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 similar to 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.