Effect of strain-enhanced microstructural coarsening on the cyclic strain-hardening exponent of Sn-Ag-Cu joints

The effects of temperature and strain-enhanced coarsening of intermetallic compounds (IMCs) on the cyclic strain-hardening exponent of Sn-Ag-Cu microsolder joints were investigated. The effect of temperature on the exponent is described by the Arrhenius function, and the cyclic strain-hardening exponent is proportional to the reciprocal square root of the average radius of the IMCs. Ag₃Sn and Cu₆Sn₅ IMCs coarsened with time, temperature, and inelastic strain. In the growth process with time and temperature, the phase-size exponent and activation energy for a Sn-Ag-Cu microsolder joint were ~3 and 50 kJ/mol, respectively. Ag₃Sn and Cu₆Sn₅ growth with isothermal aging was controlled by the diffusion of Ag and Cu in the Sn matrix. In addition, the strain-enhanced coarsening of the IMCs can be described by the growth model with consideration of isothermal aging and inelastic strain-enhanced growth. Therefore, the cyclic strain-hardening exponent decreases with temperature, and the strain-enhanced coarsening of IMCs can be described by the reciprocal square root of the average radius of the IMCs and the strain-enhanced growth model.