Intermetallic growth studies on SAC/ENIG and SAC/Cu-OSP lead-free solder joints

Lead-free solder joint reliability in electronic packaging assemblies is a concern when the product is subject to thermal exposure. The intermetallic compound (IMC) growth in Sn3.8Ag0.7Cu(SAC)/ENIG and SAC/Cu-OSP solder joint at different thermal aging condition were reported in this study. The IMC growth behavior subjected to isothermal aging exposure at 125degC and thermal cycling with upper soak temperatures of 125degC are compared. It shows that the growth of Cu-Sn and NiCuSn IMC for TC were accelerated compared to isothermal aging based on the proposed equivalent isothermal aging time. Further observation on the solder alloy near the joint shows that dynamic recrystallization of Sn-rich phase occurred and the size of grains decrease from 20 to less than 10 microns. For isothermal aging at 125degC, the grain size increased and some grain boundaries disappeared. After thermal aging with different time, ball shear test were performed to measure the strength of the solder joint. Decrease of shear strength could reach 60-80% after TC aging while no significant change after isothermal aging