Development of reworkable underfill from hybrid composite of free radical polymerization system and epoxy resin

The application of the underfill encapsulant is to enhance the solder joint fatigue life in the flip chip assembly, typically up to an order of magnitude, as compared to the nonunderfilled devices. Most of the current underfills, however, are primarily thermosetting epoxy resin curing system based materials, which transform into an infusible three dimensional network structure, and exhibit appreciable adhesion and reliability, but lack of desirable reworkability after curing. From the standpoint of polymeric material chemistry, other thermoplastic or thermosetting polymer materials could be of great economic/cost interest as encapsulants for some microelectronic packaging applications. In this paper, the experimental focus was devoted to the study of adhesion, reliability and reworkability of the free radical polymerization (FRP) system, as well as its hybrid composites or blends with phenoxy resin or epoxy resin (EPR), which could be potential underfill materials. The study encompassed formulation screening based on adhesion measurement, and assessment on reliability and reworkability performance for selected compositions developed so far.