Abstract

This study reports results of shear creep behavior of four Pb-free solders, Sn-3Ag-0.5Cu, Sn-3.5Ag, Sn-0.7Cu and Sn-10In-3.1Ag at 95θC and 130θC. At the stress levels tested, all the four solders showed the stress components close or larger than 5, typical for matrix creep. The calculated activation energies for Sn-0.7Cu, Sn-3.5Ag and Sn-3Ag-0.5Cu are from 103kJ/mol to 117kJ/mol, which are very close to the pure Sn self-diffusion activation energy (107kJ/mol). It suggested that the creep process is controlled by Sn bulk self-diffusion rate. The creep activation energy for Sn-10In-3.1Ag is higher in the range of 173–193kJ/mol.

The Sn-0.7Cu, Sn-3Ag-0.5Cu and Sn-10In-3.1Ag solder joints were also prepared with two different cooling rates, 3.5θC/min. (furnace-cooling) and 2.7θC/S (air-cooling) and tested at 130θC. It was observed that faster cooled solder joints have faster creep strain rates than slower cooled solder joints at the stress levels tested for all three solders, due to the fine and even distribution of intermetallic particles.

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