The Growth and Influencing Factors of Voids in SnAg Solder Bump and their Impact on Interfacial Bond Strength

Abstract

With the trend toward lead-free and miniaturization in consumer electronics, sub 100 micron lead-free solder bumping and its related reliability are becoming one of the important issues in today's electronic packaging industry. The growth and influencing factors of voids in the interfacial region of electroplated Sn-3.0 Ag solder bumps on electroplated Cu and their effects on interfacial bonding strength during multi-reflow and aging process were studied. Results show that the volume shrinkage during the phase transformation was the main reason for the void formation during multi-reflow. The Kirkendall effect was the main reason for the void formation during aging. A thick eta-phase and the voids at the boundaries among Cu6Sn5 grains promoted the voids growth in the epsiv-phase. Though the formation of voids had a trivial weakening effect to the shear strength of solder joints, the voids were a threat to the bonding reliability of solder bumps.