Compression Stress/Strain Response of the 95.5Sn-3.5Ag-0.6Cu Solder
P. Vianco and J. Rejent
Sandia National Laboratories
Constitutive-based, computational models can provide high-fidelity predictions of solder interconnect degradation, particularly under cyclic loading conditions. However, the development of these predictive codes requires the availability of both time independent and time dependent mechanical properties for the solder composition. Such a data base is being compiled in an effort to develop a constitutive model for the 95.5Sn-3.9Ag-0.6Cu (wt.%) Pb-free solder. Compression testing was used to assess the time independent properties of the solder in the as-cast condition as well as after a stabilization treatment (125°C, 24 hours). Yield stresses were measured over the temperatures of –25°C to 160°C, using strain rates of 4.2 x 10-5 s-1 and 8.3 x 10-4 s-1. The yield stress values ranged from approximately 40 MPa at –25°C to 10 MPa at 160°C for tests performed at 4.2 x 10-5 s-1. The values were not significantly affected by the aging treatment nor a change in strain rate. The true stress/true strain curves suggested the simultaneous occurrence of dynamic recovery and dynamic recrystallization processes. Aging the sample prior to testing, as well as a faster strain rate, mitigated both phenomena. The complication to constitutive model development resulting from recovery and recrystallization mechanisms will be discussed.
 Sandia is a multi-program laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the US Dept. of Energy under contract DE-AC04-94AL85000.