A high-reliability plastic encapsulation for transistors

A description of the design of a reliable, inexpensive, transfer-molded, silicone plastic transistor encapsulation is given. The materials selection was based upon the needs of reliability testing and suitability for requisite manufacturing processes. The dimensions of the plastic encapsulation, which replaces the TO-18 hermetically sealed metal-glass encapsulation, were determined by analyzing the stresses at the interface of the plastic encapsulant and the metal leads. The physical and mathematical models of the lead seal and a mechanical-failure criterion were used to determine the integrity of the lead seal. Results of mechanical and electrical evaluations are given to demonstrate the capability and reliability of the encapsulation.