Lead-free solder flip chips on FR-4 substrates with different surface finishes, underfills and fluxes

This study is focused on the assembly and reliability of 200-250um-pitch, lead-free (SnAgCu) flip chips on FR4 substrates. The impact of different PCB surface finishes (OSP and ENIG) was investigated from assembly and reliability perspectives. Different underfill materials (including an acid anhydrate-based material and two nonacid anhydrate-based materials) were evaluated for compatibility with the flux and lead-free solder bumps and process.