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Low Temperature Solder Alloys for Portable Electronics
Materials Tech |
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Authored By:Morgana Ribas, Ph.D., Anil Kumar, Ranjit Pandher, Ph.D., Rahul Raut, Sutapa Mukherjee, Siuli Sarkar, Ph.D. and Bawa Singh, Ph.D. Alpha South Plainfield, NJ SummaryWe present here the findings of Alpha's Alloy Development Program on the next generation of low temperature alloys that can be used in reflow soldering temperatures from 170 to 200oC. Approaches in alloy development, test methodologies and results are discussed. The alloy properties targeted for improvements include: Alloy strength, alloy ductility, microstructure stability, improvements in thermal cycling, high temperature creep and drop shock. We show how the use of micro-additives in eutectic Sn-Bi alloys improves these properties. Further, comprehensive reliability studies were undertaken for new low temperature alloys. Thermal Cycling was undertaken from -40 degrees C to +125 degrees C with a 10 minute dwell time. Compared to standard Sn-Bi systems, improvements in thermal fatigue resistance are discussed. The basic properties of the new alloys shown here were fully characterized and their use in SMT applications evaluated, especially in drop shock and temperature cycling tests. In summary, we present here a new generation of low temperature Pb-free alloys, which are capable of delivering high reliability performance at low soldering temperatures. Various alloy compositions were evaluated and alloy B showed superior performance versus the benchmark and other low temperature alloys. Overall, the new low temperature alloys show significant improvements in metallurgical properties, soldering properties for SMT assembly, and thermal and mechanical reliability. Conclusionsgenerated at every stage of the low temperature alloy development process. Multiple test methods have used to evaluate and understand the solder alloys. Basic mechanical properties and creep behavior of the bulk solder has been used to predict mechanical and thermal fatigue life of the final solder joints. Real life tests have been used to confirm the predictions. New, short listed alloy shows significant improvements in drop shock as well as thermal cycling performance as compared to Sn42Bi58 and Sn42Bi57.6Ag0.4 eutectic alloys. New alloy also shows dramatically lower Cu dissolution rate. Initially Published in the SMTA Proceedings |
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