Ultralow residue (ULR) semiconductor grade fluxes for copper pillar flip-chip

Copper pillars topped with solder microbumps are emerging as a standard flip-chip solderbump replacement in the semiconductor assembly industry. The relentless drive towards finer pitch, combined with reduced copper pillar height, makes aqueous cleaning of flip-chip flux residues more difficult. An emergent failure mode is joint damage during aqueous jet impingement. The move towards Semiconductor Grade ultralow residue no-clean fluxes and away from cleaning processes is therefore inevitable, and this paper discusses the testing of assembly materials for this purpose.