The proper heating procedure for soldering starts with preparing your iron tip, setting the right temperature for your solder type, and heating the joint itself rather than melting solder directly onto it. Getting this sequence right is the difference between a strong, shiny joint and a cold, brittle one that fails later. Here’s how to do it step by step.
Tin Your Iron Tip First
Before you touch your iron to any component, the tip needs a thin, even coating of solder. This process, called tinning, protects the tip from oxidation and allows heat to flow smoothly into the joint. When a bare tip is exposed to air at soldering temperatures, an oxide layer forms almost immediately, and that layer acts as an insulator. A properly tinned tip transfers heat far more efficiently.
To tin the tip, heat your iron to its working temperature, then wipe the tip on a damp sponge or brass wire cleaner to remove any residue. Apply a small amount of solder directly to the cleaned tip, letting it melt and coat the entire working surface. Wipe off the excess. You should re-tin periodically throughout your soldering session, and always tin the tip before putting the iron away. Keeping a fresh solder coating on the tip at all times extends its life and prevents the kind of crusty buildup that makes soldering frustrating.
Set the Right Temperature
Your temperature setting depends on whether you’re using leaded or lead-free solder. Leaded solder (the traditional tin-lead mix) melts at around 363°F (184°C). Lead-free solder melts higher, near 425°F (218°C). But your iron needs to be set well above the melting point to heat joints quickly and effectively. A setting of 650 to 700°F (343 to 371°C) works for most through-hole and general-purpose soldering with either type.
The goal is to use the lowest effective temperature. Too low and you’ll spend too long heating the joint, which can actually cause more heat damage to surrounding components than a hotter, faster approach. Too high and you risk burning flux, damaging pads, or destroying sensitive parts. If you’re working on delicate surface-mount components, keeping your iron under 350°C (662°F) is a common guideline. Start in the middle of the recommended range and adjust based on how the solder flows.
Heat the Joint, Not the Solder
This is the most important principle in soldering and the one beginners most often get wrong. You heat the parts being joined, and then let those hot parts melt the solder. You do not melt solder onto the iron and drip it onto the connection.
Place the iron tip so it contacts both surfaces of the joint at the same time. For a through-hole component on a circuit board, that means touching the tip to both the component lead and the copper pad simultaneously. Let them heat for a few seconds. Then touch the solder wire to the opposite side of the joint from the iron. The heat conducted through the metal should melt the solder on contact, and it will flow naturally toward the heat source, wicking around the joint and forming a smooth, concave fillet.
When solder is melted by the joint rather than the iron, it bonds properly to the metal surfaces. If you melt solder on the iron tip and transfer it, the joint surfaces are still too cool for the solder to wet them. The result is a “cold joint” that looks dull and grainy and has poor electrical and mechanical connection.
How Flux Works During Heating
Most solder wire has a core of flux running through it, so you don’t need to apply it separately for basic work. When the flux heats up, it activates and breaks down the thin oxide layer that naturally forms on metal surfaces. It also creates a temporary protective barrier that keeps oxygen in the air from reacting with the hot metal while you work. This is why solder flows and bonds so much better on freshly fluxed surfaces.
Different flux types activate at different temperatures, so matching your flux to your solder and application matters. If you see the flux smoking and burning off before the solder even melts, your iron is too hot or you’re dwelling too long. The flux should bubble gently and clear the surface just as the solder begins to flow.
Keep Contact Time Short
A good solder joint on a standard electronic component should take about two to five seconds of iron contact. The general maximum is seven seconds of dwell time. Beyond that, you risk damaging the component or lifting the copper pad from the circuit board.
If the solder isn’t flowing within a few seconds, pulling the iron away and reassessing is better than pressing harder or waiting longer. Common reasons for slow flow include a dirty or oxidized tip, insufficient flux, or an iron that’s set too low. Adding a tiny bit of fresh solder to the tip before touching the joint can help, because the fresh flux and molten solder improve heat transfer from the tip to the work surface.
Watch for warning signs of overheating: discoloration on the circuit board (the green mask turning brown), a pad that shifts or lifts when touched, or solder that looks dark and grainy instead of bright and smooth. If you notice any of these, stop and let everything cool before attempting the joint again.
Protecting Heat-Sensitive Components
Some components, particularly semiconductors and certain capacitors, are vulnerable to heat damage. When soldering near these parts, clip-on heat sinks placed between the iron and the component body act as a thermal buffer, absorbing excess heat before it reaches the sensitive internals. Small alligator clips work in a pinch.
For multi-pin components, avoid soldering adjacent pins in sequence. Instead, alternate between pins on opposite sides to give each area time to cool. This prevents heat from accumulating in one section of the board. If a component requires several joints, let five to ten seconds pass between each one when possible.
The Full Sequence at a Glance
- Prepare: Heat the iron, clean the tip, and tin it with a thin solder coating.
- Set temperature: 650 to 700°F for most work, lower for delicate components.
- Position: Touch the iron to both the pad and the lead simultaneously.
- Apply solder: Feed solder wire to the opposite side of the joint from the iron tip after two to three seconds of heating.
- Watch the flow: Solder should melt on contact and wick smoothly around the joint.
- Remove: Pull the solder wire away first, then the iron. Total contact time under seven seconds.
- Inspect: A good joint is shiny, smooth, and concave. A dull or blobby joint needs rework.
Re-tin the tip between joints if you notice it looking dry or dark. When you’re finished soldering, clean the tip one final time, apply a fresh coat of solder, and turn off the iron. That protective layer of solder keeps the tip from oxidizing while it sits in storage, so it’s ready to go next time.