circuit trace repair

[rusty9]

so im finally getting around to installing my folding mirrors, but i wanted to wire them up and test them to make sure they actually work before i go running wires through the car.

well, one folds and the other doesnt, but they both adjust left/right/up/down fine. after a few hours of tracing wires and experimenting (with help from 2win2rbo) and eventually taking the entire folding assembly apart i came across the source of the problem:



as you can see this trace is toasted on the circuit board. its quite a clever design. not pictured is a white plastic disk which rests on top with jumpers that stay stationary as the unit rotates therefor connecting the circuit paths and then disconnecting as it reaches a certain point e.g. fully retracted, or fully extended.

now i know the sell special pens to "draw" circuit paths onto boards, but i dont think that would work here because the jumpers rely on physical contact and may just scrape the conductive ink right off.

also the repair has to as flat and smooth as possible as not to mess up, bind or bend the springy jumpers that slide across.

any ideas?

[hill8570]

Single-sided board? If so, I'd think just cutting and etching a new board would be the easiest solution.

Otherwise, you should be able to JB Weld some copper foil in place of the old trace. It'd be tricky work, 'tho.

[rusty9]

yes, i had thought of etching a new one...but it does have a rather snug and precise home in the guts of a mini-transmission. and i dont think i have the patience to file it perfect =)

i found some copper trace tape, which is self adhesive and comes in 1/8th" widths. unfortunately i have to buy 20 feet of it when i need 3/4ths of an inch lol

[chronoti]

i have just soldered new traces especially for contact points like that, the solder is thicker and has more room to ware, as long as there is enough left on the board to adhear the solder you be fine, just do a thin run

[hill8570]

Originally Posted by rusty9

yes, i had thought of etching a new one...but it does have a rather snug and precise home in the guts of a mini-transmission. and i dont think i have the patience to file it perfect =)

Wouldn't take long to file with a dremel. Getting the resist down in that funky semi-circular pattern (assuming you were doing it by hand) would be way fussier. Heck, might be faster to just draw some guidelines and use a dremel to hog out the gaps between the traces...looks like you've got plenty of room to worth with.

Originally Posted by rusty9

i found some copper trace tape, which is self adhesive and comes in 1/8th" widths. unfortunately i have to buy 20 feet of it when i need 3/4ths of an inch lol

You might need all 20 feet by the time you manage to lay out straight tape in a semicircle I'm not sure that the standard trace adhesive would stand up to the mechanical stress of the wipers, thus the suggestion for JB Weld (or an epoxy with a faster cure time, if you're feeling lucky).

[rusty9]

Originally Posted by chronoti

i have just soldered new traces especially for contact points like that, the solder is thicker and has more room to ware, as long as there is enough left on the board to adhere the solder you be fine, just do a thin run

that is a good idea, but there is no trace left. would applying a line of flux and then applying solder work? kind of like a guide for the flow?

Originally Posted by hill8570

You might need all 20 feet by the time you manage to lay out straight tape in a semicircle I'm not sure that the standard trace adhesive would stand up to the mechanical stress of the wipers, thus the suggestion for JB Weld (or an epoxy with a faster cure time, if you're feeling lucky).

a good point i hadn't considered, but ill give it a try first as it seems to be easier than making a new board =)

[chronoti]

you could also solder in copper lines as well might be easier to just get a small strip you wount need as much solder and it prlly make a better connection

[73sport]

Short of finding a replacement nothing looks easy and I fear any self adhesive would not withstand the wear and tear that simple part gets. Heating/cooling kills tape. If you do use it, make sure it doesn't have a foam backing and clean it not allowing oil(s) (skin) near it again.

What rides on those rails and is it forgiving of a change in height?
I'd like to think I'm pretty resourceful but that is a tuff one. Your local hobbyshop likely has several sheets of brass, aluminum and stainless of varying thicknesses.

I'd opt for buying the thinist stuff you can and do an experiment on something round and flat. Buy the stuff, buy some two part epoxy (not fast settting) and rig some kind of clamp. Cut a circle leaving the ring complete and glue the ring down and cut off what you don't need.

For final prep, scuff the PCB with 100grit sand paper, scuff the copper with it too. The clean them both with lacqure thinner and don't touch them again. Mix the epoxy, apply it, lay the copper down, and clamp it to your test thing and see if you can cut the excess in a reasonable fashion.

No Dremel?
Stupid but: Strap an exacto blade to a socket that fits in the hole and spin it around until you cut the trace??????

Good luck.

When you do the real thing protect the other trace with thin tape so epoxy doesn't get on it.

Best I can offer and it gonna be fun.

[rusty9]

went down to A.C. Moore, and they have sheets of thin copper that will be easy to cut to shape and glue down.

thanks for the advice!

[hill8570]

Originally Posted by rusty9

went down to A.C. Moore, and they have sheets of thin copper that will be easy to cut to shape and glue down.

thanks for the advice!

Bingo! X-acto knife to cut, and be sure to epoxy it down. Rather than try to bridge to the existing pad (a solder bridge probably ain't gonna be temp stable) , I'd peel the entire existing copper, including the solder pad, before laying down the copper sheet.

A.C. Moore? Hmmmm -- never would've thought about using an arts & crafts store. Have to keep that in mind for the future.

[rusty9]

ok so i cut the rough shape i needed and using a tiny tiny paint brush (also from a.c. moore lol) applied a line of epoxy over where the existing path was, after sanding a bit and cleaning of course. ill wait the full 24 hours before i trim out the center circle. i found it too difficult to keep the foil flat and smooth if i cut out the 1/8" wide semi circle first.

[hill8570]

Originally Posted by rusty9

ok so i cut the rough shape i needed and using a tiny tiny paint brush (also from a.c. moore lol) applied a line of epoxy over where the existing path was, after sanding a bit and cleaning of course. ill wait the full 24 hours before i trim out the center circle. i found it too difficult to keep the foil flat and smooth if i cut out the 1/8" wide semi circle first.

Looks good so far. How are going to make electrical contact between the existing trace and the new stuff?

Don't take too long...the suspense is gonna be killing me!

Wonder if I should order the mug over on photobucket

[LynchburgCSI]

Originally Posted by hill8570

A.C. Moore? Hmmmm -- never would've thought about using an arts & crafts store. Have to keep that in mind for the future.

AC moore and Michaels are GREAT for auotmotive projects! You do need to be careful though. for example...

Rusty... be sure the copper isnt treated with anything you cant wash off....ie- tarnish preventing lacquer.

[rusty9]

Originally Posted by hill8570

Looks good so far. How are going to make electrical contact between the existing trace and the new stuff?

just a dap of solder at the beginings. which is why i cut it to come way over where it was burnt.

Originally Posted by LynchburgCSI

be sure the copper isnt treated with anything you cant wash off....ie- tarnish preventing lacquer.

already tested for surface continuity

heres a shot of the mechanism partially disassembled (little blurry...got the shaky hands...doesnt go well with macro photography lol) the board sits on top of the white disk, and then the motor sits atop all of that, with all the wires going through the central shaft.

[73sport]

All that cr@ps in the mirror? Who Knew?!

Yea, order us all t-shirts with the epoxy & slobber job holding you're stuff together. . . lol

Hard to get the crinkles out eh? How thick is that? Is the original trace still under it?

I like this guy - no messin around!
Hope it works!