Tin-zinc (Sn91Zn9 eutectic) and tin-bismuth (Sn42Bi58) low-temperature solders SnZn and SnBi

spore: profile
id: tin-zinc
spore_version: 0.2
family: low-melting-metals-and-solders
name: Tin-zinc (Sn91Zn9 eutectic) and tin-bismuth (Sn42Bi58) low-temperature solders
abbreviation: SnZn and SnBi
role: lead-free low-melting solder alloys
category: metals
type: heavy-metals
summary: |
  Two lead-free low-temperature solders are covered here. The first is the tin-zinc eutectic Sn91Zn9 (91 % tin and 9 % zinc by weight), sold by Kapp Alloy as KappAloy9 for soldering aluminium to aluminium and to copper. Kapp prints a eutectic melting point of 199 °C, a density of 7.27 g/cc, a tensile strength of 54.7 MPa and an elongation at break of 32.50 %. The second is the tin-bismuth eutectic Sn42Bi58 (42 % tin and 58 % bismuth), which AIM Solder gives a eutectic melting point of 138 °C, a density of 8.72 g/cc and a tensile strength of 8,000 psi. Both sit below the 217 to 220 °C of SAC305, and Sn-Bi is also below the 183 °C of tin-lead eutectic (Sn-Zn, at 199 °C, sits above tin-lead). Sn-Bi is brittle under shock and drop, according to an iNEMI project page. Sn-Zn corrodes in chloride, and a 0.5 M NaCl study of Sn-3Zn-xBi alloys gives corrosion current densities of 8.7 to 17.4 uA.cm-2. No corrosion number for the Sn91Zn9 eutectic itself was found.
best_for: Low-temperature soldering of heat-sensitive electronics. Sn-Bi suits second-solder reflow at 138 °C, and Sn-Zn suits aluminium-to-copper joints that need a 199 °C eutectic (Kapp, AIM)
weakest_at: Sn-Bi is brittle under mechanical shock and drop, and Sn-Zn corrodes in chloride and leaves flux residue that is slightly corrosive (iNEMI, Brunel, Kapp)
identity:
  formula: Sn91Zn9 (91 % tin and 9 % zinc by weight; eutectic) and Sn42Bi58 (42 % tin and 58 % bismuth by weight; eutectic). Both are alloys, not compounds.
  source: aim-sn42bi58-tds
  where: Major alloy ingredients table, Sn 42 +/- 0.5 and Bi 58 +/- 0.5 (AIM TDS). The Sn 91 % and Zn 9 % composition is in the Composition block of kapp-kappaloy9.
  designations:
    - system: Trade name
      code: KappAloy9
      source: kapp-kappaloy9
      where: Product page title, 91Sn/9Zn Tin-Zinc Lead-Free Solder
tags:
  applications:
    - electronics-and-chips
  stresses: []
  environments: []
properties:
  - benchmark: melting_point
    label: Eutectic melting point, Sn91Zn9 (KappAloy9)
    value: 199
    unit: °C
    scope: material
    conditions:
      alloy: Sn91Zn9 eutectic (91 % Sn, 9 % Zn)
      basis: Melting Range row printed as Eutectic at 199°C (390°F)
    method: Value printed on the manufacturer product page
    status: ground
    source: kapp-kappaloy9
    where: Properties table, Melting Range row (Eutectic @ 199°C (390°F))
  - benchmark: density
    label: Density, Sn91Zn9 (KappAloy9)
    value: 7.27
    unit: g/cc
    scope: material
    conditions:
      alloy: Sn91Zn9
      temperature: not stated on the page
    method: Value printed on the manufacturer product page (the SDS also prints a specific gravity of 7.27)
    status: ground
    source: kapp-kappaloy9
    where: Properties table, Density row (7.27 g/cc (0.263 lb/in3))
  - benchmark: ultimate_tensile_strength
    label: Ultimate tensile strength, Sn91Zn9 (KappAloy9)
    value: 54.7
    unit: MPa
    scope: material
    conditions:
      alloy: Sn91Zn9
      product_form: solid wire, ribbon and spool, as sold
      test_method: not stated on the page
    method: Value printed on the manufacturer product page, shown in parentheses after 7930 psi
    status: ground
    note: The page prints 7930 psi (54.7 MPa). No test method or standard is named, so treat it as indicative.
    source: kapp-kappaloy9
    where: Technical Data table, Tensile Strength, Ultimate row (7930 psi (54.7 MPa))
  - benchmark: elongation
    label: Elongation at break, Sn91Zn9 (KappAloy9)
    value: 32.5
    unit: '%'
    scope: material
    conditions:
      alloy: Sn91Zn9
      test_method: not stated on the page
    method: Value printed on the manufacturer product page
    status: ground
    source: kapp-kappaloy9
    where: Technical Data table, Elongation at Break row (32.50%)
  - benchmark: thermal_conductivity
    label: Thermal conductivity, Sn91Zn9 (KappAloy9)
    value: 61
    unit: W/m-K
    scope: material
    conditions:
      temperature: 85 °C, as printed in the table
      alloy: Sn91Zn9
    method: Value printed on the manufacturer product page
    status: ground
    source: kapp-kappaloy9
    where: Technical Data table, Thermal Conductivity row (61.0 W/m-K at 85.0 °C)
  - benchmark: specific_heat
    label: Specific heat, Sn91Zn9 (solid)
    value: 0.239
    unit: J/g-°C
    scope: material
    conditions:
      phase: solid (liquid value is 0.272 J/g-°C as printed)
      alloy: Sn91Zn9
    method: Value printed on the manufacturer product page
    status: ground
    source: kapp-kappaloy9
    where: Technical Data table, Specific Heat Capacity row (0.239 J/g-°C solid; 0.272 J/g-°C liquid)
  - benchmark: electrical_resistivity
    label: Electrical resistivity, Sn91Zn9 (KappAloy9)
    value: 0.000011
    unit: ohm-cm
    scope: material
    conditions:
      alloy: Sn91Zn9
      temperature: not stated on the page
    method: Value printed on the manufacturer product page, copied as printed
    status: ground
    source: kapp-kappaloy9
    where: Technical Data table, Electrical Resistivity row (0.0000110 ohm-cm)
  - benchmark: melting_point
    label: Eutectic melting point, Sn42Bi58
    value: 138
    unit: °C
    scope: material
    conditions:
      alloy: Sn42Bi58 eutectic (42 % Sn, 58 % Bi)
      basis: AIM gives one eutectic value, both solidus and liquidus
    method: Value printed on the AIM data sheet (Document Rev NF4)
    status: ground
    source: aim-sn42bi58-tds
    where: Features list and Description, eutectic melting point of 138°C (280°F)
  - benchmark: density
    label: Density, Sn42Bi58
    value: 8.72
    unit: g/cc
    scope: material
    conditions:
      alloy: Sn42Bi58
      temperature: not stated on the sheet
    method: Value printed on the AIM data sheet, Properties table
    status: ground
    source: aim-sn42bi58-tds
    where: Properties table, Density g/cc row (8.72)
  - benchmark: ultimate_tensile_strength
    label: Tensile strength, Sn42Bi58
    value: 8000
    unit: psi
    scope: material
    conditions:
      alloy: Sn42Bi58
      product_form: not stated on the sheet
      test_method: not stated on the sheet
    method: Value printed on the AIM data sheet, Properties table (no MPa figure is printed)
    status: ground
    note: The sheet prints 8,000 psi with no test method or product form, so it is not comparable with the MPa figures for SAC305 and Sn-Zn without conversion.
    source: aim-sn42bi58-tds
    where: Properties table, Tensile Strength PSI row (8,000)
  - benchmark: elongation
    label: Elongation, Sn42Bi58
    value: 55
    unit: '%'
    scope: material
    conditions:
      alloy: Sn42Bi58
      test_method: not stated on the sheet
    method: Value printed on the AIM data sheet, Properties table
    status: ground
    source: aim-sn42bi58-tds
    where: Properties table, Elongation % row (55)
  - benchmark: cte
    label: Coefficient of thermal expansion, Sn42Bi58
    value: 15
    unit: ppm/°C
    scope: material
    conditions:
      temperature: 20 °C, as printed in the table
      alloy: Sn42Bi58
    method: Value printed on the AIM data sheet, Properties table
    status: ground
    source: aim-sn42bi58-tds
    where: Properties table, Coefficient of Thermal Expansion @ 20° C row (15 PPM/° C)
  - benchmark: thermal_conductivity
    label: Thermal conductivity, Sn42Bi58
    value: 0.19
    unit: W/cm-°C
    scope: material
    conditions:
      temperature: 85 °C, as printed in the table
      alloy: Sn42Bi58
    method: Value printed on the AIM data sheet, Properties table. The printed unit is W/cm-°C; in SI units this is 19 W/m-K, converted only for comparison in the story.
    status: ground
    source: aim-sn42bi58-tds
    where: Properties table, Thermal Conductivity @ 85° C row (0.19 W/cm-° C)
  - benchmark: latent_heat_of_fusion
    label: Latent heat of fusion, Sn42Bi58
    value: 44.8
    unit: J/g
    scope: material
    conditions:
      alloy: Sn42Bi58
    method: Value printed on the AIM data sheet, Properties table
    status: ground
    note: latent_heat_of_fusion is not a name in property-canon.yaml; used as written.
    source: aim-sn42bi58-tds
    where: Properties table, Latent Heat of Fusion J/g row (44.8)
  - benchmark: melting_point
    label: Melting point, Sn63/Pb37 eutectic (comparison)
    value: 183
    unit: °C
    scope: material
    conditions:
      alloy: Sn63/Pb37 eutectic
      basis: Liquidus printed as 183 °C (361 °F), eutectic
    method: Value printed on the AIM Sn63/Pb37 data sheet (Document Rev NF5)
    status: ground
    source: aim-sn63-tds
    where: Features list (Liquidus 183°C (361°F)) and Typical Melting Temperature block (183°C (361°F) Eutectic)
  - benchmark: melting_point
    label: Melting range, SAC305 (comparison)
    value: 217
    value_high: 220
    bound: range
    unit: °C
    scope: material
    conditions:
      alloy: SAC305, Sn-3.0Ag-0.5Cu
      basis: solidus 217 °C and liquidus 220 °C as printed
    method: Values printed in the Selected Properties table of the Indium data sheet
    status: ground
    source: indium-256
    where: Indalloy 256 Properties table, Solidus 217 °C and Liquidus 220 °C rows
  - benchmark: density
    label: Density, SAC305 (comparison)
    value: 7.35
    unit: g/cc
    scope: material
    conditions:
      alloy: SAC305
      temperature: not stated in the datasheet
    method: Value printed in the Selected Properties table of the Indium data sheet
    status: ground
    source: indium-256
    where: Indalloy 256 Properties table, Density row (7.35 g/cc)
  - benchmark: thermal_conductivity
    label: Thermal conductivity, SAC305 (comparison)
    value: 61
    unit: W/mK
    scope: material
    conditions:
      alloy: SAC305
      temperature: not stated in the datasheet
    method: Value printed in the Selected Properties table of the Indium data sheet
    status: ground
    source: indium-256
    where: Indalloy 256 Properties table, Thermal Conductivity row (61 W/mK)
  - benchmark: cte
    label: Coefficient of thermal expansion, SAC305 (comparison)
    value: 21
    unit: ppm/°C
    scope: material
    conditions:
      alloy: SAC305
      temperature: range not stated in the datasheet
    method: Value printed in the Selected Properties table of the Indium data sheet
    status: ground
    source: indium-256
    where: Indalloy 256 Properties table, CTE row (21 ppm/°C)
corrosion:
  - environment: 0.5 M NaCl solution at 20 °C, potentiodynamic polarization (Sn-3Zn with 0 to 7 wt % Bi, Sn-Zn family, not the eutectic)
    headline: In 0.5 M NaCl the Sn-3Zn alloy has a corrosion current density of 13.5 uA.cm-2, and adding 1 wt % Bi raises it to 17.4 uA.cm-2.
    effect: The Brunel study reports icorr of 13.5 uA.cm-2 for Sn-3Zn, 17.4 uA.cm-2 for Sn-3Zn-1Bi, 13.4 uA.cm-2 for Sn-3Zn-5Bi and 8.7 uA.cm-2 for Sn-3Zn-7Bi. The authors link the 1 wt % Bi result to coarser and more evenly spread Zn-rich precipitates. Corrosion products were mainly Cl, O and Zn, and pits were found on the surface. The paper gives no mm/y rate, so no rating is given.
    rating: unknown
    conditions:
      electrolyte: 0.5 M NaCl, aerated, room temperature 20 +/- 2 oC
      alloy_family: Sn-3Zn-xBi, x = 0, 1, 3, 5, 7 wt %, not the Sn91Zn9 eutectic
      method: Tafel extrapolation to Ecorr
    source: brunel-sn-zn-bi
    where: Table 2 and the results paragraph (icorr values in uA.cm-2); Figure 5 and surface element mapping
  - environment: Residue of the Kapp Golden Flux used with KappAloy solders on aluminium joints
    headline: Kapp says the flux residue is electrically conductive and slightly corrosive.
    effect: The manufacturer says Golden Flux residue should be removed with warm water or alcohol and a clean rag. It is designed for aluminium-to-aluminium and aluminium-to-copper joints. Kapp gives no corrosion rate for the solder itself.
    rating: low
    conditions:
      basis: manufacturer product-page statement about the matching flux residue
      material: flux residue, not the bare solder
    source: kapp-kappaloy9
    where: Matching Kapp Golden Flux paragraph (Residue is electrically conductive and slightly corrosive)
risks:
  hazards:
    - text: The Kapp safety data sheet (SDS 121 GHS, dated 01/01/2025) says the tin-zinc solder is not considered hazardous under Regulation (EC) 1272/2008 or the OSHA Hazard Communication Standard, and has no signal word.
      ghs: []
      source: kapp-sds-121
      where: Section II, Hazard information (No signal word; Not considered hazardous)
    - text: Excessive inhalation of zinc oxide fumes may cause zinc shakes, a flu-like illness that usually stops when the person leaves the source. The SDS says the product should be used with NIOSH-approved breathing protection against dusts and fumes.
      ghs: []
      source: kapp-sds-121
      where: Section XI, Toxicology information (Zinc entry); Section VIII, Respiratory Protection
    - text: Finely divided dust of the tin-zinc alloy may form an explosive mixture with air. The SDS also warns that wet or moist ingots present an explosion hazard when submerged in molten solder.
      ghs: []
      source: kapp-sds-121
      where: Section V, Unusual Fire and Explosion Hazards; Section VII, Handling and storage (ingot warning)
    - text: PubChem's zinc record aggregates ECHA notifications. H250 (catches fire spontaneously if exposed to air) is reported for 26.7 % of company reports, and H400 and H410 (very toxic to aquatic life) for 84.9 % and 79 %. The record does not say which zinc form each notification covers, so these codes are not a classification of the tin-zinc solder.
      ghs:
        - H250
        - H260
        - H400
        - H410
      source: pubchem-zinc
      where: GHS Classification section, ECHA aggregated notifications (CID 23994)
    - text: The AIM SDS for Sn42-Bi58 NC 273LT (EU, version 1.07, issued 5/17/2024) classifies the product as Aquatic Chronic 1, H410, with signal word Warning. This SDS covers the NC 273LT product, which contains flux components, not the bare Sn42Bi58 alloy.
      ghs:
        - H410
      source: aim-sn42bi58-sds-eu
      where: Section 2.1 Classification (Aquatic Chronic 1, H410) and Section 2.2 signal word
    - text: The AIM Asia GHS SDS for Sn42-Bi58 NC 273LT (version 0.15, issued 5/6/2024) lists skin corrosion or irritation Category 3 (causes mild skin irritation) and skin sensitisation Category 1 (may cause an allergic skin reaction). Signal word Warning. It is for the same flux-containing product, not the bare alloy.
      ghs: []
      source: aim-sn42bi58-sds-asia
      where: Section 2 Classification (Skin Corrosion/Irritation Category 3; Skin Sensitization Category 1) and Hazard statements
    - text: PubChem's bismuth record shows 'Not Classified' from 324 of 382 company reports. Four notifications, from 58 of 382 reports, carry H370 (damage to organs, single exposure) and H372 (damage to organs through prolonged or repeated exposure). The record does not say which bismuth substance is covered.
      ghs:
        - H370
        - H372
      source: pubchem-bismuth
      where: GHS Classification section, ECHA aggregated notifications (CID 5359367)
  failure_risks:
    - mode: Brittle fracture of Sn-Bi joints under shock and drop
      trigger: Mechanical shock or drop at high strain rate, for compositions close to the eutectic (about 58 wt % Bi)
      consequence: iNEMI says BiSn-based joints near 58 wt % Bi are prone to brittle fracture at high strain rates and carry a high risk under mechanical shock and drop conditions in consumer electronics.
      severity: high
      source: inemi-bisn
      where: Project background text on BiSn brittle fracture (no numbers given)
    - mode: Chloride corrosion of the Zn-rich phase in Sn-Zn alloys
      trigger: Immersion in aerated 0.5 M NaCl at 20 °C (tested on Sn-3Zn-xBi, not on the eutectic)
      consequence: The Brunel study reports corrosion current densities of 8.7 to 17.4 uA.cm-2 across the Sn-3Zn-xBi series and pits in the surface, with Cl, O and Zn in the corrosion products. No service rate is given.
      severity: moderate
      source: brunel-sn-zn-bi
      where: Table 2 (icorr values) and the surface and pit analysis paragraphs
    - mode: Residual flux corrosion on aluminium joints
      trigger: Golden Flux residue left on the joint after soldering aluminium
      consequence: The residue is electrically conductive and slightly corrosive, according to Kapp. The residue should be removed with warm water or alcohol.
      severity: low
      source: kapp-kappaloy9
      where: Matching Kapp Golden Flux paragraph
  side_effects: []
  handling:
    - text: Wash thoroughly before smoking or eating, as the Kapp SDS states in capitals.
      source: kapp-sds-121
      where: Section XVI, Other information (PERSONNEL SHOULD WASH THOROUGHLY BEFORE SMOKING OR EATING)
    - text: Use NIOSH-approved breathing apparatus against dusts and fumes, and approved safety glasses or goggles, as the SDS states.
      source: kapp-sds-121
      where: Section VIII, Exposure controls (Respiratory Protection; Eye Protection)
    - text: Use with adequate ventilation and proper personal protective equipment, and refer to the SDS for emergency information. The AIM sheet is for the Sn42Bi58 alloy.
      source: aim-sn42bi58-tds
      where: Safety paragraph
    - text: Do not overheat the Golden Flux. It chars above 550 °F (288 °C), as the Kapp product page states in capitals.
      source: kapp-kappaloy9
      where: Matching Kapp Golden Flux paragraph (DO NOT OVERHEAT FLUX)
  mitigations: []
uses:
  - application: electronics-and-chips
    device: Second-solder reflow for circuit board assembly, Sn42Bi58
    example: AIM says Sn42/Bi58 is used for second-solder reflow for circuit board assembly, and for other low temperature soldering requirements. It is available as paste, solid and cored wire, foil, powder, bar, ingot and anode.
    source: aim-sn42bi58-tds
    where: Description section (Typical applications) and the product forms list
  - application: electronics-and-chips
    device: Aluminium-to-copper electrical joints and bus contacts, Sn91Zn9
    example: Kapp describes KappAloy9 for joining aluminium wire to copper busses or contacts, copper wire to aluminium busses, and electronic wires to aluminium fittings, heating panels and high-voltage components. Kapp says the low melting point limits heat damage to nearby electrical and electronic components.
    source: kapp-kappaloy9
    where: Applications list and the product description paragraph
  - application: electronics-and-chips
    device: Bismuth-containing solders
    example: The USGS says bismuth is a nontoxic replacement for lead in brass, free-machining aluminium alloys, steels and solders, and that bismuth alloys are used for low melting point uses such as fusible alloys.
    source: usgs-bismuth-2026
    where: Domestic Production and Use paragraph (metallurgical applications)
supply:
  - subject: Tin (mine production, world), for both alloys
    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 is 22 % of apparent consumption.'
    substitutes:
      - 'USGS: epoxy resins are listed as a substitute 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; Substitutes
  - subject: Zinc (mine production, world), for Sn91Zn9
    producers:
      - country: China
        share_percent: 31.5
        year: 2025
      - country: Peru
        share_percent: 11.5
        year: 2025
      - country: Australia
        share_percent: 8.5
        year: 2025
      - country: India
        share_percent: 6.7
        year: 2025
      - country: Mexico
        share_percent: 6
        year: 2025
    critical_lists: []
    recycling: 'USGS: refined zinc produced in the United States was recovered from secondary materials, including galvanizing residues and crude zinc oxide from electric arc furnace dust. No percentage is printed in the text read.'
    substitutes:
      - 'USGS: aluminium and plastics substitute for galvanized sheet in automobiles. Many elements are substitutes for zinc in chemical, electronic and pigment uses.'
    source: usgs-zinc-2026
    where: World Mine Production and Reserves table, 2025e column (world total 13,000, thousand metric tons zinc content; shares calculated by Space Mushroom from China 4,100, Peru 1,500, Australia 1,100, India 870 and Mexico 780); Recycling; Substitutes
  - subject: Bismuth (refinery production, world), for Sn42Bi58
    producers:
      - country: China
        share_percent: 88
        year: 2025
      - country: Korea, Republic of
        share_percent: 6.3
        year: 2025
      - country: Laos
        share_percent: 3.1
        year: 2025
      - country: Japan
        share_percent: 3.1
        year: 2025
    critical_lists: []
    recycling: 'USGS: recycled bismuth-containing alloy scrap was estimated to make 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 (China 88% of world production in 2025); World Refinery Production table, 2025 column (world total 16,000 t; Korea 1,000, Laos 500, Japan 500 with shares calculated by Space Mushroom); Recycling; Substitutes
documents:
  - title: 'Kapp Alloy: KappAloy9 (91Sn/9Zn) product page, Properties and Technical Data'
    type: datasheet
    url: https://kappalloy.com/collections/kappaloy9
    year: 2026
  - title: 'Kapp Alloy and Wire: Safety Data Sheet SDS 121 GHS, KappAloy Tin-Zinc Solders for Aluminum Soldering (dated 01/01/2025)'
    type: sds
    url: https://cdn.shopify.com/s/files/1/0809/8686/5687/files/SDS_121_GHS_KappAloy_Tin_Zinc.pdf
    year: 2025
  - title: 'AIM: Alloy Sn42/Bi58 (NC 273LT) technical data sheet, Document Rev NF4'
    type: datasheet
    url: https://aimsolder.com/wp-content/uploads/alloy_sn42-bi58_tds.pdf
    year: 2024
  - title: 'AIM: Alloy Sn42-Bi58 NC 273LT safety data sheet, EU CLP (version 1.07, issued 5/17/2024)'
    type: sds
    url: https://aimsolder.com/wp-content/uploads/alloy_sn42-bi58_nc273lt-clp_europe-english.pdf
    year: 2024
  - title: 'AIM: Alloy Sn42-Bi58 NC 273LT GHS safety data sheet, Asia (version 0.15, issued 5/6/2024)'
    type: sds
    url: https://www.aimsolder.com/wp-content/uploads/Alloy_Sn42-Bi58_NC273LT-GHS_Asia-English.pdf
    year: 2024
  - title: 'AIM: Alloy Sn63/Pb37 Electropure technical data sheet, Document Rev NF5'
    type: datasheet
    url: https://www.aimsolder.com/wp-content/uploads/alloy_sn63-pb37_tds.pdf
    year: 2024
  - title: 'Indium Corporation: Indalloy 256 (SAC305) for preforms, product data sheet (form 100346 R0)'
    type: datasheet
    url: https://www.indium.com/wp-content/uploads/2025/03/Indalloy256-for-Preforms-PDS-100346-R0-1.pdf
    year: 2025
  - title: 'Liu, Khorsand and Ji (Brunel University London): Electrochemical corrosion behaviour of Sn-Zn-xBi lead-free solder alloys in 0.5 M NaCl solution'
    type: paper
    url: https://bura.brunel.ac.uk/bitstream/2438/18088/1/FullText.pdf
  - title: 'iNEMI project page: BiSn-Based Low-Temperature Soldering Process and Reliability, Phases 1-3a'
    type: report
    url: https://www.inemi.org/iNEMI/Projects/BiSn-Based%20Low-Temperature%20Soldering%20Process%20and%20Reliability,%20Phases%201-3a
    year: 2026
  - 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: Zinc'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-zinc.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 compound record: Zinc (CID 23994), GHS classification'
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/Zinc
    year: 2026
  - title: 'PubChem compound record: Bismuth (CID 5359367), GHS classification'
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/Bismuth
    year: 2026
gaps:
  - No corrosion rate or corrosion potential for the Sn91Zn9 eutectic was found. The Brunel study tested Sn-3Zn-xBi in 0.5 M NaCl, and the two open MDPI Sn-Zn corrosion papers returned HTTP 403 to every fetch attempt, so their numbers are not used.
  - No corrosion data of any kind for Sn42Bi58 were found in the sources read.
  - Sn91Zn9 properties rest on one manufacturer product page (Kapp). No AIM or Indium Sn91Zn9 technical data sheet was found, and the AIM Prospector entry needs an account. Kapp prints no test method for the tensile or elongation values.
  - The Kapp SDS lists composition ranges for tin and zinc, but the PDF text is garbled in that section, so no range is recorded.
  - The AIM SDS for Sn42Bi58 covers NC 273LT, a flux-containing product, not the bare alloy. No bare-alloy SDS was found, so the bare Sn-Bi alloy has no SDS-based hazard classification here.
  - The Sn42Bi58 tensile figure is printed in psi only (8,000 psi). It is recorded as printed and not converted. The sheet gives no test method.
  - AIM prints Sn42Bi58 Brinell hardness as 23 with no unit, and an electrical conductivity line with a label that conflicts with its value (4.5 % IACS). Neither is recorded.
  - The Kapp SDS prints a melting range of 198 to 343 C. The upper figure is not a melting point for the eutectic, so only the page value of 199 C is recorded.
  - The Sn63/Pb37 data sheet read in this run gives only the melting point. Density and CTE for tin-lead are not recorded here, so the comparison table has no tin-lead density or thermal conductivity.
  - The Sn42Bi58 thermal conductivity is printed as 0.19 W/cm-°C. The SI equivalent (19 W/m-K) is used only for the comparison paragraph.
  - The iNEMI page gives qualitative brittleness statements only. No strain rate, impact energy or joint strength numbers were read for Sn-Bi.
  - The Brunel paper gives no year in the text read, so no year is recorded for it. Its results apply to Sn-3Zn-xBi, which is not the eutectic.
  - USGS 2026 text read for tin, zinc and bismuth contains no critical-mineral list statement. The USGS critical list and the EU critical raw materials list were not read for these three metals, so critical_lists is empty.
  - The USGS zinc summary does not print a recycling percentage, so none is recorded.
  - Mine and refinery shares are calculated from the USGS 2025e values, except the bismuth China share (88 %), which USGS prints.
  - Space-exposure data (outgassing, atomic oxygen, radiation, thermal cycling of Sn-Zn or Sn-Bi joints) were not searched in this run. Tin whisker data for these alloys were not read.
  - No UNS, JIS, ASTM or EN designation was found for Sn91Zn9 or Sn42Bi58 in the sources read. Only the Kapp trade name KappAloy9 is recorded.
sources:
  kapp-kappaloy9:
    title: KappAloy9 (91Sn/9Zn) Tin-Zinc Lead-Free Solder, Kapp Alloy product page
    id: Kapp Alloy and Wire, Inc., product page (collection kappaloy9)
    url: https://kappalloy.com/collections/kappaloy9
    year: 2026
    kind: datasheet
    license: manufacturer web page, cited not reproduced
  kapp-sds-121:
    title: Safety Data Sheet, KappAloy Tin-Zinc Solders for Aluminum Soldering (SDS 121 GHS R13)
    id: Kapp Alloy and Wire, Inc., dated 01/01/2025
    url: https://cdn.shopify.com/s/files/1/0809/8686/5687/files/SDS_121_GHS_KappAloy_Tin_Zinc.pdf
    year: 2025
    kind: datasheet
    license: supplier safety data sheet, cited not reproduced
  aim-sn42bi58-tds:
    title: Sn42/Bi58 lead-free solder alloy, AIM technical data sheet
    id: AIM Solder, Document Rev NF4
    url: https://aimsolder.com/wp-content/uploads/alloy_sn42-bi58_tds.pdf
    year: 2024
    kind: datasheet
    license: supplier technical data sheet, cited not reproduced
  aim-sn42bi58-sds-eu:
    title: Safety Data Sheet, Alloy Sn42-Bi58 NC 273LT (EU CLP, REACH 2020/878)
    id: AIM Solder, version 1.07, issued 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
  aim-sn42bi58-sds-asia:
    title: GHS Safety Data Sheet, Alloy Sn42-Bi58 NC 273LT (Asia)
    id: AIM Solder, version 0.15, issued 5/6/2024
    url: https://www.aimsolder.com/wp-content/uploads/Alloy_Sn42-Bi58_NC273LT-GHS_Asia-English.pdf
    year: 2024
    kind: datasheet
    license: supplier safety data sheet, cited not reproduced
  aim-sn63-tds:
    title: Sn63/Pb37 Electropure solder alloy, AIM technical data sheet
    id: AIM Solder, Document Rev NF5
    url: https://www.aimsolder.com/wp-content/uploads/alloy_sn63-pb37_tds.pdf
    year: 2024
    kind: datasheet
    license: supplier technical data sheet, cited not reproduced
  indium-256:
    title: Indalloy 256 (SAC305) for Preforms, product data sheet
    id: Indium Corporation, Form No. 100346 R0
    url: https://www.indium.com/wp-content/uploads/2025/03/Indalloy256-for-Preforms-PDS-100346-R0-1.pdf
    year: 2025
    kind: datasheet
    license: supplier product data sheet, cited not reproduced
  brunel-sn-zn-bi:
    title: Electrochemical corrosion behaviour of Sn-Zn-xBi lead-free solder alloys in 0.5 M NaCl solution
    id: Liu G, Khorsand S, Ji S; Brunel Centre for Advanced Solidification Technology, Brunel University London
    url: https://bura.brunel.ac.uk/bitstream/2438/18088/1/FullText.pdf
    kind: paper
    license: author-hosted full text, cited not reproduced
  inemi-bisn:
    title: 'iNEMI project: BiSn-Based Low-Temperature Soldering Process and Reliability, Phases 1-3a'
    id: iNEMI project page
    url: https://www.inemi.org/iNEMI/Projects/BiSn-Based%20Low-Temperature%20Soldering%20Process%20and%20Reliability,%20Phases%201-3a
    year: 2026
    kind: web
    license: public project web page, cited not reproduced
  usgs-tin-2026:
    title: 'Mineral Commodity Summaries 2026: Tin (U.S. Geological Survey)'
    id: USGS MCS 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-tin.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  usgs-zinc-2026:
    title: 'Mineral Commodity Summaries 2026: Zinc (U.S. Geological Survey)'
    id: USGS MCS 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-zinc.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  usgs-bismuth-2026:
    title: 'Mineral Commodity Summaries 2026: Bismuth (U.S. Geological Survey)'
    id: USGS MCS 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-bismuth.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  pubchem-zinc:
    title: 'PubChem compound record: Zinc, GHS classification'
    id: CID 23994; PubChem pug_view JSON
    url: https://pubchem.ncbi.nlm.nih.gov/compound/Zinc
    year: 2026
    kind: database
    license: public domain (NCBI); notifications attributed to ECHA
  pubchem-bismuth:
    title: 'PubChem compound record: Bismuth, GHS classification'
    id: CID 5359367; PubChem pug_view JSON
    url: https://pubchem.ncbi.nlm.nih.gov/compound/Bismuth
    year: 2026
    kind: database
    license: public domain (NCBI); notifications attributed to ECHA
license: CC-BY-4.0
updated: '2026-10-26'
review:
  status: draft
  method: assistant
  checked_values: 19
  unreachable: 4
  caveats: 4
  note: 'Read by an AI assistant on 2026-10-26 from the Kapp product page and SDS, the AIM Sn42Bi58 data sheet and two SDS versions, the AIM Sn63/Pb37 data sheet, the Indium SAC305 data sheet, the Brunel paper, the iNEMI page, the USGS 2026 summaries and the PubChem pug_view records. Unreachable: the two MDPI Sn-Zn corrosion papers (HTTP 403), MakeItFrom and American Elements (HTTP 403), and the AIM Prospector Sn91Zn9 sheet (account needed). Caveats: the Sn-Zn corrosion data are for Sn-3Zn-xBi, not the eutectic; the Sn-Bi SDS covers a flux-containing product; the tensile values carry no test method; the GHS notifications cover the element, not the alloy.'
story:
  recipe:
    line: Two eutectic alloys. Sn91Zn9 is tin with 9 % zinc by weight, and Sn42Bi58 is tin with 58 % bismuth by weight. No intermetallic phase is described for either alloy in the sources read, and no process route is given for either alloy.
    parts:
      - name: Tin (in Sn91Zn9)
        symbol: Sn
        share_percent: 91
        role: The matrix of the tin-zinc eutectic. Kapp describes the alloy as a soft, lower melting point tin-zinc eutectic.
      - name: Zinc (in Sn91Zn9)
        symbol: Zn
        share_percent: 9
        role: Sets the eutectic at 199 °C (Kapp). Zinc oxidises easily, so Kapp recommends a matching flux for aluminium joints.
      - name: Tin (in Sn42Bi58)
        symbol: Sn
        share_percent: 42
        role: The tin share of the tin-bismuth eutectic, which melts at 138 °C (AIM).
      - name: Bismuth (in Sn42Bi58)
        symbol: Bi
        share_percent: 58
        role: Sets the 138 °C eutectic. The iNEMI page says compositions near 58 wt % Bi are prone to brittle fracture at high strain rates.
  risk_groups:
    - title: For people
      level: 0
      verdict: 'Bare alloys: not hazardous. Flux products: check'
      lead: The Kapp SDS does not classify the tin-zinc solder. The AIM SDS for the Sn-Bi flux product is classified H410 in the EU and carries skin-irritant and sensitiser classes in Asia. The bare Sn-Bi alloy SDS was not found.
      points:
        - label: Sn-Zn alloy
          line: 'Kapp SDS 121 GHS (2025): not hazardous under Regulation (EC) 1272/2008, no signal word. Zinc oxide fumes can cause zinc shakes.'
        - label: Zinc record
          line: PubChem's zinc record shows H250 (pyrophoric) for 26.7 % of company reports, and H400 and H410 for most. The record does not say which zinc form each report covers.
        - label: Sn-Bi flux product
          line: 'AIM SDS for NC 273LT: EU classification Aquatic Chronic 1, H410, signal word Warning. Asia SDS lists mild skin irritation and possible allergic skin reaction.'
    - title: If a joint fails
      verdict: 'Sn-Bi: brittle under shock. Sn-Zn: corrodes in chloride'
      lead: The sources read give a brittle-fracture risk for Sn-Bi, and a chloride corrosion risk for the Sn-Zn family. Neither has a service rate for the eutectic.
      points:
        - label: Sn-Bi brittle
          line: iNEMI says BiSn compositions near 58 wt % Bi are prone to brittle fracture at high strain rates and carry a high risk under shock and drop.
        - label: Sn-Zn chloride
          line: In 0.5 M NaCl, Sn-3Zn has an icorr of 13.5 uA.cm-2. Adding 1 wt % Bi raises it to 17.4 uA.cm-2, and 7 wt % Bi lowers it to 8.7 uA.cm-2 (Brunel).
        - label: Flux residue
          line: Kapp says Golden Flux residue is electrically conductive and slightly corrosive, and should be removed with warm water or alcohol.
    - title: Handling and storage
      verdict: Ventilate, wash before eating, keep ingots dry
      points:
        - label: Hygiene
          line: Wash thoroughly before smoking or eating (Kapp SDS, Section XVI).
        - label: Dust and fume
          line: Finely divided dust may form an explosive mixture with air, and zinc oxide fumes can cause zinc shakes. Use NIOSH-approved breathing protection (Kapp SDS, Sections V, VIII and XI).
        - label: Wet ingots
          line: Wet or moist ingots present an explosion hazard when submerged in molten solder (Kapp SDS, Section VII).
  why: Both alloys melt below SAC305 (217 to 220 °C), and Sn-Bi also melts below tin-lead (183 °C). Sn-Bi at 138 °C is for second-solder reflow that must not remelt the first joints, and Sn-Zn at 199 °C is for aluminium joints where heat must stay low to protect nearby parts (Kapp, AIM).
  uses:
    - where: Second-solder reflow, Sn42Bi58
      line: AIM says Sn42/Bi58 is used for second-solder reflow for circuit board assembly, and for other low temperature soldering requirements.
    - where: Aluminium-to-copper joints, Sn91Zn9
      line: Kapp describes KappAloy9 for aluminium wire to copper busses, copper wire to aluminium busses, and electronic wires to aluminium fittings and high-voltage components.
    - where: Bismuth in solders
      line: The USGS calls bismuth a nontoxic replacement for lead in solders and fusible alloys.
  can_do:
    - label: Melt low
      value: 138 °C
      benchmark: melting_point
      line: AIM gives a Sn42Bi58 eutectic melting point of 138 °C (280 °F).
    - label: Melt low for aluminium
      value: 199 °C
      benchmark: melting_point
      line: Kapp gives the Sn91Zn9 eutectic at 199 °C (390 °F) for aluminium soldering.
    - label: Weight
      value: 8.72 g/cc
      benchmark: density
      line: AIM gives a Sn42Bi58 density of 8.72 g/cc. Kapp gives 7.27 g/cc for Sn91Zn9.
    - label: Carry heat
      value: 61.0 W/m-K
      benchmark: thermal_conductivity
      line: Kapp gives a thermal conductivity of 61.0 W/m-K at 85 °C for Sn91Zn9. AIM gives 0.19 W/cm-°C at 85 °C for Sn42Bi58.
  compare: Both alloys melt below SAC305, which is their reason for use. Sn-Bi melts at 138 °C, well below tin-lead's 183 °C and SAC305's 217 °C. Sn-Zn melts at 199 °C, which is still below SAC305. Sn-Zn has a density of 7.27 g/cc, close to SAC305's 7.35 g/cc, and both print a thermal conductivity of about 61 W/m-K. Sn-Bi is much denser (8.72 g/cc) and has a conductivity of 0.19 W/cm-°C, about 19 W/m-K, roughly one third of the others. The Sn-Bi weak point is brittleness under shock, and the Sn-Zn weak point is corrosion in chloride. Tin-lead density was not read in this run, so the comparison table has no tin-lead density row.
  compare_rows:
    - label: Melting point
      benchmark: melting_point
    - label: Density
      benchmark: density
    - label: Thermal conductivity
      benchmark: thermal_conductivity
  handling:
    - Check the SDS for the exact product. The bare Sn-Zn alloy is not classified by Kapp, but the Sn-Bi flux product is classified H410 in the EU.
    - Wash hands before eating, and do not overheat the Golden Flux for Sn-Zn (it chars above 550 °F).
    - Keep wet or moist ingots away from molten solder.
    - Ventilate the work area and wear NIOSH-approved respiratory protection against dust and fume.
  good_for:
    - Low-temperature second-solder reflow of Sn42Bi58 (AIM), where the first joints must not remelt.
    - Aluminium-to-copper electrical joints with Sn91Zn9 and Kapp Golden Flux (Kapp).
  watch_out:
    - Sn-Bi is brittle under shock and drop at high strain rate (iNEMI).
    - Sn-Zn corrodes in chloride (Brunel, icorr 8.7 to 17.4 uA.cm-2 for the Sn-3Zn-xBi series; the eutectic itself was not tested).
    - Flux residue on aluminium joints is slightly corrosive (Kapp).
    - The Sn-Bi SDS covers a flux-containing product, not the bare alloy.
  verdict: Sn91Zn9 (199 °C) and Sn42Bi58 (138 °C) are the two low-melting lead-free options in this profile. Sn-Bi is best for second-solder reflow where its shock brittleness is acceptable; Sn-Zn is best for aluminium joints with its matching flux. Neither has a corrosion rate for the eutectic, and both have their data from one or two vendor sheets, so the values are indicative.