Impact reliability enhancement approach of Sn-Bi-Zn-in alloy bumps under high-humidity and high-temperature tests

Sn-45Bi-2.6Zn-0.5In and Sn-45Bi-2.6Zn-1In alloys have previously been shown to be superior to Sn-58Bi under the thermal aging test. In this study, a comparative analysis of the microstructure and impact strength of Sn-58Bi, Sn-45Bi-2.6Zn-0.5In, and Sn-45Bi-2.6Zn-1In alloy bumps was conducted before and after highhumidity and high-temperature tests. Cross-sectional microstructure observations and impact tests were performed on all alloy bumps. The results indicated that the high-humidity and high-temperature conditions had a slight influence on the Sn-58Bi alloy bump, but it reduced the maximum force of Sn-45Bi-2.6Zn-0.5In and Sn-45Bi-2.6Zn-1In to almost zero and generated voids at the interface between the alloy and Cu pad after the test. This deterioration was mainly attributed to the formation of voids on the accumulated Zn at the interface under the effects of both high-humidity and high-temperature conditions. In addition, a possible approach for enhancing the impact strength of Zn-containing alloy bumps by adjusting the heating profile was proposed, and it was verified that the maximum force of the Zn-containing alloy bumps was significantly improved.