DD150762B1 - CYANIDE-FREE BATH FOR CURLY-FREE GOLD SEPARATION - Google Patents

Description

Field of application of the invention

The technical application can be made in all areas in which the deposition of gold layers for the purpose of improving the corrosion and oxidation protection and the electrical layer properties appears necessary. A particular area of application is electronics, where the application of gold plating is often difficult or impossible if the areas to be covered are single areas or isolated areas.

The use of electroless gold deposition is distinguished from comparable layer-forming processes such as vapor deposition, sputtering or the like by lower material usage and higher adhesion of the gold layer.

Characteristic of the known solutions

The use of electroless plating baths for the deposition of gold on various substrates is well known.

The deposition is usually carried out from a solution containing a gold salt, a reducing agent and various additives such as complexing agents, buffer substances and stabilizers. The known technical solutions can be subdivided into cyanide-containing and cyanide-free metallization solutions.

However, the use of cyanide-containing metallization solutions results in difficulties resulting from the toxicity of the complexing agent. In addition to the special precautions when dealing with solutions containing cyanide, above all the costs for the detoxification of the equipment used and the wastewater are considerable.

Chemical metallization solutions that do not have cyanide-containing additives do not have these disadvantages.

Various patents (eg US 3,515,571, US 4,091,128, US 4,091,172) describe cyanide-free metallization solutions in which, due to their instability, the gold salt-containing solution and the solution containing the reducing agent are stored separately. During metallization, the simultaneous spraying of the solutions takes place on the object to be metallized. However, a separate device is required for this spraying process. U.S. Patent 3,300,328 discloses a water-soluble gold salt, designated HAuCl ₄ 3H ₂ O. The disadvantage of this solution is the 3-valence of the gold. The implementation as a sulfite complex takes place only during the bath. DDR patent 82616 describes a method of depositing metallic coatings on silicon using, among other things, a cyanide-free electroless gold bath.

This bath also shows a striking instability, which allows only a short gilding time (about 5 minutes) and thus a very small layer thickness.

Another example of a cyanide-free bath for electroless gold deposition is given in the OS 2750932.

According to the inventors, the bath works stably with good deposition rate. The reducing agent used is a tertiary amine borane of the formula RO (CaH ₂₃ O) _x С _{ь ь} ггг NR, R, BH ₃ .

The preparation of this, for the electroless metallization hitherto unknown reducing agent is described in the patent application 2750922.4-42 and proves to be complicated and uneconomical compared to the commercial reducing agents.

Furthermore, SU patents are known which allow gilding only in the autoclave at 393-443K (SU 397562) or do not detect the reducing agent used, so that this is probably only a dip deposition, which allows only a small layer thickness (SU 396436).

Object of the invention

The useful effect of the invention is to enable the electroless deposition of gold layers from stable, cyanide-free electrolytes using commercially available reducing agents, thereby eliminating the difficulties resulting from the use of cyanide-containing solutions while ensuring stability.

-2- 150 Explanation of the essence of the invention

The elaborate steps to detoxify the equipment used and the effluents in cyanide-containing solutions for electroless gold deposition resulting from the toxicity of the cyanides and their compounds.

In the case of using cyanide-free metallization options, the instability of the solutions either requires special devices for spraying the separated components or only very short metallization times and thus only thin layers can be achieved. The object of the invention is to develop a solution which does not have the main disadvantages of the previously known solutions.

The stability of cyanide-containing solutions for the electroless deposition of gold is due to the strong complex formation of the cyanides and thus in the very low concentration of free gold ions.

In addition to the gold cyanide compounds, especially the gold sulfite complexes are quite easy to handle without exhibiting their toxicity. It is advantageous if one proceeds directly from the SuIf itoauratkomplex and not via the tetrachloroauric acid and additions of alkali sulfites. Due to the monovalent nature of the complex, the effective gold content is known.

The gold content of the water-soluble gold salt is about 25%. For this reason, the suitability of Alkalisulfitoauraten was tested for the electroless deposition of gold. It is necessary, the solution an excess of the corresponding

Add alkali sulfites.

To stabilize the gilding solution was a di- or Triaminoalkyl-, di- or Triaminoaryl- and / or di- or

Triaminoaralkylverbindung used. These stabilizers allow the application of the metallization solutions in a very wide pH range; At high concentrations, acidic electroless gold baths can also be realized.

Furthermore, ethylenediaminetetraacetic acid di-Na-salt is used as chelating agent and potassium bromide as accelerator. The working temperature of the electroless plating solution should preferably be 353-371K.

As a reducing agent sodium hypophosphite, methanal and hydrazine can be used. In the case of using hydrazine as a reducing agent, the use of an additional stabilizer such as thiourea is required. The choice of reducing agent as well as the concentration ratio, gold reducing agent, primarily determine the deposition rate and the appearance of the gold coatings. While matte gold layers are preferentially deposited using hydrazine and sodium hypophosphite, the use of methanal produces bright, bright yellow gold deposits. The solutions used work up to the boiling point stable and without foreign deposition.

Depending on the bath composition, deposition rates of 0.2-0.9 μmol · h ^{-1 were} achieved on the non-activated electroless nickel layers using the described solutions, the gold coatings exhibiting very good adhesion.

embodiment Example 1:

Au as sodium disulfitoaurate I (Na ₃ AU (SO ₃ I ₂ ) sodium sulfate (Na ₂ SO ₃ )

1,2-diaminoethane (H ₂ N-CH ₂ -CH ₂ -NH ₂ ) Potassium bromide KBr

Ethylenediaminetetraacetic acid di-Na salt Methanal as a 30% solution of pH (NaOH)

The deposition rate is 0.4 μιη h " ¹ .

With this and the subsequent metallization solutions are deposited on electroless nickel-plated ceramic film 0.4μπ> -11 " ¹ GoId.

Example 2:

Gold (as sodium disulfitoaurate I) 2 g / l

Sodium sulfite 12 g / l

1,2-diaminoethane 5 g / l

Ethylenediaminetetraacetic acid di-Na-salt 2 g / l

Methanal as a 30% solution 5 g / l

Potassium bromide 3 g / l

pH (H ₂ SO ₄ ) 6.5 T369-371K The deposition rate is 0.8 μήνη "¹.

Example 3:

Gold (as sodium disulfitoaurate I) 3 g / l

Sodium sulfite 15 g / l

Triethylamine 3 g / l

Ethylenediaminetetraacetic acid di-Na-salt 2 g / l

Formaldehyde as a 30% solution 5 g / l

Potassium bromide 3 g / l

pH 9.- ¹⁰ T369-371K The deposition rate is 0.6 μΓη · rT ¹ .

3 g / i 15 g / i 1 g / i 1 g / i 1 g / i 2 g / i 9 371 к

Example 4:

Gold (as sodium disulfitoaurate I)

sodium

sulfanilic

Ethylenediaminetetraacetic acid disodium salt

Formaldehyde as a 30% solution

potassium

pH

T369-371K

The deposition rate is 0.85 μ, ηη · h ~ ¹ .

Example 5:

Au as sodium disulfitoaurate I

sodium

1,2-diaminoethane

Potassium bromide Ethylenediaminetetraacetic acid di-Na salt

Sodium hypophosphite pH (NaOH)

The deposition rate is 0.5 мт · rT ¹ .

3 150 762 g / i 3 g / i 15 g / l 7.5 g / i 2 g / i 3 g / i 3 8th

Example 6:

Au as Natriumdisulfitoaurat sodium sulfite

1,2Diaminoäthan

potassium

Ethylenediaminetetraacetic acid disodium salt

Hydrazine H ₂ N-NH ₂ as a 25% solution of thiourea (NH ₂ J ₂ C = S pH (NaOH)

The deposition rate is 0.7 dt.h ^-1 .

3 g / i 15 g / i 1 g / i 1 g / i 1 g / i 4 g / i 9 369-371 к 3 g / i 15 G/' 1 g / i 1 g / i 1 g / i 2 g / i 0.2 mg / l 11 353 K

Claims (5)

Invention claim: 1. cyanide-free bath for electroless gold deposition, which contains a water-soluble gold salt, a reducing agent, alkali metal sulfite and stabilizers, characterized in that as the gold salt sodium or potassium sulfitoaurate, as a reducing agent formaldehyde, sodium hypophosphite or hydrazine, as stabilizers di- or Triaminoalkyl- , Di- or Triaminoaryl- and / or di- or Triaminoaralkylverbindungen, and potassium bromide and ethylenediaminetetraacetic acid (Na salt) are used. 2. bath after item 1, characterized in that the gold content in a liter of solution is 0.1-10g. 3. bath according to item 1 and 2, characterized in that are used as a reducing agent sodium hypophosphite, formaldehyde in a concentration of 0.5-500 mmol / l and hydrazine in a concentration of 0.5-280 mmol / l. 4. bath according to item 1, 2 and 3, characterized in that come to stabilize 0.1-1 Og / I of a di- or Triaminoalkyl-, di- or Triaminoarylverbindung used. 5. Bath according to item 1, characterized in that it contains 1-100 g / l sodium sulfite, up to 10 g / l potassium bromide and up to 50 g / l EDTA (Na salt).