The Study Of Sn-3.0Ag-0.5Cu-XNi Lead-free Solder And Joint Point Microstructure And Property

In recent years, with the development of microelectronics and Surface Mounted Technology, researching of lead-free solder becomes one of the hot projects. As a country with amount of export home appliances, the research on low cost, good properties lead-free solders with sdlf-determined property right has very important economical and social signigicance.Because of excellent synthetical capability, Sn-Ag-Cu system lead-free solder is thought of the best solder, which can replace Sn-Pb solder, in the researchful lead-free solder at present. This article chooses Sn-3.0Ag-0.5Cu lead-free to study by analyzing the effect of Ag,Cu content on the base solderability. Then we add little amount of Ni element to study the effect of Ni element on melting point,wettability,mechanics capability,joint point microstructure and property.The results shows as follow: The melting point raises a little as Ni element is added into Sn-3.0Ag-0.5Cu lead-free solder. there are no low-temperature eutectic peak, which indicated that no low-temperature eutectic phase is formed while little amount of Ni element is added into Sn-3.0Ag-0.5Cu solder and reliable soldered joints can be formed. The wettability of solder alloy was improved when Ni is added. When Sn-3.0Ag-0.5Cu lead-free solder contains 0.10wt% Ni, the wetting time is shortest by 0.92s and the wetting force is largest by 3.61mN. This value meets the practically mechanisation requirement t≤2.5s and Fmax≥3.0mN. Therefore, Sn-3.0Ag-0.5Cu-0.10Ni lead-free solder has a favorable wettability. After adding Ni into the solder theβ-Sn phase is refined, and the thin and dispersively distributed (CuxNi1-x)6Sn5 phases turn out in the mircostructure. Those are benefit to the improvement of solders mechanical property. When Ni content is at 0.10wt%, the tensile and elongation percentage of solder is 47.85Mp and 40.40%, which is 6.3% and 81.6% higher than that of Sn-3.0Ag-0.5Cu lead-free solder. When the proportions of Ni is 0.10 wt%, the shear strength of solder joint is the biggest at 40.28MPa which is 22.28% higher than that of Sn-3.0Ag-0.5Cu lead-free. The thickness of Sn-3.0Ag-0.5Cu/Cu IMC becomes a little bigger after adding Ni element, but that of Sn-3.0Ag-0.5Cu/Ni IMC is 31.04% smaller than that of before which shows that adding little amount of Ni element can restrain the growth of IMC. After aging different hours at 150℃, the thickness of IMC becomes much larger, but Sn-3.0Ag-0.5Cu-0.10Ni lead-free solder shows much better.