When liquid eats a trace or a pad lifts, the repair is a jumper: a short piece of thin enamelled or insulated copper wire from one point to another. For a signal line almost any thin wire works. For a power path, the wire must carry the current without dropping too much voltage or getting hot. This calculator gives the numbers for any common gauge.

How to use it

  1. Choose the wire gauge (AWG — a higher number means a thinner wire).
  2. Enter the length of the jumper.
  3. Enter the current the path carries — from the schematic, or estimated from what the rail feeds.
  4. Read the diameter, resistance, voltage drop and heat.

The formulas

  • Diameter: d = 0.127 mm × 92^((36 − AWG) ÷ 39)
  • Resistance: R = ρ × L ÷ A, with copper's resistivity ρ ≈ 1.72 × 10⁻⁸ Ω·m and A the cross-section.
  • Voltage drop: V = I × R; heat: P = I² × R.

Typical choices at the bench

  • Signal lines (data, clocks, enable signals, pull-ups): 36–40 AWG enamelled wire is common because it is easy to route between tiny pads.
  • Low-current supplies (tens of milliamps): 32–36 AWG.
  • Power paths of an amp or more: 28–30 AWG or thicker, kept short — or several thin wires in parallel.

These are rules of thumb. Check the voltage drop: on a 1 V rail, 50 mV lost in a jumper is 5 % of the rail. Liquid-damage repairs that need jumpers are covered in Laptop Liquid Damage Repair: What to Check First.

Worked example: a corroded trace on a 3.3 V supply

A corroded trace feeds a chip drawing up to 500 mA. A 5 cm jumper of 30 AWG wire (about 0.25 mm diameter) has roughly 17 mΩ of resistance, so it drops about 9 mV and dissipates around 4 mW — negligible. The same length of 40 AWG wire (0.08 mm) has about 170 mΩ and drops 85 mV: still workable for 3.3 V, but marginal for a low-voltage core rail. Compare with the original copper using PCB Trace Width Calculator (IPC-2221).

FAQ

What wire do technicians use for jumpers?

Thin enamelled copper (magnet wire) for signals, because it is fine and insulated. For power, thicker insulated wire.

How do I strip enamelled wire?

Tin the end with a hot iron and plenty of solder; most enamel used for jumpers burns off at soldering temperature.

Can I parallel several thin wires?

Yes. Their resistance divides like resistors in parallel, and the current shares between them.