Impact Properties of Flip Chip Interconnection Using Anisotropically Conductive Film on the Glass and Flexible Substrate

Recently, Anisotropic Conductive Film (ACF) has been attracted much interest because of ultra-fine and environmental compatibility. However, this new technology still has many limitations. Poor impact performance is the most critical limitation which not only threaten to the mechanical connection of the chip to the substrate but also make contact resistance very much unstable during vibration loading. This paper reports on the studies of the dynamic strength of flip-chip on glass (COG) and flip-chip on flexible substrate (COF) using ACF. Impact test were performed to investigate the key factors that affect the adhesion strength. The fractography characteristics were evaluated by Scanning Electron Microscopy (SEM). At first, impact strength increases with the bonding temperature, but after certain temperature, impact strength again decreases. Although bonding pressure doesn't influence the impact strength, it is still important for a good adhesion. The behaviors of the conductive particles and air bubbles also weaken the adhesion severely. From the detailed fracture mode study, it was found that impact load causes fracture to propagate in the ACF/substrate interface (for COG packages), and in the ACF matrix (for COF packages). It is proposed that the bonding temperature which actually determine the degree of curing of the ACF for a fixed process flow, should be precisely optimized. Over curing at higher bonding temperature deteriorate the impact performance of the ACF joints.