A Study on Warpage and Reflow Profile for Extreme Extension of Mass Reflow Bonding

In this study, quantification of tilt non-wet risk level was performed as a form of tilt non-wet (TNW) index and reflow profile optimization was performed to reduce bump non-wet failure rate to zero level. Joint height at equilibrium state was simulated using surface evolver, and new term of TNW (Mt non-wet) index was introduced to predict non-wet level by warpage gap, tolerances. TNW index well matched with logarithm of open rate by having strong linear relation (R-2=0.945) whereas conventional effective-gap method shows weak relation (R-2=0.156). Optimization of soak time was performed considering reduced flux quantity and bump, and showed significant improvement in BLT variance, process capability, and open rate as soak time decreased. By increasing hump height by 42% and reducing soak time from +60% to - 30% together. a significant improvement in non-wet was made by reducing non-wet rate from >2500ppm to sub 500ppm and from >500ppm to sub 50ppm at test vehicles with different TNW index. By this research, it is expected to successfully achieve extreme longevity of mass reflow bonding along with precise prediction method to reduce DOE for the advanced flip-chip structures.