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The mechanical design of a completely bondless, pressure contact IGBT is discussed and its implications on the electrical characteristics are compared to those of a similarly rated module device. It is determined that the differences in the electrical characteristics of a pressure contact IGBT may offer certain advantages in some applications. INTRODUCTIONIt has been the conclusion of a number of independent studies [l-4 and others] that the long-term reliability of the module IGBT, in some applications, is still in question. Most of the identified failure mechanisms are associated with one of the many bonded joints, both wire and substrate, which occur in this type of construction. To overcome these potential failure modes a completely bond free pressure contact IGBT package has been developed, along with specially designed chips, which have been optimised for operation under pressure contact.

Single solid-state devices or arrays of solid-state devices are being incorporated into many pulsed power applications as a means of generating fast, high-power, high repetition-rate pulses and ultimately replacing hard tubes and thyratrons. While vendors' data sheets provide a starting point for selecting solid-state devices, most data sheets do not have sufficient information to determine performance in a pulsed application. To obtain this relevant information, MOSFETs and IGBTs from a number of vendors have been tested to determine rise times, fall times and current handling capabilities. The emphasis is on the evaluation of devices that can perform in the range of lOOns pulse widths and the test devices must be capable of switching 1000 volts or greater at a pulsed current of at least 25 amperes. Additionally, some devices were retested with a series magnetic switch to evaluate the effects on switching parameters and specifically rise times. All devices were evaluated under identical conditions and the complete test results are presented.The semiconductor switch has been shown to be a realistic alternative to the thermionic device in pulse power applications [I-31. The introduction of new press-pack IGBT technology [4-51 offers the opportunity to extend the range of high power applications for which a semiconductor switch may be considered. IGBT technology considerably simplifies the ancillary circuitry conventional substrate mounted module packaging does not lend well to many of the requirements of pulse power. The pressure contact devices described in this paper are of an electromechanical design, which overcomes many of these limitations and these issues are considered in the paper. Highlighting the suitability of the packaging technology for series operation to achieve most desired circuit voltages. Issues of improved reliability and device failure mechanisms are also considered. Individual press-pack IGBT switches with pulse ratings up to several thousand amperes are now available with much higher currents anticipated for the future. The paper includes details of experimental testing of devices under a wide range of operating conditions, example waveforms as illustrated. Pulses from a few microseconds duration, with rates of rise of current of several thousand amperes per microsecond to pulses of several milliseconds are considered, as well as the requirements for series operation. Footnotes: [l] Bonthond J. et.al., 'High current, high di/dt switching with optimised GTO thyristors'. IPMS, Costa Mesa, 1994. [2] F.Wakeman and M.Baker, 'The implementation of Gate turn-off thyristos as high voltage tum-on switches for pulse power applications', IEE PP, London, 1997.

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