Study of impact of thermal refinishing process on reliability of COTS components

Aerospace, Defence and High Performance (ADHP) industry has little choice but to rely on the use of commercial-of-the-shelf (COTS) electronics components for their products and equipment. As these electronics components are now predominantly packaged as lead-free (Pb-free) to comply with RoHS and other similar legislations, their use in high reliability and long service life applications is highly problematic. Reliability of component assemblies with Pb-free finishes and Pb-free solder materials is highly uncertain due to the risk of short-circuit failures caused by tin whiskers growth. One strategy to mitigate this risk in the case of leaded components is to replace to Pb-free finishes with traditional tin-lead (SnPb) solder. This refinishing process, termed hot solder dipping, is available as fully automated robotic process. However, as it involves thermal loads, the impact of refinishing on components has to be understood. This paper details the advantages of using validated thermal models of HSD process to assess thermal responses and propensity to damage. Vulnerability of a component is strongly influenced by the package design and in particular by the nature of the heat path from the dipped terminations to the IC die.