Effects of solder wettability of resist materials on solder filling with Injection Molded Solder (IMS) technology

Abstract

Injection Molded Solder (IMS) is an advanced solder bumping technology that the solder bumps can be made by injected pure molten solder through the masks. In this study, we investigated effects of solder wettability of resist mask on solder filling performance by solder flow simulation with computational fluid dynamics (CFD) software and experiments with IMS technology. It was confirmed by the simulation that more solder was injected into opening of resist mask with lower contact angle. To vary solder wettability of resist mask experimentally, a metal (Sn) was deposited on patterned resist surface including sidewall of resist openings. Solder wettability measurements and solder filling evaluations were performed. Dynamic contact angle measurements showed improved solder wettability of Sn deposited resist mask with an appropriate substrate temperature control compared with no metal deposited resist mask. It was confirmed that solder filling was improved with the metal deposition and the optimized IMS temperature profile. Improvement of solder wettability of resist mask can widen IMS process window in terms of injection pressure and it is important especially for finer pitch application where higher injection pressure is required.