Sn42Bi58 low-temperature eutectic solder Sn42Bi58

spore: profile
id: solder-sn42bi58
spore_version: 0.2
family: low-melting-metals-and-solders
name: Sn42Bi58 low-temperature eutectic solder
abbreviation: Sn42Bi58
role: lead-free low-temperature solder alloy
category: electronics
type: solders
summary: |
  Sn42Bi58 is a lead-free eutectic solder of 42 % tin and 58 % bismuth by weight, each within ±0.5 (AIM datasheet). Its melting point is 138 °C (280 °F), printed in both the AIM datasheet and the AIM alloy information sheet. The datasheet gives a density of 8.72 g/cc and a tensile strength of 8,000 psi, while the information sheet prints 9.71 ksi for the same alloy; neither states a test method, so the two strength values are shown side by side and not reconciled. The datasheet lists a thermal conductivity of 0.19 W/cm-°C at 85 °C and a coefficient of thermal expansion of 15 ppm/°C at 20 °C. AIM rates its thermal fatigue resistance as Poor.
best_for: Second-solder reflow on circuit boards and other low-temperature soldering, where the joint has to melt at 138 °C (AIM datasheet)
weakest_at: Thermal fatigue resistance, which AIM rates Poor against Excellent for SAC305, and a wetting rating of Fair
identity:
  formula: 'Sn-42Bi-58: 42 % tin and 58 % bismuth by weight, each ±0.5 (eutectic alloy)'
  source: aim-tds
  where: Description section and Major Alloy Ingredients table (Sn 42 ± 0.5, Bi 58 ± 0.5)
  designations:
    - system: Trade name
      code: Sn42/Bi58
      source: aim-tds
      where: Title and Major Alloy Ingredients table
tags:
  applications:
    - electronics-and-chips
  stresses:
    - thermal-cycling
properties:
  - benchmark: melting_point
    label: Eutectic melting point (AIM datasheet)
    value: 138
    unit: °C
    scope: material
    conditions:
      basis: eutectic composition, 42 % Sn and 58 % Bi as printed; the datasheet also prints 280 °F
    method: Printed as the eutectic melting point in the Description and as a Features list item
    status: ground
    source: aim-tds
    where: Features (Low Melting Point 138°C (280°F)) and Description paragraph
  - benchmark: melting_point
    label: Melting point (AIM alloy information sheet)
    value: 138
    unit: °C
    scope: material
    conditions:
      basis: Sn42/Bi58 row of the technical information table
    method: Value printed in the AIM alloy information sheet, which agrees with the datasheet
    status: ground
    source: aim-info
    where: Technical Information table, Sn42/Bi58 row, Melting Point column (138)
  - benchmark: density
    label: Density (AIM datasheet)
    value: 8.72
    unit: g/cc
    scope: material
    conditions:
      temperature: not stated in the datasheet
    method: Value printed in the Properties table of the datasheet
    status: ground
    source: aim-tds
    where: Properties table, Density g/cc row (8.72)
  - benchmark: density
    label: Density (AIM alloy information sheet, as printed)
    value: 0.309
    unit: lbs/in3
    scope: material
    conditions:
      basis: Bi58 row of the bismuth section of the alloy table, printed in lbs/in.3 and not converted
    method: Value printed in the Common and Specialty Solder Alloys table of the information sheet
    status: ground
    source: aim-info
    where: Specialty Solder Alloys table, BISMUTH section, Bi58 row, Density column (.3090)
  - benchmark: electrical_resistivity
    label: Electrical resistivity (AIM datasheet)
    value: 1.72
    unit: µΩ-cm
    scope: material
    conditions:
      temperature: not stated in the datasheet
    method: Value printed in parentheses in the Electrical Conductivity row of the Properties table
    status: ground
    source: aim-tds
    where: Properties table, Electrical Conductivity row, parenthesised value (1.72 µΩ-cm)
  - benchmark: electrical_conductivity
    label: Electrical conductivity (AIM datasheet)
    value: 4.5
    unit: '% IACS'
    scope: material
    conditions:
      temperature: not stated in the datasheet
    method: Value printed in the Properties table of the datasheet
    status: ground
    source: aim-tds
    where: Properties table, Electrical Conductivity row (4.5 % of IACS)
  - benchmark: thermal_conductivity
    label: Thermal conductivity (AIM datasheet)
    value: 0.19
    unit: W/cm-°C
    scope: material
    conditions:
      temperature: 85 °C, as printed in the row label
    method: Value printed in the Properties table of the datasheet
    status: ground
    source: aim-tds
    where: Properties table, Thermal Conductivity @ 85° C row (0.19 W/cm-° C)
  - benchmark: cte
    label: Coefficient of thermal expansion (AIM datasheet)
    value: 15
    unit: ppm/°C
    scope: material
    conditions:
      temperature: 20 °C, as printed in the row label
    method: Value printed in the Properties table of the datasheet, printed as PPM/° C
    status: ground
    source: aim-tds
    where: Properties table, Coefficient of Thermal Expansion @ 20° C row (15)
  - benchmark: ultimate_tensile_strength
    label: Tensile strength (AIM datasheet)
    value: 8000
    unit: psi
    scope: material
    conditions:
      form: as printed in the datasheet; the form and test method are not stated
    method: Value printed in the Properties table of the datasheet, printed as 8,000 PSI
    status: ground
    note: The AIM alloy information sheet prints 9.71 ksi for the same alloy (see the next row). Neither source states a test method, so the two values should not be compared directly.
    source: aim-tds
    where: Properties table, Tensile Strength PSI row (8,000)
  - benchmark: ultimate_tensile_strength
    label: Tensile strength (AIM alloy information sheet)
    value: 9.71
    unit: ksi
    scope: material
    conditions:
      form: as printed in the information sheet; the form and test method are not stated
    method: Value printed in the Technical Information table of the alloy information sheet
    status: ground
    note: The AIM datasheet prints 8,000 psi (8.0 ksi) for the same alloy. The sources disagree and neither states a test method.
    source: aim-info
    where: Technical Information table, Sn42/Bi58 row, Tensile Strength (ksi) column (9.71)
  - benchmark: yield_strength
    label: 0.2 % yield strength (AIM alloy information sheet)
    value: 6.03
    unit: ksi
    scope: material
    conditions:
      basis: 0.2 % yield strength, as printed in the column header
      form: as printed; test method not stated
    method: Value printed in the Technical Information table of the alloy information sheet
    status: ground
    source: aim-info
    where: Technical Information table, Sn42/Bi58 row, 0.2% Yield Strength (ksi) column (6.03)
  - benchmark: shear_strength
    label: Shear strength (AIM datasheet)
    value: 500
    unit: psi
    scope: material
    conditions:
      test: not stated in the datasheet
    method: Value printed in the Properties table of the datasheet
    status: ground
    source: aim-tds
    where: Properties table, Shear Strength PSI row (500)
  - benchmark: elongation
    label: Elongation (AIM datasheet)
    value: 55
    unit: '%'
    scope: material
    conditions:
      test: not stated in the datasheet
    method: Value printed in the Properties table of the datasheet
    status: ground
    note: The AIM alloy information sheet prints a uniform elongation of 1.3 for this alloy without a unit, so it is not recorded. The two sheets give different elongation figures.
    source: aim-tds
    where: Properties table, Elongation % row (55)
  - benchmark: latent_heat_of_fusion
    label: Latent heat of fusion (AIM datasheet)
    value: 44.8
    unit: J/g
    scope: material
    conditions:
      basis: eutectic alloy as printed
    method: Value printed in the Properties table of the datasheet
    status: ground
    source: aim-tds
    where: Properties table, Latent Heat of Fusion J/g row (44.8)
  - benchmark: joint_strength
    label: Joint strength (AIM alloy information sheet)
    value: 6800
    unit: psi
    scope: material
    conditions:
      basis: joint strength column of the alloy performance table; the substrate and test method are not stated
    method: Value printed in the joint strength column of the alloy information sheet's performance table
    status: ground
    source: aim-info
    where: Second performance table, Sn42/Bi58 row, Joint Strength (psi) column (6800)
  - benchmark: melting_point
    label: Melting range, solidus to liquidus, Sn-58 wt% Bi (Kang et al. 2021)
    value: 130.2
    value_high: 139
    bound: range
    unit: ºC
    scope: material
    conditions:
      basis: Sn-58 wt% Bi, the same composition as Sn42/Bi58 (Bi at 58 %); the review cites earlier work for it and notes that the heating rate affects the value
    method: Range printed in the review's Section 2.1 text, which refers to its Table 1
    status: ground
    source: kang2021
    where: Section 2.1, first melting-range sentence (solidus 130.2 ºC, liquidus 139 ºC, citing Table 1)
  - benchmark: ultimate_tensile_strength
    label: Tensile strength (NIST Table 1.2, row A6 Sn-58Bi)
    value: 8766
    unit: psi
    scope: material
    conditions:
      form: not stated in the NIST table; the table credits the NCMS 1998 tensile programme
      alloy: A6 Sn-58Bi, Bi 58 % by mass
    method: Value printed in the NIST table, which also prints 60.4 MPa for the same row
    status: ground
    note: The AIM datasheet prints 8,000 psi and the AIM information sheet prints 9.71 ksi for this alloy. The three values differ, no source prints a test method, so they are shown side by side and not reconciled.
    source: nist-solder-db
    where: Table 1.2 Tensile Properties of Lead-Free Solders, row A6 Sn-58Bi, Tensile Strength (psi) column (8,766; 60.4 MPa)
  - benchmark: yield_strength
    label: 0.2 % offset yield strength (NIST Table 1.2, row A6 Sn-58Bi)
    value: 7119
    unit: psi
    scope: material
    conditions:
      basis: 0.2 % offset, as printed in the column heading
      form: not stated in the NIST table
    method: Value printed in the NIST table, which also prints 49.1 MPa for the same row
    status: ground
    note: The AIM information sheet prints 6.03 ksi for the 0.2 % yield strength of this alloy. The two sources differ and neither prints a test method.
    source: nist-solder-db
    where: Table 1.2, row A6 Sn-58Bi, Yield Strength (0.2 % offset) psi column (7,119; 49.1 MPa)
  - benchmark: elastic_modulus
    label: Elastic modulus (NIST Table 1.2, row A6 Sn-58Bi)
    value: 1720
    unit: ksi
    scope: material
    conditions:
      form: not stated in the NIST table
    method: Value printed in the NIST table, which also prints 11.9 GPa for the same row
    status: ground
    source: nist-solder-db
    where: Table 1.2, row A6 Sn-58Bi, Elastic Modulus ksi column (1,720; 11.9 GPa)
  - benchmark: elongation
    label: Total elongation (NIST Table 1.2, row A6 Sn-58Bi)
    value: 46
    unit: '%'
    scope: material
    conditions:
      basis: total elongation as printed; the same row prints a uniform elongation of 3 %
      form: not stated in the NIST table
    method: Value printed in the NIST table
    status: ground
    note: The AIM datasheet prints 55 % elongation for this alloy. The two figures differ and neither source prints a test method.
    source: nist-solder-db
    where: Table 1.2, row A6 Sn-58Bi, Elongation Total (%) column (46)
  - benchmark: shear_strength
    label: Shear strength at room temperature (NIST Table 1.16, ring-and-plug)
    value: 48
    unit: MPa
    scope: material
    conditions:
      test: ring-and-plug shear test at 1 mm/min
      temperature: room temperature, as printed in the column heading
    method: Value printed in the NIST table
    status: ground
    note: The AIM datasheet prints 500 psi shear strength with no test method, so the NIST and AIM values are not comparable.
    source: nist-solder-db
    where: Table 1.16 Mechanical Properties, Sn-58Bi row, Shear Strength Room column (48.0)
  - benchmark: shear_strength
    label: Shear strength at 100 °C (NIST Table 1.16, ring-and-plug)
    value: 15.6
    unit: MPa
    scope: material
    conditions:
      test: ring-and-plug shear test at 1 mm/min
      temperature: 100 °C, as printed in the column heading
    method: Value printed in the NIST table
    status: ground
    source: nist-solder-db
    where: Table 1.16 Mechanical Properties, Sn-58Bi row, Shear Strength 100 ºC column (15.6)
  - benchmark: electrical_resistivity
    label: Electrical resistivity (NIST Table 2.2.19)
    value: 30
    value_high: 35
    bound: range
    unit: μΩ-cm
    scope: material
    conditions:
      temperature: not stated in the NIST table
    method: Range printed in the NIST table
    status: ground
    note: The AIM datasheet prints 1.72 µΩ-cm for this alloy. The NIST range is much higher, and the two are shown side by side and not reconciled.
    source: nist-solder-db
    where: Table 2.2.19, Sn-58Bi row, Electrical Resistivity (μΩ-cm) column (30 – 35)
corrosion: []
risks:
  hazards:
    - text: PubChem lists bismuth as Not Classified in its summary, and says 324 of 382 company reports did not meet GHS hazard criteria. Four notifications from 58 of 382 reports carry hazard codes H370 and H372 (damage to organs), with the signal word Danger. The record covers bismuth, not this alloy, and does not say which bismuth form the reports cover.
      ghs:
        - H370
        - H372
      source: pubchem-bismuth
      where: Safety and Hazards, GHS Classification section (CID 5359367)
    - text: The AIM safety data sheet for Alloy Sn42-Bi58 NC 273LT (version 1.07, revised 5/17/2024) classifies the solder paste under CLP as Aquatic Chronic 1, H410 (very toxic to aquatic life with long lasting effects), with signal word Warning. Its composition table lists tin, a hydrogenated rosin and an amine salt, and no bismuth, so the sheet describes the paste, not the bare alloy.
      ghs:
        - H410
      source: aim-sds-nc273lt
      where: Sections 2.1 and 2.2 (signal word Warning, H410 text), Section 3 composition table, Section 16
    - text: The same SDS says overexposure to fumes may irritate the respiratory tract, digestive system and eyes, and that overexposure to tin oxide fumes may cause benign pneumoconiosis (stannosis). It lists the product's own toxicity data as Not available.
      ghs: []
      source: aim-sds-nc273lt
      where: Section 11.1, Carcinogenicity conclusion and Section 11 product data
  failure_risks:
    - mode: Thermal fatigue of solder joints
      trigger: Thermal cycling. AIM does not state the temperature range used for its rating.
      consequence: AIM rates the thermal fatigue resistance of Sn42/Bi58 as Poor, the same as Sn63/Pb37 and against Excellent for SAC305, on the same table.
      severity: high
      source: aim-info
      where: Second performance table, Thermal Fatigue Resistance column (Sn42/Bi58 Poor; SAC305 Excellent; Sn63/Pb37 Poor)
    - mode: Low wetting in soldering
      trigger: Soldering with the alloy. AIM does not state the flux or test conditions behind the rating.
      consequence: AIM rates the wetting characteristics of Sn42/Bi58 as Fair, against Excellent for SAC305 and Sn63/Pb37 on the same table.
      severity: moderate
      source: aim-info
      where: Second performance table, Wetting Characteristics column (Sn42/Bi58 Fair)
    - mode: Low melting point limits the service temperature
      trigger: Operating or reflow temperature at or above 138 °C
      consequence: The alloy melts at 138 °C as printed. Neither datasheet gives a service temperature limit, so the usable temperature range is not stated in any source read.
      severity: moderate
      source: aim-tds
      where: Features (Low Melting Point 138°C) and Description
  side_effects: []
  handling:
    - text: Use with adequate ventilation and proper personal protective equipment. Refer to the accompanying safety data sheet for emergency information. Do not dispose of hazardous materials in non-approved containers.
      source: aim-tds
      where: Safety section
    - text: Shelf life is 3 years for water-soluble cored wire made with this alloy. Other cored wire, solid wire and bar have an indefinite shelf life.
      source: aim-tds
      where: Handling and Storage section
    - text: The alloy is compatible with most electronic grade fluxes. Cleaning follows the flux manufacturer's data sheets.
      source: aim-tds
      where: Flux Compatibility and Cleaning sections
  mitigations: []
uses:
  - application: electronics-and-chips
    device: Second-solder reflow for circuit board assembly
    example: AIM says Sn42/Bi58 is typically used for second-solder reflow in circuit board assembly, and for other low-temperature soldering requirements.
    source: aim-tds
    where: Description section
  - application: electronics-and-chips
    device: Solder paste, solid and cored wire, foil, powder, bar, ingot and anode
    example: AIM lists these forms for the alloy, which is the form range a buyer can choose from.
    source: aim-tds
    where: Description section
  - application: electronics-and-chips
    device: Lead-free replacement in low-temperature solders
    example: USGS says bismuth is a nontoxic replacement for lead in solders, and that cadmium, indium, lead and tin can partially replace bismuth in low-temperature solders.
    source: usgs-bismuth-2026
    where: Domestic Production and Use paragraph and Substitutes paragraph
supply:
  - subject: Tin (mine production, world)
    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 estimated to have been recycled in 2025.'
    substitutes:
      - 'USGS: epoxy resins are listed as substitutes for tin in solder.'
    source: usgs-tin-2026
    where: World Mine Production and Reserves table, 2025e column (world total 290,000 t). Shares calculated by Space Mushroom from China 71,000, Indonesia 61,000, Peru 33,000, Brazil 28,000 and Congo (Kinshasa) 27,000. Recycling and Substitutes sections.
  - subject: Bismuth (refinery production, world)
    producers:
      - country: China
        share_percent: 88
        year: 2025
    critical_lists: []
    recycling: 'USGS: recycled bismuth-containing alloy scrap made up to 10% of U.S. bismuth apparent consumption for 2021 to 2025.'
    substitutes:
      - 'USGS: cadmium, indium, lead and tin can partially replace bismuth in low-temperature solders.'
    source: usgs-bismuth-2026
    where: 'Events, Trends, and Issues paragraph (printed ''China accounted for 88% of the bismuth world production in 2025''); estimated world production 16,000 tons in 2025; Import Sources (2021 to 2024): China 56%, Republic of Korea 22%, Germany 13%, other 9%; Recycling; Substitutes'
documents:
  - title: 'AIM: Sn42/Bi58 lead-free solder alloy, technical data sheet (Document Rev # NF4)'
    type: datasheet
    url: https://aimsolder.com/wp-content/uploads/alloy_sn42-bi58_tds.pdf
  - title: 'AIM: Alloy Information, common and specialty solder alloys with technical information'
    type: datasheet
    url: https://aimsolder.com/wp-content/uploads/legacy-files/alloy_information.pdf
  - 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: Bismuth'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-bismuth.pdf
    year: 2026
  - title: 'PubChem: Bismuth (CID 5359367), GHS classification summary'
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/5359367
    year: 2026
  - title: 'AIM: Safety data sheet, Alloy Sn42-Bi58 NC 273LT (solder paste), version 1.07 revised 5/17/2024'
    type: sds
    url: https://aimsolder.com/wp-content/uploads/alloy_sn42-bi58_nc273lt-clp_europe-english.pdf
    year: 2024
  - title: 'Kang, Rajendran and Jung: Low Melting Temperature Sn-Bi Solder, Metals 2021, 11, 364'
    type: paper
    url: https://mdpi-res.com/d_attachment/metals/metals-11-00364/article_deploy/metals-11-00364-v2.pdf
    year: 2021
  - title: 'NIST and Colorado School of Mines: Database for Solder Properties, Properties of Lead-Free Solders, Release 4.0'
    type: database
    url: https://www.metallurgy.nist.gov/solder/NIST_LeadfreeSolder_v4.pdf
    year: 2002
gaps:
  - No corrosion or ageing data for Sn42Bi58 in any source read this run. The corrosion list is empty, so no rate or environment is claimed.
  - No UNS, EN, JIS, ASTM or AISI designation was found in the sources read. Only the AIM trade name Sn42/Bi58 is recorded.
  - The safety data sheet read (AIM NC 273LT, version 1.07) covers the solder paste with flux, not the bare alloy. It lists tin, a hydrogenated rosin and an amine salt, and no bismuth. Hazard data for the bare alloy are not established, and the PubChem bismuth record covers bismuth metal, not this alloy.
  - 'Tensile strength disagrees across three sources: 8,000 psi (AIM datasheet), 9.71 ksi (AIM information sheet) and 8,766 psi (NIST Table 1.2). No test method is printed in any of them, so no confirmed strength value is recorded.'
  - The NIST table values come from the NCMS 1998 tensile programme and older compilations. The specimen form is not printed for each row, so they are recorded with that caveat.
  - Yield strength (6.03 ksi) and joint strength (6800 psi) rest on the AIM information sheet only. The datasheet does not print them, and neither gives a test method.
  - Uniform elongation (1.3) and Brinell hardness (23) are printed without units in the AIM sheets, so they are left out rather than given a unit.
  - 'The two AIM sheets give different elongation figures: 55 % in the datasheet and a unitless uniform elongation of 1.3 in the information sheet.'
  - Density is recorded in g/cc from the datasheet and in lbs/in3 from the information sheet as printed. No conversion between them was made.
  - Thermal conductivity and CTE rest on one datasheet. The test temperature range for the CTE is not stated.
  - No service temperature limit, creep data, or fatigue life test for Sn42Bi58 was found. The thermal fatigue rating is a qualitative AIM grade, not a measured cycle count.
  - Critical-mineral status of tin and bismuth is not stated in the USGS chapters read. The EU critical raw materials list was not read for either metal.
  - Sn-Bi reliability or ageing papers are paywalled or blocked this run (Springer, MDPI and a University of Limerick copy returned 403 or a browser check). No ageing value was taken from them.
  - No space-environment data (outgassing, radiation, thermal vacuum, flight heritage) for Sn42Bi58 was searched for in this run.
  - No environments tag is recorded because no source read names an environment.
  - electrical_conductivity, shear_strength, latent_heat_of_fusion and joint_strength are not names in property-canon.yaml. They are used as written.
  - The coefficient of thermal expansion printed for Sn-58Bi in NIST Table 2.2.19 (1.5) has no legible unit in the PDF text, so it is not recorded.
  - The thermal conductivity of 57.26 W/(m.K) in NIST Table 2.2.2 belongs to Castin (Sn-2.5Ag-0.8Cu-0.5Sb), not Sn-58Bi, so it is not used.
  - PubChem's tin GHS record could not be opened (browser check), and a REST lookup returned CID 5352425, which is lead. No tin hazard data are recorded.
  - 'Elongation now has three figures: 55 % (AIM datasheet), total 46 % (NIST Table 1.2) and a unitless uniform 1.3 (AIM information sheet). They are not reconciled.'
sources:
  aim-tds:
    title: Sn42/Bi58 lead-free solder alloy, technical data sheet
    id: 'AIM, Document Rev # NF4'
    url: https://aimsolder.com/wp-content/uploads/alloy_sn42-bi58_tds.pdf
    year: 2026
    kind: datasheet
    license: supplier technical data sheet, cited not reproduced
  aim-info:
    title: 'Alloy Information: common solder alloys, specialty solder alloys and technical information'
    id: AIM alloy information sheet (legacy file)
    url: https://aimsolder.com/wp-content/uploads/legacy-files/alloy_information.pdf
    year: 2026
    kind: datasheet
    license: supplier information sheet, cited not reproduced
  usgs-tin-2026:
    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-bismuth-2026:
    title: 'Mineral Commodity Summaries 2026: Bismuth'
    id: USGS MCS 2026, February 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-bismuth.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  pubchem-bismuth:
    title: PubChem compound record, Bismuth (CID 5359367), GHS classification
    id: CID 5359367
    url: https://pubchem.ncbi.nlm.nih.gov/compound/5359367
    year: 2026
    kind: database
    license: public domain (NCBI)
  aim-sds-nc273lt:
    title: 'Safety data sheet: Alloy Sn42-Bi58 NC 273LT (solder paste), version 1.07'
    id: AIM Solder Europe, product code GHS049, revised 5/17/2024
    url: https://aimsolder.com/wp-content/uploads/alloy_sn42-bi58_nc273lt-clp_europe-english.pdf
    year: 2024
    kind: datasheet
    license: supplier safety data sheet, cited not reproduced
  kang2021:
    title: 'Low Melting Temperature Sn-Bi Solder: Effect of Alloying and Nanoparticle Addition on the Microstructural, Thermal, Interfacial Bonding, and Mechanical Characteristics'
    id: Kang, Rajendran and Jung, Metals 2021, 11, 364, doi:10.3390/met11020364
    url: https://mdpi-res.com/d_attachment/metals/metals-11-00364/article_deploy/metals-11-00364-v2.pdf
    year: 2021
    kind: paper
    license: CC BY 4.0
  nist-solder-db:
    title: 'Database for Solder Properties with Emphasis on New Lead-free Solders: Properties of Lead-Free Solders, Release 4.0'
    id: NIST and Colorado School of Mines, Release 4.0, dated 11 February 2002
    url: https://www.metallurgy.nist.gov/solder/NIST_LeadfreeSolder_v4.pdf
    year: 2002
    kind: database
    license: NIST database, cited not reproduced
license: CC-BY-4.0
updated: '2026-11-01'
review:
  status: draft
  method: assistant
  checked_values: 23
  unreachable: 0
  caveats: 3
  note: Read by an AI assistant on 2026-11-01 from the AIM datasheet and information sheet, USGS Mineral Commodity Summaries 2026 (tin, bismuth), and PubChem. Two AIM values disagree (tensile strength); both are recorded.
story:
  recipe:
    line: Sn42Bi58 is a eutectic alloy of 42 % tin and 58 % bismuth by weight, each within ±0.5 (AIM datasheet). The datasheet also prints a table of maximum impurity levels, in percent, for twelve elements, set against the IPC standard it names.
    parts:
      - name: Tin
        symbol: Sn
        role: 42 % by weight, ±0.5 (AIM datasheet). The datasheet gives the composition only; no atomic weight is recorded here.
      - name: Bismuth
        symbol: Bi
        role: 58 % by weight, ±0.5 (AIM datasheet). The datasheet gives the composition only; no atomic weight is recorded here. Bismuth is the larger share of this eutectic.
  risk_groups:
    - title: For people
      level: 0
      verdict: Hazard data limited
      lead: The AIM datasheet asks for ventilation and protective equipment. The AIM safety data sheet read is for the NC 273LT solder paste, not the bare alloy, and classifies that paste as very toxic to aquatic life with long lasting effects (H410). The bare alloy's hazard classification is not established here.
      points:
        - label: The alloy
          line: AIM says to use the alloy with adequate ventilation and proper personal protective equipment, and to follow the safety data sheet for emergencies.
        - label: Bismuth in PubChem
          line: PubChem's bismuth record says 324 of 382 company reports did not meet GHS hazard criteria, and four notifications from 58 reports carry H370 and H372. The record is for bismuth, not this alloy.
    - title: If a joint fails
      lead: These are failure routes from the AIM ratings and the printed melting point. No field or space failure data were found.
      points:
        - label: Melting
          line: The alloy melts at 138 °C as printed. No service temperature limit is printed in either AIM sheet.
        - label: Thermal fatigue
          line: AIM rates thermal fatigue resistance Poor for this alloy, the same as Sn63/Pb37, against Excellent for SAC305.
    - title: Handling and storage
      points:
        - label: Shelf life
          line: Water-soluble cored wire with this alloy has a shelf life of 3 years. Other cored wire, solid wire and bar have an indefinite shelf life, per AIM.
        - label: Flux
          line: The alloy is compatible with most electronic grade fluxes. Cleaning follows the flux maker's data sheets.
  why: Sn42Bi58 is a lead-free eutectic solder that melts at 138 °C, printed on both AIM sheets. The lower melting point is what makes it suited to second-solder reflow on circuit boards, the application AIM names first. Bismuth is the larger share of the alloy. The sources read here rate its thermal fatigue resistance Poor, which is the main trade against its low melting point.
  uses:
    - where: Circuit board assembly
      line: AIM says Sn42/Bi58 is typically used for second-solder reflow in circuit board assembly and for other low-temperature soldering requirements. The datasheet lists paste, solid and cored wire, foil, powder, bar, ingot and anode forms.
    - where: Lead-free low-temperature solders
      line: USGS says bismuth is a nontoxic replacement for lead in solders. It also says cadmium, indium, lead and tin can partially replace bismuth in low-temperature solders.
  can_do:
    - label: Melting point
      benchmark: melting_point
      value: 138 °C
      line: The eutectic melting point is 138 °C (280 °F), per the AIM datasheet and the AIM information sheet.
    - label: Tensile strength
      benchmark: ultimate_tensile_strength
      value: 8,000 psi or 9.71 ksi
      line: The two AIM sheets disagree. The datasheet prints 8,000 psi and the information sheet prints 9.71 ksi for the same alloy, and neither gives a test method.
    - label: Joint strength
      benchmark: joint_strength
      value: 6800 psi
      line: The AIM information sheet prints 6800 psi, the highest joint strength value in its performance table. The substrate and test method are not stated.
    - label: Thermal conductivity
      benchmark: thermal_conductivity
      value: 0.19 W/cm-°C
      line: The AIM datasheet prints 0.19 W/cm-°C at 85 °C.
  compare: Sn42Bi58 melts lower than SAC305 and Sn63/Pb37 on the same AIM information sheet, which prints the melting point of each. Its joint strength of 6800 psi is the highest value in that sheet's performance table. Its thermal fatigue rating is Poor, the same as Sn63/Pb37 and below the Excellent rating for SAC305, and its wetting rating is Fair, below the Excellent rating given to both SAC305 and Sn63/Pb37. Its tensile strength is 9.71 ksi on the information sheet and 8,000 psi on the datasheet, and the two AIM sheets disagree. The sheet does not print a tensile value for SAC305, so no tensile comparison is made.
  compare_rows:
    - label: Melting point
      benchmark: melting_point
    - label: Tensile strength
      benchmark: ultimate_tensile_strength
    - label: Thermal conductivity
      benchmark: thermal_conductivity
  handling:
    - Use with ventilation and protective equipment, and follow the safety data sheet for emergencies (AIM datasheet).
    - Water-soluble cored wire has a 3-year shelf life. Other forms have an indefinite shelf life (AIM datasheet).
    - Use an electronic grade flux and follow the flux maker's cleaning instructions (AIM datasheet).
  good_for:
    - Second-solder reflow on circuit boards. The alloy melts at 138 °C as printed (AIM datasheet).
    - Joint strength. AIM prints 6800 psi, the highest value in its joint strength table (AIM information sheet).
  watch_out:
    - Thermal fatigue resistance is rated Poor by AIM, against Excellent for SAC305.
    - Wetting is rated Fair by AIM, against Excellent for SAC305 and Sn63/Pb37.
    - The two AIM sheets disagree on tensile strength (8,000 psi against 9.71 ksi), and neither gives a test method.
  verdict: Sn42Bi58 is the low-melting choice in the AIM range. It gives up thermal fatigue resistance and wetting for a 138 °C melting point, and the printed joint strength is high. The sources read here do not cover its corrosion, space or service-temperature behaviour.