Failure Analysis on Insufficient ACF Bonding Strength

Due to the rapid development towards miniaturization and integration of electronic devices, it needs high requirement for electronic packaging technology. ACF is a lead-free and green adhesive interconnect material, which is widely applied in electronic industry, such as chip on glass, flex-on-glass, flex-on-board, chip-on-flex. Due to its fine pitch capability, low cost and high efficiency, ACF bonding is very popular in panel display manufacturing. ACF provides both mechanical bonding and electric conductivity from pads of FPC in driver electronics and the glass substrate in the display system. The conductive microspheres in the film achieve the electric conductivity, while the adhesive material in the film provides the bonding strength between the glass and pads of FPC.In ACF bonding, insufficient bonding strength is one of common failures. In this paper, a failure analysis on ACF bonding failure in a panel display system is revealed with the aid of OM, SEM, EDS and ToF-SIMS. OM result demonstrates that the bonding strength of NG sample was weaker than that of OK sample, and it might be related to the surface status of FPC. SEM&EDS result shows that no difference was found between NG sample and OK sample. With the aid of TOF-SIMS, contamination of silicone oil was found on the surface of FPC, which leaded to the poor ACF bonding strength.