New approach for High Reliable & Cost-Effective Solder alloys for Automotive Applications

Commercially known as Innolot, the highly reliable lead-free alloy, allowing for high operating temperatures, is a Tin-Silver-Copper (SAC) metallurgical system with additional elements to harden the alloy and to improve 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 temperature cycle tests (TCT) from −40°C to +125°C or even extended to 150°C. Assemblies in the automotive industry increasingly require higher reliability for safety relevant and emerging applications such as Advanced Driver Assistance Systems (ADAS). Cost-reduction requirements demand a new approach for optimized soldering processes and materials. As the current reflow process prefers Nitrogen atmosphere for low defects in high reliability soldering, our research focuses around the partial and/or complete change to air soldering processes. Furthermore, we investigate the influence of different surface finishes such as Chemical Sn, NiAu, and Cu OSP, and modified alloy compositions in the soldering performance. Apart from initial characterizations for various assemblies, reliability tests on Heraeus Reliability1 printed circuit boards as well as temperature cycle tests from −40 to +150°C for up to 2500 cycles are reported and resulting failure modes are discussed. This paper furthermore describes the potential for cost reductions via process and/or material optimizations without diminishing the high reliability performance for such automotive applications.