Tips on Modifying or Repairing PC board traces Last Updated on: 6/19/2013
Yes, Virginia, there are ways to repair even cracked-in-half printed circuit boards, if you are patient, careful, and above all (hee, hee!) desperate or brave enough to want to try!

First off, let me try to ease your possible anxiety on a few points. These methods aren't very well known, that is true. However, it is not because they are mind-bogglingly difficult to perform. One important, general assumption in the electronics industry is that PC boards are disposable, expendable items. It is not considered cost effective to try to fix most board related problems, even simple ones like one dead chip that needs to be replaced.

Generally, it is assumed that if a board breaks down for any reason, you just throw it away and swap in an identical replacement, of which there are many more commonly available. "Plug-and-chuck" repair methods exists for good reason: every hour of a repair technician's time is money being billed to someone, not to mention any revenue potentially being lost while the widget is being repaired. These assumptions are so ingrained and widely spread, they aren't often questioned. For the electronics industry as a whole, the primary repair goal is speedy, economical turn-around time on each widget.

For an electronic hobbyist, the "rules" of the underlying situation are different. For instance, time spent to troubleshoot and repair the actual problem in a broken (and therefore, "worthless") electronic item would likely be considered as "wasted" time in the industry. Not so, to an open-minded, dedicated hobbyist! That person may consider that time well spent, in both an educational, and an enjoyable way. He or she gained both the repaired item, (which may be rare or commercially unavailable), and as important side benefits, gained pride and confidence in their abilities, and bragging rights or respect among fellow hobbyists.

Now that I have, hopefully, convinced you that there is no big, mysterious reason that PC boards aren't repaired more often, let's examine some background information and then quickly move on to how to do the actual repairs. It is not as hard to do as you might have believed.

Printed circuit boards are made up of a flat, thin inner "substrate" plate, made up of a non-electrically conductive material (fiberglass is common, as are epoxy-based materials) covered on one or both major surfaces with a thin copper coating. This copper coating initially comes as a complete sheet, bonded to the substrate's entire top or bottom surface. Oversimplified a bit, a printed circuit board is created by masking certain portions of the copper plating off with a temporary protective coating ("etch resist"), and then placing the entire board in a special acid solution (usually ferric chloride), which "etches" away only the exposed copper areas. The result, when this process is finished and the temporary coating has been removed, is a custom-planned maze of small strips of copper (called tracks or "traces"), bonded to the substrate's surface. Electrically speaking, these strips of copper are either joined to, or seperated from, each other. They act just as "real" insulated wiring does, even if they look quite different.

These copper traces are literally bonded or "glued" to the substrate itself. Normally, they will remain bonded "forever". Excessive heat, however, can cause this "glue" to come undone, with the result that the thin wire "traces" lift themselves off of the PC board's surface. This can probably be repaired, generally speaking, with some work. (However, it is best prevented, by using only a 30-watt or smaller soldering iron. A 15-watt iron or a temperature-controlled soldering station is preferred for PC board work.)

If a trace became damaged near its middle, it is much easier to fix than if it came undone at either end. (However, don't scrap the board in either case. It can be fixed, and what do you have to lose in trying, anyway!) What you will be doing if a trace lifted from a board, is finding some part of it that is still attached to the board's substrate, and carefully attaching a wire to it at that point, to replace the rest of the damaged trace. The wire's other end attaches directly to the component lead or pin, or onto the wire trace, close to the component.

This repair, called a "jumper", is fairly common on first-revision commercial circuit boards, which proves that it can be done, when industry feels it is an economical repair. This is because first-revision PC boards usually have one or more as yet uncorrected design flaws, where some traces went to the wrong places. Companies feel it is easier, sometimes, to hand-repair a few bad traces, than to redesign and remanufacture the entire board assembly. They'll get around to that, they figure, on the next board revision.

To install these "jumpers," factory technicians may have to physically cut the offending trace, breaking its electrical connection at some location. They then rewire it the revised way, usually with thin "wire wrap" style wire. (Now if you see a bunch of funny little wires running across a brand new board, you'll know why: someone wasn't paying attention!)

A sharp (new) "X-acto" type of razor knife works fine for this modification. (I recommend the #16 blade type.) To electrically disconnect a wire trace, CAREFULLY cut two parallel lines across the trace, spaced closely together. Then gently, CAREFULLY peel the middle piece up and off the board.

This trick is useful, for instance, if you have two pins on an edge connector that you want to swap. Disconnect both on the board (behind and away from the connector), then rewire them.

The hardest part, other than physically getting a tiny wire to go where you want it to, is due to the (usually) green coating seen on almost all PC boards. This is specifically designed to resist solder, so you cannot attach a wire to it! You have to remove a spot of it, above where you want to solder in your jumper wires. This coating is called a "solder mask." It keeps solder away from areas where the designers did not want it, during its initially assembly. The coating also protects the exposed copper from oxidizing after assembly, so it serves a dual purpose.

Fortunately, removing part of the coating to get at the bare copper under it, so that you can solder to the wire traces, isn't all that hard. Really. I personally haven't screwed up a board yet, doing this, if that makes you feel any better!

All it takes is a very fine grade (400 or 600) of "Wet or Dry" sandpaper, but be extremely careful when using it! Those wire traces are thin; not much more than a few thousands of an inch thick! Obviously, you can sand too vigorously, and go right through the traces themselves. Fortunately, I think most repairers will be naturally worried enough that they will take it easy!

Take your time. Wet the sandpaper. (But avoid splashing water on the board itself; just barely dampen the paper, and rinse it off as you work.) I recommend that you use the finest grade of wet-or-dry paper that you can buy.

All you want to do is remove the fairly thin, green coating from a small area of the PC board, so that you can reach the bare copper of the traces under it. I usually use only a small strip of the sandpaper, cut from a larger sheet. Size isn't critical, and it will vary with the size of the area you are trying to sand down. A starting-point "Rule of thumb" might be a strip about half an inch wide, and a few (3 to 5) inches long. I usually just wrap the paper around a fingertip, taking care to try to spread my sanding pressure gently and evenly, so that I don't end up lightly sanding the outside edges, while sanding right through the center!

Sand a little, then take a look at the board. Work slowly; you'll get the hang of it. And always use good lighting, of course, as with any close or delicate work.

This is truly safe, I feel. However, until you've gained some confidence in this, you may feel better about it if you first tested your skills on a truly worthless PC board. I suggest almost anything with relatively "fat" traces, as long as it is NOT powered by AC! (Perhaps practice cutting-and-jumpering some wire traces on say a throw-away, battery-powered transistor radio, before you venture on to a valued board.)

Once you know how, and feel confident, it is fairly simple to lightly "tin" the copper traces using small-diameter solder. Tin one end of a jumper wire, too. Once they are both tinned, just solder the two together and connect the other end of the jumper wire where you need it. Repairs or modifications are about the same, once you know how to do this.

Comments on this article are welcome. I hope it was useful, and of some interest to you!

Regards,
Ward F. Shrake
ward.shrake@worldnet.att.net

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