An Advanced Study on Ion Impurities on Solder Resist and the Solutions for High-Temperature Reliability Performance

It is known that the high-temperature corrosion of Cu/Al inter-metallic compound (IMC) can be accelerated by ionic impurities of epoxy molding compounds (EMC). However, to our knowledge, there is seldom report in terms of the effect of ion impurities for solder resist. In the present work, an advanced ion extraction method by PCT was developed specifically to investigate the ions emitted from the surface of cured solder resist, and the influence of the ion impurities on the reliability of High Temperature Storage Life (HTSL) test and Highly Accelerated Stress Test (HAST) have been demonstrated. The results have suggested that even though the ion impurities in solder resist may not have dominant effect on the enhancement of crack failure under HTSL conditions, it could still be considered as a key factor for the reliability of package under elevated temperature, relative high humidity and voltage bias conditions. Since the presence of ion impurities in solder resist might have catalyzed the dry metal oxidation of Cu in HTSL test or act as a catalyst to accelerate Cu corrosion electrochemical reaction under the HAST condition. For this purpose, we achieved a new type of solder resist with extremely low ion impurities content to meet the needs of high temperature reliability in the future automotive application.