Leaded vs Lead-Free Solder: What's the Difference?
The two main solder families behave very differently — and which you can use is partly a legal question. This guide explains the differences, the RoHS rules, and how to work with each.
In this guide
Almost all electronics solder falls into one of two families: traditional leaded solder and modern lead-free solder. They melt at different temperatures, handle differently and produce different-looking joints — and legislation restricts where leaded solder can be used. Understanding both helps you choose the right wire and get clean, reliable results.
1.Leaded solder
Traditional leaded solder is a tin-lead alloy, most commonly Sn63/Pb37. It is eutectic, meaning it changes straight from solid to liquid at a single low temperature (183 °C) with no pasty phase — which makes it forgiving and easy to work with. It wets readily and produces bright, shiny joints, and it remains the choice for many repair, prototyping and high-reliability applications where its use is permitted.
2.Lead-free solder
Lead-free solder replaces the lead with other metals — most commonly a tin-silver-copper alloy such as SAC305 (or lead-free tin alloys like SN100e). It melts hotter (typically around 217–227 °C), tends to produce a slightly duller, matt joint, and needs more heat and good flux to wet well. It is RoHS compliant and is required for most electronics placed on the market in the UK and EU.
3.Side-by-side comparison
| Leaded (Sn63/Pb37) | Lead-free (e.g. SAC305) | |
|---|---|---|
| Melting point | 183 °C (eutectic) | ~217–227 °C |
| Ease of use | Very forgiving, flows easily | Needs more heat & flux |
| Joint appearance | Bright, shiny | Duller, matt |
| Typical iron temp | 320–360 °C | 340–380 °C |
| RoHS compliant | No | Yes |
| Best for | Repair, prototyping, exempt high-reliability work | New commercial products, RoHS-compliant manufacturing |
4.Which should I use?
For new electronics placed on the market in the UK and EU, lead-free is generally required under the RoHS Directive, which restricts lead in electrical and electronic equipment. If you are manufacturing products for sale, lead-free is almost always the answer.
Leaded solder is still widely used for repairing and servicing legacy (pre-RoHS) equipment, for prototyping and education, and in specific exempt applications — such as certain high-reliability aerospace, medical and defence work — where RoHS exemptions apply. When repairing an existing board, it's usually best to match the solder already used on it.
5.Working with lead-free
Because lead-free melts hotter and wets less readily, a few adjustments make it much easier:
- Run a slightly higher tip temperature (around 340–380 °C) and use a station with good thermal recovery.
- Use plenty of good flux — flux is even more important with lead-free than with leaded.
- Expect a duller joint. A matt finish is normal for lead-free and doesn't mean a cold joint.
- Keep your tip in top condition — lead-free is harder on tips, so clean and re-tin diligently (see our tip-care guide).
6.Health & safety
Both types produce hazardous fume. The flux fume from either solder is a recognised cause of occupational asthma, so fume extraction is required under COSHH regardless of which solder you use — lead-free is not "safe" just because it has no lead. Leaded solder adds a surface-contamination hazard: wash your hands thoroughly and don't eat, drink or touch your face while soldering. See our fume extraction guide.
7.Common questions
Is lead-free solder safe to breathe?
No — the flux fume from lead-free solder is still a respiratory hazard and a recognised cause of occupational asthma. Fume extraction is required regardless of solder type.
Can I mix leaded and lead-free?
Best avoided. Mixing alloys can create joints with unpredictable properties and a weaker, unreliable result. When repairing, match the solder already on the board.
Why do my lead-free joints look dull?
That's normal — lead-free joints have a naturally matt finish. As long as the joint has a good concave fillet and has wetted properly, a matt appearance is fine.
Do I need a different iron for lead-free?
Not necessarily, but you'll want good power and thermal recovery to cope with the higher temperature. A quality temperature-controlled station makes lead-free far easier.
