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Repairing circuit board traces

N

NobodyIsHere

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Dec 21, 2006
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Hi,

I have an S-100 bus extender card with a broken trace. About 1 inch of trace, which is about 1/8" wide or so, has come off the board. It was previously repaired and unfortunately further damaged in shipping. Worse, the missing piece is most of one of the edge connector traces so whatever repair will have to be durable.

Does anyone know how to repair a large broken trace like this? I attached a crude photo to show the damaged trace. My plan was to get one of those silver trace repair pens from Jameco and just draw in a new trace but I wonder how durable it would be.

https://www.jameco.com/webapp/wcs/s...toreId=10001&catalogId=10001&productId=263716

The other idea I had was to get some copper solder wick and superglue it to the circuit card. After it dries, saturate it with solder and then gently pound it flat with a hammer.

Can this card be saved or is it beyond repair? Any help much appreciated! Thanks!

Andrew Lynch
 
If its not inserted and removed a lot, I've heard of people having good luck with the trace pens.
 
lynchaj said:
I have an S-100 bus extender card with a broken trace.
Click to expand...

We learnt how to repair these in advanced soldering, but by the looks of it it may be a bit more difficult because you're dealing with an edge connector.

It looks like there's still some trace left of it left on the connector so you might be able to replace it with a strip from a trace repair kit. This is just a sheet of cut tin which has traces of different widths which you can solder to the existing traces.

Problem is I don't know where you'd get a trace repair kit, best bet would be to start with Google.
 
Was going to say EXACTLY the same as thrashbarg, however trace repair kits are hard to come by. That's one of the power lines isn't it? in which case it's got to be a good repair.

Best bet is to clean off the old trace completely, removing carbon etc. then cut through the copper layer on a bit of pcb, to the right width and a bit longer than you need. (or poss. use self adhesive copper strip???) you can then remove this from the PCB backing by overheating & rubbing it with a soldering iron. The glue melts and lo-and behold a new trace!

clean it up and glue it into place with epoxy (it'll stand re-soldering, super glue just degrades to nasty compounds when you heat it), then solder a piece of wire across the join. Bit of fine abrasive paper to clean it up & the job's a good one!

I'm very inclined to fit poly-fuses to my extender card to try to stop this happening again to me! it's just TOO easy.
 
Pull the bad tooth!

Pull the bad tooth!

I have a similar but slightly different method as Nige does:

The extension card is made of a fiber material that copper traces are coated on.
It is much easier to deal with the fiber material for glueing than the copper
traces. Epoxy does a better job on the fiber than the fine trace.

1- Find yourself another bus extension card with similar trace pattern. Alternatively,
if there is a section of the card edge that is unused, you can use that section
for the repair job.

2- Based on the picture you have provided and counting from the left hand
side, trace number 2 has gone naughty! Using a fine edged saw, cut out a
rectangular section of the card that contains number 2 and 3 traces. The
reason you are cutting number 3 also is to have more room to work with. The
height of the removed section could be about 3/8th of an inch (you can cut as much
as you find it adequate). The rectangular section has copper traces in the middle and
fiber on the sides.

3- Repeat step 2 with the other card with healthy traces (or the unused section of
the card edge). Cut out a rectangular section with identical geometry so that it will
fit nice and tight into the empty space of the first card. For ease of cutting,
you can cut out a slightly larger section, and then file it down to the appropriate size.

4- By now, you have removed the bad tooth and you are replacing it with a good one.
Using Epoxy glue (or anyother kind appropriate for the job) connect the rectangular
piece with good traces into the cavity of the card. Remember that you have mainly fiber
material to glue together.

5- What remains to be done is to solder the new traces (at the upper section) to the
old traces of the card (at the lower section)!!

I hope this instruction was descriptive enough to be useful.

P.S.: As Terry would say, these are the rules that apply except when they don't, then
there are other rules :biggrin:!
 
Well, the first thing I would try, before trying to track down trace kits or trying to built up a sufficiently thick layer of trace pen to handle the current, would be to first sand down the burnt(?) area with a two-sided emery board, but not too smooth.

Then I would take some wire-wrap wire and epoxy 3 or 4 lengths, side by side, from just below the upper part of the trace (allowing some of the wire to entend over the copper) to just above where the card edge would start.

The WRW can be completely stripped or just the ends, your choice.

When the epoxy has dried, solder the ends, as a group, to the upper part of the missing trace and then solder other ends together (a flat group as close together as possible would be good), then lift them up a bit, put a drop of epoxy under them and clamp them down. It's best if the epoxy stays on the bottom, but, not essential.

Next, use the emery board to sand the card edge part flatter so that a) it fits smoothly and b) to remove any epoxy that may have got out from underneath.

It won't be pretty, but, it should work and be able to carry a reasonable load. If you can get more stands of the WRW in the space, by all means, use them for a safety margin.
 
Thanks everyone for the advice on the broken circuit trace. I have since used an exacto knife and scraped away the debris from previous repair attempts. I will be getting some epoxy and some wirewrap wire and trying a repair.

Thanks again for all your help!

Andrew Lynch
 
Success! Thanks to everyone for their suggestions. With some help from a friend, I was able to repair the trace to nearly good as new condition. Tests show it works well with no measurable impedance and good solid contact with the edge connector.

Thanks all!

Andrew Lynch
 
Speech, Speech...

Speech, Speech...

Good for you Andrew! Now give us all the gory details about how you
managed to fix the naughty trace.
 
OK, here goes... First though, the suggestions were all excellent and I appreciate everyone's help. However, the solution turned out to be right next door which I think worked well.

It is much like Thrashbarg & Nige called it. I needed a really good repair since it was the edge connector which got broken and really complicated its difficulty. Had it been just a trace, I would have just used my usual 24 gauge wire and soldered on a jumper or multiple 30 gauge wirewrap wires like Druid suggested. Its that darn edge connector which made it so nasty.

It turns out I have a friend here locally with a Pace Trace Repair kit (cir-kit?) with all the fancy tools and gold plated trace repair foil. It has epoxy backed traces you can cut out. I just removed all the debris and the remains of old trace with an exacto knife. Then cut out a similar looking trace from some scrap material and used the teflon (kapton?) plastic and the special soldering iron attachment to melt the trace right on the board. Then I soldered over the piece of the trace above the edge connector with a thin layer of solder. Basically unless you look closely, it looks just like it did when manufactured but maybe a little more lumpy.

To test it, I checked with the VOM on the lowest setting for ohms and did not measure anything at all. So I flexed the board and tried again with no problems. Then plugged it into my S-100 motherboard and checked continuity there and on the other connectors - again no problems. I pulled the card out and reseated it a few times to check the mating of the edge connector to the board (the scratches they make on all edge connectors) and it looked just like all the others. I am very happy how this turned out and it was just luck my friend has one of these Pace cir-kits which are apparently quite expensive. There is no way I could afford a kit like that or the tools you need to even use it effectively.

I appreciate everyone's helping out and please know you all contributed to the solution just not exactly as I was expecting. Still, a good ending nonetheless.

Thanks!

Andrew Lynch

PS, I attached before and after photos to illustrate
 
Last edited:
Hi -
Congrats on solving the problem. I just thoght i'd throw in my 2 cents, just in case anyone has a similar one to deal with.
1. Tracer pens are great for signal (tiny current) lines, and a must-have when you have to repair traces on flexible-substrate circuits (like membrane keyboards), but no matter how thick you paint, the result will still have high R, so they're useless for power traces. As an aside, for those who live far from electronics shops, a virtually identical pen is often sold in autoparts stores as "rear window defogger repair kit". Autoparts stores are everywhere...
2. The advice you ere given on using copper foil is great, a few changes sometimes help:
*Cut the trace *really* oversize, to the point where it may even overlap the adjacent traces, put a smear of superglue jell on the back of the trace, make sure that it overhangs the edge connector, and stick it down. Wait. When the glue is fully set (no smell), remove the excess with either an exacto knife (if you're good and have steady hands), or a dremel cut-off wheel. Remove the excess hanging over the edge connector with a flat file, filing away from the board @ ~45 degree angle. That way, the trace won't snag on the contacts as it is inserted.
*Take some fine steel wool, or 600grit wet-or-dry sandpaper, ad get id of all the remains of superglue & oxide from the trace. the point where it overlaps the trace you're repairing is the pace to do a really good job, 'coz even a tiny trace of superglue prevents the solder from flowing & bridgin.
*Tin the trace as quickly as you can - don't be afraid of the solder being a bit on the cold side - it's better than the trace peeling from the board due to overheating. The sold will, most likely, not flow over the joint area well - in that case, let things cool down, and bridge it with a bump of solder.
*if there's too much rosin left, wash it off with rubbing alcohol, and then wash the whole board with soap & warm water, dry off with a hairdryer, and, if you want to be really racy, mask off the edge connector with tape, and spray the board with clear lacquer.
*Test the new trace for close to 0 resistance (most decent digital multitesters may show some (fraction of an Ohm) resistance - that's fine - it's the probes, imperfect contact with the probes, etc. - a perfect 0 reading means that the multitester is either lousy, or that you've calibrated it for the probes (unlikely). Measure R to adjacent traces - should be close to infinity. Done.
With all this said, many times it's simpler to just make a new PCB from scratch - riser boards are intrinsically simple - just straight parallel tracers, so a ruler and a medium permanent magic marker is all you need (other than a double-sided blank board & etching solution). Making your own riser / extender / prototyping boards is *much* simpler (at least for me) than tracking one down (i guess S100s are pretty common) & waiting for it to arrive.
None of the above is hypothetical or hand-me-down / Googled-up info - just personal experience.
Hope some of this is of some use to someone...
-dim
 
First clean the area using isopropyl alcohol.

Next remove the damaged section of the circuit using a sharp Exacto style knife. The damaged circuit should be trimmed back to a point where the circuit still has a good bond to the PCB surface. Use a knife and scrape off any solder mask or coating from the ends of the remaining circuit. Remove all loose material and clean the area.

Next apply a small amount of liquid flux to the ends of the remaining circuit and tin the exposed end of each circuit using solder and a soldering iron.

Select a replacement circuit trace to match the width and thickness of the circuit to be replaced. Cut a length of replacement trace to the approximate length needed. The replacement PCB trace should overlap the existing circuit a minimum of 2 times the circuit width. Gently abrade the top of the replacement trace to remove the protective coating (used to prevent oxidation). Next, clean the circuit trace. For more details and repairing tools visit here [removed link]
 
yep all the time, 30 guage wirewrap or even better magnet wire, though I haven't ran across anything I want to repair that really REALLY needs to have matched length traces
 
gekaufman said:
Although your product might have a role in commercial situations, I don't think you'll find a lot of hobbyists looking to spend $350 on a repair kit to save a $35 PC board :)
Click to expand...

Glad to see the ban, I considered clicking on the report button. His first post on the forum contains a link to his site with shockingly and ridiculously overpriced repair products hidden behind a URL shortening service.
 
Osgeld said:
yep all the time, 30 guage wirewrap or even better magnet wire, though I haven't ran across anything I want to repair that really REALLY needs to have matched length traces
Click to expand...

A couple of years ago, I gave away a Tyan Tomcat III 2-CPU motherboard because I could barely see the damaged trace with an OptiVisor --another forum member thought he'd take a crack at it. I don't know if he succeeded.
 
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