spore: profile
id: gold-tin
spore_version: 0.2
family: precious-metals
name: Gold-tin eutectic solder (Au80Sn20)
abbreviation: AuSn
role: eutectic high-temperature solder for hermetic seals and die attach
category: metals
type: precious-metals
summary: |
  Au80Sn20 is a eutectic solder of 80% gold and 20% tin by weight. It melts sharply at 280 °C. Supplier datasheets print a thermal conductivity of 57 W/mK, a coefficient of thermal expansion of 16 ppm/°C at 20 °C, a tensile strength of 275 MPa and a Young's modulus of 68 GPa. The alloy is very hard and brittle, and the tin-rich AuSn4 phase is linked to joint embrittlement.
best_for: Hermetic lid seals and die attach where a sharp, high melting point and fluxless soldering matter more than ductility (the supplier calls the alloy resistant to corrosion and oxidation)
weakest_at: 'Brittleness: the alloy is very hard and brittle, thin forms and fine wire are hard to produce, and AuSn4 growth on gold or nickel finishes can embrittle joints'
identity:
  formula: 'Au80Sn20: 80% gold and 20% tin by weight (eutectic at 29 at.% Sn); a two-phase alloy of Au5Sn and AuSn'
  source: goodfellow-material
  where: Au80/Sn20 material information page (composition by weight, eutectic, Au5Sn and AuSn phases); eutectic 29 at.% Sn from the introduction of the Chromik et al. 2005 paper
tags:
  environments: []
  stresses:
    - thermal-cycling
  applications:
    - electronics-and-chips
    - optics-and-cameras
properties:
  - benchmark: melting_point
    label: Melting point, eutectic (80Au/20Sn)
    value: 280
    unit: °C
    scope: material
    conditions:
      composition: 80% Au, 20% Sn by weight
      basis: solidus and liquidus both printed as 280 °C
    method: Value printed in a supplier alloy properties table (solidus and liquidus)
    status: ground
    source: indium-brochure
    where: Gold Eutectic Alloys table, Indalloy Properties, Solidus and Liquidus rows, Au20Sn column
  - benchmark: melting_point
    label: Melting range across 75 to 82% gold
    value: 280
    value_high: 320
    bound: range
    unit: °C
    scope: material
    conditions:
      composition: 75 to 82% gold by weight, as stated for the plated alloy family
    method: Range printed in a plating supplier data sheet
    status: ground
    source: technic-ausn
    where: Page 1, paragraph after the process description (alloy range and melting point 280 to 320 °C)
  - benchmark: melting_point
    label: Liquidus, 80 Au 20 Sn column of comparison table
    value: 300
    unit: °C
    scope: material
    conditions:
      composition: 80% Au, 20% Sn by weight
    method: Value printed in a comparison table on a plating supplier data sheet
    status: ground
    note: The same sheet's comparison table prints 300 for the liquidus; two other sources print 280 for this alloy, so 300 is a figure specific to that sheet.
    source: technic-ausn
    where: Comparison table, row Liquidus Temperature (°C), column 80 Au 20 Sn
  - benchmark: density
    label: Specific gravity (printed as SG)
    value: 14.7
    unit: '-'
    scope: material
    conditions:
      composition: 80Au/20Sn
      basis: printed as SG in a comparison table; temperature not stated
    method: Specific gravity printed in a supplier comparison table (no density unit printed)
    status: ground
    source: indium-blog
    where: Comparison table, row SG, 80Au/20Sn column
  - benchmark: thermal_conductivity
    label: Thermal conductivity at 23 °C
    value: 57
    unit: W/mK
    scope: material
    conditions:
      temperature: 23 °C
      composition: Au 80 / Sn 20
    method: Value printed on a supplier product page (printed as W m-1 K-1)
    status: ground
    source: goodfellow-rod
    where: Thermal Properties table, row Thermal conductivity, entry 57 at 23 °C
  - benchmark: thermal_conductivity
    label: Thermal conductivity (no temperature printed)
    value: 57
    unit: W/mK
    scope: material
    conditions:
      temperature: not stated
      composition: 80 Au / 20 Sn
    method: Value printed in a supplier alloy properties table
    status: ground
    source: indium-brochure
    where: Gold Eutectic Alloys table, Thermal Conductivity (W/mK) row, Au20Sn column
  - benchmark: cte
    label: Coefficient of thermal expansion at 20 °C
    value: 16
    unit: ppm/°C
    scope: material
    conditions:
      temperature: 20 °C
      composition: 80% Au, 20% Sn
    method: Value printed in a plating supplier data sheet comparison table
    status: ground
    source: technic-ausn
    where: Comparison table, row CTE @20 °C (PPM/°C), column 80 Au 20 Sn
  - benchmark: cte
    label: Coefficient of thermal expansion, 20 to 100 °C
    value: 16
    unit: ppm/°C
    scope: material
    conditions:
      temperature_range: 20 to 100 °C
      composition: Au 80 / Sn 20
    method: Value printed as x10-6 K-1 on a supplier product page; same number as ppm/°C
    status: ground
    source: goodfellow-rod
    where: Thermal Properties table, row Coefficient of thermal expansion, entry 16 at 20 to 100 °C
  - benchmark: ultimate_tensile_strength
    label: Tensile strength
    value: 275
    unit: MPa
    scope: material
    conditions:
      composition: 80% Au, 20% Sn
      form: not stated
      temper: not stated
    method: Value printed in a plating supplier data sheet comparison table
    status: ground
    source: technic-ausn
    where: Comparison table, row Tensile Strength (MPa), column 80 Au 20 Sn
  - benchmark: ultimate_tensile_strength
    label: Tensile strength range
    value: 270
    value_high: 280
    bound: range
    unit: MPa
    scope: material
    conditions:
      composition: Au 80 / Sn 20
      form: not stated
    method: Range printed on a supplier product page
    status: ground
    source: goodfellow-rod
    where: Mechanical Properties table, row Tensile strength (MPa), entry 270 to 280
  - benchmark: shear_strength
    label: Shear strength
    value: 275
    unit: MPa
    scope: material
    conditions:
      composition: 80% Au, 20% Sn
      form: not stated
    method: Value printed in a plating supplier data sheet comparison table; shear_strength is not a canonical name in property-canon.yaml
    status: ground
    source: technic-ausn
    where: Comparison table, row Shear Strength (MPa), column 80 Au 20 Sn
  - benchmark: elastic_modulus
    label: Young's modulus
    value: 68
    unit: GPa
    scope: material
    conditions:
      composition: 80% Au, 20% Sn
      test: not stated
    method: Value printed in a plating supplier data sheet comparison table
    status: ground
    source: technic-ausn
    where: Comparison table, row Young's modulus (GPa), column 80 Au 20 Sn
  - benchmark: elastic_modulus
    label: Indentation modulus, eutectic phase mix (Au5Sn plus AuSn)
    value: 88
    unit: GPa
    scope: material
    conditions:
      composition: eutectic, 29 at.% Sn
      test: nanoindentation, indentation modulus (not a tensile test)
      uncertainty: plus or minus 6 GPa as printed
    method: Nanoindentation measurement in a peer-reviewed paper, Table I
    status: ground
    source: chromik2005
    where: Table I, row Eutectic (zeta-prime plus delta), indentation modulus column (88 plus or minus 6 GPa, 6 data points)
  - benchmark: indentation_hardness
    label: Hardness, eutectic phase mix
    value: 1.3
    unit: GPa
    scope: material
    conditions:
      composition: eutectic, 29 at.% Sn
      test: nanoindentation, hardness from the projected contact area
      uncertainty: plus or minus 0.2 GPa as printed
    method: Nanoindentation measurement in a peer-reviewed paper, Table I
    status: ground
    note: indentation_hardness is not a canonical name in property-canon.yaml; it is listed in gaps for review.
    source: chromik2005
    where: Table I, row Eutectic (zeta-prime plus delta), hardness column (1.3 plus or minus 0.2 GPa)
corrosion:
  - environment: Ambient air and reflow (supplier statement, no test conditions printed)
    headline: Suppliers describe the alloy as corrosion-resistant and low in oxide at reflow; no measured test data were found.
    effect: The Indium brochure lists resistance to corrosion and resistance to oxidation among the advantages of gold-based solders, and lists fluxless soldering among its uses. The Goodfellow page says the alloy gives minimal oxidation during reflow soldering. Neither source gives a test, an environment or a duration, so these are vendor statements rather than measured corrosion rates.
    rating: low
    conditions:
      basis: vendor statement; no environment, humidity, temperature or duration printed
      composition: 80Au/20Sn
    source: indium-brochure
    where: Gold Solder Alloys brochure, Additional advantages list (resistance to corrosion, resistance to oxidation) and the Fluxless soldering entry
risks:
  hazards:
    - text: No hazard classification, toxicity data, dust or fume warning and no SDS link is printed on the supplier's Au80/Sn20 material page. No SDS for this alloy was read in this run.
      ghs: []
      source: goodfellow-material
      where: Au80/Sn20 material information page, full text reviewed for hazard, handling and storage content
  failure_risks:
    - mode: Embrittlement from AuSn4 or (Au,Ni)Sn4 growth
      trigger: Solder on gold or gold/nickel finishes, especially with solid-state aging (the cited study examined Pb-Sn solder)
      consequence: In the cited study, growth of the tin-rich (Au,Ni)Sn4 phase was correlated with lower joint strength and brittle failures, even for sub-micron gold coatings.
      severity: moderate
      source: chromik2005
      where: Introduction, paragraph on embrittlement and the work of Zribi et al.
    - mode: Brittle failure when forming thin parts
      trigger: Forming thin forms or fine wire from the alloy
      consequence: The supplier says the alloy is very hard and brittle, which made thin forms and fine wire difficult to produce.
      severity: low
      source: indium-blog-eutectic
      where: Body text, paragraph on the alloy's mechanical behaviour
    - mode: Seam seal wetting shortfall
      trigger: 80Au-20Sn seam seals on hermetic packages where voiding or wetting limits are relaxed
      consequence: A NASA working group report records a dispute over voiding and wetting limits for 80Au-20Sn seam seals. A Sandia specialist advised against relaxing the specification and cited an AWS wetted-area criterion of 70%.
      severity: moderate
      source: nasa-nepp-2019
      where: Accomplishments slide, page 14 (seal wetting discussion)
  side_effects:
    - text: Electroplating with the Elevate AuSn 8020 chemistry uses a cyanide-based bath, which carries chemical hazards of its own. The solid alloy does not share them.
      affects: Plating line operators and waste handling
      source: technic-ausn
      where: Introduction paragraph, Elevate AuSn 8020 is a one-step cyanide-based process
  handling:
    - text: The supplier shows excellent reflow for the electroplated deposit between 280 °C and 320 °C.
      source: technic-ausn
      where: Reflow figure caption, Excellent reflow achieved between 280 °C and 320 °C
    - text: The Goodfellow page's only handling content concerns processing, such as annealing to improve ductility for stamping.
      source: goodfellow-material
      where: Au80/Sn20 material information page, processing notes
  mitigations:
    - text: The supplier shows reflow images with and without a gold cap layer of about 100 nm on an electroplated AuSn deposit.
      source: technic-ausn
      where: Reflow images, labelled Without Au Cap Layer and With Au Cap Layer (~100nm)
uses:
  - application: electronics-and-chips
    device: Hermetic seam-sealed packages (80Au-20Sn seam seals on lids)
    example: A NASA working group update discusses 80Au-20Sn seam seals on hermetic packages and the voiding and wetting limits applied to them. The report is a programme update, not a flight or qualification record.
    source: nasa-nepp-2019
    where: Accomplishments slide, page 14
  - application: electronics-and-chips
    device: Laser diode bars (high-power die attach)
    example: Technic shows a 2.2 micron electroplated AuSn deposit on a laser diode bar, with a gold flash layer, for high-power applications that need long-term reliability.
    source: technic-ausn
    where: Page 1 text and figure caption 2.2 microns AuSn on laser diode bar with gold flash plated
  - application: optics-and-cameras
    device: Optoelectronic first-attach solder
    example: A research paper says the eutectic Au-Sn solder, developed as a high-temperature first attach, is popular for optoelectronics applications where dimensional stability matters.
    source: chromik2005
    where: Introduction, first paragraph
supply:
  - subject: Gold
    producers:
      - country: China
        share_percent: 11.5
        year: 2025
      - country: Russia
        share_percent: 9.4
        year: 2025
      - country: Australia
        share_percent: 8.5
        year: 2025
      - country: Canada
        share_percent: 6.1
        year: 2025
      - country: United States
        share_percent: 4.8
        year: 2025
    critical_lists:
      - list: USGS 2025 List of Critical Minerals
        listed: false
    recycling: 'United States: about 90 tons of new and old scrap was recycled in 2025, about 60% of reported consumption (USGS domestic figure).'
    substitutes:
      - 'USGS: base metals clad with gold alloys economize on gold in electrical and electronic products; palladium, platinum and silver may substitute for gold.'
    source: usgs-mcs2026-gold
    where: World Mine Production table, 2025e (world total 3,300 t; shares calculated by Space Mushroom as country tonnes over 3,300 t); Recycling and Substitutes sections; list status from the USGS 2025 list page
  - subject: Tin
    producers:
      - country: China
        share_percent: 24.5
        year: 2025
      - country: Indonesia
        share_percent: 21
        year: 2025
      - country: Peru
        share_percent: 11.4
        year: 2025
      - country: Brazil
        share_percent: 9.7
        year: 2025
      - country: Congo (Kinshasa)
        share_percent: 9.3
        year: 2025
    critical_lists:
      - list: USGS 2025 List of Critical Minerals
        listed: true
    recycling: 'United States: about 17,000 tons of old and new scrap was recycled in 2025, 22% of apparent consumption.'
    substitutes:
      - 'USGS: epoxy resins are a substitute for tin in solder.'
    source: usgs-mcs2026-tin
    where: World Mine Production table, 2025e (world total 290,000 t; shares calculated by Space Mushroom as country tonnes over 290,000 t); Recycling section; Substitutes section
media: []
documents:
  - title: 'Technic: Elevate AuSn 8020, eutectic gold-tin alloy (data sheet)'
    type: datasheet
    url: https://www.technic.com/sites/default/files/resources/Elevate%20AuSn%208020.pdf
  - title: 'Indium Corporation: Gold Solder Alloys brochure (Indalloy properties)'
    type: datasheet
    url: https://scp.indium.com/download-files/gold_solder_alloys_98707_a4_r1
  - title: Chromik et al., Mechanical properties of intermetallic compounds in the Au-Sn system, J. Mater. Res. 20 (2005)
    type: paper
    url: https://bdt.semi.ac.cn/download/0.45868489420305025.PDF
    year: 2005
  - title: NASA NEPP government working group update, 2019 Electronics Technology Workshop
    type: report
    url: https://ntrs.nasa.gov/api/citations/20190027444/downloads/20190027444.pdf
    year: 2019
  - title: 'USGS Mineral Commodity Summaries 2026: Gold'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-gold.pdf
    year: 2026
  - title: 'USGS Mineral Commodity Summaries 2026: Tin'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-tin.pdf
    year: 2026
gaps:
  - No SDS or GHS classification was read for the Au80Sn20 alloy. The supplier material page has no hazard data and no SDS for this alloy turned up in search.
  - Density is a specific-gravity figure (14.7) from a supplier comparison table. A 14.51 g/cm3 figure printed on a Chip Quik datasheet hosted by Mouser could not be downloaded in this run.
  - 'Electrical resistivity is not recorded: the Technic table prints its unit garbled, and the Indium blog gives a value labelled as conductivity with an ohm-metre unit.'
  - Specific heat, elongation and yield strength were not found in any source opened in this run.
  - No Materion or other manufacturer datasheet for AuSn was found. The Knowles pre-deposited solder page redirected to the homepage and was not read.
  - No space qualification, flight, vacuum outgassing or radiation result for this alloy was found. The NASA report is a working group update on seal wetting, not a qualification test.
  - No UNS, EN, ASTM or AMS designation for the alloy was printed by any source read in this run. The Indium brochure uses the trade name Indalloy only.
  - Hardness and shear strength are not confirmed canonical names in property-canon.yaml; indentation_hardness and shear_strength need canon review.
  - Corrosion and oxidation resistance are supplier statements only. No measured corrosion or oxidation rate for Au80Sn20 was found.
  - The EU critical raw materials list was not checked for gold or tin.
  - Gold-germanium (Au88Ge12) is not profiled in this file; it needs its own profile.
  - The Mouser datasheet and two Indium PDFs (documents docid 640 and 2097) could not be downloaded in this run.
  - A 1998 oxidation and reduction kinetics paper on AuSn (Kuhmann et al.) was found only as a search snippet and is not cited.
sources:
  goodfellow-rod:
    title: Gold-Tin Alloy Rod, Au80-Sn20 (Goodfellow product group)
    id: Goodfellow product group, Au80-Sn20 rod
    url: https://www.goodfellow.com/usa/gold-tin-alloy-rod-au80-sn20-group
    kind: web
    license: supplier web page, linked not reproduced
  goodfellow-material:
    title: Gold/Tin Au80/Sn20 Material Information (Goodfellow)
    id: Goodfellow resources page
    url: https://www.goodfellow.com/usa/resources/gold-tin-au80-sn20-material-information/
    kind: web
    license: supplier web page, linked not reproduced
  indium-blog:
    title: '80Au20Sn: Superior Physical Properties (Indium Corporation blog)'
    url: https://www.indium.com/blog/80au20sn-superior-physical-properties/
    kind: web
    license: supplier web page, linked not reproduced
  indium-blog-eutectic:
    title: Eutectic Gold-Tin (AuSn) (Indium Corporation blog)
    url: https://www.indium.com/blog/eutectic-gold-tin-ausn/
    kind: web
    license: supplier web page, linked not reproduced
  indium-brochure:
    title: Gold Solder Alloys, Indalloy properties (Indium Corporation brochure, document 98707 A4 R1)
    url: https://scp.indium.com/download-files/gold_solder_alloys_98707_a4_r1
    kind: datasheet
    license: supplier document, linked not reproduced
  technic-ausn:
    title: Elevate AuSn 8020, Eutectic Gold-Tin Alloy (Technic data sheet)
    url: https://www.technic.com/sites/default/files/resources/Elevate%20AuSn%208020.pdf
    kind: datasheet
    license: supplier document, linked not reproduced
  chromik2005:
    title: Mechanical properties of intermetallic compounds in the Au-Sn system (Chromik et al.)
    id: J. Mater. Res. 20(8), August 2005
    url: https://bdt.semi.ac.cn/download/0.45868489420305025.PDF
    year: 2005
    kind: paper
    license: not checked
  nasa-nepp-2019:
    title: NEPP Program Task 19-294, Government Working Group Update (NASA MSFC, 2019 Electronics Technology Workshop)
    id: NASA NTRS 20190027444
    url: https://ntrs.nasa.gov/api/citations/20190027444/downloads/20190027444.pdf
    year: 2019
    kind: report
    license: public domain (NASA)
  usgs-mcs2026-gold:
    title: Mineral Commodity Summaries 2026, Gold
    id: USGS MCS 2026, February 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-gold.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  usgs-mcs2026-tin:
    title: Mineral Commodity Summaries 2026, Tin
    id: USGS MCS 2026, February 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-tin.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  usgs-crit2025:
    title: About the 2025 List of Critical Minerals (USGS)
    url: https://www.usgs.gov/programs/mineral-resources-program/science/about-2025-list-critical-minerals
    year: 2025
    kind: web
    license: public domain (USGS)
license: CC-BY-4.0
updated: '2026-10-26'
review:
  status: draft
  method: assistant
  checked_values: 14
  unreachable: 3
  caveats: 3
  note: 'Written by an AI assistant on 2026-10-26 from pages and PDFs read in that session: 14 property values across 11 sources. Not yet run through verify-values. Mouser datasheet, Knowles page and two Indium PDFs could not be opened.'
story:
  recipe:
    line: Au80Sn20 is 80% gold and 20% tin by weight. The eutectic composition is 29 atomic percent tin. The alloy solidifies into two intermetallic phases, Au5Sn and AuSn. Indium casts the alloy with a process designed to keep impurities and oxides low. Technic deposits a gold-tin alloy of 75 to 82% gold from a one-step cyanide-based plating bath.
    parts:
      - name: Gold
        symbol: Au
        share_percent: 80
        role: Main constituent by weight. Suppliers credit the gold content with corrosion resistance and low oxide formation.
      - name: Tin
        symbol: Sn
        share_percent: 20
        role: Second constituent by weight. With gold it forms the Au5Sn and AuSn phases and gives the sharp 280 °C eutectic melting point.
  risk_groups:
    - title: For people
      level: 0
      verdict: No hazard data found; no SDS read
      lead: The solid alloy is a gold and tin metal. The supplier pages reviewed carry no hazard classification, and no SDS for this alloy was read in this run.
      points:
        - label: The solid alloy
          line: The Goodfellow material page gives no hazard, toxicity, dust or fume warning and no SDS link. Treat the alloy as unclassified until a supplier SDS says otherwise.
        - label: The plating bath
          line: The Technic plating chemistry is a cyanide-based bath. Its hazards belong to the plating line and waste handling, not to the finished solid.
    - title: If a joint fails in service
      lead: The failure concerns in the sources are about joint structure rather than toxicity.
      points:
        - label: Brittle joints
          line: In the cited study, growth of AuSn4 or (Au,Ni)Sn4 on gold or nickel finishes was correlated with lower joint strength and brittle failures.
        - label: Seal wetting
          line: A NASA working group report records a dispute over voiding and wetting limits for 80Au-20Sn seam seals. It cites an AWS wetted-area criterion of 70%.
    - title: Processing temperature
      lead: Reflow needs a high temperature, so the parts being joined must tolerate it.
      points:
        - label: Reflow window
          line: The supplier shows excellent reflow between 280 °C and 320 °C for the electroplated deposit. Components and substrates must survive that temperature.
  why: 'Au80Sn20 is the gold-tin eutectic, a solder chosen when a joint must hold a high, sharp melting point and resist oxidation. Its melting point of 280 °C is high for a solder, and the suppliers describe it as strong, stiff and thermally conductive. The price is brittleness: the alloy is very hard, and its tin-rich intermetallics can embrittle joints.'
  uses:
    - where: Hermetic lids and seams
      line: Indium lists hermetic sealing, package sealing and aerospace and defense packaging among its gold solder uses. A NASA working group update discusses 80Au-20Sn seam seals on hermetic packages. It is the only space-related source found for this alloy, and it is a programme update rather than a flight record.
    - where: Laser and optoelectronic die attach
      line: Technic shows an electroplated AuSn deposit on a laser diode bar for high-power parts. A research paper says the eutectic is popular for optoelectronics where dimensional stability matters.
  can_do:
    - label: Melting point
      benchmark: melting_point
      value: 280 °C
      line: The alloy melts sharply at 280 °C, with solidus and liquidus both printed at 280 °C. A supplier sheet gives a 280 to 320 °C reflow window.
    - label: Stiffness
      benchmark: elastic_modulus
      value: 68 GPa
      line: Technic prints a Young's modulus of 68 GPa. A research paper's nanoindentation of the eutectic phase mix gives 88 GPa with a plus or minus 6 GPa spread, measured by a different method.
    - label: Strength
      benchmark: ultimate_tensile_strength
      value: 275 MPa
      line: The tensile strength is 275 MPa on the Technic sheet and 270 to 280 MPa on the Goodfellow page.
    - label: Heat flow
      benchmark: thermal_conductivity
      value: 57 W/mK
      line: Three suppliers print 57 W/mK. That is above the tin-silver, tin-lead and bismuth-tin solders in the Indium comparison table.
  compare: Against the solders in the Indium brochure table (tin-silver, tin-lead and bismuth-tin), the gold-tin alloy has the highest melting point, the highest thermal conductivity and the highest tensile strength claimed. Its trade-off is stiffness and brittleness rather than heat resistance. The Technic sheet notes that its high Young's modulus lets the alloy be deposited much thinner than indium while staying flat over a large area.
  compare_rows:
    - label: Melting point
      benchmark: melting_point
    - label: Tensile strength
      benchmark: ultimate_tensile_strength
    - label: Thermal conductivity
      benchmark: thermal_conductivity
  handling:
    - Treat the plating bath as cyanide chemistry, with the controls that requires. The solid alloy has no hazard classification in any source read.
    - Reflow in the 280 to 320 °C window the supplier shows.
    - Ask the supplier for an SDS and a certificate of analysis before use. The Indium brochure says a certificate of analysis is provided for each lot.
    - Anneal before stamping if the form must be shaped. The Goodfellow page recommends annealing to improve ductility for stamping.
  good_for:
    - Hard, high-melting seals that must stay joined above 280 °C. Indium lists hermetic sealing and package sealing as uses.
    - Thermal conduction. At 57 W/mK it is above the tin-silver, tin-lead and bismuth-tin solders in the Indium comparison table.
    - Flux-free processing. The Indium brochure lists fluxless soldering among its uses.
  watch_out:
    - Brittleness. The alloy is very hard and brittle, and thin forms or fine wire are difficult to produce.
    - Tin-rich intermetallics. AuSn4 growth at gold or nickel finishes is correlated with embrittlement in the cited study.
    - Seal wetting. The NASA working group report records a dispute over voiding and wetting limits on seam seals.
    - Unverified hazard data. No SDS was read for this alloy.
  verdict: Au80Sn20 is a high-temperature, fluxless option for sealed and bonded parts. Its strength and conductivity are strong for a solder, but its brittleness and tin-rich intermetallics need careful process control, and no hazard sheet was checked.