DD240915B1 - CYANIDE-FREE BATH FOR THE ELASTIC SEPARATION OF HARD GOLD LAYERS - Google Patents

Description

-2- 240 embodiments

The invention will be further explained with reference to three exemplary embodiments:

Example 1 Au (as Na ₃ Au (SO ₃ I ₂ ) 5 g / l

HCHO 0.5 g / l

Ethylenediamine 1.3 g / l

EDTA di-Na salt 0.7 g / l

Sodium citrate 23 g / l

Ammonium chloride 47 g / l TKaIsTINO ₃ ) 1 mg / l

Temperature 70 ° C

Hardness: HVo.ooi 215 brush transition voltage 4.3 mV

Example 2 Au (as Na ₃ Au (SO ₃ I ₂ ) 2.0 g / l

HCHO 0.3g / l

Na ₂ SO ₃ 22.0 g / l ethylenedianine 4.3 g / l

EDTA di-Na salt 0.9 g / l

TKaIsTINO ₃ ) 25mg / l pH (NaOH) 9.0

Temperature 92 ^° C

Hardness: HV _o , _OO i 200 Brush transition voltage 4.3 mV

Example 3 Au (as Na ₃ Au (SO ₃ J ₂ ) 2.5 g / l

Na ₂ SO ₃ 50.0 g / l

Triethanolamine 15.0 g / l TKaIsTINO ₃ ) 0.5 g / l

HCHO 10.5 g / l hydrazine sulfate 0.7 g / l

N-methylbenzothiazolium iodide 0.5 g / l

pH (NaOH) 9.0

Temperature 92 ^° C

Hardness: HV _OlO oi 225 brush transition voltage 4.3 mV

Claims (1)

1. Cyanide-free bath for the electroless deposition of hard gold layers, in which the gold salt is present as alkali sulfoaurate, as reducing agent formaldehyde, hydrazine derivatives, as stabilizers sodium sulfite, ethylenediamine, ethanolamine, N-methyl-benzthiazolium iodide and ethylenediaminetetraacetic acid (Na-SaIz) are used, characterized characterized that a thallium compound in a concentration of 1 to 500 mg per liter is used as the hardness-increasing additive. Field of application of the invention The technical application of the invention can be made in all areas in which the advantages of the currentless deposition should be used and at the same time a greater hardness and wear resistance of the gold layers is required. Special suitability arises for the production of functional layers in electrical engineering / electronics, which are claimed for abrasion and wear, z. B. plug contacts, Kommutatoroberflächen. Particularly suitable is the present bath for internal metallizations, where galvanic hard gold baths fail. Characteristic of the known technical solutions The known solutions for separating harder gold layers from electroless metallization baths are limited exclusively to cyanide-containing electrolytes. The increase in hardness is realized by the incorporation of nickel or cobalt or corresponding compounds which are added to the bath or intermediately formed during the deposition. As a result, the electrical properties of the gold layer are adversely affected. Another disadvantage of these additives is that the already low stability of electroless gold baths is further reduced by the addition of base metal compounds. According to studies by Y. OKINAKA, UM (J.Electrochem.Soc. 1974, 121 (1), 56-62), concentrations of 1 (T ³ MoI /! Ni ²⁺ ions and Co ²⁺ ions already lead to the uselessness of the Solution: Electroless gold solutions based on cyanide gold salts, in which sodium hypophosphite or formaldehyde are used as reducing agents, do not work chemically-reductively and can only be deposited on base substrate substrates with a limited layer thickness (DAS 1 268417, Japanese pat., 43-25881; Various electroless gold electrodes, containing nickel or cobalt salts, already show from their composition that they contain no reducing agent and therefore work only on a cementation basis (DOS 2239676, Jap: 77, 53, 732, USA 3506462) In addition, Y. OKINAKA (Gold Plating Technology, Electrochemical Publications) for US Patent 3506462 has been able to demonstrate that, despite a high concentration of cobalt chloride in the solution, no cobalt is present located in the deposited layer. The disadvantages resulting from the toxicity of the cyanide baths are excluded in cyanide-free electrolytes (DDR 150762, DOS 2750932, USA 4091128, SU 397562). However, it is known that only pure gold layers can be deposited from these baths. The addition of nickel and cobalt compounds in these cases leads to no increase in hardness, since their incorporation mechanism cyanidic intermediates are required. P.Prost-Tournier (DOS 2946165) investigated additions of Group III, IV and V metal compounds of PSE in highly alkaline cyanide gold solutions with the aim of increasing the deposition rate and improving bath development. Object of the invention The useful effect of the invention is to enable the deposition of harder wear resistant gold layers from stable cyanide-free electrolytes and thereby eliminate the difficulties resulting from the use of cyanide-containing solutions. Explanation of the essence of the invention In the present invention, a metallization is to be described, which does not have the main disadvantages of the previously known solutions. Of the known cyanide-free electroless gold solutions, especially the sulfitic solutions can be handled well (DDR 150762). Examination of the influence of metal cations on the deposition conditions and layer properties of electroless sulfite gold layers revealed that especially thallium compounds give a significant increase in hardness and wear resistance, with no significant change in electrical properties and no negative impact on the stability of the gold plating bath.