The influence of SO2 environments on immersion silver finished PCBs by mixed flow gas testing

This study focuses on the corrosion of immersion silver (ImAg) finished copper land patterns on printed circuit boards (PCBs) due to SO₂ exposure in a mixed flow gas chamber. Six test conditions were examined with varying concentrations, temperatures, relative humidity, and exposure times. The results indicated that there are two mechanisms of corrosion on ImAg-finished PCBs in an SO₂ gas environment: direct chemical corrosion and electrode reaction. No evidence shows that Ag₂S and Cu₂S or CuS were produced. In high humidity, chemical and electrode reaction both existed, and the corrosion products could included Ag₂O, AgCl, Ag₂SO₃, CuO, CuCl₂ and CuCl, In low humidity, the chemical corrosion was predominant, and the corrosion products could include Ag₂O, CuO. Passive films were formed on ImAg finished surface under long exposure time. The temperature from 30degC to 40degC did not have an obvious influence on the ImAg-finished PCBs.