Processing-adhesion relations for die attach adhesives and underfill resins

Adhesion is a major consideration in the quality and reliability of new packaging technologies. In PQFPs, adhesive failure is often seen between the die attach adhesive and copper bond pad. In the case of flip chip technology, delamination is often seen between the underfill resin and organic passivation layer. Some of these failures may be attributed to process, i.e. improper cure schedules. Previous work on adhesion-processing relationships for die attach adhesives in PQFPs led to the development of bondability diagrams for isothermal cure conditions, which identified various phenomena that influenced the adhesive bond strength. Similar adhesion-processing relationships can be developed for underfill resins used in flip-chip packaging. However, underfill resins are seldom processed under isothermal conditions and one must also consider the flow process, which was not a concern for die attach adhesives. Underfill material adhesion properties and flow characteristics are the dominant factors that determine the number of cycles to failure of flip-chip packages. Clearly, understanding the cure behavior of polymeric adhesives should provide a valuable insight on delamination and interfacial failure. The purpose of this work is to study the nonisothermal cure behaviour of die attach adhesives and underfill resins in attempt to understand the relationships between processing conditions and bond strength.