Rapid microstructure evolution of structural composite solder joints induced by low-density current stressing.

The microstructure evolution of solder matrix and interfacial intermetallic compounds (IMCs) of Cu/Sn37Pb/Sn3.0Ag0.5Cu/Sn37P/Cu structural composite joints were investigated under low-density current stressing of 2.0×10 3 A/cm 2 at 100 °C. Cu flux diffusion induced by electro-migration was delayed by Ag 3 Sn particles in eutectic phase of Sn3.0Ag0.5Cu solder, by which Cu 6 Sn 5 particles could not reach the interfacial IMC at anode side, and then the growth of interfacial IMC or regular polarity effect at node was inhibited. Coarsened Cu 6 Sn 5 particles were accumulated at the fusion zone between SnAgCu and SnPb close to anode side. Micro-cracks were found at cathode side after current stressing for as short as 100 h, and increased with current stressing time until the failure of solder joint. [ABSTRACT FROM AUTHOR]