Abstract
The Sn-3.5Ag and Sn-3.5Ag-0.2Co-0.1Ni lead-free solders were investigated on common electronics substrates, namely, organic solderability preservative (OSP) and electroless Ni/immersion Au (ENIG) surface finishes. The formation of Kirkendall voids at the interfacial region during isothermal solid aging was explored. For the Sn-3.5Ag-0.2Co-0.1Ni/OSP solder joint, the Kirkendall voids were present after isothermal solid-state aging at higher temperature (e.g., 150°C); however, the size of voids did not change remarkably with prolonged aging time due to the depressed Cu 3 Sn layer growth. For ENIG surface finishes, the 0.2Co-0.1Ni additions seemed to enhance the longitudinal groove-shaped voids at the Ni 3 P layer; however, void formation at the solder/Ni 3 Sn 4 interface was effectively reduced. This might be attributed to the reduced Sn activity in the solder matrix and the suppressed Ni-P-Sn layer formation.
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