JPH0319302B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD This invention relates generally to a method for electroless nickel plating of aluminum and its alloys.

Technical Background Electroless nickel plating is a method of great importance to metal finishers and
The method is widely applicable to many metal substrates including copper, nickel, aluminum and their alloys. However, metals to be plated such as aluminum, magnesium, and their alloys, for example, have an oxide layer on their surface that requires special treatment to prepare the surface for plating before plating. Therefore, it posed a special problem for plating companies.

While the present invention allows for the electroless plating of metals such as nickel, cobalt and nickel-cobalt alloys onto such metallic substrates, the following discussion will primarily focus on the surfaces of aluminum and aluminum alloys. It is described that the material is adapted to perform electroless nickel plating by applying a zinc coating to the material.

Generally, aluminum products are first cleaned of organic contaminants on the surface, subsequently etched to remove solid impurities and alloying components from the surface, treated to remove oxide layers, and then the cleaned surface is re-treated. Coated with a protective coating such as zinc or tin to prevent oxidation. Aluminum products are typically cleaned after each of the treatments described above and made ready for electroless nickel plating.

However, the electroless nickel plating baths used to plate zinc-coated aluminum have a limited lifespan compared to baths used to plate other alloy metals such as flat steel. is short. For example, typically a bath that can be used for about 10 turnovers for steel is about 50% for plating aluminum.
Only turnovers can be used. The bath must be discarded and replaced since further use will cause bubbles to form when plating nickel on aluminum. Here, turnover is defined as the period during which the amount of nickel plated and deposited becomes equal to the amount of nickel in the bath. For example, a bath initially containing about 6 g/nickel will typically be replenished with nickel salt as the nickel is depleted during plating to bring the concentration back to 6 g/nickel. This cumulative replenishment of 6 g/nickel represents one turnover.

Zinc coating is a commercially important method for pre-treating aluminum surfaces, as it is a relatively simple method of immersing the aluminum product in an alkaline solution containing zincate ions. The amount of zinc deposited is actually very small and depends on the type of soaking bath used and its duration, the aluminum alloy, the temperature of the solution, the method of pretreatment, and is typically down to 0.1 microns. It is used with a thickness of

An alternative method of coating zinc is disclosed in U.S. Pat. No. 3,666,529 to Wright et al., which essentially involves exposing the aluminum crystals and then nickel plating. The aluminum was etched with an acidic nickel chloride solution, the nickel coating was removed with _HNO3 , activated with an alkaline solution containing hypophosphite ions, and plated with an alkaline strike coating of nickel at 85-90°C, followed by A method of treating aluminum surfaces is disclosed which consists of electroless plating until the required nickel thickness is achieved.

Bellis et al., U.S. Pat. No. 3,672,964, pre-treats the surface of aluminum with an aqueous solution of hydrofluoric acid and a substance that replaces aluminum and is active on electroless plating nickel; It is disclosed that the pretreated aluminum surface is then plated using an electroless nickel bath with a pH of 6 to 7 containing amine borane and a monovalent or divalent sulfide compound. however,
These patents fail to address the problems encountered in electroless nickel plating of zinc-coated aluminum and offer only alternative methods that result in higher costs and wasted time.

DISCLOSURE OF THE INVENTION Electroless plating of aluminum pretreated with zinc or other protective coatings can be improved by using multiple plating baths under controlled conditions. The method of the present invention generally comprises forming a thin second protective coating of nickel on a zinc-coated surface in a nickel plating bath, such as an electroless nickel plating bath, followed by:
It consists of plating the surface using a separate nickel plating bath to the required thickness and physical properties. The method of the present invention thus uses two nickel plating baths, and the first
A plating bath is used to form a thin protective coat of nickel on the zinc coated surface, and a second plating bath is used to plate a final coat of nickel. The method of the invention results in:
The turnover life is approximately doubled compared to the conventional method of plating zinc coated aluminum to the required thickness in one plating bath. Furthermore, even though the first plating bath is used to directly form the second protective coating on the zinc surface, its ability remains undiminished until turnover reaches its limit. This method is clearly different from the conventional method of contacting a zinc-coated surface with a plating solution for a relatively short period of time to achieve a desired thickness. By using the method of the invention, the amount of work when processing, for example, through two plating baths in sequence, is substantially greater (approximately twice as much) than when using the plating baths separately. .

EMBODIMENTS OF CARRYING OUT THE INVENTION Aluminum articles to be electrolessly nickel plated are pretreated by well-known techniques and methods to provide a protective coating with other metals such as zinc, tin, etc., as described above. A small amount of metal, usually less than 10%, is plated with the metal of the protective coating for purposes such as altering the plating characteristics of the coating. Many metals such as cobalt, nickel, copper and iron etc. can be used for this purpose.

Bath compositions for electroless nickel plating to form nickel coatings are well known in the art, and plating methods and compositions have been published in various publications. For example, bath compositions for electroless nickel plating are disclosed in U.S. Pat.
No. 2690402, No. 2762723, No. 2935425, No. 2929742, and No. 3338726. Other effective compositions for plating nickel and its alloys are described in the 35th edition of Netal and Plastics Publications, Inc., Westwood, New Jersey. Metal Finishing Guidebook, published in 1989, pages 483-486. These known documents are incorporated as references in this description.

Generally, electroless nickel plating solution consists of a solvent,
It consists of four compounds, typically dissolved in water. They include (1) a source of nickel ions, (2) a reducing agent such as hypophosphite or amine borane, and (3) an acidic or alkaline PH regulator to achieve the desired hydrogen ion activity. (4) It is a sufficient complexing agent to prevent precipitation of metal ions in solution. A suitable complexing agent for electroless nickel plating solution is
Many of these are described in the above-mentioned literature. In some cases, complexing agents are useful but not essential. It is clear in the art that normally the nickel or other metal used is provided in the plating solution in the form of an alloy with other metals. For example, when hypophosphite is used as a reducing agent, nickel and phosphorus are included in the plating. Similarly, the use of amine borane results in the inclusion of nickel and boron in the plating. Thus, the use of what is referred to as nickel usually means that other components are also plated therewith.

Nickel ions can be provided using any soluble salt such as nickel sulfate, nickel chloride, nickel acetate, and the like. The concentration of nickel in solution varies widely, from about 0.1 to 100 g/
Preferably it is about 2-50 g/, for example 2-10 g/.

The reducing agent is typically added to the plating bath with hypophosphite ions from a suitable source such as sodium hypophosphite, potassium hypophosphite, ammonium hypophosphite, nickel hypophosphite, etc. supply. Other reducing agents such as amine borane, borohydride, hydrazine, etc. may also be used as appropriate. The overall concentration of reducing agent is in excess of an amount sufficient to reduce the nickel in the plating solution.

The plating bath is acidic, neutral or alkaline and the acidic or alkaline PH regulator is selected from a wide range of compounds such as ammonium hydroxide, sodium hydroxide, hydrochloric acid and the like. The pH of the plating bath is in the range of about 2 to 11.5, and when plating the second protective film, the pH is 2 to 7, for example 4 to 6.
It is preferable that it is in the range of .

The complexing agent is selected from a number of suitable compounds containing anions, such as compounds such as acetate, citrate, glycolate, pyrophosphate, etc., and mixtures thereof. The range of complexing agents is very wide, for example from about 0 to 300 g/, preferably from 5 to 50 g/, based on the anion.

Electroless nickel plating baths can also contain other well-known auxiliaries such as buffers, bath stabilizers, ratio activators, brighteners, etc. Suitable plating baths include dissolving the compounds in water; and
It is created by adjusting the pH to the required range.

Aluminum articles coated with a zinc protective coating may be prepared by using a first plating bath to prepare a second protective coating suitable for plating without blistering onto a nickel finish plating, e.g. , up to 2.5 microns (0.1 mil) or larger, preferably 0.1-2.1 microns (0.005-0.08
The second protective coating is plated by immersion in an electroless nickel plating bath to a thickness of, for example, 0.2-1.3 microns (0.01-0.05 mil). Depending on the parameters of the plating bath, an immersion time of 15 seconds to 15 minutes usually provides the required coating. The bath temperature ranges from about 25°C to the boiling point, e.g. 100°C,
Preferably a range of about 35-95°C is used.

The next step in the method of the present invention is to obtain a nickel plating of approximately 30 mm to the required thickness and physical properties.
This is carried out by immersing the nickel-plated product in a second electroless nickel plating bath maintained at a temperature of -100°C, for example the boiling point, preferably 80-95°C. up to 127 microns (5 mils),
The most common thickness is 2.5 to 51 microns (0.1 to 2 microns).
mil) range applies.

The degree of plating depends on many factors,
They are (1) pH of the plating solution, (2) concentration of the reducing agent, (3) temperature of the plating bath, (4) concentration of soluble nickel, and (5) volume of the bath cm ³ / The ratio of the area to be plated cm ² and
It is clear in the art that (6) the presence or absence of soluble fluoride salts (ratio regulators) and (7) the presence or absence of wetting agents and/or agitation, and the various parameters described above are important for the present invention. It is also clear that the present invention is exemplified as a general example of implementation, and the present invention resides in that plating can be performed effectively by using a plurality of baths as described above.

Experimental examples of various plating baths and plating conditions in methods that can be implemented are described below.

Experimental Examples Aluminum Association Number 3003 aluminum plates (21/2 x 4 inches) were alkaline cleaned, water washed, acid etched, water rinsed, desmutted, and water washed. Then the plate was coated with 100g/ZnO and 500g/
of NaOH, 1 g of FeCl ₃ and 10 g of Rothsiel's salt at room temperature.
Coated with zinc for seconds. The boards were washed in water and some boards were heated to about 90°C in an electroless nickel plating solution sold by ENPLATE, Inc. under the trade name ENPLATE NI-431.
It was held in water and immersed for about 30 minutes before being plated. about
A 102 micron (0.4 mil) coating was applied to each board. The nickel and hypophosphite concentrations were corrected when the nickel concentration decreased to approximately 4 g/min. It takes 5 minutes before blisters start to form on the nickel plating.
I was able to use turnover. The bath typically cannot be used to plate further zinc-coated aluminum at this point.

The zinc-coated aluminum plate prepared as described above is coated with a thin second layer of nickel at 40° C. for 3 minutes in a first electroless nickel plating bath as follows.
Plated with a protective coating (approximately 0.5 microns (0.02 mils)).

Nickel sulfamate 24g / Tetrapotassium pyrophosphate 60g / Sodium hypophosphite 27g / NH ₄ OH to maintain pH 10 Next, immerse the plating bath in the second plating bath, which has already used 5 turnovers, to coat the nickel without blisters. I was able to get a good understanding. A nickel thickness of about 10 microns (0.4 mils) was created with a soak time of about 30 minutes. When the plated plate was removed and the zinc coated aluminum plate (without the second protective coating of nickel) was immersed, it was blistered and blistered. As a result of repeating the above procedure several times, the zinc-coated aluminum plate with the second protective coating was able to obtain a blister-free plating compared to the one without the second protective coating. An additional 4 turnovers were used, bringing the bath to a total of 9 turnovers. The bath is usually about 9
Although it was possible to plate a board with the second protective coating even after ~10 turnovers, the plating speed became very slow.

This example experiment shows that the life of a second electroless nickel plating bath used to plate zinc coated aluminum is immersed in the second electroless plating bath. We have previously demonstrated that coating with a thin nickel second protective coating can extend life.

Experimental Example An aluminum plate coated with zinc in the same manner as described above was coated with NHOH in a first electroless plating bath adjusted to pH 7.5 at 65°C for 2 minutes, having the following composition. A thin second protective coating of nickel (approximately 0.5 microns (0.02 mils)) was plated.

NiSO ₄・6H ₂ O 4g / CoSO ₄・7H ₂ O 28g / Sodium citrate・2H ₂ O 75g / Ammonium hydroxide 9.4g / Sodium hypophosphite 28g / NH ₄ Cl 42g / This plate was used as part of the experimental example. When immersed in the plating bath No. 2 (5 turnovers used), nickel plating without blisters was obtained. An aluminum plate without the second protective coating was immersed in the same bath and was blistered.

Experimental Example An electroless nickel plating solution with the trade name ENPLATE NI-431 sold by Ensone, Inc. was used in the first plating bath.
A thin second protective coating was electrolessly plated and repeated in the same manner as the experimental example, thereby obtaining similar results. That is, the aluminum plate with the second protective coating was plated without blisters, and the aluminum plate without the second protective coating had blisters in the plating.

In the above description, preferred application examples of the present invention have been described, but it is clear to those skilled in the art that various applications are possible within the spirit and scope of the present invention, and the scope of the present invention does not extend beyond these examples. It also includes all applications.

Claims (1)

Claims: 1. Replenishment as necessary to maintain a predetermined metal concentration and until an electroless metal coating made on a zinc or tin coated aluminum substrate loses its tackiness and forms bubbles. In the first electroless metal plating bath, which is to be discarded after use, the aluminum substrate coated with zinc or tin is plated with metal to a predetermined thickness, thereby eliminating sticky bubbles. A method for plating an aluminum substrate with a thin electroless metal coating in a second electroless metal plating bath before plating to a predetermined thickness in the first electroless metal plating bath. Plating the metal film and
and the second electroless metal plating bath contains the same source of metal ions and a reducing agent for reducing the metal ions. How to increase 2. The method of claim 1, wherein the thin metal coating applied to the zinc or tin coating on the aluminum substrate is up to about 2.5 microns (0.1 mil) thick. 3. The method of claim 2, wherein the thin metal coating has a thickness of about 0.1 to 2.1 microns (0.005 to 0.008 mils). 4. The method of claim 1, wherein the first and second electroless metal plating baths are plating baths of cobalt, copper, nickel, or alloys thereof. 5. The method of claim 4, wherein the first and second electroless metal plating baths are nickel plating baths. 6. A method of plating nickel on the surface of a zinc-coated aluminum substrate, comprising: (a) plating the surface of the zinc-coated aluminum substrate with a first electroless nickel plating bath having a pH of about 2 to 12; (b) applying a second nickel coating over said first nickel coating to a predetermined thickness by a second electroless nickel plating bath having a pH of about 2 to 7; (c) the first nickel coating is thinner than the second nickel coating, and (d) the first and second electroless nickel plating baths are a source of nickel ions and for reducing nickel ions. A method for increasing the turnover life of a first electroless nickel plating bath, characterized in that the bath comprises: 7. The first nickel coating coated on the zinc or tin coating coated on the aluminum substrate is approximately
7. The method of claim 6, wherein the thickness is up to 2.5 microns (0.1 mil). 8. The method of claim 6, wherein the first electroless nickel plating bath contains a hypophosphite reducing agent. 9. The method of claim 6, wherein the second electroless nickel plating bath contains a hypophosphite reducing agent. 10. The method of claim 6, wherein the second electroless nickel plating bath contains an amine borane reducing agent. 11. The method of claim 6, wherein the first electroless nickel plating bath has a pH of about 7 to 12. 12. The method of claim 11, wherein the first electroless nickel plating bath contains a hypophosphite reducing agent. 13. The method of claim 12, wherein the second electroless nickel plating bath contains a hypophosphite reducing agent. 14. The method of claim 12, wherein the second electroless nickel plating bath contains an amine borane reducing agent.