Metallurgically bonded, glass-bodied DO-35 power rectifier diodes were electrically overstressed by applying forward and reverse current pulses. Forward current pulses varied from 0.1 to 3 ms with current amplitudes varying from 200 to 1000 A were applied to one group of diodes. Reverse bias current pulses in the microsecond range with amplitudes from 2 to 400 mA (above breakdown voltage) were applied to another group. A small-step cross sectioning in combination with electrical probing, light emission microscopy, liquid crystal technique, and chemical staining were used to reveal and compare damage in three groups of diodes: two overstressed groups and the third group which had failed during burn-in electrical testing. Failure mechanisms and peculiarities of damage created in these diodes and several case histories related to different types of diodes are discussed.

Low-pressure conditions, as experienced in space applications, are considered benign for many electronic components. However, for switching devices the probability of failure may be significantly greater than at normal atmospheric pressure due to arcing-at-break processes. This study was stimulated by a relay failure in a 60-V power bus in a spacecraft module, and it was intended to analyze failure modes and the probability of their occurring under lowpressure conditions. The effects of gas pressure, power bus voltage, and load current on arc duration and probability of arc flashover have been investigated. It was shown that arc duration mostly depends on switching power and gas pressure, significantly increasing when power is rising and pressure is decreasing. Failure analysis indicated two major mechanisms in low-pressure conditions: (1) contact damage (excessive erosion and/or microwelding) and (2) arc flashover to a grounded case and/or grounded coil post. For a relay operating in a vacuum, the effect of leak rate on the time to failure at low-pressure conditions is discussed.