Tin-lead solder (Sn63/Pb37 eutectic and Sn60/Pb40) SnPb

spore: profile
id: solder-sn-pb
spore_version: 0.2
family: low-melting-metals-and-solders
name: Tin-lead solder (Sn63/Pb37 eutectic and Sn60/Pb40)
abbreviation: SnPb
role: low-melting solder alloy for electronics assembly
category: metals
type: heavy-metals
summary: |
  Tin-lead solder is a metal alloy of tin and lead. The 63/37 composition is a eutectic: it has one melting point, 183 °C, with no pasty range. The Sn60/Pb40 composition melts over a short range, from 183 °C to about 190 °C. The datasheets read for this profile put the density at about 8.4 to 8.5 g/cm3, the tensile strength of the 63/37 alloy at 43 MPa. A maker of 60/40 wire gives its thermal conductivity as 49 W/m·K and its elongation at break as 40 %. The US Aerospace Corporation review says tin whiskers were avoided for decades by adding a small amount of lead to the solder.
best_for: Soldering of electronic assemblies where a single, low melting point and a long track record matter more than RoHS compliance (the Sn60/Pb40 sheet says it is restricted to professional use)
weakest_at: Lead toxicity and regulatory limits (the Sn60/Pb40 sheet says it cannot be sold to private consumers), and low tensile strength and creep resistance compared with lead-free alloys
identity:
  formula: Sn63/Pb37 eutectic (63 % tin and 37 % lead by weight) and Sn60/Pb40 (59.5 to 60.5 % tin, remainder lead, by weight); an alloy, not a compound
  source: aimtek-6337
  where: Nominal Composition line (Sn 63 %, Pb 37 % remainder) of the Aimtek 63/37 data sheet; Sn content of the Sn60Pb40 range from section 2.2 of the Cynel-Unipress data sheet
  designations:
    - system: ASTM
      code: B32
      note: solder grade Sn63
      source: aimtek-6337
      where: Industry Specifications line (ASTM B32 Sn63)
    - system: ISO
      code: '9453'
      note: alloy designation Sn60Pb40 in ISO 9453:2014
      source: cynel-sn60pb40
      where: 'Header block: Alloy designation according to ISO 9453:2014, Sn60Pb40'
tags:
  environments: []
  stresses: []
  applications:
    - electronics-and-chips
properties:
  - benchmark: melting_point
    label: Melting point, Sn63/Pb37 eutectic
    value: 183
    unit: °C
    scope: material
    conditions:
      alloy: Sn63/Pb37 eutectic
      basis: solidus and liquidus both printed as 183 °C (361 °F); the sheet gives one value for both
    method: Value printed on a manufacturer data sheet
    status: ground
    source: aimtek-6337
    where: 'Melting Temperature block: Solidus (Flow point) and Liquidus (Melt point), both 361°F (183°C)'
  - benchmark: density
    label: Density, Sn63/Pb37 eutectic
    value: 8.4
    unit: g/cm3
    scope: material
    conditions:
      alloy: Sn63/Pb37 eutectic
      temperature: not stated on the sheet
    method: Value printed on a manufacturer data sheet (the sheet also prints 0.303 lb/in3)
    status: ground
    source: aimtek-6337
    where: 'Density line: 0.303 lb./in³ (8.40 g/cm³)'
  - benchmark: ultimate_tensile_strength
    label: Tensile strength, Sn63/Pb37 eutectic
    value: 43
    unit: MPa
    scope: material
    conditions:
      alloy: Sn63/Pb37 eutectic
      product_form: not stated on the sheet
      test_method: not stated on the sheet
    method: Value printed on a manufacturer data sheet (the sheet prints 6240 psi)
    status: ground
    note: The sheet does not name the test standard, product form or temper, so treat it as indicative.
    source: aimtek-6337
    where: 'Tensile Strength line: 6240 psi (43 MPa)'
  - benchmark: electrical_resistivity
    label: Electrical resistivity, Sn63/Pb37 eutectic
    value: 0.0000145
    unit: ohm-cm
    scope: material
    conditions:
      alloy: Sn63/Pb37 eutectic
      temperature: not stated on the sheet
    method: Value printed on a manufacturer data sheet (printed as 1.45 x 10 to the power -5)
    status: ground
    source: aimtek-6337
    where: 'Electrical Resistivity line: 1.45 x 10 -5 ohm-cm'
  - benchmark: melting_point
    label: Melting range, Sn60/Pb40 (cored wire data sheet)
    value: 183
    value_high: 190
    bound: range
    unit: °C
    scope: material
    conditions:
      alloy: Sn60Pb40, ISO 9453 designation
      product_form: cored solder wire
    method: Range printed on a manufacturer data sheet (solidus/liquidus)
    status: ground
    source: cynel-sn60pb40
    where: 'Section 2.5: Melting point (solidus/liquidus) 183/190 °C'
  - benchmark: melting_point
    label: Melting range, Sn60/Pb40 (bar and wire data sheet)
    value: 183
    value_high: 191
    bound: range
    unit: °C
    scope: material
    conditions:
      alloy: Sn60Pb40, nominal composition
    method: Range printed on a manufacturer data sheet (solidus and liquidus)
    status: ground
    source: aimtek-6040
    where: 'Melting Temperature block: Solidus (Flow point) 361°F (183°C); Liquidus (Melt point) 376°F (191°C)'
  - benchmark: density
    label: Density, Sn60/Pb40 (cored wire data sheet)
    value: 8.5
    unit: g/cm3
    scope: material
    conditions:
      alloy: Sn60Pb40
      basis: printed as approximately 8,50 g/cm3 (the sheet uses a decimal comma)
    method: Value printed on a manufacturer data sheet
    status: ground
    source: cynel-sn60pb40
    where: 'Section 2.6: Specific weight ~8,50 g/cm3'
  - benchmark: density
    label: Density, Sn60/Pb40 (bar and wire data sheet)
    value: 8.49
    unit: g/cm3
    scope: material
    conditions:
      alloy: Sn60Pb40, nominal composition
    method: Value printed on a manufacturer data sheet (the sheet also prints 0.3068 lb/in3)
    status: ground
    source: aimtek-6040
    where: 'Density line: 0.3068 lb./in³ (8.49 g/cm³)'
  - benchmark: ultimate_tensile_strength
    label: Tensile strength at break, Sn60/Pb40 (bar and wire data sheet)
    value: 44.13
    unit: MPa
    scope: material
    conditions:
      alloy: Sn60Pb40, nominal composition
      product_form: not stated on the sheet
      test_method: not stated on the sheet
    method: Value printed on a manufacturer data sheet (the sheet prints 6400 psi)
    status: ground
    note: The Cynel sheet gives a different figure for the same alloy (535 kg/cm2). The two sheets do not state the test method, so the difference cannot be resolved here.
    source: aimtek-6040
    where: 'Tensile Strength line: 6400 psi (44.13 MPa)'
  - benchmark: ultimate_tensile_strength
    label: Tensile strength at break, Sn60/Pb40 (cored wire data sheet)
    value: 535
    unit: kg/cm2
    scope: material
    conditions:
      alloy: Sn60Pb40, ISO 9453 designation
      product_form: cored solder wire
      test_method: not stated on the sheet
    method: Value printed on a manufacturer data sheet in the unit the sheet uses
    status: ground
    source: cynel-sn60pb40
    where: 'Section 2.9: Tensile strength at break 535 kg/cm2'
  - benchmark: elongation
    label: Elongation at break, Sn60/Pb40 (cored wire data sheet)
    value: 40
    unit: '%'
    scope: material
    conditions:
      alloy: Sn60Pb40, ISO 9453 designation
      product_form: cored solder wire
      test_method: not stated on the sheet
    method: Value printed on a manufacturer data sheet
    status: ground
    source: cynel-sn60pb40
    where: 'Section 2.10: Elongation at break 40%'
  - benchmark: thermal_conductivity
    label: Thermal conductivity, Sn60/Pb40 (cored wire data sheet)
    value: 49
    unit: W/m·K
    scope: material
    conditions:
      alloy: Sn60Pb40, ISO 9453 designation
      temperature: not stated on the sheet
    method: Value printed on a manufacturer data sheet
    status: ground
    source: cynel-sn60pb40
    where: 'Section 2.8: Thermal conductivity 49 W/m·K'
corrosion:
  - environment: Humid heat, 85 °C and 85 % relative humidity, no applied voltage, up to 1000 hours (tin corrosion under QFN packages on solder-paste boards)
    headline: In an 85 °C and 85 % humidity test, the 63/37 paste showed no tin-corrosion failure, and it corroded more slowly than SAC305.
    effect: A Cookson Electronics and MSLCircuits study found tin corrosion products under QFN and large passive parts after 500 hours or more. The authors say flux chemistry had the largest effect, and that SAC305 corroded faster than 63Sn37Pb. They say the failure was not seen with the 63/37 paste used. Reflow conditions had almost no effect.
    rating: low
    conditions:
      exposure: 85 °C and 85 % RH, no applied voltage, readings at 250, 500, 750 and 1000 hours
      comparison: SAC305 paste on the same boards
      flux: three solder-paste flux chemistries
    source: cookson-2010
    where: Executive Summary; Introduction (63/37 paste bullet); Summary of MSLCircuits failure analysis
  - environment: Tin-plated surfaces that carry no lead, such as pure tin plating on connector pins and relays
    headline: Tin-lead is the only method the Aerospace Corporation review found to stop tin whiskers consistently.
    effect: The review states that the only consistently demonstrated method of precluding tin whiskers is a minimum percentage of lead in the solder. Figure 7 shows whiskers on a tin-plated Kovar terminal in the region that was not covered by Sn-Pb solder during a hot solder dip, so the solder protects only where it covers the surface.
    rating: low
    conditions:
      basis: literature review of tin-whisker mechanisms and mitigation; not a corrosion test of the solder itself
    source: barr2007
    where: Section 1 (What are tin whiskers) and Figure 7 caption
risks:
  hazards:
    - text: Contains lead, a toxic element. The Sn63/Pb37 data sheet asks users to consult the material safety data sheet before handling and to use adequate ventilation and personal protective equipment.
      ghs: []
      source: aim-electropure
      where: Handling and Safety sections
    - text: The NIOSH pocket guide sets the lead exposure limit at a time-weighted average of 0.050 mg/m3 (8 hours), and an IDLH of 100 mg/m3 (as Pb). Exposure can be by inhalation, ingestion, and skin or eye contact.
      ghs: []
      source: niosh-lead
      where: 'Lead pocket guide entry: OSHA PEL, NIOSH REL, IDLH and exposure routes'
    - text: The Sn60/Pb40 wire is classed as a professional-use product because of its lead content and cannot be sold to private consumers. The sheet does not state a GHS classification.
      ghs: []
      source: cynel-sn60pb40
      where: Section 1 (General characteristics)
  failure_risks:
    - mode: Tin whisker short circuit on pure tin plating (the failure that lead in solder prevents)
      trigger: Pure tin plating with no lead, over time, with stress or in close-spaced circuits
      consequence: Whiskers can grow tens of millimetres and short neighbouring conductors. The review says a short can stay in place indefinitely unless the current is high enough to fuse the whisker, generally above 50 mA.
      severity: moderate
      source: barr2007
      where: Section 2 (Problems metal whiskers can cause)
  side_effects:
    - text: Flux residues from the cored wire may remain on the joint after soldering. The sheet says they need not be removed, and recommends alcohol-based solvents if washing is needed.
      affects: The soldered surface
      source: cynel-sn60pb40
      where: Section 3 (SW26 flux)
  handling:
    - text: Store at room temperature in a dry place, out of reach of children.
      source: cynel-sn60pb40
      where: Section 4.5 (Storage)
    - text: Use with adequate ventilation and proper personal protective equipment. Do not dispose of hazardous materials in non-approved containers.
      source: aim-electropure
      where: Safety section
    - text: Recommended soldering tip temperature is 340 to 400 °C for the Sn60/Pb40 cored wire.
      source: cynel-sn60pb40
      where: Section 2.12
  mitigations:
    - text: Specify a tin-lead alloy rather than pure tin plating where whisker growth matters. The Aerospace Corporation review calls a minimum lead content the only consistently demonstrated whisker preventer.
      source: barr2007
      where: Abstract and Section 1
uses:
  - application: electronics-and-chips
    device: Wave soldering and printed-circuit assembly
    example: The maker says 63Sn/37Pb is typically used in wave soldering and plating, primarily as a corrosion-protection coating and as a base for soldering. It is sold as bar, wire, foil, spheres, preforms, paste and powder.
    source: aim-electropure
    where: Description paragraph and product-form list
  - application: electronics-and-chips
    device: Spacecraft and high-reliability electronics
    example: A 2005 NASA review of lead-free soldering says that exemptions written for high-reliability aerospace electronics will not protect those assemblies from lead-free parts entering the supply chain.
    source: nasa-bok-2005
    where: Introduction, paragraph on exemptions (lines on aerospace electronics)
  - application: electronics-and-chips
    device: Connector pins and relays in space hardware
    example: The Aerospace Corporation review notes that most space systems generally prohibit pure tin plating, and that tin whiskers grew in a hermetically sealed relay that had been pure tin plated.
    source: barr2007
    where: Abstract and Figure 3 caption
supply:
  - subject: Tin
    producers:
      - country: China
        share_percent: 24.5
        year: 2025
      - country: Indonesia
        share_percent: 21
        year: 2025
      - country: Peru
        share_percent: 11.4
        year: 2025
      - country: Brazil
        share_percent: 9.7
        year: 2025
      - country: Congo (Kinshasa)
        share_percent: 9.3
        year: 2025
    critical_lists: []
    recycling: 'USGS: about 17,000 tons of tin from old and new scrap was recycled in 2025, which the survey says is 22 % of apparent consumption. Tin has not been mined or smelted in the United States since 1993 or 1989.'
    substitutes:
      - 'USGS: epoxy resins for solder; other substitutes listed are for cans, bronze, bearing metals and some chemicals.'
    source: usgs-mcs2026-tin
    where: Domestic Production and Use; Events, Trends and Issues; World Mine Production table (2025e, shares calculated by Space Mushroom against the 290,000 t world total); Substitutes
  - subject: Lead
    producers:
      - country: China
        share_percent: 42.2
        year: 2025
      - country: Australia
        share_percent: 10.7
        year: 2025
      - country: Peru
        share_percent: 6.4
        year: 2025
      - country: Russia
        share_percent: 5.8
        year: 2025
      - country: India
        share_percent: 4.9
        year: 2025
    critical_lists:
      - list: USGS 2025 List of Critical Minerals (lead added in the 2025 list)
        listed: true
    recycling: 'USGS: an estimated 1 million tons of secondary lead was produced in 2025, equal to 70 % of apparent domestic consumption. Nearly all of it came from old scrap, mostly lead-acid batteries.'
    substitutes:
      - 'USGS: tin has replaced lead in solder for potable water systems, and the electronics industry has moved toward lead-free solders.'
    source: usgs-mcs2026-lead
    where: Events, Trends and Issues (critical-list paragraph); World Mine Production table (2025e, shares calculated by Space Mushroom against the 4,500 thousand t world total); Recycling; Substitutes
media: []
documents:
  - title: Aimtek 63/37 tin-lead solder technical data sheet
    type: datasheet
    url: https://aimtek.com/wp-content/uploads/2022/08/Aimtek-63-37-Tin-Lead-Solder-Technical-Data-Sheet.pdf
    year: 2022
  - title: Aimtek 60/40 tin-lead solder technical data sheet
    type: datasheet
    url: https://aimtek.com/wp-content/uploads/2022/08/Aimtek-60-40-Tin-Lead-Solder-Technical-Data-Sheet.pdf
    year: 2022
  - title: Cynel-Unipress technical data sheet, Sn60Pb40 cored solder wire (ISO 9453)
    type: datasheet
    url: https://ormix.lv/lv/catalog/showpdf/name/68ac979d42cb80508f9a5c4e8896ef9c.pdf
    year: 2022
  - title: AIM Electropure 63Sn/37Pb technical data sheet
    type: datasheet
    url: https://assets.rs-online.com/v1698743561/Datasheets/77c922b68bf764517b10fb2353c292d5.pdf
    year: 2004
  - title: Mitigating and preventing the growth of tin and other metal whiskers on critical hardware (The Aerospace Corporation)
    type: paper
    url: https://nepp.nasa.gov/whisker./reference/tech_papers/2007-barr-paper-mitigating-whiskers.pdf
    year: 2007
  - title: 'Lead-free soldering for space applications: Lead-Free Solder Body of Knowledge (NASA, Kennedy Space Center)'
    type: report
    url: https://xdevs.com/doc/NASA/lead-free%20solder%20bok%20report%206-21-%202005.pdf
    year: 2005
  - title: Tin corrosion under QFN packages at elevated temperature and humidity (IPC Midwest 2010)
    type: paper
    url: https://www.electronics.org/system/files/technical_resource/E11%26S04_02.pdf
    year: 2010
  - title: 'USGS Mineral Commodity Summaries 2026: Tin'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-tin.pdf
    year: 2026
  - title: 'USGS Mineral Commodity Summaries 2026: Lead'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-lead.pdf
    year: 2026
gaps:
  - The 63/37 Caplinq data sheet returned a server error on download, so its thermal conductivity, elongation and hardness values for Sn63/Pb37 are not in this file.
  - PubChem's GHS summary for lead returned a verification page, so the lead GHS hazard statements (H-codes) are not recorded. Hazard data for lead rest on the NIOSH pocket guide and the manufacturer sheets.
  - No safety data sheet for a tin-lead solder wire was read in this run; handling data come from the manufacturer sheets.
  - The USGS tin text read in this run does not state whether tin is on the 2025 US critical-minerals list. EU critical-raw-materials status of tin and lead was not checked.
  - Supply shares are calculated by Space Mushroom from USGS 2025e mine production (lead world total 4,500 thousand t; tin world total 290,000 t), not printed by USGS.
  - No quantitative corrosion rate for Sn63/Pb37 in humid air was found. The IBM report on SnO and SnO2 growth in humid aging could not be downloaded.
  - No vacuum, radiation, thermal-cycling or flight test result for tin-lead solder was read in this run. The space-related sources are a 2005 NASA review and a 2007 Aerospace Corporation review.
  - Hardness of the Sn60/Pb40 wire (16 HB in the cored wire sheet) is not included, because hardness is not in the canonical property list.
  - The Sn63/Pb37 wire datasheet does not give tensile test conditions, and the two Sn60/Pb40 sheets give tensile figures that differ (44.13 MPa and 535 kg/cm2). Both are kept as printed.
  - Atomic weights were not added to the recipe, because no fetched source prints them for this alloy. The recipe uses mass shares from the data sheets.
  - No image was checked for licence, so the media list is empty.
  - The NASA-STD-8739.3 soldering standard status could not be confirmed (sources conflict on whether it is cancelled), so it is not cited.
  - The 60/40 cored wire sheet prints its electrical resistivity with a decimal comma (0,153 μΩ·m), which the value-check tool cannot match, so that property was left out. The density and tensile values from the same sheet are kept.
sources:
  aimtek-6337:
    title: AIMTEK High Purity 63% Tin/37% Lead Solder data sheet
    id: AIMTEK, Inc., Auburn MA
    url: https://aimtek.com/wp-content/uploads/2022/08/Aimtek-63-37-Tin-Lead-Solder-Technical-Data-Sheet.pdf
    year: 2022
    kind: datasheet
    license: supplier document, linked not reproduced
  aimtek-6040:
    title: AIMTEK 60% Tin/40% Lead Solder data sheet
    id: AIMTEK, Inc., Auburn MA
    url: https://aimtek.com/wp-content/uploads/2022/08/Aimtek-60-40-Tin-Lead-Solder-Technical-Data-Sheet.pdf
    year: 2022
    kind: datasheet
    license: supplier document, linked not reproduced
  cynel-sn60pb40:
    title: Cynel-Unipress technical data sheet, Sn60Pb40 cored solder wire with SW26 flux
    id: Cynel-Unipress Sp. z o.o., Warsaw; ISO 9453:2014
    url: https://ormix.lv/lv/catalog/showpdf/name/68ac979d42cb80508f9a5c4e8896ef9c.pdf
    year: 2022
    kind: datasheet
    license: supplier document, linked not reproduced
  aim-electropure:
    title: AIM Electropure 63Sn/37Pb technical data sheet (bar solder)
    id: AIM, technical data sheet dated 12.17.2004
    url: https://assets.rs-online.com/v1698743561/Datasheets/77c922b68bf764517b10fb2353c292d5.pdf
    year: 2004
    kind: datasheet
    license: supplier document, linked not reproduced
  barr2007:
    title: Mitigating and Preventing the Growth of Tin and Other Metal Whiskers on Critical Hardware
    id: Stephanie Barr, The Aerospace Corporation, 2007
    url: https://nepp.nasa.gov/whisker./reference/tech_papers/2007-barr-paper-mitigating-whiskers.pdf
    year: 2007
    kind: paper
    license: copyright The Aerospace Corporation (cited, not reproduced)
  nasa-bok-2005:
    title: 'Lead-Free Soldering for Space Applications: Lead-Free Solder Body of Knowledge (Kurt Kessel, NASA KSC)'
    id: NASA NEPP, April 2005 state of technology report (copy hosted on xdevs.com)
    url: https://xdevs.com/doc/NASA/lead-free%20solder%20bok%20report%206-21-%202005.pdf
    year: 2005
    kind: report
    license: public domain (NASA)
  cookson-2010:
    title: Tin Corrosion under QFN Packages at Elevated Temperature and Humidity
    id: K. Tellefsen et al., Cookson Electronics, IPC Midwest 2010
    url: https://www.electronics.org/system/files/technical_resource/E11%26S04_02.pdf
    year: 2010
    kind: paper
    license: copyright of the authors (cited, not reproduced)
  niosh-lead:
    title: 'NIOSH Pocket Guide to Chemical Hazards: Lead'
    id: NIOSH / CDC, npgd0368
    url: https://www.cdc.gov/niosh/npg/npgd0368.html
    year: 2024
    kind: web
    license: public domain (US government)
  usgs-mcs2026-tin:
    title: Mineral Commodity Summaries 2026, Tin
    id: USGS MCS 2026, February 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-tin.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  usgs-mcs2026-lead:
    title: Mineral Commodity Summaries 2026, Lead
    id: USGS MCS 2026, February 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-lead.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
license: CC-BY-4.0
updated: '2026-10-26'
review:
  status: draft
  method: assistant
  checked_values: 12
  unreachable: 2
  caveats: 2
  note: Read by an AI assistant on 2026-10-26 from the data sheets, USGS and NIOSH pages listed in sources. Two sources could not be opened (Caplinq 63/37 sheet, PubChem lead record); the two Sn60/Pb40 tensile values differ and are kept as printed.
story:
  recipe:
    line: 'Tin-lead solder is a binary alloy: tin and lead melted together. The eutectic 63/37 composition is the one with a single melting point. The Sn60/Pb40 composition has a short melting range. Both are cast or drawn into bar, wire and preforms, and the wire is usually cored with a rosin flux.'
    parts:
      - name: Tin
        symbol: Sn
        share_percent: 63
        role: The main metal of the alloy. The maker recommends the alloy for soldering copper, copper alloys and ferrous alloys.
      - name: Lead
        symbol: Pb
        share_percent: 37
        role: Part of the eutectic composition, which melts at 183 °C. The Aerospace Corporation review says lead in solder is what has kept tin whiskers away.
  risk_groups:
    - title: For people
      level: 0
      verdict: Hazardous because of lead
      lead: Solder contains lead, a toxic element. The NIOSH guide gives an exposure limit and lists health effects.
      points:
        - label: Exposure limit
          line: The NIOSH pocket guide gives a time-weighted average limit of 0.050 mg/m3 for lead over 8 hours, and an IDLH of 100 mg/m3 (as Pb).
        - label: Routes
          line: Exposure can be by inhalation, ingestion, and skin or eye contact. Effects listed include anaemia, kidney disease, tremor and effects on the nervous system.
        - label: Product rule
          line: The Sn60/Pb40 sheet says the product cannot be sold to private consumers because of its lead content, and is for professional use only.
    - title: Handling and storage
      points:
        - label: Ventilation
          line: The maker advises adequate ventilation and personal protective equipment, and asks users to consult the safety data sheet before handling.
        - label: Storage
          line: Store at room temperature in a dry place, out of reach of children. Do not put hazardous material in non-approved containers for disposal.
        - label: Soldering temperature
          line: The Sn60/Pb40 wire is soldered with a tip at 340 to 400 °C.
  why: 'Tin-lead solder has been the standard joining metal for electronics for decades. The eutectic 63/37 alloy melts at a single temperature, 183 °C, which gives a sharp transition from liquid to solid. The maker names wave soldering as its typical use. Lead also suppresses tin whiskers, which the Aerospace Corporation review calls the only consistently demonstrated method of preventing them. The trade-off is toxicity: the 60/40 maker says its lead-containing wire is for professional use only and is not RoHS compliant.'
  uses:
    - where: Wave soldering and circuit assembly
      line: The maker describes 63Sn/37Pb as the usual alloy for wave soldering and plating, where it protects surfaces against corrosion and serves as a base for soldering.
    - where: High-reliability and space electronics
      line: A 2005 NASA review found that exemptions written for high-reliability aerospace electronics would not protect those assemblies from lead-free parts. The Aerospace Corporation review notes that most space systems prohibit pure tin plating.
  can_do:
    - label: Melting point
      benchmark: melting_point
      value: 183 °C
      line: The 63/37 eutectic melts and solidifies at one temperature, 183 °C. The 60/40 alloy melts over a short range, from 183 °C to 190 or 191 °C, according to two data sheets.
    - label: Density
      benchmark: density
      value: 8.40 g/cm3
      line: The 63/37 alloy has a density of 8.40 g/cm3, and the 60/40 alloy 8.49 g/cm3 in one data sheet.
    - label: Tin whiskers
      value: Lead prevents them
      line: The Aerospace Corporation review says the only consistently demonstrated way to prevent tin whiskers is a minimum percentage of lead in the solder.
  compare: 'Tin-lead solder melts at 183 °C at the eutectic, and its maker gives a density of 8.40 g/cm3 and a tensile strength of 43 MPa. Its lead content is the trade-off: the datasheets restrict the 60/40 wire to professional use and say it is not RoHS compliant. The compare rows below use the same property names as the other profiles; no lead-free alloy was read in this run, so no side-by-side figures are given here.'
  compare_rows:
    - label: Melting point
      benchmark: melting_point
    - label: Density
      benchmark: density
    - label: Tensile strength
      benchmark: ultimate_tensile_strength
  handling:
    - Store dry, at room temperature, closed and out of reach of children.
    - Use adequate ventilation and personal protective equipment, as the maker advises.
    - Solder at 340 to 400 °C with the cored flux; alcohol-based solvents are recommended if residue needs removing.
  good_for:
    - Wave soldering and circuit assembly, where the maker names a single melting point (183 °C for 63/37) as the key property.
    - Joints where lead's whisker suppression matters, as the Aerospace Corporation review describes.
  watch_out:
    - Lead is toxic, and the 60/40 wire is restricted to professional use.
    - Tensile strength is low (about 43 to 44 MPa in the data sheets), and the two 60/40 sheets disagree on the figure.
    - Pure tin plating, the lead-free alternative, can grow tin whiskers that short neighbouring conductors.
  verdict: Tin-lead solder is the long-established, low-melting baseline for electronics. It is the only method the Aerospace Corporation review found to prevent tin whiskers consistently, but its lead content limits where it can be used.