TECHNICAL FIELD

The present invention relates to a spring electrode for press-pack power semiconductor module which maintains an energized state while having flexibility in the vertical travel of press-pack power semiconductor chips.

BACKGROUND ART

For example, Patent Document 1 discloses a press-pack IGBT module that is a press-pack power semiconductor module (may be hereinafter referred to as a “semiconductor module”). The press-pack IGBT module includes a plurality of IGBTs that are press-pack power semiconductor chips (may be hereinafter referred to as “semiconductor chips”). The semiconductor chips obtain an electrical connection by being vertically compressed by a top electrode and a lower electrode.

Since pressure is uniformly applied to the plurality of semiconductor chips, each of the semiconductor chips needs a spring structure and play in a conducting path. The semiconductor chip includes a pressure pad for providing this play and ensuring the electrical connection. Although the semiconductor chip normally includes one pressure pad for increasing the current carrying capacity of the current, the semiconductor chip may include two pressure pads. Since a spring in the pressure pad functions as an inductance even with the electrical conductivity, the spring exhibits high impedance particularly with respect to a radio-frequency current. Moreover, a short-circuit current that is a radio-frequency current does not flow through the spring.

PRIOR ART DOCUMENT

Patent Document

[Patent Document 1] Japanese Unexamined Patent Application Publication No. 2004-528724

SUMMARY

Problem to be Solved by the Invention

It is feared that the press-pack IGBT modules may be damaged upon short circuit in the semiconductor chips. The press-pack IGBT modules are damaged because an electrical path in a module is broken, and arcing occurring in the break heats the module, which results in expansion of an atmosphere or vaporization of a solid object and causes an explosion.

The reasons why the electrical path in the module is broken upon a short circuit in a semiconductor chip are as follows. Upon a short circuit in the semiconductor chip, the short-circuit current flows through a pressure pad. Since the short-circuit current is a high current, the Joule heating caused by the short-circuit current dissolves the pressure pad, and breaks the electrical path to cause arcing. Particularly, since the short-circuit current is a radio-frequency current, it is feared that the short-circuit current concentrates on an edge portion of the pressure pad due to the skin effect and this portion gets hot and starts to be dissolved.

Thus, the press-pack IGBT modules require rugged explosion-proof structures which hinder the miniaturization and lower prices of the press-pack IGBT modules. Some press-pack IGBT modules need to limit use current areas, and separately need short-circuit protection.

The object of the present invention is to provide a technology that can prevent a spring electrode from being dissolved and broken upon a short circuit in a semiconductor chip.

Means to Solve the Problem

A spring electrode according to the present invention includes a main body that is a tubular conductor and varies in diameter in a longitudinal direction so that a side surface has bellows.

Effects of the Invention

A spring electrode according to the present invention includes a main body that is a tubular conductor and varies in diameter in a longitudinal direction so that a side surface has bellows. Since the main body of the spring electrode does not include an edge portion, the local concentration of a short-circuit current that flows through the spring electrode upon a short circuit in a semiconductor chip can be reduced. This can prevent the spring electrode from being dissolved and broken.

The object, features, aspects and advantages of the present invention will become more apparent from the following detailed description and the accompanying drawings.

