The effect of flux residue and substrate wettability on underfill flow process in flip chip packages

The surface energies of different substrates and wetting angles of fluxes on the substrates were measured and showed differences between different substrates. The viscosity of fluxes at low stress shows a good correlation with their wetting properties. The modulus of flux residue varies significantly between different fluxes and high modulus flux residue is difficult to remove. The correlation between underfill, substrate properties, and underfill flow voids will be discussed. An underfill flow study with quartz die packages was conducted. The effect of flux residue and substrate wetting properties were assessed by this underfill flow study. This study will help us in minimizing the flux residue effect on underfill flow and optimizing underfill flow process