How do you guys repair cut PCB traces?

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snacksthecat
✶✶✶✶

03 Feb 2019, 03:07

I have a really dirty space invader board that I've been fixing up. I racked my brain trying to figure out what was wrong with my mapping, because a single switch was not working. I finally determined that it wasn't my mapping and that it had to be a physical problem. The switch itself operated fine so I quickly ruled that out.

Then I started poking around with the multimeter. The traces are pretty big so following them visually was simple. But I was so confused as to why I couldn't get continuity across this single trace. The trace didn't have any obvious signs of damage, at least to the naked eye. I started spot checking it by scraping off some of the solder mask. I then got to this area, which under magnification was clearly... well... missing.

My first question is, does anyone know why/how this happened? It looks like there's some corrosion from the a nearby switch's solder pad and that somehow caused the damage, but I'm not 100% sure. I'm just wondering if I have to clean out that corrosion in order to prevent it from happening to another trace (the neighboring switch just to the right looks like it's starting to do the same thing). It's not a super expensive board or anything, I'm just curious.

My bigger question is, how do you guys typically repair these? I've done it before but it's a pain and I always feel like I just got lucky that the solder took hold. I'd like to improve in this area so that it's clean and simple.

Image

Polecat

03 Feb 2019, 03:42

Looks like someone did a repair using the wrong kind of flux. I would clean the area carefully with a fine wire brush, then scrape about an inch of solder mask off the bad trace and solder a section of solid wire along that length using some 60/40 or 63/37 rosin core solder.

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PlacaFromHell

03 Feb 2019, 06:08

I usually do two holes and use a connecting lead from a resistor, works great without doing a mess. If you want to do that be careful with the switch. Try to not scratch the PCB to avoid more corrosion. The easiest way should be use a conductive pen, but is expensive as fuck.

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kakan

03 Feb 2019, 12:20

Are other solder joints like that? They seem to be starting to corrode.

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stratokaster

03 Feb 2019, 12:23

Yes, it looks like somebody used a very aggressive flux that corroded the trace.

My first instinct would be to clean the PCB with a brush and 99% IPA.

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abrahamstechnology

03 Feb 2019, 16:12

I just run a jumper wire from the last good solder joints. But also use some flux and reflow those corroded joints on the switch.

andrewjoy

05 Feb 2019, 12:52

You can run a jumper wire form point to point or you can scrape soldermask off and run a small jumper over the crack.

I prefer the second and then i also put fresh solder mask over the repair.

I would also re solder all the corroded pins , get that lead free shit off there and replace it with some real solder.

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