CA2053342A1

CA2053342A1 - Nickel electroplating process with reduced nickel ion build up

Info

Publication number: CA2053342A1
Application number: CA002053342A
Authority: CA
Inventors: Robert A. Tremmel
Original assignee: Individual
Current assignee: MacDermid Enthone Inc
Priority date: 1990-10-22
Filing date: 1991-10-11
Publication date: 1992-04-23
Also published as: SE9103061L; ITTO910789A0; GB9122383D0; IT1249854B; ITTO910789A1; JPH04333600A; FR2668173A1; ES2034897B1; DE4134656C2; SE9103061D0; ES2034897A1; GB2249107A; DE4134656A1

Abstract

ABSTRACT OF THE DISCLOSURE

A process for electrodepositing nickel on a conductive substrate in a manner which inhibits buildup of nickel ions in the electrolyte. A sacrificial anode and insoluble iron anode are immersed in a nickel electroplating bath. The current provided to the iron anode is controlled during plating to reduce the amount of nickel buildup on solution.

Description

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NICKEL ELECTROPLATING PROCESS WITH
REDUCED NICXEL ION ~UILDUP

BACKGROUND OF THE INVENTION
The present invention relates to an improved process for electroplating wherein buildup of soluble anodic metals is reduced. More particularly, the present invention relates to the reduction of undesirable nickel ion buildup in a nickel or ferro-nickel electroplating process or bath by the utilization in the process of an insoluble ferrite electrode.
Those skilled in the art of electroplating have historically recognized that the utilization of soluble nickel anodes in ~ickel electrolyte containing baths or ferro-nickel electrolyte baths can result in a significant buildup of excess nickel ions in the electrolyte solution. The problem of metal buildup has been much more severe in recent years because of increased restrictions regarding the amount of nickel metal allowed in waste effluent. Consequently, the majority of the plating solution that is dragged out is returned to the original plating solution. This may be done by utilizing common methods such as evaporative recovery or reverse osmosis. This buildup of nickel ions creates several undesirable side effects in the electroplating bath and process. These undesirable effects could include, for example, cloudy, pitted or rough deposits that can occur because of the presence of excess amounts of nickel sulfate and nickel chloride. Precipitates can also form because conformability limits have been exceeded. The excess nickel also significantly increases the expense associated with the bath.
For example, becau5e the bath eventually needs to be diluted, the existence of excess nickel ions in the bath is not only 2~3~2 environmentally undesirable but correspondingly increases the cost of processing of the electrolyte waste prior to disposal.
Additionally, the existence of the unused nickel ions is just plain inefficient.
While not intending to be bound by theory, it is apparently known to those skilled in the art that this buildup is caused because of the disparity between ultimate anode and cathode efficiency. For instance, in a "typical" nickel bath, the anode efficiency is 100%. In contrast, the cathode efficiency is only about 95%. The difference in efficiencies causes the quantity of nickel ions in solution to increase during electrolysis.
Similarly, in a typical nickel-iron bath, the anode is 100%
efficient whereas the cathode efficiency is approximately 91%;
this increased difference in efficiencies causes an even greater increase of even -more nickel ions in solution during electrolysis.
The art has attempted to solve this problem in many ~ays.
For example, attempts have been made to solve the problem by reducing the number of anodes utilized in the solution. However, this simply increases anode current density so that more m~tal ions per given anode dissolve. Anode polarization can also occur which causes increased brightener consumption in typical baths, and in ferro-nickel baths produces undesirable ferric (Fe+3) ions. Anode polarization also leads to the breakdown of complexing agents used in ferro-nickel baths. Additionally, excessive chlorine generation (also highly undesirable in these baths) may occur when such polarized anodes are utilized.

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Insoluble anodes, such as platinum-plated titanium anodes, have been used in nickel plating electrolytes to increase plating thickness in low current density areas; such an anode can also reduce nickel ion buildup. Similarly, insoluble carbon-type anodes have also been utilized in nickel and ferro nickel electrolytes. While the nickel buildup can be reduced in these electroplating baths with such anodes, the anodes previously employed by the art (e.g. platinum plated titanium anodes) tend to deteriorate quickly; can be expensive to replace; can cause increased brightener consumption; and, can contribute to the generation of deleterious decomposition products.
Sintered ferrite electrodes are sometimes recognized in the art as insoluble anodes which may be useful in cyanide-free copper-plating processes or for reducing hexavalent chromium ions in chromium electroplating processes. Such uses are taught in Tomaszewski et al., U.S. Patent Nos. 4,469,569; 4,466,865; and 4,933,051, which are assigned to the assignee of the present invention, and are incorporated herein by reference. However, it is Applicant's belief that the use of these sintered anodes in nickel plating baths has not been disclosed or suggested in the art. Such electrodes are described in detail in S.
Wakabayashi and T. Aoki, Characteristics of Ferrite Electrodes, Journal de Physique, April 1977, Cl-241 to Cl-244.

SUMMARY OF THE INVENTION
In accordance with the present invention, a nickel electroplating process is provided wherein the buildup of nickel 2~3~
ions in a nickel-based electroplating solution is substantially reduced and/or eliminated by the use of a select class of insoluble anodes which can be separately controlled as to the amount of current passed to the insoluble anode during electroplating in the nickel bath. The insoluble anode of the present invention has a surface area which is at least partially of iron composition.
The process of the present invention includes the steps of providing an effective nickel electrolyte plating bath and immersing a first anode and a second anode in the bath. The first anode is a sacrificial nickel anode and is connected to a first rectifier. The second anode is an insoluble anode wherein at least a portion of the surface area comprises an iron material. The second anode is connected to a second rectifier.
A substrate to be plated is then immersed in the electroplating bath and cathodically electrified. The first anode is anodically electrified while the current to the second anode is controlled to provide an effective amount of current to the second anode during electroplating of the substrate for inhibiting the buildup of the excess nickel ions in the solution.
It has thus been found that with the novel process of the present invention the nickel buildup can be substantially reduced thereby increasing the life of the plating bath and correspondingly reducing concentrations of nickel ions which must be disposed of at a later time. Additionally, the iron anode of the present invention has a greatly increased life over the platinum-titanium or the carbon-type anodes which were used 2al~3~ :
in the prior art, thus reducing replacement costs and down time costs caused by prior art insoluble anodes.
other advantages and benefits of the present invention will be readily appreciated by those skilled in the art in light of the following description of the preferred embodiments taken in conjunction with the examples given below and the claims appended herewith.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
Generally speaking, the process of the present invention includes the following steps. An effective nickel-based electrolyte plating bath is first provided. A first anode is immersed in the bath which is connected to a first rectifier.
A second anode connected to a second rectifier is immersed in the bath. The second anode is an insoluble anode wherein at least a portion of the surface thereof comprises an iron composition. A substrate to be plated is then immersed in the bath. The first anode is anodically electrified and the substrate is cathodically electrified. At the same time, the current to the second anode is controlled with the second rectifier for providing an effective amount of current to the second anode to inhibit the buildup of excess nickel ions in the solution.
The present invention is based on the discovery that the use of an insoluble anode containing iron, while controlling the current provided to that anode, substantially reduces the amount of nickel ions which buildup in these nickel bath solutions.

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The process of the present invention can be utilized in standard commercial nickel plating baths or nickel-iron plating baths used today. Thus, standard commercial baths which include suitable nickel ion concentrations, brighteners, complexing or chelating agents, levelers, surfactants, and other like additives, commonly used in nickel plating baths, may be utilized in the process of the present invention. Similarly, additives and additions commonly used in nickel-iron type baths may be utilized in the process of the present invention.
The first anode used in the present invention is generally a sacrificial type anode which may include, for example, a titanium basket, or the like, filled with suitable nickel chips which are sacrificially added into the bath solution as the plating process proceeds. The first sacrificial anode is connected to a separate rectifier from the second anode such that current can be independently controlled between the two anodes during the electroplating process.
Generally, the second anode utilized in the present invention is provided in the bath with surface areas such that from about 5 to 100 amps per square foot can be provided to the second anode. Typically, surface areas in such baths are provided wherein from about 10 to about 50 amps per square foot may be applied through the second anode. Preferably, surface areas in such anodes of the second anode are provided such that from about 15 to about 25 amps per square foot may be applied through the second anode.
The second anode of the present invention is an insoluble .

33~2 anode where at least a portion of the surface comprises an iron composition. In a preferred embodiment, the second anode is a sintered iron oxide structure. In a typical commercial electroplating bath, effective surface areas of the second anode will be generally in the range of from about .1 to about 12 square meters with from about .5 to about 2.0 square meters of surface area being preferred in a typical commercial bath.

In a preferred embodiment, the sintered structure is produced from an intimate blend of sintered iron oxide in combination with nickel oxide. A typical anode formulation would comprise about 90 mol% Fe203 and about 10 mol~ divalent nickel oxides. The other metals or metal oxides could also be utilized in a sintered structure provided the metal used would not be detrimental to the plating bath. Thus, copper oxides, manganese oxides and cobalt oxides could be utilized in the sintered structure. Such sintered anode structures are set forth in S.
Wakabayashi and T. Aoki Characteristics of Ferrite Electrodes, cited above, which is expressly incorporated herein by reference.

While some can be treated more efficiently than others, the substrate structure to be plated is not critical in the present invention. The substrate must, however, be a conductive-type substrate as commonly used in electroplating arts. The substrate may, for example, be either a plastic substrate or a metal substrate, depending on a desired application.

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The sintered metal anode is connected to a rectifier which is separate from the sacrificial anode such that the current supplied to the sintered iron anode can be independently controlled. It is important in the present invention that the current be controllable to provide an effective amount of current to substantially reduce the nickel buildup in the solution.
It has been found in the present invention that the amount of current supplied to the second anode to be effective in the reduction of nickel ions is generally from about 1% to about 16~
of the total current applied during the electroplating of the substrate. Typically, the current controlled to the second anode is from about 2% to about 12% of the total current applied during the electroplating process. Preferably, from about 4% to about 8% of the total current applied is through the sintered iron anode.
Thus, in accordance with the process of the present invention, the sintered iron insoluble anode, when utilized in accordance with the above teachings, has been found to substantially reduce the amount of nickel buildup in these nickel or nickel-iron plating baths. Additionally, it has been found that the sintered type anode lasts for an appreciably longer time, i.e. several years, as opposed to the prior art insoluble auxiliary anodes which lasted for substantially shorter periods of time, usually measured in weeks or months.
Further understanding of the present invention will be had by reference to the following examples in light of the above teachings.

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EXAMPLE I
A nickel electroplating bath was pr~pared in accordance with the constituents set forth in Table I.

TABLE I
Constituents of Nickel Electroplating Bath NiS04 6H20 400z/gal NiCl2 6H~0 80z/gal Boric Acid 60z.gal UDY~ITE0 Brightener 63 2.0%
UDYLITE~ Brightener 610 1.0%
pH 4.00 Temperature 140F

The above electrolyte bath was placed in a four (4) liter plating cell equipped with a titanium basket anode filled with sacrificial nickel anode chips and was connected to a first rectifier which in turn is connected to a current source. A
second sintered ferrite anode (having approximately eight (8) square inches of surface area) was immersed in the plating jar and connected to a second rectifier in line with the current source. The anodes were hooked up to separate rectifiers and to a common cathode for electroplating. The bath was electrolyzed UDYLITE is a registered trademark of ENTHONE-OMI, INC. of Warren, Michigan.
UDYLITE Brighteners 63 and 610 are obtainable from ENTHONE-OMI of Warren, Michigan.

2 ~ 2 source. The anodes were hooked up to separate rectifiers and to a common cathode for electroplatinq. The bath was electrolyzed for over 350 amp hours using standard brightener additions during this time period. The solution composition was rigorously analyzed and the deposit appearance and integrity were periodically measured and found to be acceptable. The total current supplied to the sintered ferrite anode ranged from about 4% to 8% of the total current utilized in the plating process.
The results revealed that no serious degradation products were formed, and that the pH could be maintained by the current distribution on the anodes. Brightener consumption was only slightly higher and the ferrite anode was found to be very stable with less than 0.1% weight loss. There was no detectable nickel buildup during the test period. While some chlorine was given off from the ferrite anode, the amount was not appreciable and was eliminated by small additions of sodium bromide.

EXAMPLE II
A solution of a commercial nickel-iron plating bath (NIRON~ ) was placed in a 4 liter plating cell equipped with nickel and iron anodes which were connected to a first rectifier which, in turn, is connected to a current source. In addition, a sintered ferrite anode as described in Example I, was immersed in the plating cell and connected to a second rectifier in line with a current source. As in Example I, a common cathode was NIRON is a registered trademark of ENTHONE-OMI, INC. of Warren, Mi~higan.

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used for electroplating. The bath was electrolyzed for 891 amp hours using standard brightener and stabilizer additions during this time period. The solution composition was rigorously analyzed and the deposit appearance and integrity were periodically measured and found to be acceptable. In general, about 6% of the total current was applied to the sintered ferrite anode although at times during the test this varied between 2%
and 10%. In this case the current density on the insoluble anode varied from 10 ASF to 50 ASF. Representative analytical results are given below in Table II.

TABLE II
Analvsis of Nickel Bath Component O Amp hrs. 275 Amp hrs. 891 Am~ hrs.
Ni+2 60.31 g/l 59.75 g/l 55.23 g/l NiSO4-6H2O161.30 g/l161.72 g/l 157.90 g/l NiC12-6H2O115.93 g/l105.57 g/l 85.22 g/l H3BO3 45.91 g/l 44.30 g/l 42.97 g/l Fe+2 2.40 g/l 3.82 g/l 3.20 g/l Fe+3 0.18 g/l 0.27 g/l 0.50 g/l Stabilizer H14.62 g/l14.75 g/l 14.32 g/l Brightener FN-1 3.23 % 3.16 % 3.34 %

Brightene~r FN-2 (Index) 2.44 % 0.68 % 2.10 %
pH 3.0 2.5 3.4 Stabilizer H, and Brighteners FN-1 and FN-2 are obtainable from ENTHONE-OMI, INC. of Warren, Michigan.

2 ~ 2 Panel tests made routinely during this period indicated that no serious degradation products were found. Consumption of stabilizer H and FN-2 was unaffected. FN-l Index consumption was slightly higher than normal. The very low FN-l Index number at the 275 Amp hrs. mark was due to brightener addition errors.
Nickel metal fell in concentration during the test period which is contrary to typical nickel-iron plating baths. There was no appreciable buildup of ferric iron, however, there was a significant drop of chloride ion as indicated by the reduction of NiCl2 6H2O from 115.93 g/l to 85.22 g/l. This was probably due to the evolution of chlorine at the insoluble anode. There was only a slight odor of chlorine during the test. The addition of 1 g/l of NaBr at the end of the test further reduced the chlorine odor.
The ferrite anode was weighed periodically during the tests after operating at various current densities. The total weight loss during the test period was only 2.6%. The higher the current density on the insoluble anode the greater the weight loss, although, even at 50 ASF the weight loss was not significant.

EXAMPLE III
A commercial ferro-nickel bath (UDYLITE~ NIRON~) historically had a severe problem with nickel metal buildup, and the bath had to be diluted 20% to 30% every four (4) to six (6) weeks. While not intending to be bound by theory it is believed ~3~
that the reason for the rapid buildup of nickel metal was due to:
1) a 10% disparity between anode and cathode efficiency; 2) the drag in of metal from another nickel bath; and 3) the use of efficient recoYer~ which returns almost all of the dragged out nickel back into the NIRON2 plating bath. As a result, the bath was generally diluted when the nickel metal concentration (measured as Ni+2) exceeded 15 oz/gal.
Utilizing a conventional commercial nickel-iron (NIRON~) bath already in place, about six percent (6%) of the total anode area in the tank was replaced with insoluble ferrite electrodes, in this case, about eight (8) square ft. The anode rail, on which the insoluble ferrite anodes were placed, was separated from the main bussing and connected to a separate rectifier. The cathode was common to both rectifiers. Current was applied separately to the insoluble anodes. At first, the amount of current supplied to the ferrite anodes was only about 4% of the total current; it was to eventually be increased to 10~ to control nickel metal buildup. Some chlorine evolved, and 1 g/l of NaBr was added. Tests conducted indicated that the chlorine in the air was at acceptable levels. The test was conducted under typical production conditions of from about 55,000 to 60,000 amp hours per day with the bath running around the clock with normal down times. The test was conducted for about 2 1/2 months.
Analysis of the NIRON~ plating bath, including the addition agents, at the beginning, at 26 days, and at the end of a 75 day test period is given below in Table III

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TABLE III
Analysis of NIRONX Bath ComponentBeginninq 26 Days 75 Days Nickel Metal 12.22 oz/gal12.35 oz/gal12.080z/gal Chloride 4.00 oz/gal4.25 oz/gal4.44 oz/gal NiS04 6H20 39.88 oz/gal39.68 oz/gal37.63 oz/gal NiC12 6H20 13.41 oz/gal14.23 oz/gal14.89 oz/gal Boric Acid 5.78 oz/gal5.64 oz/gal5.78 oz/gal N~icron Stabilizer 11.0 g/l11.10 oz/gal 10.20 g/l Brightener FN 1 4.0 % 3.72 % 3.8 %
Brightener 84 1.5 % 1.51 ~ 1.4 pH 3.0 3.0 3.2 As can be seen from the above analysis the nickel level, without any bath dilution, has stabilized at about 12 oz/gal. Based on previous history, the bath would normally have been diluted twice during this time period.
The consumption rates of the organic addition agents were carefully monitored during the test period. In all cases, they were essentially unchanged from normal levels. Bath performance was not affected. The examples indicate that the use of the ferrite electrodes described herein is a viable method for controlling nickel metal buildup in commercial nickel and nickel-iron plating baths. The examples also demonstrate that the use These concentrations of these materials are maintained via regular additions to keep them in an operating range prescribed by the supplier.
Maintained via periodic additions of hydrochloric acid.

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': ' 2 ~ ~ 3 ~ ~ rd of such anodes does not adversely effect addition-agent consumption nor do they generate unacceptable levels of chlorine or harmful degradation products.
While the above specification and exemplification was given for purposes of disclosing the preferred embodiment of the present invention, they are not to be construed to be limiting of the present invention.
It will be readily appreciated by those skilled in the art that the present invention can be practiced other than as specifically stated. Therefore, the scope of the present invention shall be limited only with reference to the appended claims and the equivalents thereof.

Claims

1. A process for electrodepositing nickel on a conductive substrate in a manner which inhibits detrimental buildup of unused nickel ions in the electrolyte bath, the process comprising the steps of:
(A) providing an effective nickel based electrolyte plating bath;
(B) immersing a first anode connected to a first rectifier in said bath, said first anode comprising a sacrificial nickel anode;
(C) immersing a second anode connected to a second rectifier in said bath, said second anode comprising an insoluble anode wherein at least a portion of the surface thereof comprises iron or composition containing iron;
(D) immersing a substrate to be electroplated in said bath;
and (E) anodically electrifying said first anode and cathodically electrifying said substrate while controlling the current to said second anode with said second rectifier for providing an effective amount of current to said second anode during electroplating of said substrate for inhibiting the buildup of excess nickel ions in the solution.

2. The process of Claim 1 wherein the current controlled to said second anode is from about 1% to about 16% of the total current applied during electroplating of the substrate.

3. The process of Claim 1 wherein the current controlled to said second anode is from about 2% to about 12% of the total current applied during electroplating of the substrate.

4. The process of Claim 1 wherein the current controlled to said second anode is from about 4% to about 10% of the total current applied during electroplating.

5. The process of Claim 1 wherein said second anode further comprises a sintered iron structure.

6. The process of Claim 5 wherein the sintered iron structure further comprises a mixture of nickel and iron oxides.

7. The process of Claim 5 wherein the surface area of the sintered iron structure is selected such that a current can be provided to said structures of from about 5 to about 100 amps per square foot.

8. The process of Claim 5 wherein the surface area of the sintered iron structure is selected such that a current can be provided to said structure of from about 10 to 50 amps per square foot.

9. The process of Claim 5 wherein the surface area of the sintered iron structure is selected such that a current can be provided to said structures of from about 15 to about 25 amps per square foot.

10. The process of Claim 1 wherein said second anode is a sintered structure comprising iron oxides and nickel oxides.

11. A process for electrodepositing nickel on a conductive substrate, in a manner which inhibits detrimental buildup of unused nickel ions in the electrolyte bath, said process comprising the steps of:
(a) providing an effective nickel based electrolyte plating bath;
(b) immersing a first anode connected to a first rectifier in said bath, said first anode comprising a sacrificial nickel anode;
(c) immersing a second anode connected to a second rectifier, said second anode comprising a sintered iron oxide structure having an available surface to provide a current of from about 5 to about 100 amps per square foot;
(d) immersing a substrate to be electroplated in said bath and connecting it cathodically to the first and second rectifiers;
(e) anodically electrifying said first anode and cathodically electrifying said substrate while supplying from about 5 to about 100 amps per square foot to said second anode such that the current applied to the anode is from about 1% to about 16% of the total current applied during electroplating of the substrate.

12. The process of Claim 11 wherein from about 2 to about 12% of the total current applied is through the second anode.

13. The process of Claim 11 wherein from about 4% to about 8% of the total current is applied through the second anode.

14. The process of Claim 11 wherein from about 10 to about 50 amps per square foot is applied to said second anode.

15. The process of Claim 11 wherein from about 15 to 25 amps per square foot is applied to said second anode.

16. The process of Claim 11 wherein said second anode further comprises a sintered structure which is a mixture of iron oxide and nickel oxide.

17. A process for electrodepositing nickel on a conductive substrate, in a manner which inhibits detrimental buildup of unused nickel ions in the electrolyte bath, said process comprising the steps of:
(a) providing an effective nickel based electrolyte plating bath;
(b) immersing a first anode connected to a first rectifier in said bath, said first anode comprising a sacrificial nickel anode;
(c) immersing a second anode connected to a second rectifier, said second anode comprising a sintered iron oxide and nickel oxide structure having an available surface to provide a current of from about 15 to about 25 amps per square foot;
(d) immersing a substrate to be electroplated in said bath and connecting it cathodically to the first and second rectifiers;
(e) anodically electrifying said first anode and cathodically electrifying said substrate while supplying from about 15 to about 25 amps per square foot to said second anode such that the current applied to the anode is from about 2% to about 8% of the total current applied during electroplating of the substrate.