The importance of adhesion for electronic module encapsulation

Epoxy based systems are well suited as encapsulates fo a wide variety of electronic and electrical components because of their outstanding mechanical and electric properties as well as excellent thermal endurance and chemical resistance. In many of such applications, the components to be encapsulated are potted in thin- walled housings, typically injection molded from a variety of mineral filled thermoplastic materials. It is critical in such applications that the adhesive bond between the epoxy and thermoplastic remains intact throughout the life of the part, primarily to preclude catastrophic electrical failures but also to maintain mechanical integrity and to provide a seal from possible sources of contamination. This paper explores basic factors necessary for proper adhesion in such applications. A pull-out adhesion test is described that provides an excellent model for evaluating epoxy-based adhesive bonding that takes into account specific design and process conditions salient to most electronic and electrical encapsulating applications.