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Soldering

Soldering joins metal parts with a melted filler alloy — an electrical and mechanical connection in one. It's the skill that turns a breadboard prototype into something permanent.

What you need (the honest minimum)

  • Soldering iron — a temperature-controlled station (~$30) beats a bare $10 stick enormously. Set ~350°C for lead solder, ~370°C for lead-free.
  • Solder — 63/37 tin-lead, 0.8mm, rosin core. (Yes, lead — see Safety for handling. Lead-free works but is fussier for beginners.)
  • Brass wool or damp sponge — tip cleaner. Clean the tip every few joints.
  • Helping hands / PCB holder — a third hand. Literally.
  • Ventilation — a small fan blowing fumes away from your face.

Nice later: flux pen, solder sucker, good side cutters, safety glasses.

The joint, step by step

You're soldering a wire into a PCB hole (a "through-hole" joint — where beginners start):

  1. Tin the tip. Melt a little solder onto the clean iron tip — it should look shiny. A dry tip doesn't transfer heat.
  2. Heat the joint, not the solder. Touch the tip so it contacts both the pad and the wire lead. Count to three — the parts must reach solder-melting temperature.
  3. Feed solder into the joint — touch it to the heated parts (not the iron tip). It should melt and flow around the lead, wicking into the hole.
  4. Remove solder, then iron. About a second apart — solder first, so the joint doesn't keep cooking.
  5. Don't move it. Hold still for 2–3 seconds while it freezes. Moving makes a fractured "cold" joint.

Total heat time: ~3–5 seconds. Longer cooks the board and the component; shorter doesn't flow.

The mindset

Solder follows heat. It flows toward the hot metal. That's why you heat the parts and feed solder to them — the solder chases the heat into the joint. If your solder balls up on the iron tip, the parts weren't hot enough. Nearly every beginner problem is some version of "the parts weren't hot enough."

Through-hole vs. surface-mount

  • Through-hole — leads go through holes; solder on the other side. Big, forgiving, what this guide teaches.
  • Surface-mount (SMD) — tiny parts soldered onto pads. Doable with tweezers, flux, and practice — but learn through-hole first.

Practice before the real thing

Solder a row of spare resistors into perfboard and inspect every joint (see Reading Your Joints). Twenty practice joints cost pennies and save your actual project. Your tenth joint will embarrass your first — that's the expected curve.

Next: Reading Your Joints