Procedures for Selection of Semiconductor Diodes for Use in Undersea Cable Systems

The nonredundant transistorized repeaters used in undersea cable systems are intended to operate on the ocean floor without maintenance for twenty years. To provide the best possible assurance that this high level of reliability is in fact attained, semiconductor transistors and diodes manufactured for cable use are screened to identify and eliminate the early failures. Devices surviving the screening are then subjected, for at least six months, to real time aging which simulates the worst-case use-conditions. The devices are removed from the aging environment and certain of the devices are selected for use in undersea cable operation. It is the purpose of this paper to discuss the empirically derived procedures for selecting two types of semiconductor diodes. The test data on which the selection is based consist, in each case, of period measurements of four electrical parameters while the diodes are aging. There was apparently no accepted and well formulated statistical model for the data on which a conventional technique could be based. Thus more unconventional procedures for device selection had to be constructed. The selection procedures have been implemented and perform well.