Abstract: Experiments were carried out to investigate an area-array SnAg alloy electroplating solder bumping process with a bump size of less than 100μm.Sn-3.0Ag solder bumps with smooth and shiny surfaces,uniform distribution of Ag atoms,the height uniformity within the chip,and over Φ100mm wafer about 2.03% and 5.12% were fabricated.The intermetallic compound and micro-voids at the SnAg/Cu interface as a function of the reflow times and their effects on the bonding reliability of solder bumps were studied.The scalloped Cu6Sn5 phase grew by a ripening process during multi-reflow.Volume shrinkage during phase transformation was believed to be the main reason for the formation of voids.The average shear strength of solder bumps increased as the reflow time increased.The combination of SnAg on TiW/Cu UBM was reliable under multi-reflow.Voids showed no significant impacts on the solder bonds in this study.Voids at the layered Cu6Sn5/Cu interface would be a threat to the reliability of solder bumps.

Key words: SnAg,  solder bump,  intermetallic compound,  voids,  reliability,  multi-reflow