Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
  • C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
  • C23C18/31—Coating with metals
  • C23C18/42—Coating with noble metals
  • C23C18/44—Coating with noble metals using reducing agents
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
  • H01L2924/0001—Technical content checked by a classifier
  • H01L2924/0002—Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00

Definitions

• the invention relates to a gold-electrolyte combination for electroless gold deposition and the use of this combination.
• Electroless gold baths for the production of gold layers is generally known (Goldie, gold as a surface, technical and decorative gold plating, Eugen G. Leuze Verlag, Saulgau, 1983, p. 91 ff.).
• Electroless gold baths containing the anion disulfitoaurate (I) are known from the publications DD-PS 150 762, DD-PS 240 915 or DD-PS 244 768.
• electroless gold baths containing potassium dicyanoaurate (I) are described in the documents DD-PS 273 651 or US Pat. No. 3,506,462. Gold plating difficulties arise when depositing on nickel surfaces. Either there is no deposition on nickel or nickel alloy surfaces (US Pat. No.
• Gold layers of 0.2 - 3.0 »m are required for chip or wire bonding.
• the electrolytes indicated for this with a high deposition rate are only stable to a limited extent (Rich, DW, Proc. Am. Electroplat. Soc. 1971, p. 58 and US Pat. No. 4,169,171).
• Alkaline soluble photoresists or varnishes are often used for selective coating tasks to cover surfaces that are not to be coated. It is therefore not possible to work in the alkaline range, in particular pH> 9 Gold electrolytes are used (Dettke, electroless coating, Eugen G. Leuze Verlag, 1988, pp. 74-78).
• DD-PS 263 307 also describes an electroless gold bath with a high deposition rate.
• the disadvantage of this bath is that a simultaneous cementation process takes place.
• the object of the present invention is therefore to achieve stable deposition of adhesive, bondable gold layers with layer thicknesses> 0.2 »m within short deposition times.
• the gold prebath electrolyte can contain disulfitoaurate (I) in the form of its ammonium or alkali salts.
• Suitable reducing agents for the gold prebath electrolyte are, for example, aldehyde and aldehyde-sulfite adducts.
• Formaldehyde (methanal) and the adduct formaldehyde / sodium sulfite are particularly suitable.
• a complexing agent for example ethylenediamine, can optionally be added to the prebath.
• dicyanoaurate (I) can also be used in the form of its ammonium or alkali salts become.
• Thiourea or its derivatives are added to the main bath as stabilizers; for example thiosemicarbazide.
• cobalt (II) salts are added to the electrolyte, for example cobalt (II) halides, cobalt (II) sulfate, cobalt (II) nitrate, cobalt (II) formate or Cobalt (II) acetate.
• a nickel salt for example a nickel halide, with particular advantage nickel (II) chloride, can be added to the main bath to increase the deposition rate.
• This pickling solution consists of a hydroxycarboxylic acid, for example tartaric acid or citric acid, or its salts and ammonium chloride.
• the invention further relates to the use of the gold-electrolyte combination for electroless gold deposition together with a decapitation solution and a starter solution.
• the decapitation solution is to be used if the nickel or nickel alloy surface present in the gold coating has a high level of cementation and there is an additional dissolution of the nickel layer by the acidic electrolyte solution.
• a gold prebath electrolyte that works in the neutral range up to a maximum of pH 8 and also contains an alkali or ammonium carboxylic acid and ammonium chloride ensures that gold layers are deposited firmly. An additional dissolution of the passive nickel layers (for example selective under the gold layers) does not occur.
• the dense layer deposited from the gold prebath electrolyte protects the nickel surface from the selective dissolution in the acidic gold main bath electrolyte.
• the acidic gold main bath electrolyte is additionally stabilized by the use of thiourea or its derivatives, whereby, with the stability remaining, an adapted concentration of nickel ions (nickel chloride) in the electrolyte accelerates the catalytic reduction reaction and thus achieves a deposition rate of 2 »m / h becomes.
• a starter solution in the case of gold plating of gold surfaces and / or gold-plated surfaces can accelerate the start reaction of the deposition of the gold layer deposited from the gold main bath electrolyte.
• the starter solution contains heavy metal ions, e.g. Ni2+ ions in an acidic environment, which are adsorbed on the gold surface and change the surface potential.
• the subject of the invention is particularly well suited for the deposition of gold layers on conductive ceramic chip carrier housings. These are metallized with chemical-reductive nickel-phosphor layers and gold (layer thickness: 2 - 3 »m) as an external contact layer system.
• the nickel-phosphorus layer was first treated with the following pickling solution for 30 seconds at room temperature: 10 g sodium citrate / liter 15 g ammonium chloride / liter.
• Gold prebath electrolyte 30 minutes treatment time, 60 ° C Gold as Na3 [Au (SO3) 2] 0.6 g / l Methanal 0.1 g / l Sodium citrate 10.0 g / l Na2SO3 5.0 g / l Ethylenediamine 0.84 g / l NH4Cl 15.0 g / l
• Gold main bath electrolyte 90 minutes treatment time, 82 - 84 ° C K [Au (CN) 2] 5.0 g / l Thiourea 24.8 g / l CoCl2. 6 H2O 20.0 g / l NiCl2. 6 H2O 10.0 g / l Ammonium dihydrogen citrate 20.0 g / l
• a miniature printed circuit board partially covered with alkali-soluble solid resist Riston 3615 should be selectively gold-plated on existing, chemically-reductively nickel-plated copper contact layer structures. Decapitation solution as in example 1.
• the gilding was then carried out using the following combination according to the invention: a) Gold prebath electrolyte: 15 minutes treatment time, 60 ° C, adjustment to pH 5.1 with citric acid Gold as (NH4) 3 [Au (SO3) 2] 1.0 g / l Methanal 0.15 g / l Sodium citrate 15.0 g / l Na2SO3 7.0 g / l Ethylenediamine 0.84 g / l NH4Cl 10.0 g / l b) Gold main bath electrolyte: 30 minutes treatment time, 82 - 84 ° C K [Au (CN) 2] 4.0 g / l Thiourea 20.0 g / l CoCl2.6
• the adhesive strength of the Ni x P y -Au layer system was 1300 N / cm2.
• Au wires (diameter 20 »m) bonded with the Thermosonic process showed tear strengths of 9.1 ⁇ 1.3 cN (pull test).
• the Au layers were reflow solderable (controlled with the PCB bending test).
• a stripline circuit on Al2O3 ceramic should be built up with the layer system Ni x P y -galvanic Cu - Ni x P y Au.
• the circuit structure including galvanic copper was first produced using lift-off technology. After the photoresist had been removed, the layer system Ni x P y -galvanic copper was coated with Ni x P y from an alkaline electrolyte and gold-plated with the combination according to the invention as follows: a) Gold prebath electrolyte: 30 minutes treatment time, 60 ° C analogous to Example 2, but with Gold as (NH4) 3 [Au (SO3) 2] 1.2 g / l Ammonium dihydrogen citrate 20.0 g / l (instead of sodium citrate) b) Starter solution for gold: 4 minutes treatment time, 82 - 84 ° C NiCl2.
• the adhesive strength of the layer system was 1800 +/- 100 N / cm2 (forehead pull test).
• Ni x P y structure was produced from an alkaline electrolyte on Al2O3 ceramic by laser metallization. This structure should be gold-plated for the production of wire bond islands.
• Gold prebath electrolyte 15 minutes treatment time, 60 ° C Gold as (NH4) 3 [Au (SO3) 2] 2.0 g / l Methanal 0.1 g / l Sodium citrate 10.0 g / l Na2SO3 5.0 g / l Ethylenediamine 0.84 g / l NH4Cl 15.0 g / l
• Gold main bath electrolyte 30 minutes treatment time, 82 - 84 ° C, adjustment to pH 5 with NH4OH, K [Au (CN) 2] 5.0 g / l Thiourea 24.8 g / l CoCl2.6 H2O 20.0 g / l NiCl2.6 H2O 10.0 g / l Ammonium dihydrogen citrate 20.0 g / l
• the IC chip was attached by gluing.

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• Chemical & Material Sciences (AREA)
• General Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Chemically Coating (AREA)
• Electroplating And Plating Baths Therefor (AREA)
• Electroplating Methods And Accessories (AREA)
• Conductive Materials (AREA)

Applications Claiming Priority (3)

Publications (2)

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• 1990
  • 1990-06-28 DE DE4020795A patent/DE4020795C1/de not_active Expired - Lifetime
• 1991
  • 1991-06-13 AT AT91910402T patent/ATE127166T1/de not_active IP Right Cessation
  • 1991-06-13 KR KR1019920703362A patent/KR930701639A/ko not_active Ceased
  • 1991-06-13 CA CA002086341A patent/CA2086341C/en not_active Expired - Lifetime
  • 1991-06-13 US US07/962,582 patent/US5320667A/en not_active Expired - Lifetime
  • 1991-06-13 WO PCT/DE1991/000498 patent/WO1992000398A1/de not_active Ceased
  • 1991-06-13 EP EP91910402A patent/EP0536170B1/de not_active Expired - Lifetime
  • 1991-06-13 DE DE59106385T patent/DE59106385D1/de not_active Expired - Fee Related
  • 1991-06-13 JP JP3509884A patent/JPH0649947B2/ja not_active Expired - Lifetime
  • 1991-06-28 CN CN91105281A patent/CN1060504A/zh active Pending

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