copper wire for trace repair - Page 1
Forum section: electronics / beginners

author: tony359
author_rank: Frequent Contributor
timestamp: June 01, 2022, 05:36:16 pm
content: Hi all,I have a question about what type of copper wire to use to repair a broken trace. I've got some enamelled copper wire which I guess it's great to run it across a PCB as it's enamelled - hence won't short on other traces. But sometimes I need to fix a small trace using a short piece of copper to use as a small bridge over the break. Now, the enamel on the copper will prevent the solder from sticking so I usually try to burn it/scrape it first.Today I discovered that "non-enamelled" copper wire is also available.What would you normally use for the task? And how does the non-enamelled copper wire avoid getting oxidised?Thank you!

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: June 01, 2022, 06:04:23 pm
content: Go to your local craft store and buy a small roll of silver coated jewelry wire. whatever small gauge you think will work.It solders like a dream and although it is a bit more expensive, you do not use very much.

author: Gyro
author_rank: Super Contributor
timestamp: June 01, 2022, 06:16:24 pm
content: You didn't mention what wire diameter wire you're using, or the trace thicknesses that you're replaring.30awg (0.05mm2) Kynar insulated wire-wrap wire is the traditional choice for PCB modification and repair. The copper is silver plated and the Kynar easilly stripped to length with the appropriate sized strippers. If you get it in green, it blends with the solder resist and tends to hide your more embarrasing errors!

author: MikeK
author_rank: Super Contributor
timestamp: June 01, 2022, 06:33:33 pm
content: I would use the ubiquitous tinned copper wire. Just pull off the PVC jacket. Jacket stays on where needed.

author: Ian.M
author_rank: Super Contributor
timestamp: June 01, 2022, 06:39:57 pm
content: Quote from: Gyro on June 01, 2022, 06:16:24 pm... and stripped bare, it can be used to bridge cracks and short gaps in traces. Hint: put a 45 deg bend at the end of the insulation, and don't cut off the rest of the wire till you've got the bridge soldered in place both sides of the break.If you need different sizes of wire for short track repairs, strip strands from stranded tinned copper wire. If the track you are repairing is too wide/heavy for that consider using self-adhesive copper foil tape, cut to shape, with the ends prepared by removing the adhesive and tinning the underside so it can be sweated*onto the tinned track end.* the process of making a thin solder joint between two prepared tinned flat surfaces with only the solder that is already on them (+ added flux), by indirectly heating the joint e.g. with a soldering iron on the other side of one of them. Do not confuse it with the North American usage of 'sweat soldering' for heating plain#capillary pipe joints with a gas torch while feeding in solder at the end of the joint.# plain bare copper, as opposed to ones with a fluxed solder preform ring inside each end of the fitting, which are actually sweated.

author: tony359
author_rank: Frequent Contributor
timestamp: June 01, 2022, 07:59:31 pm
content: thanks for all the replies.The smallest copper wire I've got is 0.14mm diameter which should make it around 35-36AWG. I also have some 29AWG.I think I have some Kynar insulated as well - can I get it to 29 and 35AWG as well?

author: TimFox
author_rank: Super Contributor
timestamp: June 01, 2022, 08:09:19 pm
content: American wire-wrap Kynar-insulated wire is almost always AWG 30.

author: MathWizard
author_rank: Super Contributor
timestamp: June 01, 2022, 08:39:14 pm
content: The strands in small stranded copper wire are probably the smallest wire I have, but that's bare copper. I've used it a few times when soldering to some fine pitch chips, and it still looks huge under the microscope compared to some package leads. Works good for traces too.I might have smaller stranded wire in like a USB cable.I have some pretty fine enameled wire, I think from an induction fan . That might be around 30AWG.I have 2 projects I sort of made a mess of years ago, and messed up some traces/pads, pins, for a little MCU and something else. I want to try and fix it soon, makes for good soldering practice.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: June 01, 2022, 08:57:02 pm
content: For really small wires, save the ends you trim off coax, hopefully the silver coated shield from test equipment grade coax.

author: Gyro
author_rank: Super Contributor
timestamp: June 01, 2022, 08:58:47 pm
content: Quote from: tony359 on June 01, 2022, 07:59:31 pmYou can get almost anything if you're willing to pay enough for it. Enammelled copper wire is, of course, available in a very large range of diameters. Manufactureres of stranded copper wire clearly source their strands from somewhere but without searching, I don't know if you can find bare copper. Tinned copper is available, but I've only ever seen it in larger diameters. Stripping down stranded copper wire is your best bet.Kynar is, by default, 30awg as that was the specification for its original wire-wrap use. I doubt if you would be able to get thinner because of the tollerancing of the strippers and the likelyhood of nicking or snapping the inner copper wire during stripping. Again, 30awg is the only viable size in cost terms, even if you can find others.As an aside, Vero used to have a product called 'Penwire'. It used small diameter polyurethane insulated wire in a pen with a small bobbin on the back. Under soldering heat, the polyurethane burned away and allowed direct soldering. The downsides were that you needed a very high tip temperature (think dull red in a darkened room!), the fumes were toxic... and the soldering temperature was so high that it would strip pads off PCBs. It was normally used for prototyping on matrix boards, where you would make a couple of turns round the component leg and proceed (via plastic comb strips) to the next connection, going back and soldering afterwards. I think most modern 'enamelled' copper wire insulations have too high a melting point to try this trick.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: June 01, 2022, 09:57:08 pm
content: You can get spools of quite thin wire from Ali / Ebay / China. The stuff is sold for repairing phones, repairs under BGA's and other difficult places. Thickness is just a handful of micrometers.I regularly use "enameled" wire, which solders quite well with a tip of 350 to 400 Celcius.There are a few disadvantages with this higher temperature:* Flux evaporates quicker, so you have less soldering time.* Tips wear faster.* Higher risk of pads getting loose from the PCB.Ideally you have two soldering irons. A hot one (which can be stationary!) to burn of the coating and tin the wire, and an iron with a lower temperature to solder the cleaned wire normally.You can also buy spools of tinned copper wire (without insulation!) A disadvantage of this is that it becomes hard to solder after a few years when the very thin layer of tin oxidizes. For occasional use it's probably easier to have some pieces of multi-stranded wire, and then strip the isolation when you need a bit. Normally the copper stays clean under the isolation and is easy to solder.

author: TimFox
author_rank: Super Contributor
timestamp: June 01, 2022, 10:00:07 pm
content: Some enameled "magnet wire" has a polyurethane insulating coating that is designed for disintegrating at soldering temperatures, but other coatings are far more difficult to remove with heat.It's relatively easy to clean the tin oxide off tinned wire, and if you can find appropriate-diameter silver-plated wire with a strippable (e.g., Kynar) insulation, the clean silver under the insulation works well.For small quantities, the jewelry suppliers on eBay, etc., can supply good plated wire.