Note: Descriptions are shown in the official language in which they were submitted.
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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
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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
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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
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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
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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.
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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.
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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
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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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.
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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.
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