spore: profile id: aluminium-gold spore_version: 0.2 family: aluminium-alloys name: Gold-aluminium intermetallics and bonding abbreviation: Au-Al IMCs role: intermetallic phases that form where gold wire or gold foil meets aluminium metallization in wire bonds and thermocompression joints category: metals type: aluminium summary: | When gold meets aluminium in a bonded joint the two metals react and form intermetallic phases. The main ones are AuAl2, called purple plague, and Au2Al, with Au5Al2 and Au8Al3 also named in the sources. A patent reports that Au2Al forms at about 100 degC during heat treatment and converts to AuAl2 at about 230 degC when the aluminium layer is thicker than the gold. A 2025 Korean study of 15.3 µm gold wire on 1 µm and 5 µm aluminium pads, annealed at 175 degC, found voids after 250 hours and stable bonds up to 1,000 hours on the thinner pads. The reaction is a known reliability limit of gold-to-aluminium bonds. best_for: Gold-to-aluminium bonds on chips that are kept cool and free of halide contamination, where the joint must carry current for a long time at moderate temperatures (KJMM 2025 and the background of US patent 5184206) weakest_at: Long exposure above about 175 degC, which grows voids in the joint; the sources read here give no melting point, density, hardness or strength for the phases identity: formula: AuAl2 (purple plague, about 78.5% Au and 21.5% Al by mass); Au2Al (about 93% Au and 7% Al by mass); Au5Al2 (about 95% Au and 5% Al by mass); Au8Al3 and Au4Al also named as phases in the bonded joint source: wiki-au-al where: Lead and Properties sections, composition by mass for AuAl2, Au2Al and Au5Al2; Au8Al3 and Au4Al named in the Xu et al. 2011 abstract (Intermetallics), which is a different source tags: environments: [] stresses: - extreme-heat applications: - electronics-and-chips properties: - benchmark: gold_mass_percent label: Gold content of AuAl2 (purple plague), by mass value: 78.5 unit: '%' scope: material conditions: basis: mass fraction of gold, as printed as about 78.5% Au and 21.5% Al phase: AuAl2 method: Composition printed in an encyclopedia article; stated as about status: ground source: wiki-au-al where: Properties section, AuAl2 composition - benchmark: gold_mass_percent label: Gold content of Au2Al, by mass value: 93 unit: '%' scope: material conditions: basis: mass fraction of gold, as printed as 93% Au and 7% Al phase: Au2Al method: Composition printed in an encyclopedia article status: ground source: wiki-au-al where: Properties section, Au2Al composition - benchmark: gold_mass_percent label: Gold content of Au5Al2, by mass value: 95 unit: '%' scope: material conditions: basis: mass fraction of gold, as printed as typically 95% Au and 5% Al phase: Au5Al2 method: Composition printed in an encyclopedia article; the source says the phase typically forms at this composition status: ground source: wiki-au-al where: Lead, Au5Al2 composition sentence - benchmark: formation_temperature label: Au2Al first forms in a gold-aluminium bond during heat treatment value: 100 unit: degC scope: material conditions: basis: first interaction of gold and aluminium layers; the patent calls it heat treatment at about 100 degC phase: Au2Al method: Value stated in the background section of a US patent on thermocompression bonding of thin power chips; no measured data set status: ground note: The patent gives a single temperature, not a rate or time. source: us5184206 where: Description, Background Information - benchmark: formation_temperature label: Au2Al converts to AuAl2 when the aluminium layer is thicker than the gold value: 230 unit: degC scope: material conditions: basis: heating with the aluminium stratum thicker than the gold stratum from: Au2Al to: AuAl2 method: Value stated in the background section of the same patent status: ground source: us5184206 where: Description, Background Information - benchmark: corrosion_onset_temperature label: Halide-accelerated purple plague formation above this temperature value: 180 unit: degC bound: lower scope: material conditions: basis: corrosion induced by bromide, fluoride or chloride impurities at temperatures over 180 degC effect: accelerates purple plague formation and premature bond failure at the Au-Al interface method: Value stated in the background section of the same patent status: ground note: A patent background statement, not a test with a stated rate; iodide is not named in it. source: us5184206 where: Description, Background Information - benchmark: failure_temperature_long_exposure label: Chip contact likely to fail after long exposure above this temperature value: 200 unit: degC bound: lower scope: material conditions: basis: temperatures exceeding 200 degC for long periods; also cited together with halide presence method: Statement in the background section of the same patent; no test data status: ground note: Custom benchmark name because the canonical list has no failure temperature. The patent says the contact will probably fail; it gives no time. source: us5184206 where: Description, Background Information - benchmark: annealing_temperature label: Annealing range used to follow the phase change in Au-Al wire bonds value: 175 value_high: 250 bound: range unit: degC scope: material conditions: basis: annealing range printed in the abstract; HRTEM observation of the interface material: gold wire bonds on aluminium method: Range printed in the abstract of a 2011 paper on Au-Al wire bond phase transformations status: ground source: anu-intermetallics-2011 where: Abstract - benchmark: void_onset_time label: Voids at the bond interface, 15.3 µm gold wire on 1 µm aluminium pads value: 250 unit: h scope: cell conditions: temperature: 175 degC annealing wire: 15.3 µm gold pad: 1 µm aluminium atmosphere: not stated in the abstract method: Annealing test followed by cross-section; voids reported at the lateral sections status: ground note: Custom benchmark name. The abstract says voids began to form at the lateral sections after 250 hours. source: kjmm-2025 where: Abstract - benchmark: void_onset_time label: Voids beneath the bond, 2N gold wire on 5 µm aluminium pads value: 250 unit: h scope: cell conditions: temperature: 175 degC annealing wire: 2N gold pad: 5 µm aluminium note: as early as 250 hours method: Annealing test followed by cross-section; the abstract says significant voids were observed beneath the bond interface as early as 250 hours status: ground note: The source says as early as 250 hours, so this is the earliest reported time, not a typical value. source: kjmm-2025 where: Abstract, 5 µm pad result - benchmark: bond_stability_time label: Bond stayed stable on 1 µm aluminium pads up to the end of the test value: 1000 unit: h bound: lower scope: cell conditions: temperature: 175 degC annealing pad: 1 µm aluminium wire: 15.3 µm gold method: Annealing test ending at 1,000 hours with bonding still stable status: ground note: Custom benchmark name. This is the end of the test, not a failure time; the same paper reports voids earlier on 1 µm pads. source: kjmm-2025 where: Abstract corrosion: - environment: Halide impurities (bromide, fluoride, chloride) at the gold-aluminium interface above about 180 degC headline: Halides attack the interface and accelerate purple plague, which causes early bond failure. effect: The patent background says corrosion induced by these impurities at temperatures over 180 degC accelerates purple plague formation and gives premature bond failure at the Au-Al interface. Excess gold in conventional gold wire bonding means the reaction can continue, so purple plague may become critical. rating: severe conditions: basis: patent background statement; no test rate given impurities: bromide, fluoride, chloride source: us5184206 where: Description, Background Information - environment: Annealing at 175 degC with 1 µm and 5 µm aluminium pads headline: Kirkendall voids form at the interface within 250 hours at 175 degC. effect: The abstract reports voids at the lateral sections after 250 hours on 1 µm pads and significant voids beneath the bond interface as early as 250 hours on 5 µm pads with 2N wire. On 5 µm pads, AuAl2 grew into Au2Al in 2N wire, which the authors link to the voids. rating: moderate conditions: temperature: 175 degC atmosphere: not stated in the abstract wire: 15.3 µm gold, 2N and 4N grades source: kjmm-2025 where: Abstract risks: hazards: - text: 'Aluminium is a flammable solid and reacts with water to release flammable gas, according to the PubChem aggregate of ECHA notifications for the element (4079 company reports): H228 in 60.6% of hazard reports, H250 in 34.2% and H261 in 90.8%. The aggregate covers all forms, so check the supplier''s safety data sheet for the powder or foil you handle.' ghs: - H228 - H250 - H261 source: pubchem-aluminium where: Safety and Hazards, GHS Classification failure_risks: - mode: Kirkendall voiding at the gold-aluminium interface trigger: Annealing at 175 degC for 250 hours or more consequence: Voids reduce the bonded area; the abstract reports voids on 1 µm and 5 µm pads severity: high source: kjmm-2025 where: Abstract - mode: Halide-accelerated purple plague trigger: Bromide, fluoride or chloride impurities above 180 degC consequence: Premature bond failure at the Au-Al interface severity: critical source: us5184206 where: Description, Background Information - mode: Chip contact failure after long hot exposure trigger: Temperatures above 200 degC for long periods consequence: The patent says the chip contact will probably fail severity: high source: us5184206 where: Description, Background Information side_effects: - text: In the 2N wire on 5 µm pads, AuAl2 grew into Au2Al, and the abstract links this change to the voids that formed beneath the bond. affects: Bond interface of the joint source: kjmm-2025 where: Abstract handling: - text: The aluminium aggregate PubChem record lists H261, so keep aluminium powder or foil away from water and store it dry. source: pubchem-aluminium where: GHS Hazard Statements mitigations: - text: Keep halide contamination out of the bonding area; the patent ties halide attack to temperatures over 180 degC. source: us5184206 where: Description, Background Information uses: - application: electronics-and-chips device: Gold wire bonds to aluminium pads on integrated circuits example: The 2025 study bonded 15.3 µm gold wire to 1 µm and 5 µm aluminium pads and annealed the joints at 175 degC to watch the interface grow. source: kjmm-2025 where: Abstract - application: electronics-and-chips device: Thin electronic power chips joined by thermocompression bonding of gold foil to aluminium metallization example: The patent describes the Au2Al and AuAl2 sequence in these joints, with the aluminium layer thickness setting which phase ends the reaction. source: us5184206 where: Title and Description, Background Information supply: - subject: Gold abundance: Not read in this run 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 - list: EU critical raw materials list as printed on the Commission page listed: false recycling: 'USGS gold chapter: an estimated 90 tons of new and old scrap was recycled in 2025, about 60% of reported consumption.' substitutes: - 'USGS: base metals clad with gold alloys are widely used to economize on gold in electrical and electronic products; palladium, platinum and silver may substitute for gold.' source: usgs-gold-mcs2026 where: World Mine Production table, 2025e (shares calculated by Space Mushroom against the 3,300 t world total); Recycling; Substitutes - subject: Aluminium producers: - country: China share_percent: 60.8 year: 2025 - country: India share_percent: 5.7 year: 2025 - country: Russia share_percent: 5.3 year: 2025 - country: Canada share_percent: 4.5 year: 2025 - country: United Arab Emirates share_percent: 3.6 year: 2025 critical_lists: - list: USGS 2025 List of Critical Minerals (listed as Aluminum) listed: true - list: EU critical raw materials list as printed on the Commission page (bauxite entry; the page says aluminium and bauxite are merged) listed: true recycling: 'USGS aluminium chapter: aluminium recovered from old scrap was equivalent to about 28% of apparent consumption in the United States.' substitutes: - 'USGS: composites, magnesium, steel and titanium can substitute for aluminium in ground transport; copper can replace aluminium in electrical and heat-exchange applications.' source: usgs-aluminum-mcs2026 where: World Smelter Production table, 2025e (shares calculated by Space Mushroom against the 74,000 thousand t world total); Recycling; Substitutes; US net import reliance 60% documents: - title: Xu et al. 2011, Intermetallic phase transformations in Au-Al wire bonds (Intermetallics 19, 1808-1816) type: paper url: https://doi.org/10.1016/j.intermet.2011.07.003 year: 2011 - title: Korean Journal of Metals and Materials 63(12), 946-954, gold wire bonds on aluminium pads (2025) type: paper url: https://doi.org/10.3365/KJMM.2025.63.12.946 year: 2025 - 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, Aluminum type: report url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-aluminum.pdf year: 2026 - title: 'PubChem: Aluminum (CID 5359268), GHS classification summary' type: database url: https://pubchem.ncbi.nlm.nih.gov/compound/Aluminum year: 2026 gaps: - No density, melting point, electrical resistivity, hardness or elastic modulus for AuAl2, Au2Al or Au5Al2 was read in a fetched non-Wikipedia page. The melting points of 575 degC (Au5Al2) and 1,060 degC (AuAl2) appear on Wikipedia only, and the brief limits Wikipedia to composition and history, so they are not used. Springer phase-diagram papers (s13404-014-0140-2 and s13404-014-0146-9) redirected to a login page. - Thin-film Al/Au diffusion work (Xu, Sritharan and Mhaisalkar, Thin Solid Films 2007, activation energy 33.602 kJ/mol) was seen only in a search summary, not in a fetched page, so no value is used. Azadmanjiri et al. 2016 on sputtered Al/Au films (Springer redirect) was not readable. - 'Sputtering: no Al-Au binary sputtering target datasheet was found; the search returned only patents on multi-component gold targets, which report composition by weight and are not Al-Au binaries. No sputtering use is included.' - 'Space: no NASA or ESA source on gold-aluminium bond reliability was fetched; NTRS search hits were not opened.' - 'Gold hazard: PubChem gold GHS record was not retrieved (CID 79 and 23947 returned other compounds). No gold hazard entry is included.' - 'Humidity and atmospheric corrosion of Au-Al bonds: no source read. The corrosion section covers high temperature and halides only. The Tampere University thesis on halogen corrosion (trepo.tuni.fi) was blocked by an access check.' - Au5Al2 and Au8Al3 are named separately in different sources; equivalence of the two names was not read in a fetched page, so both names are kept as printed. - 'Custom benchmark names used: gold_mass_percent, formation_temperature, corrosion_onset_temperature, failure_temperature_long_exposure, annealing_temperature, void_onset_time, bond_stability_time. None is in spores/property-canon.yaml.' - 'Aluminium crustal abundance: not in the Table A1 rows read in PP 1802-A (aluminium, iron and phosphorus were not among the rows printed).' - No media files were added. sources: wiki-au-al: title: Gold–aluminium intermetallic (Wikipedia) id: Wikipedia article, composition and history only url: https://en.wikipedia.org/wiki/Gold%E2%80%93aluminium_intermetallic kind: web license: CC BY-SA 4.0 kjmm-2025: title: Gold wire bonds to aluminium pads, 15.3 µm wire, 1 µm and 5 µm pads, annealing at 175 degC (Korean Journal of Metals and Materials) id: doi:10.3365/KJMM.2025.63.12.946 (KJMM 63(12), pp. 946-954) url: https://doi.org/10.3365/KJMM.2025.63.12.946 kind: paper year: 2025 license: as published by KJMM anu-intermetallics-2011: title: Intermetallic phase transformations in Au-Al wire bonds (Intermetallics 19, 1808-1816) id: doi:10.1016/j.intermet.2011.07.003 url: https://researchportalplus.anu.edu.au/en/publications/intermetallic-phase-transformations-in-au-al-wire-bonds/ kind: paper year: 2011 license: ANU research portal record us5184206: title: US Patent 5184206, direct thermocompression bonding for thin electronic power chips (background section on purple plague) id: US 5184206 url: https://patents.google.com/patent/US5184206 kind: web license: patent document usgs-gold-mcs2026: title: Mineral Commodity Summaries 2026, Gold id: USGS MCS 2026, February 2026 url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-gold.pdf kind: report year: 2026 license: public domain (USGS) usgs-aluminum-mcs2026: title: Mineral Commodity Summaries 2026, Aluminum id: USGS MCS 2026, February 2026 url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-aluminum.pdf kind: report year: 2026 license: public domain (USGS) usgs-critical-2025: title: About the 2025 List of Critical Minerals (USGS, 60 minerals) id: 2025 List of Critical Minerals url: https://www.usgs.gov/programs/mineral-resources-program/science/about-2025-list-critical-minerals kind: web year: 2025 license: public domain (USGS) ec-crm: title: Critical raw materials (European Commission, Regulation (EU) 2024/1252) id: Regulation (EU) 2024/1252 url: https://single-market-economy.ec.europa.eu/sectors/raw-materials/areas-specific-interest/critical-raw-materials_en kind: web year: 2024 license: European Commission web page pubchem-aluminium: title: PubChem compound record, Aluminum (CID 5359268), GHS classification id: CID 5359268 url: https://pubchem.ncbi.nlm.nih.gov/compound/Aluminum kind: database year: 2026 license: public domain (NCBI) license: CC-BY-4.0 updated: '2026-10-26' review: status: draft method: assistant checked_values: 11 unreachable: 3 caveats: 4 note: Written by an AI assistant on 2026-10-26 from pages read in this run. 11 properties; 3 sources could not be opened (two Springer phase-diagram papers and the Tampere halogen thesis); the thin-film activation energy was only in a search summary and is not used. story: recipe: line: The bonded phases are intermetallics of gold and aluminium. AuAl2 is about 78.5% gold and 21.5% aluminium by mass; Au2Al is about 93% gold and 7% aluminium; Au5Al2 is about 95% gold and 5% aluminium. The phases grow from the two metal layers during heating, and a patent describes how the thickness of the aluminium layer sets which phase ends the reaction. parts: - name: Gold symbol: Au share_percent: 78.5 basis: mass, AuAl2 role: The gold wire or foil. The gold diffuses into the aluminium and forms the purple AuAl2 and the tan Au2Al phases. - name: Aluminium symbol: Al share_percent: 21.5 basis: mass, AuAl2 role: The aluminium pad or metal layer. Its thickness decides whether the reaction stops at Au2Al or runs to AuAl2 at about 230 degC. risk_groups: - title: For people level: 0 verdict: Aluminium powder is flammable lead: The intermetallic joint is a solid and is not a hazard in normal use. The metal feedstock is the concern, mainly as fine powder. points: - label: The aluminium feedstock line: The PubChem record for aluminium aggregates ECHA notifications and lists H228 (flammable solid), H250 (catches fire spontaneously if exposed to air) and H261 (releases flammable gas on contact with water), depending on the form. - label: The gold line: No gold hazard statement was retrieved in this run; check the supplier safety data sheet for the gold you handle. - title: If a joint overheats lead: These results come from laboratory tests and a patent background, not field failures. points: - label: Long annealing line: At 175 degC, a 2025 study saw voids in the joint after 250 hours on 1 µm aluminium pads and as early as 250 hours on 5 µm pads with 2N gold wire. - label: Halides line: The patent says halide impurities (bromide, fluoride, chloride) above 180 degC speed up purple plague and cause early bond failure. - label: Long hot exposure line: The patent says the chip contact will probably fail after long periods above 200 degC. why: Gold and aluminium react at a bonded joint and form several intermetallic phases. The reaction matters for electronics because gold wire bonds are made on aluminium pads on chips. The phases grow with time and temperature, and voids form where the metals diffuse unevenly, which can weaken the bond. uses: - where: Integrated circuits line: Gold wire bonds connect chips to packages by joining gold wire to aluminium pads. A 2025 study bonded 15.3 µm gold wire to aluminium pads of 1 µm and 5 µm and annealed the joints to track the interface. - where: Power chips line: A US patent on thermocompression bonding of thin electronic power chips describes gold foil joined to aluminium metallization, with the Au2Al and AuAl2 sequence set by the aluminium layer thickness. can_do: - label: Bond life at 175 degC benchmark: void_onset_time value: 250 h line: Voids appeared after 250 hours at 175 degC on the thinner pads in one 2025 study. On the same test, bonding stayed stable up to 1,000 hours on 1 µm pads. - label: Temperature threshold benchmark: corrosion_onset_temperature value: 180 degC line: A patent background says halide impurities accelerate purple plague above about 180 degC, which is the figure to keep bonds below when halides are possible. compare: The sources here are about the joint, not about the bulk metal. The patent names 100 degC for the first Au2Al formation and 230 degC for conversion to AuAl2 when the aluminium is thicker. The 2025 test saw voids at 175 degC within 250 hours. No source read in this run gives density, hardness or strength for the phases, so the table compares the reaction temperatures and times that were read. compare_rows: - label: First Au2Al formation benchmark: formation_temperature - label: Halide corrosion onset benchmark: corrosion_onset_temperature - label: Voids in a 175 degC anneal benchmark: void_onset_time handling: - Keep halide contamination out of the bonding area, since halides speed up the reaction above about 180 degC. - Keep aluminium powder dry and away from water; the aluminium record lists H261. - Limit long exposure above 175 degC if the joint must stay sound for years. good_for: - Gold wire bonds on aluminium pads that run cool and stay free of halides, where the joint only has to last a set time. - Thin power chips joined by thermocompression, where the aluminium layer thickness is controlled. watch_out: - Voids form within 250 hours at 175 degC in the 2025 study, so long hot storage is the main risk. - Halides at temperatures above about 180 degC cause early bond failure. - Sputtered Al-Au film data and phase melting points were not readable in this run, so this profile does not cover sputtering. verdict: The gold-aluminium joint is a known reliability limit. It works for moderate temperatures and clean bonds, and the time-at-temperature and halide data are the figures to design around.