Effects of additional Ni and Co on microstructural evolution in Sn-Ag-Bi-In solder under current stressing

With continuously shrinking process rules of electronic devices, the decreasing dimension of interconnections results in increasing electrical current density, and recalls the risk of massive electromigration (EM) of metal elements in solder joints. This paper reports that minor additions of Ni and/or Co to Sn-Ag-Bi-In lead-free solder to improve the EM behavior and microstructural evolutions in the solder material subjected to high electric current density of 10 kA/cm² over 200 hours. With additional Co elements, EM resistance of solder joint was improved as twice before with microstructural evolution by it.