4. Conclusion(s)

In this paper, we investigated the resin properties and bonding parameters on the solder joint morphologies of Sn-Bi58 ACF joints. As a result, we found storage modulus of resin adhesives was the determined factor for solder joint cracks and regardless of bonding pressures. We thought cracks at solder joints happened, probably due to the high elasticity of polymer resin. Apart from that, two suggestions were listed to solve the solder joint cracks by increasing the resin storage modulus. The 1st one was to remain the hot-bar until cooling to its Tg, but this method will excessively consume solder and lead to brittle IMC at interfaces in TC bonding, while it is ok to US bonding. The other method was to add silica fillers in polymer resin to increase its thermos-mechanical property and reduce the polymer rebound when bonding process was finished. For ultrasonic bonding, storage modulus above 5 MPa of was at least needed to prevent solder joint cracks. On the contrast, 70 seconds for maintaining bonding pressure was too long. More than 1.38 MPa storage modulus at 200°C was needed for a crack-free Sn-58Bi solder joint morphology for a conventional TC bonding.
