The anand parameters of aging resistant doped solder alloys

Due to growing environmental concerns, lead-free solder materials are being widely used in electronic assemblies. The Anand viscoplastic constitutive model is frequently used to represent mechanical behavior of lead-free solder materials in finite element simulations. However, prior experimental results have demonstrated that properties of lead-free solder materials degrade over time when exposed to isothermal aging. These aging-induced degradations are more severe in harsh environments (e.g. high temperature). Our previous studies have revealed that dopants in SAC (Sn-Ag-Cu) alloys can be successfully used to reduce, and in some cases prevent, aging-induced degradations. In the present study, we have explored the mechanical properties of a new lead-free doped SAC solder alloy referred to as SAC_Q (commercially known as CYCLOMAX). SAC_Q has been recommended for high-reliability applications by its vendor. Uniaxial samples were prepared for the alloy, and some samples were aged in an oven at T = 100 °C for 3 months. Uniaxial tensile tests were performed with the doped alloy of both non-aged and aged microstructures. Testing conditions included three different strain rates (0.001, 0.0001 and 0.00001 sec
⁻¹
) and five different test temperatures (25, 50, 75, 100 and 125 °C). Tensile test results for the doped alloy, before and after aging, were compared with those of standard SAC305. Anand parameters of the doped alloy for the various aging conditions were determined from the stress-strain test results. A good correlation was found between Anand model predictions and the experimentally obtained results. A microstructure study has revealed that the Bismuth (Bi) present as a dopant in the SAC_Q alloy plays an important role to make the alloy relatively insensitive to aging-induced degradations.