Lead-free flip chip process development

Abstract

With environmental concerns increasing, the electronics industry is focusing more attention on lead free solder alternatives. One challenge is to find an alternative solder that is as manufacturable, reliable and cost effective as the industry standard eutectic tin-lead or high lead solders. This study details the process development for a flip chip assembly using one of these alternative lead-free solders. Specifically, three flip chip fluxes and five underfills were used to assemble flip chip parts while keeping the no-lead solder, die passivation and substrate solder mask constant. Solder wetting characteristics were observed optically after cross sectioning the assemblies. The compatibility of different flux and underfill types, defined as no underfill voiding after assembly, was determined via acoustic microscopy. Assembled parts were subjected to JEDEC Level 3 moisture preconditioning. Post JEDEC preconditioning electrical and adhesion data helped identify one or more compatible flip chip material sets to be used for further lead free solder development work.