Soldering Basics: Tools, Technique, and Common Mistakes

Soldering is the foundational skill for all electronics work — connecting wires, assembling PCBs, modding hardware. A good solder joint takes 30 seconds to learn and a few hours of practice to do consistently well.

Tools You Need

Soldering iron: A temperature-controlled station (Hakko FX888D, TS100, or Pinecil) is worth every dollar over a fixed-wattage stick iron. Set to 320–370°C for most work. Variable temperature lets you dial in the right heat for each job.

Solder: 60/40 or 63/37 tin/lead, 0.6–0.8 mm diameter. Lead-free solder (SAC305) needs higher temps and is less forgiving. Start with leaded. For through-hole work, 0.8 mm is ideal. For SMD, 0.4 mm.

Flux: Rosin flux in a pen or paste form. Flux cleans the surfaces and helps solder flow. Most solder has flux in its core, but additional flux helps with difficult joints and desoldering.

Brass tip cleaner: The curly brass wool type — not a wet sponge, which thermally stresses the tip. Keep the tip clean at all times.

Solder wick / desoldering pump: For fixing mistakes.

Helping hands or PCB vise: Keeps the work steady.

The Technique: Five Steps

1. Tin the Tip

A shiny, silver-coated tip transfers heat efficiently. A dull/dark tip doesn't. Keep the tip tinned at all times — wipe on brass, re-apply fresh solder, wipe again. Never leave the iron hot with a bare/oxidized tip.

2. Clean the Pads

For PCB work, flux any pad that's dull or has oxidation. For wire splices, strip, twist, and tin each wire before joining.

3. Heat the Joint, Not the Solder

Touch the iron to the pad and lead simultaneously for 1–2 seconds, then bring the solder wire to the joint (not to the iron). The joint should be hot enough to melt the solder. If you're melting solder on the iron and dropping it onto the pad, the result is a cold joint.

4. Feed Solder and Remove

Feed in just enough solder to fill the joint — for through-hole, a small volcano shape around the lead. Remove the solder wire first, then the iron. Don't move the joint while solder is solidifying (3–5 seconds).

5. Inspect

A good solder joint is shiny and concave (flows up around the lead). A cold joint is dull, grey, or blobby. Reheat cold joints; they're electrically unreliable.

Common Problems

Cold joint (dull, blobby): Not enough heat or moved too soon. Reheat with fresh flux.

Solder bridges: Too much solder bridging adjacent pads. Wick away excess with desoldering braid.

Lifted pad: Too much heat dwell. The pad has delaminated from the PCB — difficult to repair.

Solder won't flow: Oxidized surfaces. Clean with flux and light abrasion.

Burns on PCB: Iron too hot or held too long. 350°C, 2–3 seconds max per joint.

Desoldering

Use desoldering wick: lay it over the joint, press with the iron tip until solder is absorbed, lift. Or a vacuum pump (solder sucker): heat the joint, press and release the pump over the molten solder.

For through-hole components, ChipQuik low-melt alloy makes desoldering entire ICs easy.

Safety

Solder flux fumes are irritants — work in a ventilated area or use a fume extractor. Wash hands after handling leaded solder. The iron tip is 350°C — don't touch it.