The reliability of semiconductor devices in the bell system

The history of reliability of semiconductor devices in the Bell System is a story of sequential application of principles-first, of reliability-enhancing processing principles, which are applied in the absence of completely knowledgeable design and testing control; second, of testing-control principles, which follow growing knowledge of process defects and their susceptibility to exposure by test; third, of design-control principles, which derive from mature processing and the essentially automatic elimination of workmanship defects. These principles were generally applied to the design and reliability technologies of successive decades of semiconductor-device manufacture. The 1950's saw the development of new device designs with no really severe reliability requirements; a history of this period shows, in fact, that semiconductor devices were better than reasonable testing specifications could prove they were; although one of the reliability advances of that period was promoted by Bell Laboratories-the use of a sampling technique which provided the user a statistical guarantee of the reliability he was buying. The 1960's saw the implementation of, first, the manufacture of diffused devices capable of high-stress testing and, second, the use of high-stress burn-in and life-testing controls which were rigorously relatable to expected reliability at the low stress of application. The motivating forces behind this high-stress testing were the need for low-failure-rate devices and the recognition that such failure rates, of the order of 0.001 percent per thousand hours, could not be proved by life tests at the stresses of the application. The technology of the 1970's is that of the beam-lead sealed-junction device, representing elimination by design of the major failure mechanisms of the devices of the 1960's. Although the elimination of the need for a hermetic seal raised the additional need for demonstration of the ability of a device and its plastic coating to survive in a high-humidity environment, this demonstration was also found to be amenable to physically based relationships between humidity and temperature conditions and device life. The successful development of relationship between effective device test requirements and system life objectives is attributed to the Bell System interrelationships by which the device designer is responsible both to the user (the system designer), with whom he has agreed upon a reliability objective, and to the device manufacturing organization, to which he owes the most economical combination of processes, process controls, and final testing requirements to meet the system objective.