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Solder and Low-Melting Alloys

Solders and low-melting alloys are the metals that melt below 450 °C — low enough to join copper and electronics without damaging them, to cast in silicone or rubber moulds, or to give way on purpose in a fuse or a sprinkler head. Tin-silver-copper (SAC) is the lead-free electronics standard; 63/37 tin-lead is the eutectic it replaced and is still used where RoHS does not apply; bismuth and indium alloys melt as low as 47 °C for step soldering, heat-sensitive assemblies and fusible links; babbitts are the soft tin- or lead-based bearing metals still lining large engine and turbine bearings. This is a reference family: we list it so the joint or bearing you are designing can be specified correctly, not because we cast solder parts.

Solders and fusible alloys by group

Lead-free soldersSn-Ag-Cu (SAC305, SAC405), Sn-Cu, Sn-Ag, Sn-Zn · 217–227 °C208 – 42RoHS electronics assembly, copper plumbing (Sn-Cu, Sn-Ag), food and potable-water joints — SAC305 is the reflow and wave standard; Sn-Cu the low-cost wave and plumbing alloy; Sn-Ag for higher-strength copper joints.
Tin-lead solders & lead alloysSn63Pb37 eutectic, Sn60Pb40, Pb-rich high-melt, antimonial and chemical lead · 183–330 °C486 – 38Legacy and exempt electronics (aerospace, military, medical), rework of tin-lead assemblies, radiator and sheet-metal work — the eutectic 63/37 wets best and melts sharply at 183 °C; high-lead alloys for step soldering and die attach; antimonial and chemical lead for battery grids, shielding and chemical linings.
Bismuth & indium low-melting alloysSn42Bi58 (138 °C), In-Sn, In-Bi, Field's, Wood's, Cerro alloys · 47–160 °C171 – 45Step soldering, LED and heat-sensitive components, thermal fuses and sprinkler links, tube-bending mandrels, workholding for machining, indium thermal interfaces and cryogenic seals — melting point is the specification.
Babbitt bearing metalsSn-Sb-Cu (tin-base), Pb-Sb-Sn (lead-base) · ASTM B231725 – 60Large plain bearings for turbines, compressors, marine and mill equipment — cast onto a steel or bronze shell, machined in place; embeds debris, conforms to the shaft and fails gracefully. Tin-base for speed and temperature, lead-base for cost.
Pewter & specialty alloysSn-Sb-Cu pewter, Sn-Zn, fusible specialty grades610 – 43Cast decorative and tableware pieces, model figures, low-temperature prototype castings in silicone moulds; Sn-Zn as a lower-cost lead-free solder for aluminum.

Choose a solder or fusible alloy for

Joining electronic components and copper assemblies (SAC305, SAC405, Sn63Pb37, Sn96.5Ag3.5); step soldering and heat-sensitive assemblies (Sn-Bi, In-based alloys); thermal fuses, safety plugs and sprinkler links that must release at a set temperature (Wood's, Field's, Cerro alloys); fixturing and holding delicate parts for machining — a fusible alloy cast around the part and melted away afterwards; conformable, high-conductivity thermal interfaces (indium); large plain bearings cast in place and machined (babbitt); pewter castings and low-temperature prototype casting.

Look elsewhere when

The joint carries structural load or sees temperature above ~100 °C (braze with a silver or copper filler, or weld), the part must have real strength (no solder alloy exceeds about 60 MPa yield; most creep at room temperature), lead is prohibited (RoHS, potable water, food, medical — use SAC or Sn-Cu grades), or the bearing runs fast and hot (bronze, or a polymer bearing). Bismuth alloys are brittle, indium is expensive, and tin-lead is banned in most consumer electronics.

Tensile strength against elongation at break, every solder & low-melting alloy grade

No materials in view have both of these properties.

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Manufacturing notes

Soldered assemblies
Electronic sub-assemblies and copper / brass fabrications we supply are soldered to the alloy you specify — SAC305 by default for RoHS work, Sn63Pb37 where an exemption applies, Sn-Ag or Sn-Cu for plumbing-style copper joints. Specify the alloy, flux type and cleanliness class on the drawing.
Fusible-alloy workholding
Thin, fragile or oddly shaped parts are sometimes cast into a low-melting alloy block for machining and released in hot water afterwards — a technique for turbine blades, thin-wall castings and optics. Ask if a part is proving impossible to fixture.
Babbitt bearings
Large plain bearings are cast with tin-base babbitt onto a machined steel or bronze shell (spun or static cast), then bored and finished in place to the shaft. Re-babbitting worn bearings is common in rotating-equipment repair.
Design notes
Solder joints creep at room temperature and lose strength quickly above 100 °C — give them a mechanical lock and treat them as electrical and sealing connections, not structural ones. Match the alloy melting point to the assembly sequence in step-soldered products; keep lead-free and tin-lead processes separate to avoid low-melting contamination.

Solder & Low-Melting Alloy — frequently asked

SAC305 or Sn63Pb37?

SAC305 (96.5 % Sn, 3 % Ag, 0.5 % Cu, melting 217–220 °C) for anything sold into RoHS markets — consumer, industrial and most commercial electronics. Sn63Pb37 (183 °C eutectic) only where an exemption applies (aerospace, defense, some medical and high-reliability) or when reworking existing tin-lead assemblies: it wets better, flows at a lower temperature and has a longer thermal-cycling record, but lead is prohibited almost everywhere else.

What melts at the lowest temperature?

Gallium-based alloys are liquid near room temperature (Galinstan, –19 °C) but are corrosive to aluminum and rarely used as solders. Among practical alloys: Field's metal (Bi-In-Sn) at 62 °C, indium-bismuth eutectics from 72 °C, Wood's metal (Bi-Pb-Sn-Cd) at 70 °C, In52Sn48 at 118 °C and Sn42Bi58 at 138 °C — the last being the common low-temperature electronics solder for heat-sensitive parts and step soldering.

How strong is a solder joint?

The bulk alloy has a yield strength around 30–60 MPa — roughly a tenth of aluminum — and it creeps at room temperature under sustained load. A well-designed lap or fillet joint in shear can hold 20–40 MPa briefly, far less over years or with thermal cycling. Design solder joints as electrical and sealing connections with mechanical retention (clinched leads, crimps, adhesive) carrying the load.

What is babbitt, and is it still used?

Babbitt is a soft tin- or lead-based bearing alloy (ASTM B23) cast as a 1–5 mm lining inside a steel or bronze shell and machined to the shaft. It conforms to misalignment, embeds dirt instead of scoring the shaft, and melts before the shaft is damaged if lubrication fails. Still standard in steam and gas turbines, large compressors, marine engines and mill drives — anywhere a rolling-element bearing would be too large or a failure too expensive.

Do you cast parts in solder or pewter?

Pewter and fusible alloys cast well in silicone moulds at 250–300 °C, so decorative pieces, badges, model figures and low-temperature prototype castings are possible — ask for a quote as a casting job. We list the solder alloys mainly so that the joints and bearings in the assemblies we build can be specified precisely; we do not machine parts from solder stock.