Aging aware constitutive models for SnAgCu solder alloys

Recent studies on SnAgCu alloys have identified aging-time and aging-temperature as factors that significantly alter solder material behavior and microstructure [1-3]. Microstructural changes are driven by dislocation motion and diffusion processes. Together they affect the flow behavior in solder alloys. In this paper, we build on the results from our earlier analysis of creep data on aged Sn3.0Ag0.5Cu [4] solder alloy. We address three aspects of solder microstructure and behavior as affected by aging. We develop an analytical model for intermetallic particle growth and an aging aware creep law that captures Secondary creep-plasticity in solders. The basis for the constitutive models is exhaustive aging and creep test experiments conducted on the alloy. Solder samples were aged for different aging times (15, 30, 60, 90 days) and at different aging temperatures (25°C, 75°C, 125°C) prior to running creep tests. Another set of solder samples were similarly aged to characterize the microstructure. The creep data for the experiments are from a series of sixty four experiments performed using a micromechanical tester that is specially fitted with a sensitive capacitance gauge (with a resolution of 0.1 microns) to accurately measure viscoplastic responses of solder to applied loads.