Fatigue life studies on defect-free solder joints fabricated from modified reflow soldering

This paper describes the improved characteristics of defect-free solder joints fabricated through modified reflow soldering. The modified method only requires that the solder joints are split for a very short time during a conventional solder reflow. The fatigue properties and microstructure of the solder joints are critically studied. It is found that the method of splitting is effective in eliminating pore formation (both gas and shrinkage pores) and inclusions in solder joints. The method is applicable to various solder pastes, whether it be no-clean or water-soluble. Thermal and mechanical fatigue cycling tests show that the fatigue life of the solder joints can be prolonged by more than 60% as compared to that without splitting. Fractographs illustrate that the fracture in the fatigued joints occurs quite often at the interfaces of printed circuit board (PCB) and copper pads when splitting has been applied to the joints. This affirms that the solder joints have been strengthened considerably by splitting. The proposed method is particularly suitable for specimens with a large pad area in each joint or when the pores or inclusions are likely to form during solder joint fabrication.