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

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.