Partially-Activated Flux Residue Influence on Surface Insulation Resistance of Electronic Assembly
Authors: Xiang Wei, Ph.D., Kyle Loomis, Jennifer Allen, Bruno Tolla, Ph.D. Company: Kester, Inc Date Published: 9/27/2015
Abstract: Surface insulation resistance (SIR) and electrochemical migration (ECM) are two of the primary reliability drivers in consideration of the performance of electronic assemblies. In recent years, the concern of “partially-activated” flux residue and their influence on reliability have been significantly raised due to the miniaturization along with high density design trend, selective soldering process adoption, and the expanded use of pallets in wave soldering process. When flux residue becomes trapped under low stand-off devices, pallets or unsoldered areas (e.g. selective process), it may contain unevaporated solvent, "live" activators and metal complex intermediates with different chemical composition and concentration levels depending on the thermal profiles. These partially-activated residues can directly impact the corrosion, surface insulation and electrochemical migration of the final assembly. In this study, a few application tests were developed internally to understand this issue. Two traditional liquid flux and two newly developed products were selected to build up the basic models. The preliminary results also provide a scientific approach to design highly reliable products with the goal to minimize the reliability risk for the complex PCB designs and assembly processes.