Evaluation of High Compliant Low Ag Solder Alloys on OSP as a Drop Solution for the 2nd Level Pb-Free Interconnection

Low Ag content alloys (Sn1.2Ag0.5Cu) with or without Ni doping on Cu organic solderability preservative (OSP) were evaluated as a high G drop solution to Sn4.0Ag0.5Cu with Ni/Au surface finish for the mobile electronics. Three key points are studied in this paper. First, the effect of increasing compliance of alloy was studied. High compliance and high plasticity energy dissipation effectively toughened the crack tip and prolonged the time to reach the critical stress for the fracture. Second, the effect of Ni doping to the interfacial phase formation was studied. The substitution of Ni for Cu effectively suppresses growth kinetics of intermetallic compounds (IMCs) and makes the IMC layer thin. Finally, reliability tests were conducted to evaluate thermomechanical and high G drop resistance of low Ag alloys with Cu OSP surface finish. Overall, low Ag content alloy systems enhance high G shock resistance significantly without sacrificing thermomechanical performance.