Effects of printed circuit board surface finish and thermomechanical fatigue on the microstructure and mechanical strength of small outline J leads/Sn-X (X = AgCu and Pb) solder joints

摘要

The effects of printed circuit board (PCB) surface finish and thermomechanical fatigue (TMF) on the microstructure evolution and mechanical strength of SOJ/SnAgCu and SOJ/SnPb solder joints were investigated. Experimental results revealed that the load bearing length decreased as the lead back side contact angle increased. The load bearing length determined the initial pull strength of the as-soldered solder joints. The pull strengths of the solder joints decreased as the number of TMF cycles increased. Gradual coarsening of the Pb particles in the SnPb solder matrix due to TMF resulted in a decline in the pull strength of the SOJ/SnPb solder joints. Thickening of the HAC layer at the interfaces of SOJ lead and SnAgCu solder due to TMF caused the strength of the SOJ/SnAgCu solder joints to decrease.