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A major Army rocket system may incorporate the use of an electronic fuze timer fabricated using two plastic encapsulated hybrid microcircuits and one encapsulated monolithic integrated circuit. The Electronics Technology and Devices Laboratory at Fort Monmouth, New Jersey was tasked with assessing the storage reliability of these devices through accelerated testing and detailed failure analysis to determine failure mechanisms. From this analysis, corrective actions would be proposed which could permit attainment of the desired reliability. (Author)

Field testing of hermetic and plastic encapsulated semiconductors has shown that ceramic dual-in-line packages (DIP) are superior than most plastic packages. Hermetic flat packs, however, are poorer than most plastic packages and a device fabricated with a trimetal interconnection metallization and an epoxy novolac encapsulant can be as good as ceramic DIPs. Silicone encapsulated devices are usually the poorest performers. Devices tested in the storage condition have, in some cases, poorer results than their equivalent, which have been biased. This can be attributed to reduction of the relative humidity at the chip surface due to a higher temperature produced by the power dissipation of the device. In general, in this field test program, plastic devices have not performed as poorly as had been expected. Newer devices, which include CMOS circuits and integrated circuits fabricated with various tape-chip carrier processes, are beginning evaluation. Results from tests on these units will be a good yard stick in assessing the reliability of semiconductors in the future.

The problem of current crowding in transistors is reviewed and its relationship to transistor per formance described. A method is described where by a quantitative value can be assigned as a measure of the extent of crowding that occurs. The possible implications of current crowding in the operational reliability are described. An empirical figure of merit is developed relating the crowding factor to the physical parameters of the semiconductor device. Recommendations in device design are made which should improve the current handling capability of transistors.

The RF operating voltage of power transistors designed for operation in HF, VHF and UHF regions was found to be greater than previously realized. This higher operating voltage is attributed to the slow response of the device surface with respect to the operating frequency of the circuit. Since most devices have breakdown voltages which are initially surface limited, their voltage operation at the higher frequencies is superior to the 60-cycle curve tracer behavior. (Author)

Burn-out of power transistors is a continuing problem that we are all aware of. The problem is not only unique with audio devices but is also prevalent with devices for HF, VHF, and UHF operations. Limited technical information is available as to the conditions leading to the failure of RF power devices under operating conditions. By applying infrared scanning techniques, insight has been obtained on the mechanisms leading to failure. The infrared scanning results have proved, by means of operational amplifier results, that failures formerly noted can be eliminated, thus leading to trouble-free operations. The infrared radiometer used is commercially available. It has the potential of resolving a hot spot of 0.3 mils in diameter. RF hot-spot temperature measurements were made on several devices having different design parameters. Evaluation of devices was made by analysis of 'hot-spot' thermal resistance plots. Included are data of experiments made on devices under pulsed dc operation. Results from the operational amplifiers are then compared with the pulsed data. RF operational data is presented at both 30 MHz and 76 MHz. Data of various load terminations are presented and analyzed. From these results it has been possible to realistically rate RF power transistors to operate under nearly any load termination. (Author)

Hot-spot formation was studied as a function of collector resistivity and thickness variations for a similar group of epitaxial and triple-diffused silicon planar transistors. An infrared radiometer was used for locating and measuring hot-spot temperatures. Hot-spot thermal resistance is used in the analysis of both forward and reverse bias second breakdown performance. (Author)

Transistors which have become inoperative due to collector-emitter short circuits have usually been driven into second breakdown itself, however, is not the destructive mechanism. Alloying of the contact metalization into the device produces the short circuit which is observed. This report describes the experimental results of transistors having molybdenum-aluminum metalization compared to devices with only aluminum contacts. The results indicated that devices with molybdenum, when driven into second breakdown, would outlive aluminum units with respect to current by a factor of three. (Author)

By the application of an infrared radiometer as the sensor, hot-spot formation is detected and a hot-spot thermal resistance is calculated. Hot-spot formation for both forward and reverse biased second breakdown is analyzed. Pulsed DC techniques are used in the investigation which allows for a wide range of possible operating biases to be applied. (Author)

The current state-of-the-art of pulsed thermal resistance measurements is reviewed. Some of the reasons are presented for the apparent lack of correlation in thermal measurements when these techniques are used. Two techniques of continuous thermal resistance measurements are presented and possible sources of error indicated. Some preliminary data is presented which indicates that thermal resistance measurements made by the continuous hFE technique is the most sensitive method currently known. (Author)