Investigation of factors that influence creep corrosion — iNEMI project report

Creep corrosion is a mass transport process in which solid corrosion products (typically sulfide) migrate over a surface. The corrosion product creeps onto the solder mask surface and causes short circuits between the adjacent pads and traces. Creep corrosion of electronic assemblies is a growing problem. Commonly seen in harsh environments, the failures result from the formation of copper sulfide films on Printed Circuit Board (PCB) assemblies in short period of time. The iNEMI Creep Corrosion Group working on understanding this issue has recently communicated the feasibility of simulating these corrosion signatures on electronic assemblies using a modified Mixed Flow Gas (MFG) test method. Since October 2009, iNEMI has organized phased projects to investigate creep corrosion. Phase 1 consisted of a survey to collect the data on creep corrosion failures and related factors in the electronics industry. The team also has communicated with ASHRAE, IPC 3–11g and Lawrence Berkley National Laboratory on related issues. In Phase 2, the team analyzed the output from Phase 1 and narrowed down the major factors that influenced creep corrosion. Phase 3 performs laboratory based experiments to further investigate the sensitivities of the influencing factors identified in Phase 1 and 2, including surface finish, flux, solder mask geometry, solder paste coverage, reflow and wave soldering and MFG test conditions (corrosive gas concentration, humidity, temperature). Results from the electrical resistance measurements coupled with detailed material analysis of the corrosion products will be presented in this paper.