JPH09213723A - Power semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate deformation in external electrodes due to pressure during machining, heat treatment or compression bonding by selecting as external electrode material a material having a breakdown strength of specific value or above, excellent in strength, electrical conductivity, thermal conductivity and heat resistance. SOLUTION: A large number of cathode electrodes 2 placed on the cathode plane on a semiconductor device substrate 1 are pressurized and brought into contact by a cathode post 4 with a cathode stress relieving board 3. An anode electrode plate 5 is pressurized and brought into contact by an anode post 7 with an anode stress relieving board 6. A copper-chromium alloy or copper- silver alloy, excellent in heat radiation and electrical conductivity, and having such a high strength that the 0.2% breakdown strength of the post electrode material is 1kg/mm<2> or above, is used for the cathode post 4 and the anode post 7. The posts are provided with a structure that contributes to uniform pressurization. This eliminates contact resistance due to uneven pressurization to numerously divided cathode electrodes, and enables best parallel operation, which gets the best performance from a GTO thyristor.

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, and more particularly to a power semiconductor device capable of suppressing local surface pressure distribution during pressurization.

[0002]

2. Description of the Related Art A pressure contact type semiconductor device in which a power semiconductor element such as a diode, an optical thyristor, a GTO (gate turn-off) thyristor and the like is brought into pressure contact with an electrode, that is, a power semiconductor device includes heat dissipation, a current capacity, a semiconductor element. A pressure contact (pressure contact) type package such as a stat type or a flat type is used to satisfy special conditions such as a substrate diameter.

2 (a) and 2 (b) schematically show an example of an alloy type and a pressure contact type structure of a conventional pressure contact type GTO thyristor, respectively. Where 16 is pn
It is a semiconductor element substrate having a junction, and electrodes are formed on both main surfaces. The peripheral end surface of the semiconductor element substrate is covered with silicone rubber 17.

In the alloy type structure shown in (a), the anode side of the semiconductor element substrate is fixed to the internal electrode material (molybdenum, tungsten, etc.) 18 via a brazing metal, and the internal electrode member 18 is attached to the cathode side of the semiconductor element substrate. Are arranged and pressed from both sides by the external electrode material (copper) 19.

In the pressure contact type structure shown in (b), the external electrode material 19 is arranged in a state of being pressed against the electrodes on both main surfaces of the semiconductor element substrate 16 via the internal electrode members 18, respectively. In this case, the facing surfaces of the semiconductor element substrate 16, the internal electrode member 18, and the external electrode material 19 are not fixed to each other but are pressed in a state of being in contact with each other.

In a semiconductor device such as GTO, sufficient electrical characteristics cannot be obtained unless uniform pressure contact is realized. The stress distribution generated in the semiconductor element of the pressure semiconductor device having this structure is
It strongly depends on the shape of the external electrode. When the external electrode is plastically deformed during the pressure contact, a portion where the surface pressure distribution (compressive stress) is high and a portion where the surface pressure is low are generated, and the internal electrode electrode material and the electrode formed on the semiconductor substrate cannot be contacted uniformly. In particular, in a semiconductor device having a large number of electrodes on the cathode side such as a GTO and a transistor for high power, the pressure contact form of the contact portion may not be uniform, and the electrical characteristics of the individual electrode contact portions may deteriorate.

[0007]

The above-mentioned prior art has a structure in which the semiconductor element substrate and the electrode member are all brought into contact with each other by pressurization. Therefore, especially when the electrodes of the semiconductor element substrate are divided into a large number, When the electrodes are plastically deformed, it is difficult to make electrical and mechanical uniform pressure contact over the entire surface of the divided electrodes.

When a non-uniform pressure is applied to the semiconductor element substrate, the contact resistance between the many electrodes of the semiconductor element substrate and the metal plate in contact therewith becomes non-uniform, and in the case of the GTO thyristor, many electrodes are applied. The distribution of the current flowing through the electrodes becomes uneven, and the current concentrates on the electrodes with low contact resistance. Then, when the current is cut off, the current concentration is increased, and when it is significant, the semiconductor element is broken at the portion where the current is concentrated, that is, the breakdown resistance is low.

An object of the present invention is to eliminate the plastic deformation during processing, heat treatment, and pressure contact of the external electrodes to make the contact between the semiconductor element and the electrode plate uniform, so that the current is evenly distributed to a large number of electrodes. Another object of the present invention is to provide a pressure contact type semiconductor device in which the breakdown resistance of the semiconductor element is increased.

[0010]

In order to achieve the above object, the present invention selects a material having high strength, high electrical conductivity, high thermal conductivity and high heat resistance as an external electrode material.

By selecting a material having high strength, high electrical conductivity and high thermal conductivity as the external electrode material, deformation of the external electrode due to pressure during processing, heat treatment and pressure welding can be eliminated. As a result, an unbalanced load does not occur in the semiconductor element, so that the semiconductor element can be uniformly pressed over a wide range. Further, since the sharing of the current flowing through a large number of electrodes is made uniform, the current concentration at the time of current interruption can be reduced and the current can be safely interrupted.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIG. FIG. 1 is a cross-sectional view of a pressure contact type GTO thyristor. A large number of cathode electrodes 2 arranged on the cathode surface of a semiconductor element substrate 1 are connected to a cathode post 4 via a cathode stress buffer plate 3, and an anode electrode plate 5 is connected to an anode stress. The anode posts 7 are brought into pressure contact with each other via the buffer plate 6. A peripheral end portion of the semiconductor element substrate 1 is covered with an encap material (silicone rubber) 15.

On the other hand, a gate lead 9 is brought into pressure contact with the gate electrode 8 by a disc spring 12 via a gate insulator 10 and a washer 11 at a constant pressure. And the semiconductor element substrate is
It is hermetically sealed by the insulator 13 and the flange 14.

The cathode stress buffer plate 3 and the anode stress buffer plate 6 alleviate the thermal stress received from the cathode posts 4 and the anode posts 7 and protect the semiconductor element substrate 1.
Molybdenum or tungsten having a plate thickness of 1 mm or more and having a thermal expansion coefficient close to that of silicon of the semiconductor element substrate 1 is used as the material.

Cathode post 4 and anode post 7
Include a copper-chromium (Cu-Cr) alloy having excellent heat dissipation and electric conductivity and high strength, or copper-silver (Cu-
It uses an Ag) alloy and has a structure that contributes to uniform pressurization.

Pure copper, Cu-Cr alloy, and Cu-Ag
The 0.2% yield strength of the alloy for various heat treatment temperatures is shown in FIG. The heat treatment time is 20 minutes.

Here, the temperature range in which the flange 14 and the cathode post 4 and the flange 14 and the anode post 7 are joined by using a brazing material is 600 to 800 ° C.

Pure copper has a 0.2% proof stress when the heat treatment temperature exceeds 250 ° C., and 0.2% when the heat treatment temperature exceeds 600 ° C.
% Proof strength decreases to about several MPa. In the power semiconductor device of the present embodiment in which the cathode post 4 and the anode post 7 are pressed to be used, the pressure exerted on each post when pressurized is often several MPa to 10 MPa. Therefore, when pure copper is used as the post material, the stress at the time of pressurization exceeds 0.2% proof stress, resulting in plastic deformation. As a result, an unbalanced load is generated and the semiconductor substrate cannot be pressed uniformly.

The Cu-Cr alloy and the Cu-Ag alloy have a 0.2% proof stress of 50 MP after heat treatment at 800 ° C for 20 minutes.
There is more than a. Cu-Cr alloy or C for post material
If the u-Ag alloy is used, uniform pressing can be realized without being deformed by the above-mentioned pressing force.

If the brazing filler metal used when joining the flange 14 and the cathode post 4 and the flange 14 and the anode post 7 to each other has a low melting point, a more reliable semiconductor device can be realized.

According to the present embodiment, the post electrode material is divided into a large number by using a material having excellent heat dissipation and electrical conductivity, high strength, and not plastically deformed even under a high applied pressure. With respect to the cathode electrode, it is possible to eliminate the contact resistance due to the non-uniformity of pressurization and perform the best parallel operation, so that the performance of the GTO thyristor can be fully brought out.

Further, the semiconductor device having the structure of this embodiment is applied not only to GTO thyristors but also to pressure contact type semiconductor devices such as pressure contact type thyristors, transistors, diodes and SI thyristors which control a relatively large current. As a result, the characteristics of each device can be maximized.

In the present invention, the post electrode material is C
Not only u-Cr alloys and Cu-Ag alloys, but also excellent in heat dissipation and electrical conductivity, having high strength, not plastically deformed even under high pressure, and forming a semiconductor element substrate with a thermal expansion coefficient. A copper-tungsten (Cu-W) material that can reduce thermal stress because it is close to silicon (Si) is also useful.

[0024]

According to the present invention, a material for a post electrode that is excellent in heat dissipation and electric conductivity, has high strength, and is not plastically deformed even under high pressure is applied. Since it is possible to avoid the occurrence of an unbalanced load, it is necessary to uniformly press-contact the electrodes arranged in large numbers on the semiconductor element substrate and the internal electrode plate, that is, non-uniform contact resistance due to non-uniform pressure, and further contact resistance. Since the increase in current concentration at the time of current interruption due to the non-uniformity of can be reduced, the current interruption performance is improved.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment of a pressure contact type semiconductor device according to the present invention.

FIG. 2 is a cross-sectional view of a conventional pressure contact type semiconductor device.

FIG. 3 is a characteristic diagram showing 0.2% proof stress of pure copper, Cu—Cr alloy, and Cu—Ag alloy at various heat treatment temperatures.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Semiconductor element substrate, 2 ... Cathode electrode, 3 ... Cathode stress buffer plate, 4 ... Cathode post, 5 ... Anode electrode,
6 ... Anode stress buffer plate, 7 ... Anode post, 8 ... Gate electrode, 9 ... Gate lead, 10 ... Gate insulator, 1
1 ... Washer, 12 ... Disc spring, 13 ... Insulator, 14 ... Flange, 15 ... Encap material.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mitsuo Sato 7-1-1, Omika-cho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi Research Laboratory

Claims (2)

[Claims] 1. A semiconductor device substrate having at least one pn junction, first electrode plates provided on both main surfaces of the semiconductor device substrate, and a semiconductor having a thermal expansion coefficient for protecting the semiconductor device substrate. A second electrode plate close to the element substrate,
In a power semiconductor device including a post electrode that press-contacts both main surfaces of the semiconductor element substrate through the first electrode plate and the second electrode plate, a 0.2% proof stress of the post electrode material is 1 kg / mm. ^A semiconductor device for electric power, characterized in that it is ² or more. 2. The post electrode according to claim 1, wherein the post electrode is made of copper.
Chromium (Cu-Cr) alloy, or copper-silver (Cu-A)
g) A power semiconductor device which is an alloy.