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

Abstract

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 Ϫ25°C to 160°C. The 125°C, 24-h aging treatment caused the formation of coarsened Ag 3 Sn particle boundaries within the larger ternary-eutectic regions. The 150°C, 24-h aging treatment resulted in contiguous Ag 3 Sn boundaries in the ternary-eutectic regions as well as a general coarsening of Ag 3 Sn 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 Ͼ10 5 sec and stresses of 3-10 MPa. The creep kinetics exhibited a sinh term (stress) exponent, p, of 5.3 Ϯ 0.6 and an apparent-activation energy, ∆H, of 49 Ϯ 5 kJ/mol when data from all test temperatures were included. A good data correlation was observed over the [Ϫ25-125°C] temperature regime. Steady-state creep kinetics exhibited a greater variability in the [125-160°C] regime because of the simultaneous coarsening of Ag 3 Sn 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 Ϫ25°C, 25°C, and 75°C. The values of p and ∆H were 4.9 Ϯ 0.3 kJ/mol and 6 Ϯ 5 kJ/mol, respectively. Only a slight improvement in the data correlation was observed when the analysis examined separated [Ϫ25-75°C] and [75-166°C] temperature regimes. Creep testing did not cause observable deformation in any of the sample microstructures.

Temperature Dependence of Creep and Hardness of Sn-Ag-Cu Lead-Free Solder

“…Incidentally, the stress exponent values in our study are comparable to the range of stress exponents (n = 7 to 4) and (n = 8 to 4) obtained, respectively, in bulk tension samples of Sn-3.9Ag-0.6Cu (from À25°C to 160°C) 22,23 and Sn-3.5Ag-(0 to 1.5)Cu (at 100°C). 24 The results in this study also reveal the same observation as reported by other researchers, [22][23][24] in that increasing temperature leads to decreasing stress exponent (n). It is well established that the applied stress and the testing temperature are factors influencing creep.…”

Effect of reflow and thermal aging on the microstructure and microhardness of Sn-3.7Ag-xBi solder alloys

“…However, the coarsening of Ag 3 Sn particles is relatively slow because it is a covalently bonded compound. 21 A high activation energy is required to break the covalent bonds in the particles in order to allow Ag to diffuse toward growing particles. At the aging temperature of 150°C, the solubility of Bi in Sn is around 18 wt.%.…”

Dynamic Recrystallization (DRX) as the Mechanism for Sn Whisker Development. Part I: A Model

“…For example, in terms of D o , the Sn grain size changes very little with typical annealing treatments at 150°C (e.g., 1 h to 24 h). 30,31 Concurrently, the Sn whisker density did not change significantly as a consequence of the annealing treatment. 31 A similar observation was made by Cheng et al on evaporated Sn films ($1 lm grain size).…”