GB1583923A - Electrodeposition of tin/nickel alloys - Google Patents

Description

(54) ELECTRODEPOSITION OF TIN/NICKEL ALLOYS (71) We, PMD CHEMICALS LIMITED, a British company, of Broad Lane, Coventry, CV5 7AY, Warwickshire, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to the electrodeposition of tin/nickel alloys and the like. While it is principally concerned with tin/ nickel alloys as such (particularly bright tin/ nickel alloys) and will be described with reference to such alloys, other elements such as cobalt may be co-deposited. Such a ternary system is described for example in U.S. Patent Specification 3,772,168.

Electrodeposition of tin/nickel alloys is known in the art and the above-mentioned U.S.

Specification is but one example of the several patent specifications in this field. There is also a general discussion in an article by Dillenburg entitled "Die Abscheidung von Zinn Nickel-Legieurungsniederschlägen" in Galvanotechnik D7963 Saulgau 63(1972) Nr.4 at pages 343-346. The basic Parkinson electrolyte referred to therein contains 250 g/l Nickel chloride 50 g/l Divalent Tin chloride 40 g/l NH4HF2 and is operated at a pH of 2.5 (adjusted with ammonia) and, fairly critically for a semi-bright finish, a temperature of 68-72"C. High temperatures and low pH's lead to corrosion and oxidation problems and one of the solutions to the problem is described in the above article namely a purely chloride electrolyte which can be used at a higher pH.

A further discussion of the prior art is set out in the above U.S. Patent which claims an electrolytic method for depositing corrosion resistant tin-nickel, tin-cobalt and tin-nickelcobalt coatings on a metal base comprising providing an aqueous acid bath at pH 3.8 to about 5.5 containing bivalent water soluble salts of nickel, tin and cobalt in amounts for nickel and cobalt equivalent to 125 to 450 grams per liter as bivalent nickel chloride and 25 to 110 grams per liter as stannous chloride, there being also present in said bath the combination of 20 to 100 grams per liter (1) alkali or ammonium fluoride or (2) alkali or ammonium fluoroborate with a non-volatile amine derivative reactive with said fluoride or fluoroborate to form the amine salt thereof, the amine of said amine salt being present in an amount of from 40 to 100 cubic centimetres per liter; maintaining said bath at a temperature of about 40 to 90"C; and passing current through said bath at an average current intensity between 0.1 to 5 amperes per square decimeter using a nickel anode and providing said metal base as the cathode. The amine is said to give good throwing power and a bright finish and a number of amines are described particularly ethylene diamine and triethylenetetramine. However the polyethylene imines are all of low molecular weight and are used in relatively large amounts as pH adjusters.

According to the invention there is provided an aqueous solution for the simultaneous electrodeposition of tin and nickel, containing nickel and stannous ions and, in addition, a polyethylene imine having a molecular weight in the range 10,000 to 30,000 as a brightener.

The nickel and tin are preferably present as chloride but the fluorides, for example, could be used instead. Other preferred features of the basic solutions will be apparent from the above U.S. Patent.

Ethylene imines are conveniently prepared by copolymerising ethylene dichloride and ammonia and for the purposes of this invention the preferred molecular weight of the imine is about 20,000. The pH is desirably adjusted with ammonia to 4-6 preferably about 5.5.

Operating temperatures should be in the range 68-75"C.

Preferably ammonium bifluoride is present in an amount of at least 40 g/l, and the polyethylene imine in an amount from 0.01 to 0.03% by volume.

It has been found that naphthalene trisulfonic acid is particularly suitable as a stress reducer in the solutions of the invention.

The alloy may be deposited direct on copper and copper base alloys. On steel an undercoat of not less than 0.0003 in. (0.008 mm) of copper is recommended. Aluminium and zinc-base alloys should also be first plated with copper.

The plating tank is desirably of steel lined with rubber or plastic; however free sulphur and filler contents of the rubber should be low and plastics containing plasticiser are unsuitable.

The electrolyte is usually operated at 700C (158"F) and suitable heating methods are external water jacket steam coils or internal electric heaters cased in nickel. Piping, pumps and filters may be neoprene lined or of nickel. The electrolyte should be kept clear by filtration and cloth alone is unsuitable for a filter medium as it will not retain fine particle which cause pitting. Nickel anodes are preferably used with the tin content maintained by regular additions of stannous chloride (approximately 3.8 lib/1000 A hr depending on drag-out). Separate tin and nickel anodes can be used in the ratio 1:2 on the same anode circuit; the tin anodes must be bagged and withdrawn from the electrolyte when not in use, but nickel anodes should remain in the electrolyte.

The pH may be measured with narrow range indicator papers and adjusted by additions of hydrochloric acid or ammonia.

The stannous tin concentration should be maintained at the desired concentration; this concentration will tend to decrease with time due to oxidation to the stannic form. Adjustment is conveniently by addition of stannous chloride and ammonium bifluoride in equal amounts but they should be dissolved in water and brought into operating pH before adding to the main tank.

The nickel concentration may be maintained by additions of nickel chloride.

Purification of the bath can be carried out with activated carbon at 2 gpl and maintaining at 70"C for 2 hours then filtering. If contamination with metallic impurities is found, plating out overnight steel cathodes at 5 a.s.f. will purify the electolyte.

The tin nickel deposit has little self-smoothing action and its brightness will therefore depend on the quality of the surface to be plated, a bright deposit is obtained on a clean polished article.

Example Composition of Bath Tin chloride (SnCl2 2H20) - 50 g/l Nickel chloride (NiC12 6H20) - 250 g/l NH4F HF - 40 g/l NH4 OH - 35 mls/l Naphthalene trisulfonic acid (NTSA) - 0.2 g/l Aripol S5 - 0.025% (= 0.25 mls/litre) Aripol S5 consists of a polyethylene imine based polymer as a 20% solution with a pH of approximately 7. This material is sold by Float Ore Ltd. of Uxbridge.

Procedure for making up the bath A tank is filled with about half the required volume of demineralised water and heated to 65"C. The constituents are added in the following order: 1. Ammonium bifluoride 2. Ammonia 3. Stannous chloride 4. Nickel chloride The solution is allowed to stand and is then carbon treated with 2 g/ l carbon at 65"C for three hours. It is then filtered. The pH of the solution is adjusted to 5.5 and the NTSA and Aripol S5 are added followed by water to make up to the required volume.

Operating Conditions Temperature - 70"C pH - 5.5 Current density - Rack plating 10-40 A/ft2 Barrel plating 5-15 A/ft2 Plating rate - Rack plating 0.6,a/min at l8 A ft3 Barrel plating 7.5,u in 20 min at 10 A ft2 The composition of the alloy was 65 % Tin/ 35 % Nickel which corresponds to the equiatomic ratio and is achieved unless the electrolyte composition or the operating conditions are grossly out of balance.

A particular advantage obtainable using the electrodeposition method of the present invention is that a barrel plating technique can be used having conventional apparatus.

WHAT WE CLAIM IS: I. An aqueous solution for the simultaneous electrodeposition of tin and nickel. containing nickel and stannous ions and, in addition, a polyethylene imine having a molecular weight in the range 10,000 to 30,000 as a brightener.

2. A solution according to claim I wherein the polyethylene imine has a molecular weight of about 20,000.

3. A solution according to claim 1 or 2, wherein the amount of the polyethylene imine present is from 0.01 to 0.03% by volume.

4. A solution according to any preceding claim wherein the pH is in the range 4 - 6.

5. A solution according to claim 4 wherein the pH is about 5.5.

6. A solution according to claim 4 or 5 which contains ammonia as pH adjuster.

7. A solution according to any preceding claim which contains nickel chloride and stannous chloride.

8. A solution according to claim 7 which contains 125 - 450 g/l nickel chloride and 25 110 g/l stannous chloride.

9. A solution according to any preceding claim which contains at least 40 g/l ammonium bifluoride.

10. A solution according to any preceding claim, which also contains naphthalene trisulfonic acid.

11. A solution according to claim 10, wherein the amount of naphthalene trisulfonic acid is about 0.2 g/l.

12. A method for the simultaneous electrodeposition of tin and nickel in which there is employed a solution according to any preceding claim.

13. A method according to claim 12, wherein the solution is maintained at a temperature in the range 68-75"C.

14. A method according to claim 12 or 13 which employs a barrel plating process.

15. A method according to claim 12 substantially as hereinbefore described.

16. A tin/ nickel alloy electrodeposited by a method according to any one of claims 12 to 15.

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

Claims (16)

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

   The composition of the alloy was 65 % Tin/ 35 % Nickel which corresponds to the equiatomic ratio and is achieved unless the electrolyte composition or the operating conditions are grossly out of balance.

   A particular advantage obtainable using the electrodeposition method of the present invention is that a barrel plating technique can be used having conventional apparatus.

   WHAT WE CLAIM IS: I. An aqueous solution for the simultaneous electrodeposition of tin and nickel. containing nickel and stannous ions and, in addition, a polyethylene imine having a molecular weight in the range 10,000 to 30,000 as a brightener.
2. 2. A solution according to claim I wherein the polyethylene imine has a molecular weight of about 20,000.
3. 3. A solution according to claim 1 or 2, wherein the amount of the polyethylene imine present is from 0.01 to 0.03% by volume.
4. 4. A solution according to any preceding claim wherein the pH is in the range 4 - 6.
5. 5. A solution according to claim 4 wherein the pH is about 5.5.
6. 6. A solution according to claim 4 or 5 which contains ammonia as pH adjuster.
7. 7. A solution according to any preceding claim which contains nickel chloride and stannous chloride.
8. 8. A solution according to claim 7 which contains 125 - 450 g/l nickel chloride and 25 110 g/l stannous chloride.
9. 9. A solution according to any preceding claim which contains at least 40 g/l ammonium bifluoride.
10. 10. A solution according to any preceding claim, which also contains naphthalene trisulfonic acid.
11. 11. A solution according to claim 10, wherein the amount of naphthalene trisulfonic acid is about 0.2 g/l.
12. 12. A method for the simultaneous electrodeposition of tin and nickel in which there is employed a solution according to any preceding claim.
13. 13. A method according to claim 12, wherein the solution is maintained at a temperature in the range 68-75"C.
14. 14. A method according to claim 12 or 13 which employs a barrel plating process.
15. 15. A method according to claim 12 substantially as hereinbefore described.
16. 16. A tin/ nickel alloy electrodeposited by a method according to any one of claims 12 to 15.