Influence of rapid thermal cycling on the microstructures of single SnAgCu and SnPb solder joints

Lead-free solder joints in electronic packages experience the thermal cycles as the electronic packaging products encounter the temperature fluctuations. This study provides some prospectives into the microstructural changes of the solder joints interconnection by rapid thermal cycles. The goal of this paper is to investigate the thermal fatigue behavior of a single Sn-3.0Ag-0.5Cu (SAC) lead-free and 63Sn-37Pb (SnPb) lead-containing solder joint treated by rapidly alternating heating and cooling cycles. The microstructure and morphology of the interface between the solder ball and Cu substrate was observed using scanning electron microscopy (SEM). The intermetallic compounds (IMC) and the solder bump surface were analyzed by energy dispersive X-ray (EDX) and respectively. The experimental results showed that rapid thermal cycling had an evident influence on the interfacial microstructure of a single solder joint. The experiment revealed that microcracks initiate at the bottom of the SAC solder joint. In addition, rimous cracks initiated and propagated on the superficial oxide of the solder bump after rapid thermal cycling. The temperature distribution can be explained by finite element modeling (FEM) according to heat deformation theory in materials physics and based on metal thermal fatigue mechanism.