Comparison of strength degradation for SnAgCu solders with various Ag contents during thermal cycling

Abstract

The mechanical damage of Sn-0.3Ag-0.7Cu, Sn-xAg (x = 1.0, 2.0, and 3.0)-0.5Cu solder joints were investigated under the harsh isothermal aging and thermal–mechanical cycling, respectively. The results reveal that the shear properties of the single ball SAC/Cu after reflow soldering have a strong positive correlation with the Ag content. While after 250–1000 h aging at 170 °C, their shear strength all decreases and the effect of Ag contents on the shear strength variation eliminates, indicating that aging-induced Ag₃Sn coarsening leads to a weaker difference in strength. Similar results are observed in the solder joints of 0603 resistor packages subjected to − 40–125 ℃ thermal–mechanical cycling during 0–1000 cycles. While after 1000–2000 cycles, the shear strength of xAg joints exhibit an opposite trend with Ag contents. Meantime, the cracks appear, and their length is proportional to Ag content. Thus, their shear strength variation mainly relies on their crack length. Namely, the strength degradation of xAg joints of 0603 resistor packages during thermal cycling can be divided into the Ag₃Sn coarsening-dominated stage and the late crack length-dominated stage. This study provides a theoretical basis for understanding the damage degradation mechanism of varying Ag content alloys and the possibility of reducing the Ag content.