Semiconductor Component Reliability in an Equipment Operating in Electromechanical Telephone Exchanges

The reliability of an electronic equivalent of an electromechanical impulse regenerator has been monitored on well over 6000 units for periods of up to nearly 3 years. The electronic regenerator incorporates an mos integrated circuit as well as transistors, diodes and passive components including a reed-relay. The exercise sought to ascertain the reliability benefits of electronic replacement and provide component failure-rate information such as might be expected to guide future equipment developments. The multiply-censored nature of the available data is suited to the maximum-likelihood method of estimating the statistical parameters of the lifetime distributions from which the hazard rate of the regenerator itself as well as those of the mos integrated circuit and the transistors is found to decline steadily with an approximately root-reciprocal time dependence. The results reveal that the reliability of the electronic regenerator is vastly superior to that of its electromechanical predecessor. At the same time, a failure mode in the mos integrated circuit is exposed, namely corrosion of the aluminium inter-connection tracks, which would have seriously imperilled an equipment using integrated circuits extensively. Although this problem appears as a transient manufacturing deficiency, its occurrence emphasises the need for component procurement to adequate reliability specifications.