The iNEMI technical subcommittee on creep corrosion is developing a flowers-of-sulfur (FOS) based qualification test for creep corrosion on printed-circuit boards (PCBs). In phase 1 of the project, the performances of FOS chambers of two designs were evaluated by measuring the corrosion rates of copper and silver foils. This paper deals with the phase 2A of the project in which PCBs with immersion silver (ImAg) and lead-free hot-air-surface- level (HASL) finishes soldered with rosin and organic acid fluxes were tested. The test variables were chamber temperature, type of saturated salt solution determining the relative humidity, chamber setup and particulate contamination. The results of test runs conducted at 4 laboratories involved in the round robin testing are very promising. The ImAg PCBs soldered with organic acid flux suffered the most creep corrosion in agreement with the generally agreed to field experience. There were fewer instances of creep corrosion on test PCBs with ImAg finish soldered with rosin flux and on test PCBs with lead-free HASL finish. Creep corrosion was generally associated with plated through holes (PTHs). Contaminating the test PCBs with ammonium salts contributed to more creep corrosion but made the test somewhat less discriminatory in that even test PCBs with HASL finish soldered with rosin flux suffered some creep corrosion.
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