Compression stress-strain and creep properties of the 52In-48Sn and 97In-3Ag low-temperature Pb-free solders

Abstract

Lead (Pb)-free, low melting temperature solders are required for step-soldering processes used to assemble micro-electrical mechanical system (MEMS) and optoelectronic (OE) devices. Stress-strain and creep studies, which provide solder mechanical properties for unified creep-plasticity (UCP) predictive models, were performed on the Pb-free 97In-3Ag (wt.%) and 58In-42Sn solders and counterpart Pb-bearing 80In-15Pb-5Ag and 70In-15Sn-9.6Pb-5.4Cd alloys. Stress-strain tests were performed at 4.4 × 10⁻⁵ s⁻¹ and 8.8 × 10⁻⁴ s⁻¹. Stress-strain and creep tests were performed at −25, 25, 75, and 100°C or 125°C. The samples were evaluated in the as-fabricated and post-annealed conditions. The In-Ag solder had yield stress values of 0.5–8.5 MPa. The values of ΔH for steady-state creep were 99 ± 14 kJ/mol and 46 ± 11 kJ/mol, indicating that bulk diffusion controlled creep in the as-fabricated samples (former) and fast-diffusion controlled creep in the annealed samples (latter). The In-Sn yield stresses were 1.0–22 MPa and were not dependent on an annealed condition. The steady-state creep ΔH values were 55 ± 11 kJ/mol and 48 ± 13 kJ/mol for the as-fabricated and annealed samples, respectively, indicating the fast-diffusion controlled creep for the two conditions. The UCP constitutive models were derived for the In-Ag solder in the as-fabricated and annealed conditions.

Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the US Dept. of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.