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Combined Alloy and Flux Approach Cost-Effective Reliable Solder Joints
Materials Tech |
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Authored By:Manu Noe Vaidya, Sebastian Fritzsche, Peter Prenosil, Katja Stenger, Stefan Gunst, Stefan Merlau Heraeus Deutschland GmbH & Co. KG, Hanau, Germany SummaryInnolot® is a commercially well-known high reliable lead free alloy suitable for high operating temperatures. It is based on the Tin-Silver-Copper (SAC) metallurgical system and contains additional elements to harden the alloy and to increase its creep strength in order to significantly improve the reliability of solder joints. Compared to traditional SAC alloys, the characteristic lifetime can be enhanced on the base of TCT from -40°C to + 125°C or even extended to 150°C. Assemblies in automotive industry increasingly require higher reliability for safety relevant and new emerging applications such as ADAS. Cost-reduction requirements demand a new approach for optimized soldering materials and processes. Our investigations showed that with an improved alloy composition the material cost of our new high reliable alloy can be reduced. Additional cost benefits are achieved by transferring the reflow process to air atmosphere while maintaining high solder joint quality. This break-through was possible due to a combined approach of alloy and flux optimization, which resulted into an innovative high reliable solder paste system. This paper will show basic alloy and flux properties as well as temperature cycle test (TCT) results comparing the new formulation with SAC305 and Innolot® solder pastes in temperature ranges between -40°C to +125°C as well as +150°C. ConclusionsThe above reported results from the development of a high reliable solder alloy as well as the corresponding solder paste show that the choice of the right dopants and flux chemistry can ensure at least the same, if not even better performance than the Standard Innolot® alloy with a significantly lower metal costing. The known trade-off between material and process cost vs. the reliability performance was better understood with these studies and can help to select the right alloy composition. Therefore, the initial performance study on voids and blowholes showed a significant improvement with the high rel. solder alloy B3 especially for reflow processes in air atmosphere compared to other high Ag alloys – as Innolot® - even soldering in pure air is possible. In addition to the optimized Innolot® alloy, a new flux system could be developed which significantly improves solderability of Innolot® alloys in an air atmosphere and is able to achieve a performance close to a process using a nitrogen atmosphere. Both, the improved Innolot® alloy and the new flux system in combination provide the potential to reduce process costs by decreasing nitrogen consumption. For the introduction into cost-sensitive electronic assembly processes further reliability investigations on the advanced High Reliable Solder B3 formulation are ongoing - including temperature cycling tests with additional temperature ranges and more detailed evaluations. The results of these studies will be reported in upcoming publications. Initially Published in the SMTA Proceedings |
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