Development and reliability of non-conductive adhesive flip-chip packages

Driven by miniaturization, cost and environmental friendliness, non-conductive adhesive (NCA) is emerging as one of the potential alternatives for solder-less flip-chip interconnections. It offers inherent characteristics such as finer pitch interconnect, green process, good electrical performance, lower cost and low processing temperature compatible with organic substrates. A reliability evaluation of NCA for flip chip application was carried out to investigate the degradation of the NCA joint in environmental tests. Finite element analysis was also performed to understand the observed phenomenon. In order to obtain accurate material properties for precise finite element simulation, NCA pastes are characterized, as close as possible to reliability test condition, in terms of their thermo-mechanical, moisture diffusion, and viscoelastic properties. The results showed that failures occurring in NCA joints are caused by moisture induced hygroscopic swelling and stress relaxation. All these factors affect the degradation of the compressive force that maintains the mechanical contact in NCA flip chip. The common failure modes observed were interfacial delamination, bump/pad opening as well as cracking.