HOW-TO GUIDE
How to Repair a PCB Trace Using Solder and Jumper Wire
By the OhmSavvy Research Team ·
1Assess the damage under magnification
Look at the break with a loupe or microscope and follow the trace both ways. Note how long the damaged section is, whether the copper is merely cut or actually missing or charred, and what is next to it. A burnt trace often means something drew too much current, so find and fix that cause first, and cut away any copper that has blackened or lifted, since it will not take solder. If the damage is a pad that came up during desoldering rather than a broken trace, see how to repair lifted PCB pads.
2Scrape back the solder mask
The green (or other color) solder mask over the trace must come off before solder will stick. Use a fiberglass pen, a sharp hobby blade held almost flat, or a small scraper to remove it for a few millimeters on each side of the break, stopping as soon as bright copper shows. Work along the trace, not across it, so you do not cut into the copper or the neighboring lines.
3Tin the exposed copper
Clean the area with isopropyl alcohol, add flux, and run a fine tip loaded with a tiny amount of solder along each exposed end. A starting point of about 300-340°C for leaded solder is usually plenty for a thin signal trace. You want a thin, shiny coat, not a mound; excess solder spreads sideways and narrows the gap to the next trace.
Short gap vs long run
Which method to use depends on how much copper is left. A clean cut of a millimeter or two with sound copper on both sides suits a bare wire laid along the trace. A long scorched section, missing copper, or a break under a component calls for insulated wire routed between the nearest solid points.
4Bridge the gap
For a short gap, take a single strand from stranded wire or a trimmed resistor lead, lay it flat along the tinned trace so it overlaps sound copper on both sides, and reflow each end with a quick touch. For a long run, strip 1-2mm from each end of the Kynar, tin it, and solder it to the chosen pad, lead or via. Keep the wire short and flat against the board, and route it around, not over, parts that get hot.
Matching wire to trace width
A useful rule of thumb is that the jumper should have at least as much copper cross-section as the trace it replaces. Standard 1oz board copper is about 35µm thick, so a trace's cross-section is simply its width times 0.035mm. The comparison below is pure geometry; check current ratings for your wire type before trusting it on high-current lines.
5Test, then seal the repair
With the board unpowered, measure from one end of the original trace to the other on continuity or low ohms; a good repair reads essentially the same as the probe leads shorted together. Then probe from the repair to each neighboring trace to confirm there is no short. Once both checks pass, clean off flux and cover bare copper with UV-cure solder mask, and tack long jumpers down with epoxy or UV glue every centimeter or so.
Test before you seal
Diagnosing a failed repair
| Symptom | Likely cause | Fix |
|---|---|---|
| Open circuit after repair | Solder did not wet scraped copper | Scrape cleaner, flux, re-tin and reflow |
| Short to the next trace | Solder spread or blade cut the mask between | Wick excess; separate with a blade; re-test |
| Works, then fails when flexed | Unsupported wire or solder-only bridge | Add a wire strand; tack down with epoxy |
| Jumper insulation melted | Long dwell near the joint | Use heat-resistant wire; shorter touches |
| Trace lifts while tinning | Copper overheated or already burnt loose | Cut back to firm copper; jumper to pads instead |
Safety: discharge first, ventilate always
Irons for fine trace repairs
Trace repair is fine work on fragile copper, so steady, displayed temperature and a small tip matter more than peak power. These picks from our reviews fit that job.
Irons for trace and jumper work
ESD-safe 70W station with digital control, a sensible match for jumper work near static-sensitive chips.
A compact USB-C iron whose screen-set temperature suits tacking thin Kynar wire to a via without guessing at heat.
Takes Hakko's T18 tips and holds ±1°C at idle per Hakko, so a fine tip stays at the temperature you chose.
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Frequently asked questions
Can I just fill a broken trace with a blob of solder?
For a hairline crack, solder alone sometimes bridges it, but it is not a durable fix. Solder is weak across a gap with nothing to reinforce it, and board flex or thermal cycling cracks it again. Lay a strand of bare wire along the trace and solder over it so the wire carries the joint mechanically.
What is Kynar wire and why is it used for PCB repair?
Kynar is a common name for thin wire-wrap wire, usually 30 AWG, with a thin, heat-resistant insulation that does not shrink back much under an iron. It is easy to route along a board, small enough to land on fine pads, and stays insulated where it crosses other traces.
Do I have to connect the jumper to the exact spot where the trace broke?
No, and for long runs you usually should not. Follow the trace to the nearest intact pad, component lead or via on each side of the damage and land the wire there. Those points are already solderable and mechanically anchored, which makes a stronger joint than soldering onto a sliver of scraped copper.
How do I know whether a trace is a power line or a signal line?
Width is the first clue: power and ground traces are usually much wider than signal traces. Following it to a regulator, connector power pin or large capacitor confirms it. If you have a schematic, check the net name. Power traces need a heavier jumper than 30 AWG.
Should I cover the repair with UV solder mask or epoxy?
Either works, and both are worth doing on a board that will be handled or mounted in a vibrating enclosure. UV-cure solder mask gives a thin, neat coat over bare copper. A small dot of epoxy or UV glue along a jumper wire stops it snagging and stops flex from reaching the solder joints.
