Fluxless Low-Temperature Flip Chip Solder Interconnect for Cost Reduction

This paper studies low temperature Sn- Bi solder as interconnect material for flip chip bonding on Trace-in-bump (TIB). The results demonstrated that the flip chip to TIB bonding using Sn- Bi solder is feasible. The micro-analysis showed that intermetallic compound (IMC) layer formation consisted of Sn, Au, and Ni with good electrical connection. The interconnect system survived the reliability test conditions for application with no crack or delamination was observed. This indicated the low temperature Sn- Bi solder in the TIB interconnect structure with the underfill material was able to overcome the brittleness and demonstrated the ability to survive the package integrity test. This provides opportunities in reduction of packaging cost through material cost, carbon footprint and package thermal stresses due to lower temperature soldering process.