The right solder wire is the single cheapest upgrade to your soldering. For most electronics, the best choice is 0.8mm rosin-core 63/37 leaded solder: it melts low, flows beautifully and is the most forgiving to use. Choose lead-free only if you need RoHS compliance. This guide explains exactly how to choose solder wire, the alloy, the diameter, the flux core and the quality, so you pick the right reel for electronics, PCBs or electrical wires.
Quick recommendation
For general electronics and learning: 0.8mm 63/37 leaded, rosin (flux) core. For fine SMD: drop to 0.5 to 0.7mm. For RoHS or lead-free work: a Sn99.3/Cu0.7 or SAC lead-free wire. Always use rosin-core electronics solder, never acid-core plumbing solder. See our solder wire range.
What Is Solder Wire (and What Is It Made Of)?
Solder wire is a metal alloy, drawn into a thin wire, that melts at a low temperature to join two metal parts and conduct electricity between them. Electronics solder is not solid metal: it has one or more cores of flux running down the centre.
So a reel of electronics solder is two materials working together:
- The alloy. Either tin-lead (leaded) or a lead-free mix of tin with copper and sometimes silver. This is the metal that forms the joint.
- The flux core. A rosin-based cleaner inside the wire that removes oxide as the metal heats, so the molten solder can wet and flow. Without flux, solder beads up and will not stick.
That is why you should never sand or scrape a joint to help it: the cored flux does that job. It is also why plumbing solder, which uses corrosive acid flux, must never be used on electronics.
How to Choose Solder Wire: The 4 Things That Matter
Every solder wire decision comes down to four properties. Get these right and the rest is detail:
- Alloy: leaded (63/37) for easy, forgiving soldering, or lead-free for RoHS compliance.
- Diameter: 0.8mm for general work, thinner for fine and SMD, thicker for large joints.
- Flux core: rosin-cored electronics solder (never solid wire and never acid-core).
- Quality: genuine, consistent solder with a reliable flux core, not cheap wire that spits and leaves poor joints.
The rest of this guide takes each of these in turn.
Leaded vs Lead-Free Solder: Which to Choose
The alloy is the biggest decision. There are two families:
Leaded solder (63/37, 60/40)
Tin-lead solder is the easiest to use. 63/37 is eutectic, meaning it melts and sets at a single low temperature (183°C) with no mushy in-between stage, so joints are shiny and set instantly. It is the best choice for hobby electronics, learning and repair work.
Lead-free solder (Sn99.3/Cu0.7, SAC)
Lead-free is required for any product sold under RoHS, and preferred by anyone avoiding lead. It melts higher (around 217 to 227°C) and wets less freely, so it needs a slightly hotter iron and a little more patience.
The short version: 63/37 leaded for the easiest hands-on soldering, lead-free for compliance. Beginners should learn on leaded. Either way, set your iron correctly, see the soldering temperature guide.
Types of Solder Wire
Solder wire is grouped by its alloy and by its flux core. Here are the types you will actually meet for electronics:
| Type | What it is | Best for |
|---|---|---|
| 63/37 leaded | Eutectic tin-lead, melts 183°C | Easiest all-round electronics solder |
| 60/40 leaded | Tin-lead, small plastic range | General electronics, very common |
| Sn99.3/Cu0.7 lead-free | Tin-copper, melts ~227°C | RoHS work, everyday lead-free |
| SAC (tin/silver/copper) | Lead-free with silver, melts ~217°C | Higher-performance lead-free joints |
| Rosin / no-clean core | Standard flux core in the above | Almost all hand soldering |
| Acid-core | Corrosive flux (plumbing only) | Never use on electronics |
For electronics you want a rosin-cored (or no-clean) wire in a leaded or lead-free alloy. Ignore solid (un-cored) wire and acid-core wire entirely.
What Diameter Solder Wire Should You Use?
Thinner wire feeds less solder per second, giving more control on small joints; thicker wire delivers solder faster on big ones. Match the diameter to your work:
| Diameter | Best for |
|---|---|
| 0.3 to 0.5mm | Very fine SMD, tiny pads, precision rework |
| 0.6 to 0.7mm | SMD and small through-hole, fine control |
| 0.8mm | The best all-round size for general electronics |
| 1.0mm and up | Through-hole, thick wires, connectors, large joints |
If you buy one reel, make it 0.8mm. It handles the great majority of electronics jobs, and many people keep a second thinner reel for fine work.
Best Solder for Specific Jobs
Best solder for electronics and PCBs
0.8mm 63/37 leaded rosin-core for general work, or a fine 0.5 to 0.7mm reel for surface-mount. Lead-free Sn99.3/Cu0.7 if you need RoHS. This is the bread-and-butter electronics solder.
Best solder for electrical wires and connections
The same rosin-core electronics solder works for joining wires, connectors and terminals. Go up to 1mm for thicker cable so you can lay solder down quickly. Do not use plumbing or acid-core solder on electrical wiring.
Best solder for copper wire
Copper wets easily, so standard rosin-core leaded or lead-free solder bonds to it well. For heavy copper wire, a 1mm wire and a little extra heat help the joint flow.
What we stock
For everyday electronics we recommend our 63/37 high-purity leaded solder, and for RoHS work the lead-free Sn99.3/Cu0.7 solder (0.8mm and 1mm). Both are genuine, rosin-cored and in UK stock.
Does Solder Wire Conduct Electricity?
Yes. Solder is a metal alloy (tin with lead, copper or silver), and like all metals it conducts electricity. That is the whole point: a soldered joint carries current between the two parts it joins, which is why solder is used to build and repair circuits.
The flux residue left around a joint is a different matter. With modern no-clean and rosin fluxes the residue is essentially non-conductive and safe to leave, though you can clean it off for a tidy finish. Solder itself, though, is fully conductive.
Watch: Choosing the Right Solder Wire
A short walkthrough of solder types, flux and diameter, and how to pick the right one:
Frequently Asked Questions
What is the best solder wire for electronics?
For most people, 0.8mm 63/37 leaded solder with a rosin (flux) core. It melts low, flows cleanly and is the most forgiving to use. Use a 0.5 to 0.7mm reel for fine SMD, or a lead-free Sn99.3/Cu0.7 wire if you need RoHS compliance.
What is solder wire made of?
A metal alloy with a flux core. The alloy is either tin-lead (leaded) or a lead-free mix of tin with copper and sometimes silver. The core is rosin-based flux that cleans the metal so the solder can flow.
What diameter solder wire should I use?
0.8mm is the best all-rounder for general electronics. Use 0.5 to 0.7mm for fine SMD work and 1mm or more for through-hole, thick wires and large joints.
What type of solder is best for electrical wires?
Rosin-core electronics solder, leaded 63/37 or lead-free, in 0.8mm to 1mm depending on wire thickness. Never use acid-core or plumbing solder on electrical wiring, as it corrodes the connection.
Is leaded or lead-free solder better?
Leaded (63/37) is easier to use and best for hobby and repair work. Lead-free is required for products sold under RoHS. Beginners should start with leaded, then move to lead-free only if compliance demands it.
Does solder wire conduct electricity?
Yes. Solder is a conductive metal alloy, which is exactly why it is used to make electrical joints. Modern flux residue is essentially non-conductive and safe to leave on the board.