Corrosion on printed circuit boards can range from simple tarnish on pads to damaged or destroyed runs. Likewise, repairs range from simple to complex. An experienced technician should estimate the time and cost of a repair as compared to replacing the entire board assembly.
Repair a tarnished copper pad by cleaning it with a pencil eraser. A tarnished pad has a dull brown colour. Polish it with the eraser, then clean it with cotton swabs and alcohol. Cleaning is important because the eraser gets its colour from some oils that should not be left on the board. A tarnished pad or one contaminated by oil will not bond with solder. The resulting joint will have a convex appearance much like a drop of water, while the desired joint should have uniform concave fillets.
Repair a small corroded pad or run with a piece of bus wire. This is for a short run of half an inch or less. First, remove any remaining corrosive liquids with alcohol and cotton swabs. Cut the corroded run or pad, and remove the section. Form a piece of bus wire to replace it. Scrape the ends of the run to reveal copper. Apply flux and then tin to the ends with solder. Set the bus wire in place, and solder both ends. Clean up with cotton swabs and alcohol.
Repair long runs with replacement runs from the board repair kit. Cut out the damaged part. Select a run from the kit that is approximately the same width. It may be necessary to use several replacements if the original had any bends. Use the hobby knife to scrape down to the copper on the existing ends. Apply flux and then tin to the ends with solder. Carefully position the replacement run, and solder its ends. Clean up with alcohol. Tack the run in place with epoxy, and cover it with conformal coating.
Alcohol is flammable. Keep it away from a hot soldering iron.
Tips and warnings
- Alcohol is flammable. Keep it away from a hot soldering iron.