Influence of silver content on fatigue life and failure mechanism of lead-free solder joints under drop conditions

Drop tests were carried out with three kinds of materials (Sn-3.0Ag-0.5Cu, Sn-1.0Ag-0.5Cu and Sn-0.3Ag-0.7Cu), respectively. Half-sine acceleration loads was applied in the experiment, the peak value of half sine acceleration and pulse duration were 3200g and 1ms. The failure position of solder joint was identified and analyzed using electrical test, optical microscope, scanning electron microscope. The results show that most of the failures joints for the three kinds of materials locate at the printed circuit board (PCB) side. The solder joints at four outermost corners fail at first. And the failure modes of Sn-3.0Ag-0.5Cu and Sn-1.0Ag-0.5Cu were all brittle fractures, while the Sn-0.3Ag-0.7Cu is brittle-ductile fracture. The thickness of intermetallic compound(IMC) gradually decreases and the life of solder joint enhances with the reduction of Ag content.