Technical overview
Soft solders are tin-based joining alloys with a liquidus at or below 430 °C (800 °F), the boundary used by ASTM B32. The standard covers tin-lead, tin-antimony, tin-silver, tin-copper-silver and lead-tin-silver families, in bar, ingot, powder, solid wire, flux-cored wire and paste forms.
ASTM B32 covers non-electronic applications. Electronic-grade solders are governed by IPC standards. The ITA estimates lead-free solders made up about 86% of electronics solder in 2022.
Grades & standards
Grades are distinct materials — properties and uses below apply to the named grade only.
Tin-lead (Sn-Pb)
Conventional soft solder
Composition: Alloy ratio to be specified (e.g. per ASTM B32 designations)
- Covered by ASTM B32 for non-electronic use
- Subject to lead restrictions in many end uses
Listed specifications: ASTM B32
Lead-free (Sn-Ag, Sn-Cu-Ag)
Lead-free soft solder
Composition: Alloy ratio to be specified
- Dominant in electronics manufacture
- Electronic grades fall under IPC rather than ASTM B32
Listed specifications: ASTM B32 (non-electronic) · IPC (electronic grades)
Technical properties
| Property | Value | Applies to | Source |
|---|---|---|---|
| Liquidus (scope of ASTM B32) | ≤ 430 °C | All ASTM B32 solders | ASTM International |
Typical or specified values for the named grade from the cited source. Actual values depend on temper, size and the producing mill — rely on the mill certificate for your lot.
Forms
Typical industry forms for this material. They are not a stock list — form, size and availability are confirmed per enquiry.
- Wire (solid or flux-cored)
- Bar / stick
- Ingot
- Paste
Applications & industries
- Plumbing and sheet-metal joints
- Electrical connections
- Electronics assembly (IPC-grade alloys)
- Radiator and heat-exchanger joints
Selection notes & limitations
- Soft solder joints are weaker and lower-temperature than brazed (silver-solder) joints.
- Lead-bearing solders are restricted for many electronics and potable-water uses — state the end use.
⚠ Lead content
Tin-lead solders contain lead. OSHA links chronic occupational lead exposure to kidney, blood-pressure and nervous-system effects. Specify lead-free alloys where regulations require and request the SDS.
Source: US Occupational Safety and Health Administration (OSHA)
What to specify when requesting a quote
- 1Alloy composition (e.g. tin-lead ratio or lead-free system)
- 2Flux type and core, if flux-cored
- 3Wire diameter or bar size
- 4Grade and the standard it must conform to (ASTM, EN, IS, UNS or your drawing)
- 5Form and dimensions — thickness or diameter, width, length and tolerances
- 6Approximate quantity, and whether the requirement is one-off or recurring
- 7Intended application, so the grade can be cross-checked before quoting
- 8Documents required — e.g. mill test certificate, chemical analysis, certificate of conformity
- 9Delivery city / site and the date you need material by
Documents buyers may request
Mill test certificate
e.g. EN 10204 type 3.1 inspection certificate, where the producing mill issues one
Chemical analysis report
heat / lot composition against the specified grade
Certificate of conformity
confirming the material meets the ordered standard
Heat / lot traceability
heat numbers marked on material and documents
Dimensional inspection report
for cut-to-size or machined material
Safety Data Sheet (SDS)
especially for lead, beryllium-, cadmium- or lead-bearing products
Which documents can be provided depends on the source mill and is confirmed with each quotation.
Frequently asked questions
How is soft solder different from silver solder?
Soft solder melts below about 430 °C. "Silver solder" normally means silver brazing alloy — for example BAg-7 melts at roughly 618–652 °C — giving stronger joints at higher temperatures.
Sources & technical references
- ASTM B32 — Standard Specification for Solder Metal — ASTM International. Checked 2026-10-14.Full standard is paywalled — only the public abstract and scope on astm.org were read. Composition tables were not accessed.
- ITA tin use survey press release (Oct 2023) — International Tin Association. Checked 2026-10-14.
- Lead — Health Effects — US Occupational Safety and Health Administration (OSHA). Checked 2026-10-14.
