Development of a high curing latency no-flow underfill with self-fluxing ability for lead-free solder interconnects

Tin-lead solders have been used as joining materials in the electronics industry for many years. As present there are great concerns about the potential harm of lead-containing solders to human beings and many efforts have been made to remove the lead from the electronics packages. However, there is no no-flow underfill currently on the market that is compatible with the lead-free solder. In this study, a new no-flow underfill for flip chip bumped with lead-free solder has been developed based on a curing agent and catalysts with high curing latency. The curing agent itself has the fluxing ability, so the need of extra flux is eliminated. Compared with the underfill for lead-containing solder, the new underfill has a higher curing temperature, compatible with the melting profile of lead-free solder. The wetting compatibility of the underfill with the lead-free solder has been studied by wetting experiments. The material properties of the underfill have been investigated using DSC, TGA, TMA and DMA. The results show that the newly developed underfill material has the potential to be used in lead-free interconnects.