CH630415A5 - Bath for the currentless nickel plating of metal and metal alloys, in particular aluminium and aluminium alloys - Google Patents

Description

The invention relates to a bath for electroless nickel plating of metal and metal alloys, in particular aluminum and aluminum alloys, with a high deposition speed.

Electroless nickel plating baths, in particular high-performance baths with a high deposition rate, tend under certain conditions, e.g. local overheating, excessive concentration of reducing agent when adding supplementary solutions, to instability, that is, to a more or less rapid self-decomposition. This can be seen in an ever increasing “game deposition” of nickel, especially on the floor and on the walls of the bath tub. The game deposition of nickel leads to an increasing consumption of chemicals, the formation of faulty, rough coatings and the need for frequent cleaning of the bath vessel. In extreme cases, instability in the bathroom causes the bath to spontaneously decompose itself, which then necessitates an immediate shutdown of operations.

German Offenlegungsschrift 2,253,491 discloses baths for electroless nickel plating of metal, plastic and ceramics which, in order to increase the deposition rate, contain a certain amount of a water-soluble polyhydroxybenzene, which may contain at least one further functional group, and as a stabilizing agent, optionally copper in the form of a water-soluble one Copper salt included. Such baths are also extremely useful for the electroless nickel plating of objects made of steel, copper and copper alloys in manufacturing operations. They are also well suited for the electroless nickel plating of aluminum and aluminum alloys, provided there are smaller volumes and smaller throughputs. In the case of larger baths and / or a high throughput of parts to be nickel-plated made of aluminum, however, difficulties arise which are primarily due to the stability of the bath being too low.

The invention sees its task in the development of baths for electroless nickel plating of metal and metal alloys, in particular aluminum and aluminum alloys, which are also suitable for production-free electroless nickel plating with high throughput. Furthermore, the stability of the baths should be maintained while maintaining a high deposition rate.

This object is achieved with a bath containing nikke salt, complexing agent, sodium hypophosphite, an accelerating additive in the form of a water-soluble polyhydroxy derivative of benzene and a water-soluble copper salt, the bath according to the invention a) containing 30-150 g / l of at least one complexing agent b) a content of 10-50 g / 1 of sodium hypophosphite and 5-10 g / 1 of accelerator.

c) has a stabilizer content and d) has a nickel content of at least 7 g / 1.

The baths according to the invention are distinguished by excellent bath stability while maintaining a high deposition rate. Shiny nickel coatings are also obtained in higher thicknesses. Particularly good adhering galvanic coatings of, for example, silver on aluminum can be obtained on the nickel intermediate layers produced without current using the baths according to the invention. Another very important advantage of the baths according to the invention is that they can be operated at lower temperatures of 80 to 94 ° C. while maintaining the high deposition rate. The odor nuisance caused by ammonia is particularly low. Electroless thick nickel plating of approx. 50 (as required, for example, for flanges for coolant pumps or pressure regulators or for impellers for ring compressors) can also be produced in a rational manner with the baths according to the invention.

For many applications, it is of particular advantage that the most diverse parts made of cast aluminum and kneaded material that are coated with a galvanic coating, e.g. Silver, which are to be provided, are electrolessly nickel-plated beforehand. The nickel intermediate layer provides good corrosion protection on the one hand, and particularly good adhesion of the galvanic coating on the other. Furthermore, electroless nickel-plated copper-clad wires or wire connections can be soldered particularly well to a semiconductor using the baths according to the invention.

A particularly suitable accelerator is 3,4-dihydroxy-benzoic acid.

Nickel complex salt solutions, preferably consisting of nickel sulfate, lactic acid, ammonium sulfate, 3,4-dihydroxybenzoic acid and copper (II) sulfate, are used as supplementary solutions.

Suitable complexing agents are citric acid, glycolic acid, acetic acid and succinic acid, malonic acid, malic acid, propionic acid or the alkali salts of these acids. Lactic acid and lactates have proven to be particularly suitable.

The baths according to the invention are used with particular advantage for nickel-plating a wide variety of parts made of cast aluminum and wrought alloys, for example antenna parts, satellite parts, cable connector housings, etc. In many cases, especially for high-frequency parts, the electroless nickel-plated aluminum parts are then galvanically silver-plated in order to achieve a high surface conductivity. The baths according to the invention are also well suited for electroless nickel plating of

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Transistor feet. The baths according to the invention can also advantageously be used for electroless nickel plating with subsequent galvanic silvering of contact blades made of aluminum for high-current fuses. Thick nickel plating of flanges for coolant pumps and pressure regulators, as well as impellers for ring compressors, have proven their worth.

The invention is illustrated by the following examples.

example 1

Metal objects, e.g. Copper or copper alloys are electroless nickel-plated in a nickel bath of the following composition after a pretreatment that is common in electroplating technology:

Nickel sulfate NÌS04- 6H2O 35 g / 1

tri-sodium citrate CeHsNasCb-5,5H20 100 g / 1

Ammonium sulfate (NH4) 2SÜ4 25 g / 1

Sodium hypophosphite N aPH2Cte • H2O 20 g / 1

3,4-Dihydroxybenzoic acid (HO) 2C6H4COOH 6 g / 1 copper (II) sulfate CuSCU-5H2O 0.05 g / 1

pH 7.2-7.5 temperature 88-94 ° C

Deposition rate 20-25 | j.m / h surface load of the bath up to 2 dm2 / l

Every 10 minutes, 10 cm3 of an ammoniacal nickel complex salt solution (supplementary solution A) and 5 cm3 of reducing solution (supplementary solution B) are added to the bath per dm2 of product surface.

The supplementary solutions have the following composition:

Every 10 minutes, 10 cm3 of an ammoniacal nickel complex salt solution (supplementary solution A) and 5 cm3 of reducing solution (supplementary solution B) are added to the bath per dm2 of product surface.

The supplementary solutions have the following composition:

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1. Nickel complex salt solution (supplementary solution A) nickel sulfate lactic acid ammonium sulfate 3,4-dihydroxybenzoic acid copper (II) sulfate ammonia

2. Reduction solution (supplement B) sodium hypophosphite

190 g / 1 50 g / 1 30 g / 1 6 g / 1 2 g / 1 350 cm3 / l

395 g / 1

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As soon as a certain bath density is reached, part of the electrolyte volume is discarded and replaced with water in order to keep the bath density within certain limits (1.051 g / cm3-1.161 g / cm3 at working temperature).

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1. Nickel complex salt solution (Supplementary solution A)

Nickel sulfate 190 g / 1

tri sodium citrate 75 g / 1

Ammonium sulfate 30 g / 1

3,4-dihydroxybenzoic acid 6 g / 1

Copper (II) sulfate 2 g / 1

Ammonia 350 cm3 / l

2. Reduction solution (supplement solution B) sodium hypophosphite 395 g / 1

As soon as a certain bath density is reached, part of the electrical volume is discarded and replaced by water in order to keep the bath density within certain limits (1.051 g / cm3-1.262 g / cm3 at working temperature).

Example 2

Objects made of aluminum or aluminum alloys are electrolessly nickel-plated in a nickel bath of the following composition after a pretreatment that is common in electroplating technology:

Nickel sulfate NÌSO46H2O 35 g / 1

Lactic acid CHsCHOHCOOH 50 g / 1

Ammonium sulfate (NH4) 2S04 50 g / 1

Sodium hypophosphite NaPH2Cte * H2O 20 g / 1

3,4-Dihydroxybenzoic acid (HO) 2C6H4COH 6 g / 1 copper (II) sulfate CuSÜ4 • 5H2O 0.05 g / 1

pH: 7.2-7.5 temperature: 88-94 ° C

Separation speed 25-35 | im / h surface load of the bath up to 2 dm2 / l

Example 3

Objects made of cast aluminum are electroless nickel-plated after a pretreatment that is common in electroplating technology. The bath used for this has the following composition:

Nickel sulfate NiSCU-6H2O 35 g / 1

Sodium glycolate HOCH2-COO Na 50 g / 1

35 ammonium sulfate (NH4) 2S04 50 g / 1

Sodium hypophosphite NaPH2Cte ■ H2O 20 g / 1

2,3-Dihydroxybenzoic acid (HO) 2C6H4COOH 6 g / 1 copper (II) sulfate CuSCU-5H20 0.05 g / 1

pH 7.2-7.5 40 temperature 88-94 ° C separation rate 25-35 jim / h surface load of the bath up to 2 dm2 / l

Every 10 minutes, 10 cm3 of an ammoniacal nickel complex salt solution (supplementary solution A) and 5 cm3 of reducing solution (supplementary solution B) are added to the bath per dm2 of product surface.

The supplementary solutions have the following composition:

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1. Nickel complex salt solution (Supplementary solution A)

Nickel sulfate sodium glycolate ammonium sulfate 2,3-dihydroxybenzoic acid copper (II) sulfate ammonia

2. Reduction solution (supplement B) sodium hypophosphite

190 g / 1 50 g / 1 30 g / 1 6 g / 1 2 g / 1 350 cm3 / l

395 g / 1

As soon as a certain bath density is reached, a part 65 of the electrolyte volume is discarded and replaced by water in order to keep the bath density within certain limits (1.051 g / cm3-l, 61 g / cm3 at working temperature).

Which show with 50 (in thick nickel-plated aluminum parts

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excellent corrosion resistance against water and alkaline solutions.

Example 4

Aluminum objects should be silver-plated to make them surface conductive for high-frequency currents. The parts are previously electrolessly nickel-plated to achieve an adherent silver coating.

The nickel intermediate layer is applied by electroless nickel plating in an electrolyte of the following composition:

Nickel sulfate Ni SO4.6H2O 35 g / 1

Sodium acetate CH3COO Na 50 g / 1

Ammonium sulfate (Na4) 2SÛ4 25 g / 1

Sodium hypophosphite NaPFfcCte • H2O 20 g / 1

2,5-Dihydroxybenzoic acid (HO) 2CeH4COOH 6 g / 1 copper (II) sulfate CuSC> 4-5H2O 0.05 g / 1

pH 7.2-7.5 temperature 88-94 ° C

Deposition rate 25-35 [im / h surface load of the bath 2 dm2 / l

Every 10 minutes, 10 cm3 of an ammoniacal nickel complex salt solution (supplementary solution A) and 5 cm3 of reducing solution (supplementary solution B) are added to the bath per dm2 of product surface.

The supplementary solutions have the following composition:

1. Nickel complex salt solution (supplement solution A) nickel sulfate sodium acetate ammonium sulfate 2,5-dihydroxybenzoic acid copper (II) sulfate ammonia

190 g / 1 50 g / 1 30 g / 1 6 g / 1 2 g / 1 350cm3 / l

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Reduction solution (supplement B) sodium hypophosphite 395 g / 1

As soon as a certain bath density is reached, part of the electrolyte volume is discarded and replaced by water 15 in order to keep the bath density within certain limits (1.051 g / cm3-l, 161 g / cm3 at working temperature).

In the manner described, a nickel intermediate layer of 10 (in thickness) is applied over the course of about 20 minutes.

20 The parts treated in this way are electroplated with 10 vol.% Sulfuric acid and rinsed in running water at a current density of 6-8 A / dm2 for 10 seconds and then silvered at a current density of 1.2 A / dm2. After 15 minutes, the 25 layer thickness is 10 | j, m.

In this way, a specifically light body is obtained with a surface layer which, with excellent adhesion, has excellent conductivity for high-frequency currents.

B

Claims (4)

630415 1. Bath for electroless nickel plating of metal and metal alloys, containing nickel salt, complexing agent, sodium hypophosphite, an accelerated addition in the form of a water-soluble polyhydroxy derivative of benzene and a water-soluble copper salt, characterized in that the bath a) 30-150 g / 1 at least a complexing agent contains b) a content of 10-50 g / 1 sodium hypophosphite and 5-10 g / 1 accelerator, c) a stabilizer content, and d) a nickel content of at least 7 g / 1. 2. Bath according to claim 1, characterized in that it contains lactic acid. 2nd PATENT CLAIMS 3. A method for electroless nickel plating of metal and metal alloys using a bath according to claim 1, characterized in that one works at a bath temperature of 88-94 ° C and a bath density of 1.051-1.262 g / cm3. 4. The method according to claim 3 for electroless nickel plating of components made of aluminum and aluminum alloys.