Abstract
A long-term (1, 3, and 6 months) outdoor exposure test was performed for lead-free hot air solder leveling printed circuit boards (PCB–HASL) in typical environments in China and the corrosion behavior and mechanism of outdoor PCB–HASL were investigated. In a dry environment PCB–HASL corroded slightly, because of the protective effect of surface oxide films. Corrosion spread from places where dust particles were deposited or mold spores were adsorbed. Under the combined effects of humidity and contamination, large amounts of granular corrosion products with a loose structure were generated, greatly reducing the protective effect of the Sn layer. Furthermore, protection of the edges of the plates was poor, and corrosion products from these regions migrated rapidly on the FR-4 board. When a 12 V electrical bias was applied, Sn and Cu migrated simultaneously. In the electrochemical migration process the effect of humidity was much more critical than that of contamination.
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