Moisture Exclusion from Encapsulation of Long-Life Transistors

The requirement for long-life transistors places stringent demands on sealing processes. There are empirical reasons for believing that water content is a critical factor and should be preserved at a very low value. The first consequent problem is to design the sealing operation so that the encapsulate is sufficiently dry at the beginning of life. A practicable solution demands the use of moisture getters and the properties and usage of these are compared. The second problem is to reduce later leakage of water vapor into the can to a low level. The radioactive method of leak detection is shown to be the most satisfactory to use for controlling the quality of the high-grade packages required.