Simulation of Microstructural Evolution During Thermomechanical Cycling inpb-Sn Solders
- PDF / 740,998 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 54 Downloads / 217 Views
Simulation of Microstructural Evolution During Thermomechanical Cycling in Pb-Sn Solders Michael Woodmansee and Veena Tikare1 The Georgia Institute of Technology, The George W. Woodruff School of Mechanical Engineering, Atlanta, GA 30332-0405, U.S.A. 1 Sandia National Laboratories, Albuquerque, NM 87185-1411, U.S.A.
ABSTRACT Pb-Sn solders are known to coarsen and deform heterogeneously under shear thermomechanical cycling. Solder joint failure often occurs within these coarsened shear bands. The connection between microstructure and materials properties is well documented, which leads to the conclusion that an improved understanding of the interaction between stress and microstructural evolution will better enable the prediction of materials properties over time. In this paper, we simulate microstructural evolution of Pb-Sn solders using a novel two-phase version the Potts model, a kinetic Monte Carlo model that is coupled to a finite element mechanics model. Using this model, possible mechanisms for heterogeneous coarsening are explored.
INTRODUCTION Near-eutectic Sn-Pb solder (63Sn-37Pb) is a binary, two-phase alloy. The Sn-rich phase, the dominant or matrix phase, is an alloy of composition 97.5Sn-2.5Pb. The Pb-rich phase, the secondary phase, is an alloy of composition 80.8Pb-19.2Sn. Sn-Pb solders became popular for use in electronics manufacturing primarily because of their low liquidus temperature of about 183°C for the eutectic. This property helps avoid high processing temperatures that tend to damage the substrate and components during assembly. Soldered interconnects in electronic packages are designed to maintain an electrical, mechanical and thermal interconnect between two components. Pressure to miniaturize electronic devices has popularized the use of surface mount technologies that put solder joints in a more prominent role as load-bearing members in electronic packages. During temperature changes within the electronic package, temperature gradients and mismatches in the coefficients of thermal expansion (CTE) between component and substrate are usually resolved as shear stresses in the solder joint when it is the only structural bridge. Soldered interconnects in an electronic package may be exposed to temperatures ranging from -55°C to 125°C (0.45 < T / Tmelt < 0.90) depending on the specific application. This is a significantly higher homologous temperature than other traditional high temperature structural alloys such as titanium alloys (0.25 < T / Tmelt < 0.55) and nickel base superalloys (0.20 < T / Tmelt < 0.70). Therefore, deformation and degradation mechanisms of solder alloys are dominated by time-dependent, thermally-activated processes such as creep and stress relaxation. W6.4.1 Downloaded from https://www.cambridge.org/core. Columbia University Libraries, on 28 Aug 2017 at 07:32:15, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/PROC-731-W6.4
Mat. Res. Soc. Symp. Proc. Vol. 731 © 2002 Materials Research Society
O
Data Loading...
