How solder is made
Solder is a metal blend chosen to melt below the parts it joins, and one classic mix melts at a single sharp temperature.
- stations
- 6
- things upstream
- 19
- raw sources
- 10
- steps from the ground
- 4
The short version
Solder is a fusible alloy, usually tin with lead, or tin with silver and copper in the lead-free versions. The metals are melted together in precise proportions and cast into bars, which are extruded or drawn into wire. Wire for electronics is often hollow, with a core of flux that cleans the joint as it melts.
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Melt the metals together
Tin is melted with its partner metals. In classic soft solder that is lead, in amounts from 5 to 70 percent tin by weight, and in the modern lead-free solders it is silver and copper. More tin makes the joint stronger.
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Set the recipe exactly
The proportions decide the melting behavior. The eutectic mix of 61.9 percent tin and 38.1 percent lead melts at one point, 183 °C, instead of over a range. Lead-free tin-silver-copper alloys became standard after rules took effect in the EU on July 1, 2006.
183 °C for tin-lead eutectic
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Cast into bars
The alloy is cast into bars. Plumbers use thick bars of solder and apply flux separately.
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Draw it into wire
Bars are reduced to solder wire, with diameters from ultra-fine 0.25 to 0.5 millimeters to heavy gauge 1.5 to 2.0 millimeters and above.
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Fill it with flux
Wire for hand soldering is often made with cores of flux. Flux strips oxide from the metal surfaces as the joint heats, so that the molten solder can wet them.
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Spool it up
Wire is wound onto spools of a convenient weight. Solder is also sold as paste, as thin sheets for jewelers, and as preformed foil shapes.
Worth repeating
- Soft solder melts between 90 and 450 °C, and alloys that melt between 180 and 190 °C are the most commonly used.
- Since 1974, lead has been prohibited in solder and flux for drinking-water plumbing in the United States.
- Lead-tin solder easily dissolves gold plating and forms brittle intermetallic compounds.
Back to the ground
Follow every input upstream and solder starts as these 10 raw sources.
Everything it is made of See it on the map
Open the whole family tree
Where it goes next
Solder feeds 27 lines directly and reaches 54 things in total.
Further down the line
Keep walking
Sources
Cite this page: "How solder is made." Assembly Line, 2026-11-03. https://assemblyline.org/make/solder