicon carbide particles imparting nonlinear resistance. A power semiconductor device as described in the above. 4. The silicon carbide particles having an average particle size of 0.1.
The power semiconductor device according to claim 3, wherein the power semiconductor device has a range of 1 to 2 m. 5. The method according to claim 1, wherein the coating film comprises inorganic particles of 5 to 5.
The power semiconductor device according to any one of claims 1 to 4, wherein the power semiconductor device contains 60% by volume.