Silicon planar transistors and diodes for deep water submarine cable repeaters

Abstract

The methods used for the production and evaluation of high reliability silicon planar transistors and diodes for the first major use of such components in deep water submarine repeaters are described. The production methods were essentially those used for commercial devices, which had themselves undergone a series of reliability improvement exercises since manufacture started in 1961. The diodes were encapsulated in a conventional metal transistor can. Especially high reliability was achieved by meticulous control of pieceparts, processes and sub-assemblies and by very careful screening of the finished devices. A 20 yr life was required for the devices with no more than one transistor failure in 1200 and one diode failure in 2400 every four years. Assurance of this high reliability was obtained by: (a) performing accelerated tests in the temperature range 240–280°C; (b) subjecting 2642 transistors and 4793 diodes to a severe mechanical/thermal test; (c) subjecting similar numbers of devices to a three months' operating life test using the electrical conditions of the repeater, but with the device temperature raised so that the test was equivalent to the required life; and finally carrying out a radioactive krypton hermeticity test to a limit of 5 × 10 −12 atm. cm 3 per sec. No device failures were obtained in tests (b) and (c).