Creep behavior of the ternary 95.5Sn-3.9Ag-0.6Cu solder: Part II—Aged condition

Compression creep tests were performed on the 95.5Sn-3.9Ag-0.6Cu (wt.%) solder. The specimens were aged prior to testing at 125°C, 24 h or 150°C, 24 h. Applied stresses were 2–40 MPa. Test temperatures were −25°C to 160°C. The 125°C, 24-h aging treatment caused the formation of coarsened Ag₃Sn particle boundaries within the larger ternary-eutectic regions. The 150°C, 24-h aging treatment resulted in contiguous Ag₃Sn boundaries in the ternary-eutectic regions as well as a general coarsening of Ag₃Sn particles. The 125°C, 24-h aging treatment had only a small effect on the strain-time curves vis-à-vis the as-cast condition. Negative creep was observed at 75°C for time periods >10⁵ sec and stresses of 3–10 MPa. The creep kinetics exhibited a sinh term (stress) exponent, p, of 5.3±0.6 and an apparent-activation energy, ΔH, of 49±5 kJ/mol when data from all test temperatures were included. A good data correlation was observed over the [−25–125°C] temperature regime. Steady-state creep kinetics exhibited a greater variability in the [125–160°C] regime because of the simultaneous coarsening of Ag₃Sn particles. The aging treatment of 150°C for 24 h resulted in a more consistent stress dependence and better reproducibility of the creep curves. Negative creep was observed in samples aged at 150°C for 24 h when tested at −25°C, 25°C, and 75°C. The values of p and ΔH were 4.9±0.3 kJ/mol and 6±5 kJ/mol, respectively. Only a slight improvement in the data correlation was observed when the analysis examined separated [−25−75°C] and [75–166°C] temperature regimes. Creep testing did not cause observable deformation in any of the sample microstructures.