{
  "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.\n",
  "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",
    "designations": [],
    "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,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "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)",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "melting_point",
      "label": "Liquidus, 80 Au 20 Sn column of comparison table",
      "value": 300,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "density",
      "label": "Specific gravity (printed as SG)",
      "value": 14.7,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "thermal_conductivity",
      "label": "Thermal conductivity at 23 °C",
      "value": 57,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "thermal_conductivity",
      "label": "Thermal conductivity (no temperature printed)",
      "value": 57,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "cte",
      "label": "Coefficient of thermal expansion at 20 °C",
      "value": 16,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "cte",
      "label": "Coefficient of thermal expansion, 20 to 100 °C",
      "value": 16,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "ultimate_tensile_strength",
      "label": "Tensile strength",
      "value": 275,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "shear_strength",
      "label": "Shear strength",
      "value": 275,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "elastic_modulus",
      "label": "Young's modulus",
      "value": 68,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "elastic_modulus",
      "label": "Indentation modulus, eutectic phase mix (Au5Sn plus AuSn)",
      "value": 88,
      "bound": "exact",
      "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)",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "indentation_hardness",
      "label": "Hardness, eutectic phase mix",
      "value": 1.3,
      "bound": "exact",
      "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)",
      "source_detail": {
        "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"
      }
    }
  ],
  "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."
  ],
  "story": {
    "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",
        "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.",
        "benchmark": "melting_point",
        "scope": "material",
        "value": "280 °C"
      },
      {
        "label": "Stiffness",
        "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.",
        "benchmark": "elastic_modulus",
        "scope": "material",
        "value": "68 GPa"
      },
      {
        "label": "Strength",
        "line": "The tensile strength is 275 MPa on the Technic sheet and 270 to 280 MPa on the Goodfellow page.",
        "benchmark": "ultimate_tensile_strength",
        "scope": "material",
        "value": "275 MPa"
      },
      {
        "label": "Heat flow",
        "line": "Three suppliers print 57 W/mK. That is above the tin-silver, tin-lead and bismuth-tin solders in the Indium comparison table.",
        "benchmark": "thermal_conductivity",
        "scope": "material",
        "value": "57 W/mK"
      }
    ],
    "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",
        "scope": "material"
      },
      {
        "label": "Tensile strength",
        "benchmark": "ultimate_tensile_strength",
        "scope": "material"
      },
      {
        "label": "Thermal conductivity",
        "benchmark": "thermal_conductivity",
        "scope": "material"
      }
    ],
    "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.",
    "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",
          "role": "Main constituent by weight. Suppliers credit the gold content with corrosion resistance and low oxide formation.",
          "share_percent": 80
        },
        {
          "name": "Tin",
          "symbol": "Sn",
          "role": "Second constituent by weight. With gold it forms the Au5Sn and AuSn phases and gives the sharp 280 °C eutectic melting point.",
          "share_percent": 20
        }
      ]
    },
    "risk_groups": [
      {
        "title": "For people",
        "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."
          }
        ],
        "level": 0,
        "verdict": "No hazard data found; no SDS read"
      },
      {
        "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."
          }
        ]
      }
    ]
  },
  "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."
  },
  "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",
  "url": "https://spacemushroom.com/profiles/gold-tin/"
}