Indium-tin and indium-silver solders In-Sn / In-Ag

spore: profile
id: indium-tin
spore_version: 0.2
family: low-melting-metals-and-solders
name: Indium-tin and indium-silver solders
abbreviation: In-Sn / In-Ag
role: low-melting solder and seal alloy (In52Sn48 eutectic, In97Ag3)
category: metals
type: heavy-metals
summary: |
  Indium-tin solder is an indium-rich alloy that melts at about 118 degC. The In/Sn rod sold by SA Materials is called eutectic at 118 degC, with a density of 7.3 g/cm3, a thermal conductivity of 34 W/m K and a tensile strength of 12 MPa. The 52 wt% indium and 48 wt% tin composition (In52Sn48) is the one the McMaster-Carr catalogue lists, but the rod page itself does not print its composition. Indium-silver solder (In97Ag3, 97 wt% indium and 3 wt% silver) melts at 143 degC in two supplier listings. A NASA Ames report used a flat indium/silver alloy seal for demountable cryogenic joints and found no detectable leak at 4.2 K and 1.6 K. Both alloys are soft and low-strength, and both are mostly indium, so the indium supply and oxide film apply to them too.
best_for: Soft, low-melting joints and seals where the joint must melt near 118 degC (indium-tin) or 143 degC (In97Ag3) and strength matters less than a low melting point
weakest_at: 'Strength: tensile strength of about 12 MPa for the In/Sn rod, and no strength value is printed for In97Ag3'
identity:
  formula: In52Sn48 eutectic solder (52 wt% indium, 48 wt% tin, from the catalogue); In97Ag3 solder (97 wt% indium, 3 wt% silver)
  source: mcmaster-indium-alloys
  where: Low-Melting-Point Solder (wire) table, item 8514N13 (In52Sn48 row); In97Ag3 composition from sa-in97ag3-wire and cte-sdr9703
tags:
  stresses:
    - extreme-cold
  applications:
    - electronics-and-chips
    - thermal-control
    - mechanisms
properties:
  - benchmark: melting_point
    label: Melting temperature of In/Sn solder rod (SA Materials)
    value: 118
    unit: degC
    scope: material
    conditions:
      alloy: indium-tin, called eutectic by the supplier; composition not printed
      form: rod, 5 mm diameter
    method: Value printed on the supplier product page, given as a solid-phase and liquid-phase value
    status: ground
    source: sa-in-sn-rod
    where: Product specification, melting or eutectic temperature line (118 degC)
  - benchmark: melting_point
    label: Melting temperature of In97Ag3 solder (Custom Thermoelectric listing)
    value: 143
    unit: degC
    scope: material
    conditions:
      alloy: In97Ag3, 97 % In and 3 % Ag
      form: wire, 0.030 in diameter
    method: Value printed on the reseller listing (the listing also prints 290 degF)
    status: ground
    source: cte-sdr9703
    where: Product specification, Melt point line (143 degC, 290 degF)
  - benchmark: melting_point
    label: Melting point of In97Ag3 wire (SA Materials)
    value: 143
    unit: degC
    scope: material
    conditions:
      alloy: In97Ag3, 97 wt% In and 3 wt% Ag
      form: wire, 1 mm diameter
    method: Value printed on the supplier product page, described as a single melting point of the eutectic alloy
    status: ground
    source: sa-in97ag3-wire
    where: Product description, text "single melting point at 143 C"
  - benchmark: density
    label: Density of In/Sn solder rod (SA Materials)
    value: 7.3
    unit: g/cm3
    scope: material
    conditions:
      alloy: indium-tin, composition not printed on the page
      temperature: not stated on the page
    method: Value printed on the supplier product page
    status: ground
    source: sa-in-sn-rod
    where: Product specification, Density line (7.3 g/cm3)
  - benchmark: thermal_conductivity
    label: Thermal conductivity of In/Sn solder rod (SA Materials)
    value: 34
    unit: W/m·K
    scope: material
    conditions:
      alloy: indium-tin, composition not printed
      form: rod
      temperature: not stated on the page
    method: Value printed on the supplier product page
    status: ground
    source: sa-in-sn-rod
    where: Product specification, Thermal conductivity line (34 W/m·K)
  - benchmark: ultimate_tensile_strength
    label: Tensile strength of In/Sn solder rod (SA Materials)
    value: 12
    unit: MPa
    scope: material
    conditions:
      alloy: indium-tin, composition not printed
      form: rod
    method: Value printed on the supplier product page
    status: ground
    source: sa-in-sn-rod
    where: Product specification, Tensile strength line (12 MPa)
  - benchmark: electrical_resistivity
    label: Electrical resistivity of In/Sn solder rod (SA Materials)
    value: 0.147
    unit: µΩ·m
    scope: material
    conditions:
      alloy: indium-tin, composition not printed
      form: rod
      temperature: not stated on the page
    method: Value printed on the supplier product page (about 14.7 µΩ·cm)
    status: ground
    source: sa-in-sn-rod
    where: Product specification, Electrical resistivity line (0.147 µΩ·m)
  - benchmark: cte
    label: Coefficient of thermal expansion of In/Sn solder rod (SA Materials)
    value: 20
    unit: ppm/K
    scope: material
    conditions:
      alloy: indium-tin, composition not printed
      unit_in_source: 20 x 10-6 per degC (printed with a superscript minus sign and a degree-C unit sign)
      temperature: not stated on the page
    method: Value printed on the supplier product page; the unit is printed as x10-6 per degC, which is the same as ppm/K
    status: ground
    source: sa-in-sn-rod
    where: Product specification, Coefficient of thermal expansion line (20 x 10-6/degC)
corrosion:
  - environment: Room-temperature air (indium-rich alloy; no test on the In52Sn48 alloy found)
    headline: In room-temperature air the indium-rich surface forms a thin indium oxide (In2O3) crust. In-Sn oxidation was not tested in any source read here.
    effect: NASA Goddard's bump-bonding report says indium readily oxidizes in air at room temperature to form a thin In2O3 crust, which resists rupture during bonding and can block electrical conduction. The report measured pure indium, not the In52Sn48 alloy, and gives no oxide thickness or growth rate.
    rating: moderate
    conditions:
      basis: NASA Goddard observation on pure indium during flip-chip hybridization; cleanroom air
      thickness: not given in the source
    source: ntrs-mosaic
    where: Section 2.2 (Plasma Cleaning) and the ellipsometry discussion that follows
  - environment: Outdoor use of the indium-tin thermal interface foil
    headline: The supplier rules out outdoor use of the indium-tin foil and prints no corrosion data.
    effect: 'The McMaster-Carr table prints ''For Use Outdoors: No'' for both indium-tin foil items. The page gives no salt-spray, humidity or corrosion-rate test for the foil.'
    rating: unknown
    conditions:
      basis: supplier product table only; no environmental test data
    source: mcmaster-indium-alloys
    where: Thermal Interface Foil table, For Use Outdoors column, items 8898N17 and 8898N15
risks:
  hazards:
    - text: PubChem's GHS summary for indium metal lists H302 (15.1 %), H312 (12.7 %), H315 (15.4 %), H319 (13.2 %), H332 (14.8 %) and H335 (14.3 %), with H303 and H372 in a second block. The record does not say which indium substance each report covers, so the codes are a guide for the indium component and not a check on the alloy.
      ghs:
        - H302
        - H312
        - H315
        - H319
        - H332
        - H335
        - H303
        - H372
      source: pubchem-in
      where: GHS Classification section (ECHA C&L notifications, percentages as printed)
    - text: The NIOSH excerpt in PubChem lists inhalation, ingestion and skin or eye contact as exposure routes for indium compounds, with target organs the eyes, skin, respiratory system, liver, kidneys, heart and blood.
      ghs: []
      source: pubchem-in
      where: Health Hazards section, NIOSH Pocket Guide excerpt
  failure_risks:
    - mode: Dust explosion of indium powder
      trigger: Indium in powder or granular form mixed with air. No alloy-powder test was read.
      consequence: PubChem's physical-dangers entry says a dust explosion is possible, and that finely dispersed particles form explosive mixtures in air.
      severity: moderate
      source: pubchem-in
      where: Physical Dangers and Fire Potential sections
    - mode: Leakage of an indium/silver seal on rapid cooling
      trigger: Rapid cooling of a demountable indium seal, especially after repeated cycles
      consequence: NASA Ames notes that leakage frequently occurs under rapid cooling of indium seals. Its flat indium/silver alloy seal in a stainless steel guard showed no detectable leak at 4.2 K (9 cycles) or 1.6 K (4 cycles), and each seal was mounted and demounted 13 times.
      severity: moderate
      source: ntrs-seal-1989
      where: Introduction and results, NASA TM 102190 (1989)
    - mode: Oxide film blocks an electrical joint
      trigger: Indium exposed to room-temperature air before bonding, or a surface reduced but then returned to air
      consequence: The In2O3 crust resists rupture when bonding, and the report says it can block electrical conduction. The oxide regrows once a reduced surface is exposed to air again.
      severity: moderate
      source: ntrs-mosaic
      where: Section 2.2 (Plasma Cleaning)
  side_effects: []
  handling:
    - text: 'PubChem fire-prevention guidance for indium powder: no open flames, no sparks and no smoking. Use a closed system, dust-explosion-proof electrical equipment and lighting, and prevent dust from settling.'
      source: pubchem-in
      where: Fire Prevention section
    - text: PubChem's fire-fighting excerpt, taken from ERG Guide 170 for metal powders, says not to use water, foam or CO2 on metal fires because water can generate hydrogen. It is a generic guide for metal powders, not a test of the alloy.
      source: pubchem-in
      where: Fire Fighting section, ERG Guide 170 excerpt
  mitigations:
    - text: NASA Goddard cleaned indium surfaces in a plasma of nitrogen-rich, reducing gas just before bonding, which removed the native oxide and gave a good electrical joint.
      source: ntrs-mosaic
      where: Section 2.2 (Plasma Cleaning)
uses:
  - application: electronics-and-chips
    device: Low-melting-point solder wire and ribbon, In52Sn48 eutectic
    example: McMaster-Carr sells In52Sn48 solder as 0.030 in diameter wire and 0.002 in thick ribbon, with a melting temperature printed in degF.
    source: mcmaster-indium-alloys
    where: Low-Melting-Point Solder (wire) table, item 8514N13; Low-Melting-Point Solder Ribbon table, item 7906N12
  - application: electronics-and-chips
    device: In97Ag3 solder wire for no-clean soldering
    example: The Custom Thermoelectric listing sells In97/Ag3 solder (SDR-9703) as 0.030 in (0.762 mm) wire, to be used with an RMA or RA flux, with a melting point of 143 degC.
    source: cte-sdr9703
    where: Product specifications for SDR-9703
  - application: thermal-control
    device: Indium-tin thermal interface foil (48 % tin) between surfaces in electronics
    example: 'McMaster-Carr lists this foil at 0.004 in and 0.01 in thickness and prints a thermal conductivity and maximum temperature for it. The page prints no thermal-resistance value, and the foil is marked ''For Use Outdoors: No''.'
    source: mcmaster-indium-alloys
    where: Thermal Interface Foil table, items 8898N17 and 8898N15
  - application: mechanisms
    device: Flat indium/silver alloy seal in a stainless steel guard for demountable cryogenic joints (ground test, not flown)
    example: NASA Ames leak-tested two demountable seals of this design at 4.2 K (9 cycles) and 1.6 K (4 cycles), with no detectable leak above the helium background. The report says indium is used for demountable cryogenic seals because it is easy to form into an O-ring from wire.
    source: ntrs-seal-1989
    where: Introduction and results, NASA TM 102190 (1989)
supply:
  - subject: Indium (refinery production, used in both solders)
    abundance: 0.25 ppm in the Earth's crust (USGS Professional Paper 1802-A, Table A1)
    producers:
      - country: China
        share_percent: 70
        year: 2025
      - country: Republic of Korea
        share_percent: 16.4
        year: 2025
      - country: Japan
        share_percent: 5.9
        year: 2025
    critical_lists:
      - list: USGS 2025 Final List of Critical Minerals (CRS IF13145 lists indium)
        listed: true
    recycling: 'USGS: indium is most commonly recovered from ITO scrap in Japan and the Republic of Korea. Recycling quantities were not available.'
    substitutes:
      - 'USGS: antimony tin oxide, carbon nanotube coatings, PEDOT, copper or silver nanowires, graphene and zinc oxide nanopowder have been developed or explored to replace ITO. No substitute for indium in solder is named in the source.'
    source: usgs-mcs2026-indium
    where: World Refinery Production and Capacity table, 2025e column (world total 1,100 t). China 70 % is as printed in Events, Trends, and Issues; Korea 16.4 % and Japan 5.9 % are calculated by Space Mushroom (180 and 65 over 1,100)
  - subject: Tin (mine production, the other metal in In52Sn48)
    abundance: 2.3 ppm in the Earth's crust (USGS Professional Paper 1802-A, Table A1)
    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
    critical_lists:
      - list: USGS 2025 Final List of Critical Minerals (CRS IF13145 lists tin)
        listed: true
    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 named as substitutes for tin in solder, alongside aluminum, glass, paper and plastic for cans.'
    source: usgs-mcs2026-tin
    where: World Mine Production and Reserves table, 2025e column (world total 290,000 t, tin content; shares calculated by Space Mushroom against that total); Recycling; Substitutes; Abundance from PP 1802-A
  - subject: Silver (mine production, the other metal in In97Ag3)
    producers:
      - country: Mexico
        share_percent: 24.2
        year: 2025
      - country: Peru
        share_percent: 13.8
        year: 2025
      - country: China
        share_percent: 13.1
        year: 2025
      - country: Chile
        share_percent: 5.4
        year: 2025
    critical_lists:
      - list: USGS 2025 Final List of Critical Minerals (silver added in 2025; CRS IF13145 lists silver)
        listed: true
    recycling: 'USGS: about 1,000 tons of silver was recovered from new and old scrap in 2025.'
    substitutes:
      - USGS silver substitutes are for photography, surgical pins and flatware. The source does not discuss solder substitutes.
    source: usgs-mcs2026-silver
    where: World Mine Production and Reserves table, 2025e column (world total 26,000 tons; shares calculated by Space Mushroom); Events text for the 2025 critical list; Recycling; Substitutes
documents:
  - title: 'USGS Mineral Commodity Summaries 2026: Indium'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-indium.pdf
    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: Silver'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-silver.pdf
    year: 2026
  - title: 'McMaster-Carr indium alloys: low-melting-point solder wire, ribbon and thermal interface foil'
    type: datasheet
    url: https://mcmaster.com/indium-alloys
    year: 2026
  - title: SA Materials IN5829 indium tin alloy rod, product specification
    type: datasheet
    url: https://samaterials.com/in5829-indium-tin-alloy-rod.html
  - title: SA Materials IN6669 In97/Ag3 spooled wire, product specification
    type: datasheet
    url: https://www.samaterials.com/product/in6669-indiumsilver-alloy-spooled-wire-in97ag-3.html
  - title: 'NASA TM 102190: Performance of All-Metal Demountable Cryogenic Seals at Superfluid Helium Temperatures'
    type: report
    url: https://ntrs.nasa.gov/api/citations/19890013479/downloads/19890013479.pdf
    year: 1989
  - title: 'NASA Goddard: Enabling large focal plane arrays through mosaic hybridization'
    type: report
    url: https://ntrs.nasa.gov/api/citations/20130013418/downloads/20130013418.pdf
  - title: PubChem compound record for indium (CID 5359967)
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/Indium
    year: 2026
gaps:
  - No flight, vacuum, outgassing, atomic-oxygen, UV or radiation data for the indium-tin or indium-silver solders were found in any source read. The seal and bump-bonding sources are ground tests of indium-rich metal.
  - No corrosion, oxidation or ageing test on the In52Sn48 or In97Ag3 alloys was found. The oxide entry uses NASA's measurement on pure indium.
  - The In/Sn rod page does not print its composition, so its values (density, conductivity, resistivity, CTE, tensile strength) are recorded under 'indium-tin, composition not printed' and not assigned to In52Sn48.
  - The McMaster-Carr indium alloy table (wire and foil melting temperatures, thermal conductivity, tensile strength, electrical resistivity and maximum temperature) was read through a rendered view, but its values are not in the page's static HTML, so verify-values cannot confirm them. They are left out of properties; the page is cited for product forms, composition and the outdoor-use statement.
  - The In97Ag3 sources print only composition, form, diameter, flux and melting point. No density, conductivity, resistivity, strength or thermal-expansion value was found for In97Ag3.
  - No UNS, ASTM, EN or other grade designation was found in a source read for In52Sn48 or In97Ag3, so designations are left out.
  - The Indium Corporation data sheets, the MDPI 2023 In-Sn mechanical paper, and the Conro, Digi-Key and Chip Quik listings could not be read (403 errors or timeouts). The In97Ag3 melting value rests on two supplier pages.
  - Shelf life conflicts between listings (one lists 60 months for an In-Sn wire, another states no limited shelf life for solid solder). Neither was read on the supplier's own page, so no shelf life is stated.
  - Hazard data are from PubChem's indium record. No safety data sheet for the In52Sn48 or In97Ag3 alloy was read, and the tin component's hazards were not read.
  - The silver abundance in the crust was not read in PP 1802-A Table A1 in this run.
  - The In-Ag seal alloy in the NASA report is printed as indium/silver without a composition, so it is not assigned to In97Ag3.
sources:
  mcmaster-indium-alloys:
    title: 'McMaster-Carr: Indium alloys (low-melting-point solder wire, ribbon, casting metals, thermal interface foil)'
    url: https://mcmaster.com/indium-alloys
    kind: datasheet
    license: supplier catalogue, cited not reproduced
  sa-in-sn-rod:
    title: 'SA Materials IN5829: Indium tin alloy rod, product specification'
    url: https://samaterials.com/in5829-indium-tin-alloy-rod.html
    kind: datasheet
    license: supplier product page, cited not reproduced
  sa-in97ag3-wire:
    title: 'SA Materials IN6669: In97/Ag3 indium-silver alloy spooled wire, product specification'
    url: https://www.samaterials.com/product/in6669-indiumsilver-alloy-spooled-wire-in97ag-3.html
    kind: datasheet
    license: supplier product page, cited not reproduced
  cte-sdr9703:
    title: 'Custom Thermoelectric: Solder In97/Ag3 (SDR-9703), melt point 143 degC'
    url: https://customthermoelectric.com/solder-in97-ag3-melt-point-143-deg-c.html
    kind: web
    license: reseller product page, cited not reproduced
  usgs-mcs2026-indium:
    title: 'Mineral Commodity Summaries 2026: Indium (U.S. Geological Survey)'
    id: USGS MCS 2026, February 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-indium.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  usgs-mcs2026-tin:
    title: 'Mineral Commodity Summaries 2026: Tin (U.S. Geological Survey)'
    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-silver:
    title: 'Mineral Commodity Summaries 2026: Silver (U.S. Geological Survey)'
    id: USGS MCS 2026, February 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-silver.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  pp1802a:
    title: 'Critical Mineral Resources of the United States: An Introduction (USGS Professional Paper 1802-A), Table A1, crustal abundances'
    id: USGS PP 1802-A
    url: https://pubs.usgs.gov/pp/1802/a/pp1802a.pdf
    year: 2017
    kind: report
    license: public domain (USGS)
  crs-if13145:
    title: 'Congressional Research Service IF13145: USGS Critical Minerals List (final 2025 list)'
    id: IF13145, updated 2026-01-07
    url: https://www.everycrsreport.com/files/2026-01-07_IF13145_e385924a2f20b8b1460afc40322d4137f1956556.pdf
    year: 2026
    kind: report
    license: public domain (CRS)
  ntrs-seal-1989:
    title: Performance of All-Metal Demountable Cryogenic Seals at Superfluid Helium Temperatures (NASA Technical Memorandum 102190, Ames Research Center)
    id: NTRS 19890013479
    url: https://ntrs.nasa.gov/api/citations/19890013479/downloads/19890013479.pdf
    year: 1989
    kind: report
    license: public domain (NASA)
  ntrs-mosaic:
    title: Enabling large focal plane arrays through mosaic hybridization (NASA Goddard Space Flight Center)
    id: NTRS 20130013418
    url: https://ntrs.nasa.gov/api/citations/20130013418/downloads/20130013418.pdf
    kind: report
    license: public domain (NASA)
  pubchem-in:
    title: 'PubChem compound record: Indium (CID 5359967), including GHS, NIOSH and ERG excerpts'
    id: CID 5359967; CAS 7440-74-6; PubChem REST pug_view JSON
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/5359967/JSON
    year: 2026
    kind: database
    license: PubChem (NCBI), public domain; sections attributed to ECHA, NIOSH and ERG
license: CC-BY-4.0
updated: '2026-10-26'
review:
  status: draft
  method: assistant
  checked_values: 8
  unreachable: 4
  caveats: 3
  note: 'Values read by an AI assistant on 2026-10-26 from the pages and PDFs named in each entry. Eight property values pass verify-values against the SA Materials and Custom Thermoelectric pages. Six McMaster-Carr table values were removed because the page''s static HTML does not contain them. Unreachable (403 or timeout): Indium Corporation solder pages, the MDPI 2023 In-Sn paper, the Conro and Digi-Key listings, and the Mouser Chip Quik datasheet. Caveats: the In/Sn rod composition is not printed, so the In/Sn rod values are not assigned to In52Sn48; the In-Ag figures are supplier catalogue values only; the resistivity is printed as 0.147 uOhm m (about 14.7 uOhm cm).'
story:
  recipe:
    line: In52Sn48 is a two-metal eutectic of indium and tin (52 wt% indium, 48 wt% tin, from the McMaster-Carr catalogue). In97Ag3 is indium with 3 wt% silver. The sources give composition and product forms (wire, ribbon, foil, rod) but not the melting or casting route.
    parts:
      - name: Indium
        symbol: In
        share: 52 wt% in In52Sn48; 97 wt% in In97Ag3 (McMaster-Carr, SA Materials)
        role: The base metal in both solders. It sets the low melting point and the softness, and it forms the oxide film in air.
      - name: Tin
        symbol: Sn
        share: 48 wt% in In52Sn48 (McMaster-Carr)
        role: Second metal in the eutectic. It brings the melting point down to about 118 degC, far below that of pure indium.
      - name: Silver
        symbol: Ag
        share: 3 wt% in In97Ag3 (SA Materials, Custom Thermoelectric)
        role: Alloying addition in the In97Ag3 solder, which melts at 143 degC.
  risk_groups:
    - title: For people
      level: 1
      verdict: PubChem indium hazard codes, little alloy data
      lead: The hazard data here come from the indium record in PubChem and not from a safety data sheet for either solder. The record lists skin, eye and inhalation irritation codes and possible organ effects from indium compounds.
      points:
        - label: The metal in PubChem
          line: PubChem's GHS summary for indium lists H302, H312, H315, H319, H332 and H335, with H303 and H372 in a second block. It does not say which indium substance each report covers.
        - label: Dust
          line: PubChem says indium powder can form an explosive dust cloud in air, so keep dust down and use dust-explosion-proof equipment.
    - title: If it fails
      lead: The failure routes in these sources are a leaking seal on rapid cooling and an oxide film that blocks a joint.
      points:
        - label: Seals
          line: NASA Ames notes that indium seals often leak on rapid cooling. Its flat indium/silver seal showed no detectable leak at 4.2 K or 1.6 K, after 13 mount and demount cycles.
        - label: Oxide
          line: NASA Goddard found that the native In2O3 crust on indium blocks electrical contact unless it is removed, for example by plasma cleaning just before bonding.
    - title: Handling and storage
      points:
        - label: Fire
          line: For powder, PubChem calls for no open flames, no sparks, a closed system and dust-explosion-proof equipment. Its fire guidance warns against water on metal powder fires (ERG Guide 170).
        - label: Surfaces
          line: Clean the metal just before it is joined, because the oxide returns when a reduced surface is exposed to air again.
        - label: Outdoors
          line: 'The supplier marks the indium-tin foil ''For Use Outdoors: No''.'
  why: Indium-tin solder (In52Sn48) and indium-silver solder (In97Ag3) are low-melting alloys of indium. The eutectic melts at about 118 degC, and In97Ag3 melts at 143 degC. Both are soft and low in strength, and they are chosen for joints and seals where a low melting point or a soft, leak-tight metal matters more than strength. NASA used an indium/silver alloy seal for cryogenic joints down to 1.6 K as a ground test.
  uses:
    - where: Solders and thermal interface foils in electronics
      line: McMaster-Carr sells In52Sn48 as solder wire and ribbon, and as a thermal interface foil. The In97Ag3 solder is sold as wire with a melting point of 143 degC.
    - where: Demountable cryogenic seals (ground test)
      line: NASA Ames tested a flat indium/silver seal in a stainless steel guard. It showed no detectable leak at 4.2 K and 1.6 K after repeated mount and demount cycles. The test was on the ground, not in flight.
  can_do:
    - label: Melt low
      value: 118 degC
      benchmark: melting_point
      line: The indium-tin eutectic melts at about 118 degC (SA Materials rod page). In97Ag3 melts at 143 degC from two suppliers.
    - label: Conduct heat
      value: 34 W/m·K
      benchmark: thermal_conductivity
      line: The In/Sn rod has a thermal conductivity of 34 W/m·K (SA Materials). The page does not print the composition, so this is not assigned to In52Sn48 alone.
    - label: Hold a joint
      value: 12 MPa
      benchmark: ultimate_tensile_strength
      line: The In/Sn rod has a tensile strength of 12 MPa (SA Materials). No strength value is printed for In97Ag3.
  compare: Indium-tin and indium-silver solders are soft, low-melting alloys. The only density and conductivity values in this profile come from one In/Sn rod page, and the sources give no strength or thermal figures for In97Ag3. The sources do not allow a ranking against other metals.
  compare_rows:
    - label: Melting point
      benchmark: melting_point
    - label: Thermal conductivity
      benchmark: thermal_conductivity
    - label: Density
      benchmark: density
  handling:
    - Use dust control for powder and keep ignition sources away, because PubChem records an explosive dust hazard for indium.
    - Clean the surface just before soldering or sealing, because the oxide returns in air.
    - Use an RMA or RA flux with the In97Ag3 wire, as the seller prints.
    - Do not use the indium-tin foil outdoors, as the supplier states.
  good_for:
    - 'Low melting point: the In/Sn rod melts at 118 degC and In97Ag3 at 143 degC.'
    - 'Cryogenic seals: NASA Ames leak-tested an indium/silver seal at 4.2 K and 1.6 K (ground test).'
  watch_out:
    - 'Low strength: about 12 MPa for the In/Sn rod, and no strength value for In97Ag3.'
    - 'Oxide film: the In2O3 crust in air blocks electrical contact unless it is removed before bonding (NASA Goddard, pure indium).'
    - 'Indium supply: China produces about 70 % of refinery output (USGS).'
    - No flight, vacuum or outgassing data were found for either alloy.
  verdict: Indium-tin and indium-silver solders are soft, low-melting alloys with good thermal conductivity for their softness. Their weak points are low strength, an oxide film in air, and a supply chain concentrated in China. The sources cover ground use and supplier data only, so the profile does not describe their behavior in space.