Investigation of Solder Resist Opening Uniformity on Flip Chip Substrate

Good solder resist (SR) opening uniformity can effectively avoid electrical defect in the connection between the chip and substrate, including device short, open issue and bump crack issue. The main objective of this research is to propose an optimized process control to improve SR uniformity by controlling queue time through DOE test, including the queue time of tear off PET film after exposure, exposure to development queue time and development chemical renew time. Among them, queue time of tear off PET film after exposure were selected from 1min. to 20min. The exposure to development queue time was set to 1hr to 4hr. The development chemical renew timing was also set. The best SR opening uniformity was revealed by tolerance of opening size, which can be reduced from ±5um to ±3um when queue time of tear off PET film after exposure were set to ≤1min of tear off PET after exposure. The DOE test result sheds light in improving the performance between chip and IC substrate.