How to solder a wire to a PCB pad
Step-by-step guide to soldering a wire to a PCB pad or through-hole: stripping, tinning, joining, insulating and strain relief so the wire does not break off.
Choose the wire
Use stranded, silicone-insulated wire: flexible, and the insulation does not shrink back from the heat. 26 AWG for signals, 22 AWG for up to about 2 A. Use a colour code and stick to it: red for supply, black for ground.
Prepare both sides
- Slide heat-shrink onto the wire now if the other end will be closed. You will forget later.
- Strip 2 to 3 mm for a pad, 4 to 5 mm for a through-hole. Do not nick the strands.
- Twist the strands and tin them: heat the wire, feed solder until it wicks in. The strands should become one solid, shiny piece.
- Put a little flux on the pad and tin it with a small, flat layer of solder.
Make the joint
- Fix the board in a holder and hold the wire with helping hands or tape, touching the pad.
- Press the tip on the wire over the pad. Both tinned surfaces melt together in about a second.
- Remove the iron and hold still for two seconds.
- For a through-hole: insert the tinned wire from the top, solder from the bottom like any lead.
Strain relief is not optional
A wire soldered only to a pad will break the pad off the board the first time someone pulls the cable. Fix the wire to the board a few millimetres from the joint: a drop of hot glue or UV glue, a cable tie through a mounting hole, or Kapton tape for a temporary fix. If the board has a free mounting hole, pass the wire through it before the pad.
Check it
Pull the wire gently. Then use a multimeter in continuity mode between the wire end and a point on the same net, and between the wire and the neighbouring pads to confirm there is no short.
Common mistakes
- Too much stripped wire, which shorts to neighbouring pads.
- Untinned strands that splay out.
- No strain relief: the pad rips off later.
- Soldering to a pad on a large ground plane with a small tip. Use a bigger tip and more flux.
Stop if the wire carries more than a few amperes, connects to mains, battery terminals or a high-voltage section, or if you have to cut or bridge tracks to make it work. That is a design change, and it belongs in the next board revision, not on a bodge wire.
Kit list
| Item | What to look for | Buy |
|---|---|---|
| Temperature-controlled soldering iron | Adjustable 200 to 450 °C, 60 W or more, fast heat-up, replaceable tips. The single most important tool. | View on Amazon ↗ |
| Leaded solder wire, 0.5 to 0.8 mm | Sn63/Pb37 or Sn60/Pb40 with flux core. Easiest to use; for repairs and prototypes, not for products sold in the EU. | View on Amazon ↗ |
| No-clean flux pen | Makes solder flow and wet properly. The difference between a struggle and a clean joint. | View on Amazon ↗ |
| Wire stripper | Self-adjusting stripper for 30 to 10 AWG wire. Knives nick the strands. | View on Amazon ↗ |
| Silicone-insulated wire kit, 22 to 26 AWG | Flexible, and the insulation does not melt back when soldered. | View on Amazon ↗ |
| Heat-shrink tubing kit | Insulates and strain-relieves soldered wires. | View on Amazon ↗ |
| Kapton tape | Heat-resistant tape to mask nearby parts and hold wires. | View on Amazon ↗ |
| Helping hands or PCB holder | Holds the board and the wire so both of your hands are free. | View on Amazon ↗ |
| Digital multimeter | Auto-range with continuity beeper, CAT III rated. You will use it every day. | View on Amazon ↗ |
Links go to Amazon. As an Amazon Associate we earn from qualifying purchases, at no extra cost to you. We only list tools of the kind we use on our own bench.
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