Effect of microstructure and IMC on single SnAgCu solder joint by rapid thermal cycles

Lead-free solder has been widely used in electronic packaging products in printed circuit boards (PCB). Because soldering in the microelectronics industry not only provides the electronic connection, but also ensures the mechanical reliability of solder joints under the complex service conditions. This study provides some prospective 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 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.