Mechanical Behavior And IMC Evolution Of Low-Ag Lead-Free Solder Micro-Joints

It is gradually recognized that low-Ag Sn-Ag-Cu solder is one of the bestlead-free solders alloy systems for its low cost and anti-dropping capability is thesame as or better than that of Sn-37Pb solders, but they still exist some problemsin industry. Therefore, it’s necessary to improve the performance by adding somealloy elements. A low-Ag solder, SAC-Bi solder alloy has been developed in ourlaboratory for its superior performance in melting temperature and wettability.This paper studied the effect of Ni(0~0.15wt%) on IMC morphology of solderjoints, the growth rate and the shear strength of joint, plasticity, Hit and E ofSAC-Bi-based solder after aging at160℃for0h,200h and400h. In older to getthe soldering process curve of new low-Ag lead-free solder, we can study the sizeof IMC particle and shear strength of low-Ag lead-free solder when the solderingparameters (peak temperature, cooling rate) was changed. In older to get theeffect of shear parameter on the shear strength, we can study the shear strength oflow-Ag lead-free solder when the shear parameter (shear hight, shear speed,diameter of pad) was changed.The results indicated that SAC-Bi-xNi/Cu got bigger shear strength, Young’smodulus, hardness, plasticity and less fracture dimples while the Ni content was0.10%; got thinner thickness of IMC while the Ni content was0.05%before andafter aging. The size of IMC particle enlarged obviously, the thickness of IMCincreased, the micromechanical property of solder joint decreased after aging.The size of IMC particle decreased with the increasing of Ni content.The size of IMC particle increased with increasing of peak temperature, theshear strength of solder joint was the biggest when the peak temperature was250℃. The size of IMC particle increased with the decreasing of cooling rate,and the shear strength of solder joint was the biggest with air cooling.The shear strength of solder joint increased with the increasing of shearheight while the shear speed and the diameter of pad were constant. The shear strength of solder joint increased with the increasing diameter of pad while shearheight and shear speed was constant. While the shear height exceeds50μm andshear speed exceed0.1mm/s, the range of solder joint shear strength decreasedwas not obvious. The shear strength of solder joint decreased with the increasingof pad diameter while the shear speed and shear height was constant. The rangeof solder joint shear strength decreased was obvious while the shear heightexceeds760μm.