Circuit Board Carbon Arc

Epoxy. G10/FR4 boards are made from fiberglass matting and epoxy binder. If your PCB is made from phenolic instead of epoxy, use epoxy anyway. Scrape out the carbonized material. Place some PTFE tape on one side of the hole. Hold it in place with a mess of sticky tape and maybe a temporary cardboard stiffener. The idea is that the epoxy will not stick to the PTFE tape. Mix some "2hr" epoxy (not the 5 min variety) and smear it into the hole. When set, remove the tape. Let cure for at least 24 hrs before applying power.

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Jeff Liebermann     jeffl@cruzio.com
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I'd scrub the board with alcohol & a toothbrush, then spray it with a conformal coating. I can't think of any brandnames off the top of my head, but I'm sure that many people here will have suggestions.

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    W
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How do you get carbon arcs on a low voltage door chime board?

Meat Plow Inscribed thus:

From the open contact points spark/arc. Though I would have thought that it could be cleaned off.

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This doesn't sound right, you can't arc with 24 volts. But, if it fact it has happened, I'd recommend using a dremel to grind out the bad parts of the board, and spray with a insulating coating, or even fingernail polish.

Yes you can, but the gap is quite narrow. I've seen sustained arcs at

5 volts on new PC boards when the board house damaged the negatives we supplied. That narrowed the gap on the +5 volt rail and ground buss. You had to look under a microscope to see it, but the +5 volt current would go way up when the arc started. When we checked the remaining raw boards the entire production run had the same defect. There wasn't enough time to have a new batch made so the boards were hand trimmed with an Exacto knife to remove the inch long strip of excess copper. We had them return the negatives, and it was obvious they had been mishandled. A lot of scratches had been touched up, but several layers were so bad that we had a new set made before sending the work to a different company.

As long as it isn't a multi layerboard. If it is, you can cut right through the next layer. I prefer the Exacto knife, for better control.

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The carbon builds up then it arcs across. If you are thinking that low voltage will not arc, you are mistaken. Take a 9volt battery and put steel wool across both contacts. It will cause a fire. My kids use to love doing this at the kitchen table when they were young.

Chris

You can arc with 24 volts. That is like saying a car battery will not arc. It happens quite often.

Chris

I scrape out the black manually or with a Dremel tool. I then coat the bad part with nail polish with a couple coats. You could use epoxy if there needs more support. Mesure the resistance across the arc points to get an idea of the problem first.

greg