International Conference on Electronic Packaging Technology & High Density Packaging, 2009. ICEPT-HDP '09., Vol., No., pp 116-122, August 10-13 2009

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

Shunong Zhang, Michael Osterman, Member, IEEE , Anshul Shrivastava, Rui Kang, and Michael G. Pecht, Fellow, IEEE
Dept. of System Engineering of Engineering Technology, Beijing University of Aeronautics and Astronautics, Beijing, 100191, P. R. China
Center for Advanced Life Cycle Engineering (CALCE), University of Maryland, College Park, MD 20742
Dept. of Electronic Engineering, City University of Hong Kong


This study focuses on the corrosion of immersion silver (ImAg) finished copper land patterns on printed circuit boards (PCBs) due to SO 2 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 SO 2 gas environment: direct chemical corrosion and electrode reaction. No evidence shows that Ag 2S and Cu 2S or CuS were produced. In high humidity, chemical and electrode reaction both existed, and the corrosion products could included Ag 2O, AgCl, Ag 2SO 3 , CuO, CuCl 2 and CuCl, In low humidity, the chemical corrosion was predominant, and the corrosion products could include Ag 2O, CuO. Passive films were formed on ImAg finished surface under long exposure time. The temperature from 30°C to 40°C did not have an obvious influence on the ImAg-finished PCBs.

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