Moisture Effects on NCF Adhesion and Solder Joint Reliability of Chip-on-Board Assembly Using Cu Pillar/Sn-Ag Microbump

Abstract

Electronic devices as well as electronic packaging technology have required higher speed, I/O capability, and density. To meet these requirements, flip-chip solder bumps interconnection combined with reflow assembly process has been a widely used. In spite of the many advantages of flip-chip solder bump joints, there is a limitation for less than 100 mu m fine pitch interconnection due to the solder bump bridging during the assembly process. Therefore, nonconductive films (NCFs) and Cu pillar/Sn-Ag microbump interconnection become a promising interconnection solution for fine pitch assembly. However, NCFs technology has some problems for flip-chip assembly. Epoxy-based NCF can easily absorb moisture, causing delamination reliability problem at moisture environment. In order to solve the interconnection, the NCF adhesion should be enhanced. Silane coupling agent (SCA) was added to NCFs to secure the microbump joint reliability for chip-on-board assembly by increasing the adhesion strength in the pressure cooker test. After the humidity test, the NCFs' modulus and Tg were increased by adding SCA content. Moreover, the measured adhesion strength and energy showed similar results after the humidity test that higher SCA content showed high adhesion strength and energy than lower SCA content and unmodified NCF at the interface between NCF and solder resist of the printed circuit board substrate. The bump joint lifetime of 5wt% SCA NCF was longer than 1wt% SCA and unmodified NCF after the humidity test. In this paper, we report results of our investigations on effects of employing SCA in NCF composition for improved moisture resistance.