Effects of Mechanical Deformation and Annealing on the Microstructure and Hardness of Pb-Free Solders

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The microstructure-property relations of several Pb-free solders have been investigated in order to understand the microstructure changes during thermal and mechanical processes of Pb-free solder joints. Pb-free solder alloys investigated include pure Sn, Sn-0.7%Cu, Sn-3.5%Ag and Sn-3.8%Ag-0.7% Cu (in weight). To reproduce a typical microstructure observed in solder joints, the cooling rate, ingot size and reflow conditions of cast alloys are carefully controlled. The cast alloy pellets are subjected to compressive deformation up to 50% and annealing at 150°C, 48 h. The microstructure of Pb-free solders is evaluated as a function of alloy composition, plastic deformation and annealing. The changes in mechanical property are measured by microhardness test. The work hardening in Sn-base alloys is found to increase as the amount of alloying elements and/or deformation increases. The changes in microhardness upon deformation and annealing have been correlated with the microstructural changes, such as recrystallization or grain growth in Pb-free solder alloys.

By: Paul A. Lauro, Sung K. Kang, Da-Yuan Shih, Won Kyoung Choi

Published in: Journal of Electronic Materials, volume 32, (no 12), pages 1432-40 in 2003


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