Soldering Solder is not glue and not filler. A good joint is a metallurgical bond, and understanding what is physically happening makes the technique click far faster than practice alone — which is why this page exists before the iron arrives.

When molten solder meets clean, hot metal it wets the surface — spreading out and forming a thin alloy layer with the metal underneath. That intermetallic bond is the joint. Solder sitting on top of a cold surface, however neat it looks, is not a joint at all.

Wetting requires two conditions: both surfaces hot enough (so you heat the pad and the lead, not the solder), and both free of oxide. Metals oxidise in air, faster when hot, and oxide prevents wetting entirely. Flux is the chemical that strips oxide at soldering temperature and briefly protects the surface — it is not optional, which is why solder wire has it built into the core.

Counter-intuitive but important: hotter and faster damages less than cooler and slower. Long dwell times at low temperature are what lift pads and cook components. If joints are taking five seconds, the iron is too cool or the tip too small, not your hand too slow.

• Temperature: around 320–350°C for leaded solder, 350–370°C for lead-free. This is why a temperature-controlled iron matters — an unregulated one drifts wildly and is the main reason people conclude they are bad at soldering.
• Leaded (Sn60/40 or Sn63/37) is far easier to learn on: lower melting point, better wetting, more forgiving. Legal for hobby use in the UK. Ventilate, wash your hands, do not eat at the bench. Lead-free is a genuine step up in difficulty and worth avoiding while learning.
• Wire diameter: 0.6–0.8mm for general through-hole. Thinner gives far more control than you would expect.
• Tip choice: a chisel tip around 1.6mm for almost everything. It transfers heat much better than the fine conical tip people instinctively reach for — more contact area means faster joints at lower temperature. Fine tips are for dense SMD only.
• Extra flux in a pen or paste form fixes most wetting problems instantly and makes desoldering dramatically easier.

Tip care — most of iron longevity

• Tin the tip with fresh solder before and after every session, and leave it coated when you switch off.
• Wipe on brass wool rather than a wet sponge; thermal shock from wet sponges shortens tip life.
• Never file or sand a tip — the plating is what makes it work, and removing it ruins the tip permanently.
• Never leave it hot and bare for long periods; it oxidises and stops wetting, which then feels like a technique problem.

Start with through-hole. Leads pass through holes, joints are large and visible, and mistakes are recoverable. Surface-mount is entirely learnable but wants tweezers, flux paste, magnification and usually hot air — a second-month problem, not a first-day one.

Undoing things

• Desoldering braid — copper wick that draws molten solder away by capillary action. Add flux, lay the braid on the joint, press with the iron until it wicks up. The single most useful recovery tool.
• Solder sucker — a spring-loaded pump, better for clearing through-holes so a new component can pass through.
• Add solder to remove solder — counter-intuitive but real: fresh solder brings fresh flux and improves heat transfer, making a stubborn old joint flow so you can wick it away.