Q. Zhang, P. Haswell, A. Dasgupta, and Michael Osterman
CALCE Electronic Products and Systems Center
University of Maryland
College Park, MD 20742
The isothermal mechanical durability properties of two lead-free solder alloys, Sn3.5Ag and Sn3.9Ag0.6Cu, are presented and compared to that of the baseline eutectic Sn37Pb solder. Cyclic mechanical tests are performed at room temperature at various strain-rates and load levels, using a thermo-mechanical-microstructural (TMM) test system developed by the authors. The data is analyzed using standard power-law durability models based on work and inelastic strain range. Durability is characterized in terms of crack propagation rate. The Sn3.9Ag0.6Cu lead-free solder is found to be most durable, followed by the Sn3.5Ag solder and finally the baseline Sn37Pb eutectic solder, under the test conditions investigated. However, tests at high load levels show a greater difference in durability than tests at low load levels. This trend is opposite of the trends observed under thermal cycling.
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