Influence of thermomigration on lead-free solder joint mechanical properties

Thermomigration experiments were conducted to study the change in mechanical properties of 95.5Sn-4Ag-0.5Cu (SAC405) lead-free solder joint under high temperature gradients.This paper presents some observations on samples that were subjected to 1000°C/cm thermal gradient (TG) for 286 h, 712 h, and 1156 h.It was observed that samples subjected to thermal gradient did not develop a Cu₃Sn intermetallic compound (IMC) layer, and we observed disintegration of Cu₆Sn₅ IMC.On the other hand, samples subjected to isothermal annealing exhibited IMC growth.In samples subjected to thermomigration, near the cold side the Cu concentration is significantly higher compared with hot side.Extensive surface hardness testing showed an increase in hardness from the hot to cold sides, which possibly indicates that Sn grain coarsening is in the same direction.