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

• Firstly study the electro-migration on SnAgCu/SnPb structural composite joints.
• Interfacial IMC growth at anode side caused by polarity effect was depressed.
• Coarsened Cu6Sn5 particles were produced in fusion zone between SnAgCu and SnPb.

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 2.0×103 A/cm2 at 100 °C. Cu flux diffusion induced by electro-migration was delayed by Ag3Sn particles in eutectic phase of Sn3.0Ag0.5Cu solder, by which Cu6Sn5 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 Cu6Sn5 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.