DD299382A7 - CHEMICAL REDUCTIVE GOLD ELECTROLYTE COMBINATION AND METHOD OF GOLD DECISION USING THIS COMBINATION - Google Patents

Abstract

The invention relates to a chemical-reductive gold-electrolyte combination and to a method for gold deposition using this combination, preferably for gold deposition on nickel and nickel alloy layers. The combination consists of a pre-bath and a main bath and optionally a Dekapierloesung and optionally a pretreatment. The resulting gold layer is chip- and wire-bondable. {Chemical-reductive gold-electrolyte combination; Gold deposition; Gold deposition on nickel layers; Gold deposition on nickel alloy layers; chip-bondable gold layer; wire bondable gold layer}

Description

Field of application of the invention

The chemically-reductive gold-electrolyte combination and the gold deposition process using this combination can be used for the production of adherent gold layers, preferably on Ni, Ni _x Py or Ni _x B _y surfaces. In particular, the stable electrolyte combination is suitable for the production of chip and wire bond islands.

Characteristic of the known state of the art »

The use of chemical-reductive metallization baths for the production of gold layers is well known (Goldie, Gold as surface, technical and decorative gilding, 1983). Gilding difficulties arise in deposition on nickel layer surfaces. Either no deposition on nickel or nickel alloy surfaces takes place (US Pat. No. 1,322,203) or it is a cementation deposit (US Pat. No. 3,123,484) which only permits the deposition of thin gold layers (DD-PS 265 915). Cementation of the gold also has the disadvantage of leading to deterioration in the adhesion of the gold layer to longer treatment zooms.

For chip or wire bonding, gold layer thicknesses of 0.2-3.0 μm are required. However, the high deposition rate electrolytes therefor are only marginally stable (Rich, D.W., Proc. Am. Electropl.foe.71, p.58 and U.S. Patent 4,169,171). Frequently, alkali-soluble photoresists or lacquers are used to cover surfaces that are not to be coated for selective coating tasks. Therefore, it is not possible to use any gold electrolytes working in the alkaline range,> pH 9 (Dettke, Stromlose Coating, Eugen G. Leeu Verlag 1988, pp. 74-78).

Likewise, DD-PS 263307 describes a chemically-reductive gold bath with a high deposition rate. Disadvantage of this bath, however, is that a simultaneous cementotopic deposition process takes place.

Object of the invention

The aim of the invention is the development of a stable chemical-reductive metallization in the non-alkaline range for the production of adherent gold layers on Ni, Ni _x Py or Ni _K B _y surfaces.

Explanation of the essence of the invention

Aufgab'e the invention is to achieve a stable deposition of adherent, bondable gold layers of> 0.2μιη with particularly fast Abscheldungszeiten.

According to the invention, this object is achieved by a gold electrolyte Kombinatlon consisting of a pre-bath containing a gold-Strlke electrolyte with the anion disulfitoaurate-I ([Au (SOa) ₂ ) ³ ') as gold salt, an alkali and / or Ammonium sulfite (SO ₃ ) ² 'as a stabilizer and a reducing agent, and a main bath containing the anion Dlcyanoaurat-I [Au (CN) ₂ ^- ) as a gold salt, thiourea or its derivatives as stabilizers and cobalt-II salts as a reducing agent, optionally fines complexing agent and optionally a nickel-II salt, dissolved.

The pre-bath Gold Strike Elaktrolyt with the anion disulfitoaurate-I can be used in the form of its ammonium or alkali metal salts. Suitable reducing agents of the pre-bath are, for example, aldehydes and aldehyde-sulfite adducts. Particularly suitable is formaldehyde (methanal) and the adduct formaldehyde / sodium sulfite (Rongalit *). If desired, a complexing agent, for example ethylenediamine, may be added to the prebath. The gold anion used in the main bath, dicyanoaurate-I, can also be used in the form of its ammonium or alkali metal salts. Thiourea or its derivatives are added to the main gold as stabilizers; for example thiosemicarbazide.

As an essential part of the main bath, CobalMI salts are added to the electrolyte, for example cobalt-Ilhalogenide, cobalt-II-sulfate, cobalt-II-nitrate, cobalt-II-formate or cobalt-II-acetate.

Optionally, a nickel salt, for example a nickel-II-halide, with particular advantage nickel-Il chloride, be added to the main gold to increase the deposition rate.

For coating nickel or nickel alloy surfaces, it may be necessary to additionally use a pickling solution. This Dekapierlösung consists of a hydroxycarboxylic acid or its salts and ammonium chloride. Examples of suitable hydroxycarboxylic acids are tartaric acid or citric acid.

The pickling solution is to be used when the existing nickel or nickel alloy surface in the gold plating exhibits high cementation and additional dissolution of the nickel layer by the acidic electrolyte solution occurs. Solutions of alkali or ammonium carboxylic acids, for example, sodium citrate with ammonium chloride at pH 6-8 more passively nickel or nickel alloy surfaces. The cementation rate is thereby reduced. A gold strike electrolyte operating in the neutral range up to a maximum of pH 8, which also contains an alkali or ammonium carboxylic acid and ammonium chloride, ensures adherent deposition of gold layers. An additional dissolution of the passive nickel layers (for example selectively below the gold layers) does not occur. The dense pre-gold layer protects the nickel surface from selective dissolution in the acid main gold electrolyte. The acidic main gold electrolyte is additionally stabilized by the use of thiourea or its derivatives, with stability of an adjusted concentration of nickel ions (nickel chloride) in the electrolyte acceleration of the catalytic Roduktionsreaktion and thus a deposition rate of 2 μιη / η is achieved ,

By a pre-treatment solution in the case of gold and / or gold surface gold plating, the initial reaction of the deposition from the main gold can be accelerated. The pretreatment solution consists of heavy metal ions, e.g. B. NI ^{J +} ions and / or Co ²⁺ ions in an acidic medium, which are adsorbed on the gold surface and change the surface potential. The invention further relates to a method for gold deposition using the electrolyte combination according to the invention and optionally the Dekapierlösung.

embodiments The invention will be explained in more detail with reference to 4 examples. example 1 The subject of the invention is particularly suitable for depositing gold layers on a conductive ceramic chip. Carrier packages. They are using chemical-reductive nickel-phosphorus layers and gold (2-3pm) as the outer Contact layer system metallized. The nickel-phosphorus layer is first treated with the following decapping solution at room temperature for 30 seconds:

10 g / l sodium citrate

15g / l ammonium chloride.

Subsequently, the gilding with the combination according to the invention.

a) Gold Strike Electrolyte: 30 minutes, 6O ⁰ C GoIdBIsNa ₃ Au (SO ₃ I ₂ 0.6 g / l Methanal 0.1 g / l sodium hydroxide 10.0 g / l Na ₂ SO ₃ 5.0 g / l Ethylenediamine 0.84 g / l NH ₄ Cl 15.0 g / l

b) Gold main electrolyte: 90 minutes, 82-84 ⁰ C KAu (CN) ₂ 6.0 g / l thiourea 24.8 g / l CoCI ₂ 6H ₂ O 20.0 g / l NiCl ₂ -6H ₂ O 10.0 g / l ammonium dihydrogen citrate 20.0 g / l

Example 2 A miniature printed circuit board partially covered with alkaline-soluble solid-state "Riston 3615" · should be applied selectively to existing,

chemically reductively nickel-plated copper contact layer structures are gold plated.

Pickling solution as in Example 1. The gold plating is then carried out with the following combination according to the invention:

a) Gold Strike electrolyte: IS minutes, 6O ⁰ C, pH 5.1 with citric acid gold as (NH ₄ ) JAu (SOj) ₂ 1.0 g / l

Methanal 0.15 g / l Sodium citrate 15.0 g / l

Na ₂ SO ₃ 7.0 g / l

Ethylenediamine 0.84 g / l

NH ₄ Cl 10.0 g / l

b) Gold main electrolyte: 30 minutes, 82-84 ⁰ C KAu (CN) ₂ 4.0 g / l of thiourea, 20.0 g / l CoCI ₂ 6H ₂ O 20.0 g / l NlCI ₂ -6H ₂ O 15.0 g / L ammonium dihydrogen citrate 15.0 g / L <

Example 3

A stripline circuit on Al ₂ O ₃ ceramic is to be used with the layer system Ni _x P _y -galv. Cu-Ni _x Py-Au are built up. With lift-off technology, first the interconnect structure including galv. Copper is produced. After removing the photoresist, the layer system Ni "P _y is -galv. Coated with Ni _x Py from an alkaline electrolyte and gilded with the combination according to the invention as follows:

a) Gold Strike electrolyte: 30 minutes, 6O ⁰ C analogously to Example 2, but with gold as (NH ₄ IaAu (SO ₃ I ₂ 1.2 g / l ammonium dihydrogen citrate 20.0 g / l

(instead of sodium citrate)

b) pretreatment solution for gold: 4 minutes, 82-84 ⁰ C NiCl ₂ -6H ₂ O, 15.0 g / l

CoCl ₂ -6H ₂ O 20.0 g / l

dissolved in 15% hydrochloric acid

c) GoID main electrolyte: 30 minutes, 82-84 ⁰ C KAu (CN) ₂ 7.0 g / l of thiourea, 25.0 g / l CoCI ₂ 6H ₂ O 15.0 g / l NiCl ₂ -6H ₂ O 15.0 g / l ammonium dihydrogen citrate 20.0 g / l

Example 4 By laser metallization, a Ni _x P _y structure is prepared from an alkaline electrolyte on Al ₂ O ₃ ceramic. to Production of wire bond islands is said to be gilded this structure. A special picking solution is not used. ' Subsequently, the gilding with the combination according to the invention.

a) Gold Strike electrolyte: 15 minutes, 6O ⁰ C gold as (NH ₄ J ₃ Au (SO ₃ ) J 2.0 g / L Methanal 0.1 g / L sodium citrate 10.0 g / L Na ₂ SO ₃ 5.0 g / l of ethylenediamine 0.84 g / l of NH ₄ Cl 15.0 g / l

b) Gold main electrolyte: 30 minutes, 82-84 ^e C, pH 5 with NH ₄ OH KAu (CN) ₂ . 5.0 g / l thiourea 24.8 g / l

CoCl-6H ₂ O 20.0 g / l

NiCl ₂ -6H ₂ O 10.0 g / l

Ammonium dihydrogen citrate 20.0 g / l

Claims (7)

1. chemically-reductive gold-electrolyte combination, characterized in that these from a prebath, containing a gold-strike electrolyte with the anion disulfitoaurate-I ([Au (SO ₃ I ₂ ] ³ ") as a gold salt, an alkali - or ammonium sulfite (SOa) ^2- as a stabilizer and a reducing agent and optionally a complexing agent and a main bath containing the anion dicyanoaurate-I [Au (CN) ₂ ^- ] - as a gold salt, thiourea or its derivatives as stabilizers, cobalt-Il- Salts as a reducing agent, and optionally a nickel-Il salt consist. 2. Chemically-reductive gold-electrolyte combination according to claim 1, characterized in that the gold strike electrolyte 0.3-2.0 g / l gold as Na ₃ [Au (SOa) ₂ ), 3-15g / l Sodium sulfite, 0.05-1.0 g / l ethylenediamine, 0.1-0.5 g / l methanal, 10-25 g / l ammonium chloride and 5-25 g / l salt of a hydroxycarboxylic acid. 3. Chemical-reductive gold-electrolyte combination according to at least one of claims 1-2, characterized in that the main gold electrolyte 3-10g / l K [Au (CN) ₂ ], 5-25g / l thiourea, 10-30 g / l CoCl ₂ · 6H ₂ 0.5-15 g / l NiCl ₂ · 6H ₂ O and 10-30 g / l of an ammonium salt of a hydroxycarboxylic acid. 4. A method for gold deposition, characterized in that a chemically-reductive gold-electrolyte combination according to claim 1 and optionally a Dekaoierlösung, consisting of a hydroxycarboxylic acid or its salts and ammonium chloride, is used as the bath. 5. A method for Goldabschoidun according to claim 4, characterized in that a Dekapierlösung containing 1-2ug / l of a hydroxycarboxylic acid or its salt and 5-25g / l ammonium chloride, is used. 6. A method for gold deposition, characterized in that a bath as a chemically-reductive gold-electrolyte combination according to claim 1 and optionally a pretreatment solution for surfaces to be gilded, consisting of an acidic solution, the Ni ²⁺ ions and / or Co ^{2 +} ion is used. 7. The method for gold deposition according to claim 6, characterized in that a heated to 60-9O ⁰ C pretreatment solution containing 10-30g / l NiCl ₂ · 6H ₂ O and 5-15g / l CoCI ₂ · 6H ₂ O is used.