Lead-Free vs Leaded Solder: Which Should You Use?

Use lead-free solder for work that needs to remain lead-free, and check the requirements before choosing leaded solder for repairs. The choice depends on the equipment, the solder already present and any rules that apply to the finished item. A solder alloy that flows easily is useful, but ease of use is only part of the decision.

Tin-lead solder melts at a lower temperature and is generally easier to work with. Lead-free solder needs more heat at the joint. Both can make sound electrical connections with a clean tip, suitable flux and enough heat transfer. For an existing repair, identify the original solder where possible before adding another alloy.

Choose solder wire made for electronics. Most electronics solder wire contains a flux core. Acid flux and plumbing solder must not be used on circuit boards or electronic connections.

The melting point of solder depends on its alloy, with tin-lead solder melting below common lead-free types. Some alloys melt at a single temperature. Others soften and melt across a short range. That difference affects how the joint behaves as it cools.

63/37 tin-lead solder is eutectic, so it melts at 183°C without a pasty stage between solid and liquid. 60/40 solder melts over about 183 to 190°C. Keep a fresh joint still while it sets, especially with an alloy that passes through a soft stage.

Common lead-free alloys melt roughly 35 to 45°C higher than tin-lead solder. The melting point is not the iron setting. The tip must be hotter because it loses heat into the connection.

• 63/37 tin-lead solder: melts at 183°C.
• 60/40 tin-lead solder: melts over about 183 to 190°C.
• SAC305 solder: melts at about 217 to 220°C.
• 99.3% tin and 0.7% copper solder: melts at about 227°C.

SAC305 solder is a lead-free alloy containing 96.5% tin, 3% silver and 0.5% copper. It is one option for electronics work where lead-free solder is needed. Tin-copper solder is another lead-free choice. The alloy name describes the metal mix, rather than the flux inside the wire.

Check both the alloy and the flux type on the solder label. Rosin and no-clean flux cores are used for electronics. A flux core helps solder flow onto the heated metal, but it cannot make up for poor contact between the iron and the joint.

Lead-free solder can feel less forgiving than tin-lead solder during hand work. Start with a suitable tip and a clean connection. If the solder struggles to melt, check heat transfer before raising the temperature.

Start at about 300 to 350°C for leaded solder or 330 to 380°C for lead-free solder. These are tip settings for hand soldering, not fixed rules. Small surface-mount parts usually suit the lower end. Thick wire, large joints and ground planes may need more heat.

A larger tip can transfer heat better than a fine tip at a higher setting. Choose a tip that makes good contact without touching nearby parts. The aim is to heat the connection so solder flows onto it, then remove the iron.

Running hotter than needed speeds up tip oxidation and can lift PCB pads. Temperature-controlled stations let you adjust the setting. Fixed-temperature irons cannot be adjusted, so tip choice and contact matter when working with them.

Lead-free solder joints usually look duller and more grainy than tin-lead joints, even when they are sound. A shiny finish is therefore a poor test on its own. Judge how the solder has flowed onto the pad and lead, rather than checking shine alone.

A sound joint should show that solder has wetted the surfaces being joined. Solder that sits as a separate blob or pulls away from the metal suggests a problem. Dirt, oxidation, weak heat transfer or a lack of suitable flux can stop solder from flowing.

Avoid reheating a lead-free joint simply to make it shiny. Extra heat may damage the board without changing the finish. If the connection looks doubtful, inspect the contact and flow before deciding to rework it.

Leaded solder needs careful handling because lead is toxic. Wash your hands after handling it. Do not eat or drink at the bench. Keep solder, clipped ends and bench waste away from food and items used for eating.

The visible fumes during soldering come mainly from flux, rather than lead. Ventilation or a fume extractor is advised for both leaded and lead-free solder. Choosing lead-free wire does not remove the need to control flux fumes.

The EU RoHS directive has restricted lead in most new electrical and electronic equipment since 1 July 2006. The UK has its own RoHS regulations with the same restriction. Leaded solder is widely labelled for professional use in the UK and EU, and many sellers restrict it that way. Check the seller's terms before buying.