EP0149029A1 - Palladium bath - Google Patents

Abstract

With the palladium baths hitherto known it was virtually not possible, at least not under economical conditions, to produce bright, highly ductile crack-and-pore-free palladium coatings. The invention provides a palladium bath which deposits, virtually without maintenance, bright, highly ductile crack- and-pore-free palladium coatings at high limit current density, that is to say at high efficiency, and which is characterised by the addition of pyridine or a pyridine derivative as complexing agent.

Description

The invention relates to a bath for the rapid galvanic deposition of shiny, highly ductile, crack and pore-free palladium layers, which contains palladium in the form of a palladium salt.

Palladium layers are required for both decorative and ₇ µm technical use. In technical use, it is used in particular as a substitute for gold. In decorative use, slight cracking or pore formation can still be accepted, but not in technical use. Here, the palladium layers must be absolutely free of cracks and pores and generally also highly ductile in order to meet the requirements placed on these palladium layers.

• a) Bäder auf Sulfatbasis, die auch mit löslichen Palladiumanoden betrieben werden,
• b) alkalische Bäder auf der Basis des Palladiumhydroxokomplexes,
• c) Bäder auf Chloridbasis oder auf der Basis der Nitratbeziehungsweise Nitritkomplexe in neutralem oder ammoniakalischem Medium.

With palladium baths one can differentiate:

• a) sulfate-based baths which are also operated with soluble palladium anodes,
• b) alkaline baths based on the palladium hydroxo complex,
• c) Baths based on chloride or on the basis of nitrate or nitrite complexes in neutral or ammoniacal medium.

The sulfad-based palladium baths are almost always aggressive and attack a number of base metals. This aggressiveness also causes rapid contamination by foreign metal ions. Since they also usually separate powdery precipitates, these known palladium baths only meet subordinate requirements.

The alkaline baths listed under b) also only give imperfect precipitation with more or less strong pores, which are shiny even in relatively thin layers.

The palladium baths belonging to the last group are preferred in practice, platinum or platinized titanium generally being used as the insoluble anode material. However, the relatively good yield of such baths is offset by the disadvantages that it is difficult to achieve pore-free coatings, that the constantly evaporating ammonia creates uncomfortable operating conditions and requires extensive suction devices, and that the pH of such baths is also unstable and therefore very difficult to maintain constant can be held.

In order to nevertheless achieve pore-free coatings, ea has also become known to use an aqueous neutral or alkaline solution with a palladium compound and an ammonium salt of a weak organic acid which does not form an insoluble compound with the palladium compound for the deposition of palladium coatings. A bath for depositing tough palladium coatings on electrical contacts has already become known, which contains palladium in the form of a nitrogen-containing complex, the complex consisting of an aqueous alkaline-ammoniacal solution of tetramine-palladium-bromide. Although an improvement was achieved in this way, it is also not possible to achieve thick, completely non-porous coatings with palladium; in addition, the need to extract ammonia vapors remains.

It should also be noted that as a result of the hydrogen absorption of the palladium during cathodic deposition from the known baths, in spite of the low current yield, that is to say the low current density, the ductility generally remains below the requirement and the internal tension of the precipitates is also relatively high.

The invention specifies a palladium bath which deposits the shiny, highly ductile, crack- and pore-free palladium layers to be deposited quickly, that is to say with a high limiting current density. This is achieved in the manner according to the invention by adding pyridine or a pyridine derivative as a complexing agent.

As was found when using the bath according to the invention, with high current efficiency and accordingly high limiting current density, correspondingly rapid deposits result in shiny, highly ductile, crack-free and pore-free palladium layers, the gloss also being retained even with thick layers. There are none pleasant side effects, especially if good suction is provided when adding pyridine, such as in baths with ammoniacal medium. In addition, the hardness of the precipitation can be set between a hardness of 100 to 500 HV. It is noteworthy that even the soft precipitation is extremely resistant to abrasion.

Particularly good results can be achieved if the side group of the pyridine derivative is in the 3-position. Pyridilacetic acid is preferably added here.

For special conditions, it is advisable to add secondary complexing agents and organic buffer systems to the wheel. Di-ammonium hydrogenphosphate, which is also a good buffer / conducting salt system, has proven itself quite well for this. Potassium sodium tartrate can be used in a similar way. Salts of organic polyhydroxy acids, such as, for example, gluconic acid sodium salt, have proven useful as organic buffer systems. Of course, these organic buffer systems can also be complexing agents for palladium at the same time, similar to, for example, (NH ₄ ) ₂ HPO ₄ .

Suitable sulfur-containing additives can also be added to the bath to modify the mechanical precipitation properties, in particular to adjust the desired hardness. According to the invention, these sulfur-containing additives are expediently added in the form of organic sulfur compounds, in particular as sulfonic acid, as sulfonate or as sulfonamide.

example

• 10...50 g/1 (^NH ₄)₂ ^{H P0} ₄
• 2...19 g/1 Polyoxisäure
• 10...40 g/1 Pyridinessigsäure
• 10...20 g/1 Pd²⁺
• pH = 12
• Temperatur = 10...50 °C
• i = 0,5 - 3 A/dm² im Standbad = 95 - 100 %
• t = 0,5 - 1 µm/min (Standbad)

Batch: 20 ... 60 g / 1 K Na tartrate

• 10 ... 50 g / 1 ( ^NH ₄ ) ₂ ^{H P0} ₄
• 2 ... 19 g / 1 polyoxyacid
• 10 ... 40 g / 1 pyridine acetic acid
• 10 ... 20 g / 1 Pd ²⁺
• pH = 12
• Temperature = 10 ... 50 ° C
• i = 0.5 - 3 A / dm ² in the standing bath = 95 - 100%
• t = 0.5 - 1 µm / min (standing bath)

Precipitation: Crack-free and shiny. The absence of cracks remains even after the heat test (heating to 150 ° C for 60 min, then quenching in cold water).

It is extremely worth mentioning that the adhesion of the layer, especially on nickel and on non-ferrous metals, is very good.

Claims (9)

1. Bath for the rapid electrodeposition of shiny, highly ductile, crack and pore-free palladium layers, which contains palladium in the form of a palladium salt
by adding pyridine or a pyridine derivative as a complexing agent. 2. Bath according to claim 1,
characterized,
that the side group of the pyridine derivative is in the 3-position. 3. bath according to claim 1 or 2,
characterized,
that the pyridine is added as pyridilacetic acid. 4. Bad after one or more
of the preceding claims,
characterized,
that additional secondary complexing agents and organic buffer systems are added. 5. Bath according to claim 4,
characterized,
that di-ammonium hydrogen phosphate is added as a secondary coplexing agent. 6. Bath according to claim 4,
characterized,
that potassium sodium tartrate is added as a secondary complexing agent. 7. Bath according to claim 4,
characterized,
that polyhydroxy acid is added as an organic buffer. 8. Bad after one or more
of the preceding claims,
characterized,
that organic sulfur compounds, in particular sulfonic acids, sulfonates and sulfonamides, are added in addition to the complexing agents. 9. Bad after one or more
of the preceding claims,
marked by
20 ... 60 g / 1 K-Na-tartrate, 10 ... 50 g / 1 (NH ₄ ) ₂ H PO ₄ , ² ... ¹⁹ g / 1 polyoxyacid, 10 ... 40 g / l pyridine acetic acid , 10 ... 20 g / l Pd ²⁺ , pH = 12, temperature = 10 ... 50 ° C, i = 0.5 - 3 A / dm ² in the standing bath