I had a 286 motherboard from the late 1980s with battery damage. A leaky battery corroded two traces completely through, severing them and rendering the board inoperable. Here’s how I repaired the damaged PCB traces with wire.
Fixing broken traces is a bit of a lost art, because it’s easier to just swap the board. But when the board is rare and/or expensive, it makes sense to repair the broken traces instead. These types of repairs can be a bit intimidating, but they’re easier than replacing a chip. And then you’ve saved a scarce board from oblivion.
Neutralizing and removing the battery juice and battery
The first order of business is containing the damage. Some people desolder the battery, but I remember reading in one of Forrest Mims’ books that batteries can explode when heated. So I avoid that. I snip the leads with a pair of diagonal cutters instead.
Next, there’s the issue of the battery juice. Douse the board in vinegar to neutralize that, which is something I’ve covered before. It may take more than one application to get all of it. You’ll probably find the traces are blue in spots and don’t want to come clean. For those, scrub with a toothbrush with vinegar. The strong base from the battery creates salts when it reacts with the copper. Vinegar dissolves it. If you have any that still won’t go away, you can sand it off with fine sandpaper. Use about 200 grit.
You will find spots where the copper is completely gone, leaving bare fiberglass in its stead. That’s OK; we’ll get to fixing that next.
After the vinegar bath, I rinse the board with a combination of baking soda and water. This neutralizes the vinegar. Then I rinse with plain water and let the board dry. Be sure to let it dry thoroughly.
Bridging broken PCB traces with wire
You won’t be able to solder directly over the broken traces. There’s a coating called solder mask over most of the metal that solder won’t adhere to. You can scrape away the epoxy with an awl or a pick until you get down to bare copper. You’ll know when you reach copper, as the color changes from the tint of the PCB to bright, shiny copper like a new penny. Expose a good 1/8 inch or 3 mm of the trace, if not a bit more. Clean the area, then apply a bit of flux to the bare copper. Using no more than a 30-watt soldering iron (15-20 watts is better), apply a bit of solder to the area to tin it.
As for the wire, professionals use fine 30AWG wire wrap wire. Heavier wire will work, it’s just (arguably) harder to work with and harder to conceal. I used thicker wire because it was what I had.
Strip a bit of wire and tin the end, then solder the wire to one side of the trace. Cut the wire to length, then strip and tin the other end. Position the wire on the board and apply a bit of tape to hold the wire in place if you need to. Solder the other end, then remove the tape. Let the solder cool, then check to make sure the wire stays in place. You want bright, shiny solder joints, not dull ones. Dull joints indicate both a weak electrical and mechanical bond.
Jumping off existing solder joints to bypass damaged traces
If you can track the trace to a nearby solder joint on one or both ends, you can skip the scraping. Use a solder joint to a component, not a test point. You can tell the difference by looking for a pin in the joint. If there’s no pin, it’s a test point. If you have a good solder joint, add just a little solder to that solder joint, then bend your wire into a tight loop and tin it. Position the wire on the pin, being sure not to short any of the adjacent pins. Solder the wire to the pin. If you can locate another joint on the other side of the break, run the wire to that joint. If not, scrape the other side of the break and solder there.
Whichever way you do it, once you restore electrical conductivity, the board will probably start working again. Wash the board to eliminate any residual vinegar, and let the board dry thoroughly overnight. If it doesn’t post, it’s not dry yet. Chances are once the board is dry, it will post and it will work for you, especially if it’s an older board with just two layers.