Melting solder requires a heat source (typically a soldering iron) set to at least 360°F (183°C) for standard leaded solder, direct contact with both the solder wire and the metal surfaces being joined, and clean surfaces free of oxidation. The process is straightforward once you understand the handful of variables that determine whether solder flows smoothly or clumps into a useless blob.
Melting Points by Solder Type
The temperature you need depends on which solder you’re using. Standard 60/40 leaded solder (60% tin, 40% lead) melts between 361°F and 374°F (183–190°C). It transitions through a pasty range rather than melting all at once, which makes it forgiving for beginners. Lead-free solder, now standard for commercial electronics, requires higher temperatures, generally 420–450°F (215–230°C) depending on the alloy. It also tends to flow less easily, so expect a slightly steeper learning curve.
Your soldering iron needs to be set well above these melting points to account for heat loss at the tip. A good starting point for most electronics work is just under 400°C (about 750°F). If you see the circuit board discoloring or browning, the temperature is too high. If the solder takes more than a second or two to flow, it’s too low.
Why Flux Matters
Solder won’t bond to oxidized metal. Every metal surface exposed to air develops a thin oxide layer that acts as an insulating barrier, preventing the molten solder from making true metal-to-metal contact. Flux solves this problem in three ways: it chemically dissolves existing oxide, it coats the hot surface to block oxygen and prevent new oxide from forming, and it improves the ability of liquid solder to spread and “wet” the joint.
Most solder wire sold for electronics has a rosin flux core built right in. As the solder melts, the flux releases automatically. For plumbing and metalwork on steel or copper pipe, acid core solder uses a more aggressive flux that strips heavier oxidation. Never use acid core solder on electronics. The corrosive residue will eat away at delicate components and traces over time. Rosin core is the standard for circuit boards and wiring.
Preparing the Surfaces
Even with flux, solder flows best on clean metal. Grease, dirt, and heavy oxidation can prevent a good bond. For electronics work, lightly scrubbing pads or leads with fine abrasive (a fiberglass pen or fine sandpaper) is usually enough. For plumbing or sheet metal, you may need to file or scrape the joint area down to bright metal first.
Chemical cleaning works too. A weak alkaline solution in hot water removes grease, and a diluted acid dip strips rust and tarnish. For most hobbyist and repair work, though, mechanical cleaning followed by the flux in your solder wire handles everything.
Step-by-Step: Melting Solder on a Joint
Before you touch anything, tin your soldering iron tip. Turn the iron on, let it reach temperature, wipe the tip on a damp sponge or brass wire cleaner to remove old buildup, then immediately feed a small amount of fresh solder onto the tip’s working surface. The solder should melt and flow across the tip instantly, giving it a shiny, silvery coating. A properly tinned tip transfers heat far more efficiently than a dry or oxidized one.
To make a joint, press the tinned tip against the spot where the two pieces of metal meet. Hold it there for about one second to let the metal heat up. Then feed solder wire into the junction where the iron tip meets the workpiece. The solder should melt on contact with the heated metal and flow into the joint on its own, drawn in by capillary action. This whole process takes two to four seconds for a typical electronics joint.
The key mistake beginners make is melting solder onto the iron tip and then trying to carry it to the joint like paint on a brush. This doesn’t work. The flux burns off before it can do its job, and the solder cools before it wets the surfaces. Always heat the work first, then introduce the solder.
Recognizing a Good Joint vs. a Bad One
A properly melted joint looks shiny, smooth, and slightly concave, with solder that feathers out at the edges where it meets the metal. It indicates the solder fully melted and bonded to both surfaces.
A cold solder joint happens when the solder never fully melted or the surfaces weren’t hot enough for proper bonding. These joints look dull, lumpy, or grainy, often with a rough, frosty texture or fine cracks around the edges. They’re brittle and will fail under even moderate stress. The most common cause is an iron tip that’s too cool or that only touched the joint for a split second. If you see a dull, blobby joint, reheat it by pressing the iron back against the joint until the solder flows shiny again.
Melting Solder to Remove It
Sometimes you need to melt existing solder to remove a component or fix a mistake. Two tools handle this well.
- Desoldering wick (copper braid): Place the flat copper braid over the solder joint, then press your hot iron tip on top of the wick. The iron heats the wick, the wick heats the solder, and as the solder melts it gets drawn up into the copper braid by capillary action. Slowly drag the wick along the joint to absorb as much solder as possible. Clip off the saturated section and use fresh braid for the next joint. Adding a dab of flux to the wick before use speeds things up considerably.
- Desoldering pump (solder sucker): Heat the joint with your iron until the solder is fully liquid, then quickly position the pump’s nozzle next to the molten solder and trigger it. The pump creates a burst of vacuum that sucks the liquid solder away. This works well for clearing through-hole component leads on circuit boards.
After removing solder with either method, inspect the joint. If residue remains, repeat the process with a fresh section of wick or another pass with the pump. Clean your iron tip afterward with a brass cleaner or damp sponge to prevent flux residue from building up.
Matching Your Iron to the Job
A basic fixed-temperature soldering iron (around 25–40 watts) works fine for simple wire joints and basic through-hole electronics. For surface-mount components, rework, or anything requiring precision, an adjustable-temperature soldering station gives you control. Smaller components need less heat; larger connections like motor wires or ground planes need more, because the surrounding metal acts as a heat sink and pulls energy away from the joint.
Tip shape matters too. A pointed conical tip works for fine work, while a wider chisel tip contacts more surface area and transfers heat faster for larger joints. If you’re struggling to melt solder on a big joint, switching to a broader tip often solves the problem faster than cranking up the temperature.