GB2115440A

GB2115440A - Electroplating bath for the production of palladium-nickel alloy contact material

Info

Publication number: GB2115440A
Application number: GB08205617A
Authority: GB
Inventors: Peter Wilkinson
Original assignee: Engelhard Industries Ltd
Current assignee: BASF Catalysts UK Holdings Ltd
Priority date: 1982-02-25
Filing date: 1982-02-25
Publication date: 1983-09-07

Abstract

A palladium-nickel alloy of improved wear resistance when used as a contact material for an electrical or electronic contact or connection is formed by electrodeposition from a bath containing palladium and nickel ammine cations and an additive which improves the wear resistance of the deposited alloy, the additive being an aromatic sulphonamide derivative represented by the general formula: <IMAGE> wherein Ar is an optionally substituted phenyl group; R1 is hydrogen or an aliphatic radical; and R2 is a nitrogen- containing group selected from: <IMAGE>

Description

SPECIFICATION Electroplating bath for the production of contact material This invention relates to the electrodeposition of palladium-nickel alloys and is concerned with a plating bath for use in the production of contact material by the electrodeposition of bright palladium-nickel alloys and with a method of producing contact materials composed of bright electrodeposits of such an alloy using said plating bath.

Gold has for many years been the principal material used as the contact material in high performance electrical and electronic contacts and connectors. However, because of its relatively high cost and the frequency fluctuations in the price of gold, alternative less costly materials have been sought and there have recently become commercially available electroplating baths from which palladium-nickel alloys can be electrodeposited to provide deposits which are suitable in many applications as a replacement for gold in the production of electrical and electronic equipment.

One such bath for the electrodeposition of a palladium-nickel alloy containing 30 to 90% by weight of palladium is disclosed in British Patent Specification No. 1,143,178 and the corresponding United States Patent No. 3677909. The bath comprises an aqueous solution of palladium and nickel ammines, the palladium and nickel content of the solution each being from 5 to 30 grams per litre with the relative proportions of palladium and nickel being such as to produce the required content of palladium in the electrodeposited alloy. The specification states that the brightness of the deposited alloy can be enhanced by adding a brightening agent, of the type conventionally used in nickel plating baths, such as a naphthalene sulphonic acid salt, for example sodium naphthalene-1 ,3,6-trisulphonate, or an aromatic sulphonamide, for example saccharin (or its sodium salt) and p-toluenesulphonamide.However the specification also states that the presence of these brightening agents in the bath has no appreciable effect on the composition or mechanical properties of the electrodeposited alloy. In practice, however, the bath described in the foregoing British specification containing sodium naphthalene-1 3,6-trisulphonate as the brightening agent has been found to produce deposits having relatively poor corrosion resistance in an acidic environment.

To be of use as a contact material for a separable connector in electrical or electronic equipment, the palladium-nickel electrodeposit must be capable of maintaining a high wear resistance. In connection with gold electrodeposits it has been postulated that wear resistance can be considered to be a composite effect of the hardness, internal stress and ductility of the electrodeposit. It is also known that gold electrodeposits can exhibit various structures, for example an amorphous structure, a columnar structure or a laminar structure.

We have unexpectedly found that if there is incorporated into a palladium-nickel electroplating bath of the type described in the above-mentioned British patent specification an aromatic sulphonamide derivative of the class hereinafter defined, there is obtained a palladium-nickel electrodeposit of generally laminar structure and lower internal stress and which therefore exhibits improved wear resistance.

Thus in accordance with one aspect of the invention, there is provided a plating bath for the electrodeposition of a palladium-nickel alloy comprising an aqueous solution of palladium and nickel ammines containing from 5 to 30 grams per litre of palladium and from 5 to 30 grams per litre of nickel with the relative proportions of palladium and nickel being such that the alloy obtained from the solution by electrodeposition has a palladium content of from 30 to 95% by weight, preferably 70 to 90% by weight, characterised in that the bath contains as a wear resistance improvement additive an effective amount of an aromatic sulphonamide derivative represented by the general formula:

wherein Ar is an optionally substituted phenyl group, preferably phenyl;R1 is hydrogen or an aliphatic radical, preferably hydrogen; and R2 is a nitrogen- containing group selected from: (1) -CO-NH2;

Presently preferred compounds falling within the definition of formula I are benzenesulphonylurea and sulphadiazine.

The plating bath may advantageously also contain an unsaturated aliphatic monosulphonic acid, for example vinyl sulphonic acid or preferably allyl sulphonic acid, generally in the form of the sodium salt thereof, since the presence thereof will help to improve the corrosion resistance of the deposit.

The plating bath of the inventin will contain, as previously mentioned, from 5 to 30 g/l of palladium, generally 8 to 22 g/l, and from 5 to 30 g/l of nickel, generally 5 to 20 g/l. For plating at normal speeds the palladium and nickel may be present in a weight ratio of, for example, 1-2.75:1, preferably between 1.8:1-2.3:1. For high speed plating, other ratios may be more suitable.

The palladium and nickel are present in the plating bath in the form of their ammines and these may be used as such in preparing the bath or may be formed in situ from aqueous ammonia and a soluble salt of palladium and nickel respectively, for example palladium chloride (PdC12) and nickel sulphate (Ni SO4.7H2O or NiSO4.6H2O). The inclusion in the bath of an ammonium salt of an organic or inorganic acid, for example ammonium sulphate, is advantageous in that it increases the conductivity of the bath.

The additive of formula I will generally be present in the bath in an amount of at least 1 girl, for example from 1 to 10 g/l. Similarly, the unsaturated aliphatic monosulphonic acid, when use, may be present in the bath in an amount of at least 1 gil, preferably from 1 to 10 gil.

The pH of the plating bath will generally be in the range from 7.5 to 10, preferably about 8.0, and the bath will generally have a density (i.e. specific gravity) in the range from 8 to 16"Be (1.058-1.125 g/cc), preferably about 12"Be(1.09 g/cc).

The plating bath can, in accordance with another aspect of the invention, be used to produce a bright electrodeposit of a palladium-nickel alloy by a method which comprises electrodepositing said alloy on to an electrically conductive substrate, for example brass, from the plating bath of the invention.

In effecting such electrodeposition, it is generally advantageous to operate at a bath temperature in the range from 20 to 55"C., preferably about 35"C., and a cathode current density in the range from 0.5 to 2.5 A/dm2, preferably about 1A/dm2, using a platinum, platinisedtitanium or graphite anode. For high speed plating processes, a higher cathode current density may be employed, for example up to 20 A/dm2.

During the operation of the bath, insoluble palladium diammine dichloride (Pd (NH3)2C12) tends to form around the anode and this can interfere deleteriously with deposition at the cathode, resulting in the formation of a patchy, dull deposit. To prevent this, the bath can be subjected, in accordance with a preferred embodiment of the invention, to continuous filtration through active carbon, for example an active carbon impregnated filter cartridge, to remove the Pd (NH3)2C12, which gradually re-dissolves in the plating bath which eventually reaches a steady state: Pd (NH3)4CI2 < Pd (NH3)2C12 The following Examples illustrate the bath and method of the invention.

Example 1 A plating bath having the following composition was made up using known techniques: Pd (NH3)4C12 20 g/l (as palladium) Ni(NH3)6SO4 9 g/l (as nickel) Ammonium sulphate 40 g/l Benzenesulphonylurea 2 g/l Sodium allyl sulphonate 3.0 g/l Nonyl phenol ethoxylate 0.25 g/l surfactant Demineralised water qs. to 1 litre The pH of the bath was adjusted to 8.0 with dilute sulphuric acid or ammonia.

Sufficient male and female electrical connectors were electroplated in the foregoing bath with moderate agitation at a cathode current desity of 1.0 A/dm2, a bath temperature of 25"C., and for a time sufficient to deposit 2.51l of Pd/Ni alloy, using a platinised titanium mesh anode and continuous filtration of the bath through a carbon impregnated filter cartridge, to make therefrom a 40-way two-part edge connector.

To test the wear resistance of the palladium-nickl electrodeposit on the mated pairs of the edge connector, the latter was parted and re-connected 500 times and the force required to make each insertion was measured. Any increase in the force required would show that the surface of the electrodeposit had become roughened and hence that the wear resistance was poor. By way of comparison, a similar two-part edge connector bearing an electrodeposit obtained from the same bath save that the benzenesulphonylurea was omitted therefrom was tested in the same manner.These tests showed that whereas the comparison connector produced from the bath containing no benzenesulphonylurea exhibited a great increase in the force required for insertion, the connector produced from the bath in accordance with the invention exhibited only a relatively small increase in the insertion force after the 500 insertions.

Microscopic examination of a cross-section of the palladium-nickel electrodeposit obtained from the bath of the invention described in the foregoing Example showed it to exhibit a laminar structure, whereas the comparison electrodeposit exhibited an amorphous orcolumnarstructure. It was also found that the presence of benzenesulphonylurea in the bath produced a reduction in the internal stress of the palladium-nickel deposit.

Example 2 A plating bath was made up having the composition described in Example 1 except that the benzenesulphonylurea was replaced by the same quantity of sulphadiazine.

Using the same process parameters as in Example 1, connectors for a two-part edge connector consisting of 100-way mated pairs were formed with a 2.5 y thick deposit of Pd/Ni alloy having a laminar structure and a reduced internal stress.

CLAIMS (Filed on 4/2/83) 1. A bath for the electrodeposition of a palladium-nickel alloy of improved wear resistance comprising an aqueous solution contaning palladium and nickel ammines and having a palladium content of from 5 to 30 grams per litre and a nickel content of from 5 to 30 grams per litre with the relative proportions of palladium and nickel beng such that the alloy obtained from the solution by electrodeposition has a palladium content of from 30 to 95% by weight, characterised in that the bath contains as a wear resistance improvement additive an effective amount of an aromatic sulphonamide derivative represented by the general formula:

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. Example 1 A plating bath having the following composition was made up using known techniques: Pd (NH3)4C12 20 g/l (as palladium) Ni(NH3)6SO4 9 g/l (as nickel) Ammonium sulphate 40 g/l Benzenesulphonylurea 2 g/l Sodium allyl sulphonate 3.0 g/l Nonyl phenol ethoxylate 0.25 g/l surfactant Demineralised water qs. to 1 litre The pH of the bath was adjusted to 8.0 with dilute sulphuric acid or ammonia. Sufficient male and female electrical connectors were electroplated in the foregoing bath with moderate agitation at a cathode current desity of 1.0 A/dm2, a bath temperature of 25"C., and for a time sufficient to deposit 2.51l of Pd/Ni alloy, using a platinised titanium mesh anode and continuous filtration of the bath through a carbon impregnated filter cartridge, to make therefrom a 40-way two-part edge connector. To test the wear resistance of the palladium-nickl electrodeposit on the mated pairs of the edge connector, the latter was parted and re-connected 500 times and the force required to make each insertion was measured. Any increase in the force required would show that the surface of the electrodeposit had become roughened and hence that the wear resistance was poor. By way of comparison, a similar two-part edge connector bearing an electrodeposit obtained from the same bath save that the benzenesulphonylurea was omitted therefrom was tested in the same manner.These tests showed that whereas the comparison connector produced from the bath containing no benzenesulphonylurea exhibited a great increase in the force required for insertion, the connector produced from the bath in accordance with the invention exhibited only a relatively small increase in the insertion force after the 500 insertions. Microscopic examination of a cross-section of the palladium-nickel electrodeposit obtained from the bath of the invention described in the foregoing Example showed it to exhibit a laminar structure, whereas the comparison electrodeposit exhibited an amorphous orcolumnarstructure. It was also found that the presence of benzenesulphonylurea in the bath produced a reduction in the internal stress of the palladium-nickel deposit. Example 2 A plating bath was made up having the composition described in Example 1 except that the benzenesulphonylurea was replaced by the same quantity of sulphadiazine. Using the same process parameters as in Example 1, connectors for a two-part edge connector consisting of 100-way mated pairs were formed with a 2.5 y thick deposit of Pd/Ni alloy having a laminar structure and a reduced internal stress. CLAIMS (Filed on 4/2/83)

1. A bath for the electrodeposition of a palladium-nickel alloy of improved wear resistance comprising an aqueous solution contaning palladium and nickel ammines and having a palladium content of from 5 to 30 grams per litre and a nickel content of from 5 to 30 grams per litre with the relative proportions of palladium and nickel beng such that the alloy obtained from the solution by electrodeposition has a palladium content of from 30 to 95% by weight, characterised in that the bath contains as a wear resistance improvement additive an effective amount of an aromatic sulphonamide derivative represented by the general formula:

wherein Ar is an optionally substitued phenyl group; R1 is hydrogen or an aliphatic radical; and R2 is a nitrogen-containing group selected from: (1) -CO-NH2;

2. A bath as claimed in Claim 1, wherein the aromatic sulphonamide derivative is benzenesulphonylurea or sulphadiazine.

3. A bath as claimed in Claim 1 or 2, wherein the aromatic sulphonamide derivative is present in an amount of from 1 to 10 grams per litre.

4. A bath as claimed in Claim 1, 2 or 3, wherein the bath also contains as a further additive an unsaturated aliphatic monosulphonic acid or a sodium salt thereof.

5. A bath as claimed in Claim 4, wherein the further additive is sodium allyl sulphonate.

6. A bath as claimed in any preceding claim, wherein the bath has a pH in the range from 7.5 to 10.

7. A bath for the electrodeposition of a paliadium-nickel alloy, substantially as hereinbefore described in Example 1 or 2.

8. A method of producing a bright laminar electrodeposit of a palladium-nickel alloy, which comprises electrodepositing said alloy on to an electrically conductive substrate from a bath as claimed in any one of Claims 1 to 6, the bath being operated at a temperature in the range from 20 to 550C and a cathode current density in the range from 0.5 to 2.5 A/dm2.

9. A method of producing a bright laminar palladium-nickel alloy electrodeposit, substantially as hereinbefore described in Example 1 or 2.

10. An electrical or electronic contact or connector having a contact surface composed of a palladium-nickel alloy obtained by the method claimed in Claim 8 or 9.