The comparison on the corrosion resistance of different kinds of PCB surface finishing: OSP, LF HASL and ENIG

Abstract

This study focuses on the evaluation and comparison on the corrosion resistance of different kinds of surface finishing on printed circuit boards (PCBs) under high sulfur environments. The modeling clay being used is made by Chavant (type J-525) Company in this experiment. The content of sulfur in this clay was measured by an X-ray energy dispersive spectroscope and was about 18% (weight percentage). Clays containing sulfur were heated with water to simulate high sulfur environment and to drive creep corrosion on organic solderability preservative (OSP), lead free hot air solder level (LF HASL) and electroless nickel immersion gold (ENIG) PCB finishing via plugging methods and paste test via. The corrosion rate and the dendrite length of creep corrosion will increase when the retention time increases. The creep distance and the content of copper sulfide in the corrosion area were dependent on the relative location of the pad edges and the solder mask. Eight test conditions were examined with varying sizes of via plugging and paste test via. The results indicated that there are no obvious corrosion found in both via plugging and paste test via. The more via is plugged, the more corrosion resistance is achieved. Pasting test via can also enhance the corrosion resistance ability. The creep corrosion began by growth of dendrites on pad edges and the creep corrosion was detected by SEM-EDS. Copper sulfide was the main components of creep corrosion regions. ENIG PCB has the best corrosion resistance ability, whereas LFHASL PCB and OSP PCB can have the same creep corrosion resistance ability as ENIG with via plugging and paste test via processes.