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Author Topic: ideas on fixing damaged circuit board traces  (Read 5879 times)

EDWARDEFFECT1

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ideas on fixing damaged circuit board traces
« on: October 20, 2010, 08:43:53 PM »
looking for ideas on fixing circuit board traces.what glue would you use for glueing a physically good trace that is loose from the circuit board ,but is in good shape otherwise?what fixes do you recommend for broken traces.(examples:buss wire,.030wire)  how do the circuit trace pens work?is it to high of a temperture that causes traces to get broken and removed from the board?any other ideas?jump in!!!thanks....ed

DJPhil

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Re: ideas on fixing damaged circuit board traces
« Reply #1 on: October 21, 2010, 07:19:34 AM »
There's an IPC video somewhere on this, but they're methods are a little extreme and meant for 'as new' board manufacture. They use flat copper trace and epoxy it down, but there's a lot of intermediate steps to make sure you don't harm lower layers on a multilayer board. Often the simplest way to go is to trim the broken area out, clean up the ends so they'll take solder well, and just jumper in some wire that's not too thin for the current, i.e. the same cross section or more.
You can use pretty much anything, but stripped solid core wire has worked best for me in the past. You can bend it to whatever shape you need and flatten it a bit with a piece of pipe so it'll lie flush on the board, solder it in, then glue with epoxy or fingernail varnish (whatever's handy). Just about anything will do so long as it's not layout sensitive, so try to keep in in the same general area the old trace was. If you reroute the trace, say by using free hanging wire, you might pick up more interference or hum than the trace would have. Board repair gets sketchy at higher frequencies too (tens of MHz) but that's rarely an issue with amplifiers.
Most traces break from having to support heavy components. Banging a board on a table edgewise when it has some heavy inductors soldered in (especially smt components) is a common example. This is why you see a lot of heavier components hot glued or gooped to the board to help provide support. Boards also expand and contract with heat cycling, though they're designed to do it as uniformly as possible. Using too much heat when soldering can wreak all kinds of havoc too. There's probably a million ways to damage traces.

Hope that helps. :)

J M Fahey

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Re: ideas on fixing damaged circuit board traces
« Reply #2 on: October 21, 2010, 08:31:45 AM »
Excellent advice.
I use some epoxy. it's what they used originally !!
What *many* designers forget is that parts are *not* soldered "to the board" , but to a very flimsy, thin, pad or track which is *glued* to the board.
The best "when designing) is to go for as large or wide pad or track as possible, no mater the current they carry.
If you look at one of my boards, they are ridicule.
Worst ones ar Marshall JCM and Valvestate era or many Fender ones, thin as in PC boards.
Peavey were always generous.
Now you know why Peaveys are more reliable (among other things)

scooperman

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Re: ideas on fixing damaged circuit board traces
« Reply #3 on: October 21, 2010, 06:19:10 PM »
for broken power  (fat) traces, I scrape off the photoresist with a scalpel type X-acto to expose clean copper, then solder some Solder-Wick across the break.  Smaller traces I use solid wire, typically 30AWG wire-wrap wire to repair 8mil to 12mil traces.  Clean the board with a good flux remover like Techspray 1631, then lock the wire down with superglue.  If its a long wire, tack-solder one end, then route it by bending with tweezers, after it goes a small distance you use a tiny piece of Scotch tape to clamp it down, then continue routing it, continue with Scotch tape until it ends up where you want it.  Then superglue it down between the pieces of Scotch tape.  After it dries pull off the tape, you have a nice tidily routed hackwire.

Sometimes when removing a surface mount component, the old part yanks a pad off the board.  Check the part datasheet, usually this happens at pins which have no function (NC), so the pad has no trace to take away the heat.  This is no problem, bend the NC pin up and solder the new part down with those pins unsoldered.  But sometimes chip removal yanks off a good pad and some of the attached copper trace.  For some packages, like SOICs or flatpacks, and even J-leads like PLCCs, this is easily fixable, scrape the remaining pcb trace and solder on a new piece of ww wire which ends up with a stripped end being in the location of the old pad, bend the pin of the new part up and place the part. Solder it down, finally rebending the pin down to land on your new wire, solder that down on top of your hackwire.  About the smallest I have done is TQFPs with 0.4mm pin spacing, you need about a 30X microscope to do it.  No coffee.

Enzo

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Re: ideas on fixing damaged circuit board traces
« Reply #4 on: October 21, 2010, 07:49:28 PM »
Move beyond scraping off the coatings.

I have used these fiberglass brush erasers for about 35 years now.  The fiberglass is strong enough to peel off the coatings and oxides, but soft enough not to scratch into the copper.   Good for cleaning off conformal coatings to expose feresh solderable copper.  Also great for cleaning and shining up edge connectors.

Just avoid the temptation to run your finger across the brush, or you'll get little fiberglass bits in your skin.

http://www.eraser.com/catalog.cgi?mode=details&product_id=1222




EDWARDEFFECT1

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Re: ideas on fixing damaged circuit board traces
« Reply #5 on: October 21, 2010, 10:22:56 PM »
thanks enzo for the tip. looks like the brushes i have used on cars for chip repair...thanks....ed

DJPhil

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Re: ideas on fixing damaged circuit board traces
« Reply #6 on: October 22, 2010, 06:34:44 AM »
I have used these fiberglass brush erasers for about 35 years now . . .
I didn't know about these, neat stuff! That looks like just the thing for stripping enamel off of fine magnet wire too. I'll definitely have to pick one up.