1. Field of the Invention
The invention relates to a press-connection semiconductor device and a press-connection semiconductor assembly, and more particularly to a press-connection power semiconductor device with reliability improved in terms of a temperature cycle test and a power cycle test.
2. Description of the Related Art
Conventionally, a high-power semiconductor device is used for an inverter which is used to control the running speed of a drive motor in an electric vehicle, an air conditioner, various types of machine tools and the like.
FIG. 8 and FIG. 9 show a configuration of such a conventional power semiconductor device.
In the drawings, reference numeral 1 denotes a ceramic wiring substrate, which has a wiring layer 1a of a copper foil formed on both faces of a ceramic substrate such as aluminum nitride or aluminum oxide (alumina). Two types of semiconductor elements 2 of IGBT (insulated gate bipolar transistor) and FRD (fast recovery diode) are die-bonded by soldering at predetermined positions on the main face of the ceramic wiring substrate 1. The ceramic wiring substrate 1 having the semiconductor elements 2 is soldered onto a copper radiator plate 3. The ceramic wiring substrate 1 mounted onto the copper radiator plate 3 is accommodated into a casing 8 of insulating resin having an anode member 4, a cathode member 5, a common electrode member 6, and a plurality of signal terminals 7. Electrode pads of the semiconductor elements 2 and the wiring layer 1a of the ceramic wiring substrate 1, said wiring layer 1a and the electrode members mounted on the casing 8 are wire-bonded with an Al wire 9. It is not shown but the wire-bonded portion is covered with a sealing layer of insulating resin and further covered with a cap.
When such a semiconductor device is subjected to a thermal cycling or power cycling, a stress is applied to the semiconductor device due to a difference in thermal expansion coefficient among the different materials used. This thermal stress has a possibility of causing a fatigue failure or breakage in a solder connection or a connection of the bonding wire.
Specifically, in the conventional semiconductor device, the ceramic wiring substrate 1 and the semiconductor element 2 are bonded with Sn--Pb solder, and the electrode pads of the semiconductor element 2 and, the wiring layer 1a of the ceramic wiring substrate 1, said wiring layer 1a and the electrode member are connected by wire bonding. Accordingly, a temperature of the device as the whole rises and drops repeatedly because of heating generated when the semiconductor element 2 is operating, leading to a fatigue in the solder connecting portions or the joint of the Al wire 9, and possibly resulting in breaking the device.