Note: Descriptions are shown in the official language in which they were submitted.
~3~34
Case No . Pull ,135
EIECTROLESS NICKEL INSHORE S~LUlloN
AND PROCESS FOX REJUVENArICN
Background of the Invention
The present invention is broadly applicable to the
deposition of a metallic plating on polymeric plastic substrates,
and more particle lye to an improved initiator solution and
process for treating copper and copper alloy substrates to render
them receptive to the electroless deposition of nickel on copper
and copper alloy substrates.
An electroless copper plating followed by an electroless
nickel plating has be found to be a very useful composite
metallic coating on polymeric substrates such as electrical
component housings because of the excellent electromagnetic
interference (EM) shielding which is provided by such coating.
; The deposition of about 20 to about 40 micro inches of electroless
copper on such a polymeric substrate provides the requisite EM
shielding and the subsequent electroless nickel over plate provides
for improved corrosion resistance and decorative appearance of the
cc~osite plate.
A continuing problem has been encc~ntered in effecting a
uniform electroless nickel deposit on copper or copper alloy
substrates in that the electroless nickel process is somewhat
unpredictable depending upon the specific type of electroless
nickel process employed. Generally, electroless nickel processes
can be categorized as being of the high temperature ~175 to
212F) acid process and the low temperature (75 to 160F)
1~3~
alkaline pro ox so. Initiation of a nickel deposit will occur much
faster from hot acid electroless nickel processes than in fewer
temperature alkaline electroless nickel pro ox sues in which the
initiation time may exceed 30 minutes which is commercially
unsatisfactory. The initiation time as herein used is defined as
the period commencing when a copter substrate is immersed into the
bath and ending when the nickel plating common ox s. In order to
reduce the initiation time, three general methods are currently in
use to effect fairly rapid initiation of an electroless nickel
plate on copper and copper alloy Of fax ox s which include the
electrolytic deposition of an initial nickel strike, the direct
reduction method in which the copper substrate is contacted with a
reducing agent, and, finally, the cathodic ox if method employing
an aqueous solution containing noble metal ions such as gold or
palladium to deposit catalytic reduction sites on the copper
substrate by chemical displacement. Of the foregoing, the
cathodic ox if method is considered technically superior and is
better adapted for high volume production installations.
In accordant ox with prior cathodic ox if initiator
techniques, a noble metal, particularly palladium is employed in
the aqueous solution in which a previously electroless copper
plated substrate is immersed for a controlled time period. It has
been found, however, that after only several days of heavy
production use, certain such palladium containing initiator
solutions become ineffective no ox ssitating disposal and
replacement. Because of the relatively few own ox nitration of
palladium in the initiator solution, it is not presently
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economical to subject such waste initiator solutions to recovery
of the valuable palladium constituents therein. In addition to
the cost and waste disposal problems associated with the
discarding of such spent initiator solutions, the progressive
degradation of such solutions during use also causes erratic and
unpredictable behavior of the substrates being treated in the
electroless nickel plating solution detracting from the attainment
of uniform nickel deposits thereon.
he present invention overcomes the problems and cost
disadvantages associated with prior art noble metal initiator
solutions by providing a composition which provides for a
stabilization and prolonged effective operating life of such
initiator solutions as well as a process for rejuvenating such
initiator solutions which have been rendered ineffective or
impaired due to the progressive contamination thereof particularly
by organic metal ion completing agents.
Summary of the Invention
.
It his now been discovered that the rapid degradation
and loss of effectiveness of such initiator solutions is at least
in part attributable to the progressive contamination thereof by
drag-in of residual solutions employed in the pretreatment and
electroless copper plating of polymeric substrates including
organic completing agents present in the electroless copper
plating bath. In view of the complex configuration of many such
polymeric substrates including housings for electronic components,
it is virtually impossible from a commercial standpoint to
eliminate such detrimental drag-in. Experimental tests conducted
have shown that as little as 0.3 percent by volume of a typical
electroless copper plating solution can render a palladium
initiator solution ineffective for initiating nickel deposition in
a subsequent electroless nickel plating bath within commercially
acceptable times.
It has been further discovered that the degradation and
loss of effectiveness of such initiator solutions such as
palladium initiator solutions is in part attributable due to a
precipitation of palladium compounds including palladium metal
rendering the solution less effective or totally inoperative for
initiating nickel deposition in a subsequent electroless nickel
plating bath.
Accordingly, the benefits and advantages of the present
invention in accordant ox with the process aspects thereof include
the rejuvenation of an aqueous initiator solution containing noble
metal ions which has become ineffective due to a contamination
with organic completing agents from a prior electroless copper
plating solution rendering it incapable of treating topper plated
substrates to make them receptive to a subsequent electroless
nickel plating step. In accordance with the process, bath soluble
and compatible ferris metal ions are introduced into the impaired
initiator solution in an amount sufficient to restore the
initiator solution to effective operation and generally, are
employed in amounts of about 10 Mel to about 5 g/l.
In accordance with a further process aspect of the
present invention, a stabilization and substantial prolongation of
the useful operating life of such aqueous initiator solutions is
achieved by adding controlled effective amounts of ferris ions to
the initiator solution in anticipation of progressive
contamination thereof with organic metal ion complex m g agents and
precipitation of the noble metal ions thereby maintaining the
noble metal ions present in the initiator solution available for
reaction with the copper and copper alloy substrates immersed
therein assuring rapid and predictable uniform deposition of
nickel in a subsequent electroless nickel plating step.
In accordance with the composition aspects of the
present invention, an improved aqueous initiator solution is
provided containing a controlled effective amount of noble metal
ions present to effect rapid initiation of an electroless nickel
deposit on the substrate following the pretreatment thereof in
further combination with contaminating organic metal ion chelating
agents and an effective amount of ferris ions. Preferably, the
ferris ions are present in amounts of about 40 to about 500 Mel
Additional benefits and advantages of the present
invention will become apparent upon a reading of the Description
of the Preferred EhhxIlunents taken in conjunction with the
specific examples provided.
description of the Preferred Ehtx~diments
he composition and process of the present invention is
particularly applicable for providing a composite topper and
nickel electroless plating on polymeric substrates including
playable plastics and polymeric plastics including acrylonitrile-
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butadiene-styrene (AS), polyaryl ethers, polyphenylene oxide,
polystyrene, ply carbonate nylon or the like. Such electroless
plating processes conventionally comprise a plurality of
sequential pretreatment steps to render the polymeric substrate
no ox ptive to the application of the electroless copper plating.
Conventionally, the pretreatment steps employed include a cleaning
or series of cleaning steps, if no ox scary, to rewove surface films
or contaminating substances followed thereafter by an aqueous
acidic etching step employing a hexavalent chromium solution to
achieve a desired Æ fax ox roughness or texture which enhances the
mechanical interlock between the substrate surface and the
metallic plating to be applied there over. The etched substrate is
subjected to one or a plurality of rinse treaters to extract and
rove any residual hexavalent chromium ions on the surf ox s of
the substrate which may also include a neutralization step
incorporating reducing agents to substantially convert any
residual he~avalent chromium to the trivalent state. m e rinsed
etched substrate is thereafter subjected to activation treatment
in an aqueous acidic solution containing a tin-palladium complex
to form active sites on the surf ox of the substrate followed by
one or more rinsing steps after which the activated surf ox is
subjected to an a ox berating treatment in an aqueous solution to
extract any residual tin constituents or compounds on the surface
thereof. The accelerated plastic part is again rinsed and
thereafter subjected to an electroless plating operation to effect
the deposition ox a Shapiro plate thereon over all or selected
sections of the surface thereof thereafter the topper plated
1~3~
substrate is rinsed and subject to the activator treat-
mint prior to the electroless nickel plating step.
Typical of plating processes for pretreatment of
polymeric substrates are those described in United States
Patent Nos. 3,622,370: 3,961,109, 3,962,497 and
4,204,013. US. Patent No . 3,962,497 discloses a typical
neutralization treatment while US. Patent No. 3,011,920
and 3,532,518 disclose typical one-step activation treat-
mints. US. Patent No. 4,204,013 teaches typical come
positions for etching, neutralizing, activating and
electroless copper plating of polymeric substrates. Such
electroless copper plating solutions contain organic come
flexing agents in an amount sufficient to maintain the
copper ions in solution. Typical of such completing
agents are ethylene Dunn twitter acetic acid, gluco-
heptonate, NUN tetrakis (2-hydroxy propel) ethylene
Damon or the like.
The aqueous acidic solution in accordance with
the composition aspects of the present invention contains
hydrogen ions in an amount to provide an acidic pi and
usually, a pi of less than about 1. Acidification of the
solution can be achieved by employing a variety of acidic
substances of which mineral acids are generally preferred
and among which hydrochloric acid is particularly sails-
factory. The activator solution further
i~3210~1
obtains noble metal ions such as gold, platinum, palladium and
mixtures thereof of which palladium itself constitutes a preferred
material. The concentration of the noble metal ions can generally
range from as low as about I Mel to concentrations up to about
100 Mel and higher. Generally higher concentrations are
undesirable for economic considerations and in view of the fact
that such concentrations above about 100 Mel do not provide for
any appreciable benefits aver those obtained at relatively lower
concentrations. Particularly satisfactory results are obtained
I the noble metal ion concentration is controlled within a
range of about up to about ED nil
m e copper or copper alloy substrate is contacted such
as by inversion with the aqueous activator solution which is
usually controlled at a temperature of about room temperature
(60F) up to about 100F for periods of time of about 10 seconds
up to about 5 minutes or longer. Typically, in high volume
commercial operation, immersion times of about 15 seconds up to
about 2 m m vies have provided satisfactory pretreatment for the
subsequent electroless nickel plating step. Pretreatment of the
copper or copper alloy substrate in the activator solution is
preferably done in the preset ox of bath agitation such as
mechanical agitation, cathode rod agitation, and preferably air
agitation itch has further been surprisingly found to effect a
redissolving of any noble metal precipitates formed in the
activator bath in the presence of the ferris ions in the solution.
In addition to the foregoing constituents, the aqueous
acidic initiator solution further contains controlled effective
LIZ
amounts of ferris ions present in an amount effective to stabilize
and maintain the operating efficiency of the initiator solution
aver prolonged time periods as well as to rejuvenate an initiator
solution the effectiveness of which has become impaired due to the
preset ox of con tam m cling completing agents and/or the
precipitation of the noble metal ions present. It has been
discovered that concentrations of the ferris ions as low as about
10 mgtl are effective while concentrations substantially higher
than that can key employed up to a level below that at which
excessive etching of the copper or copper alloy substrate occurs
as a result of excessive oxidation attack by the ferris ions
causing the copper substrate to deplete. The particular maximum
concentration of ferris ions will vary in consideration of the
duration of the initiation cycle, the temperature of the initiator
solution and the acidity thereof. m e higher the temperature, the
longer the treatment time and the lower the pi of the initiator
solution will necessitate a corresponding reduction in the
permissible ferris ion concentration. Generally, the
concentration of ferris ions is controlled within a range of about
10 Mel up to stout 5 g/l with concentrations of about 40 Mel to
about 500 Mel being preferred.
The ferris ions are included in the initiator solution
by the addition of bath soluble and compatible ferris salts or con
be formed in situ by the addition of iron particles and/or ferrous
salts or compounds which are subsequently oxidized to the ferris
state such as by the use of various oxidizing agents, and
I
preferably, by the bubbling of air or oxygen through the bath as
conventionally performed during air agitation thereof.
In the preparation of a fresh initiator solution, the
ferris ion concentration can be controlled within the foregoing
ranges with the concentration preferably increasing from the lower
concentration toward the upper concentration during use of the
solution to maintain stability and effectiveness thereof. I the
process of rejuvenating an initiator solution which has become
impaired due to the presence of contaminating vexing agents
therein and/or the precipitation of the noble metal constituent,
it is preferred to intrude ox the ferris ions by gradual addition
in the presence of agitation to restore activity of the solution
within a period of about one to about two hours. When an
initiator solution has been impaired primarily due to
precipitation of the noble metal ions therein, it is preferred to
intrude ox the ferris ions in the preset ox of air agitation
providing an oxidizing medium for redissolving the noble metal
ions such as palladium in the solution in which they are effective
to pretreat the copper substrate prior to the subsequent
electroless nickel plating.
In order to further illustrate the composition and
pro ox so of the present invention, the following specific examples
are provided. It will be understood that the examples are
provided for illustrative purposes and are not intended to be
limiting of the scope of the invention as herein disclosed and as
set forth in the subjoined claims.
EXALT 1
A series of molded AS plastic panels of a nominal size
of about 3 inches by about 4 inches by about one-tenth inch thick
comprised of a plastic commercially available under the
designation PUG 298 from Monsanto Chemical Ccmpa~y were subjected
to a conventional replating cycle including cleaning followed by
a water rinse and an etch treatment in an aqueous acid solution
cannoning 356 g/l chronic acid, 412 g/l sulfuric acid and 0.2 g/l
of a per fluorinated proprietary wetting agent commercially
available under the designation FC-98 from Minnesota Mining Ox
Manufacturing Company for a period of 5 m mutes at 140F. The
etched panels were thereafter cold water rinsed for 1 minutes at
70F followed by a neutralization treatment for a period of 5
minutes at 120F employing an aqueous solution containing 18 g/l
hydrochloric acid and 3 g/l hydroxyl Anne sulfate. the
neutralized test panels were thereafter water rinsed for 1 minute
at 70F and subjected to an activation treatment for a period of 5
minutes at 110F employing an aqueous acid solution containing
0.77 g/l palladium, 9 g/l stuns chloride, 35.2 g/l hydrochloric
acid and 192 g/l sodium chloride. Following activation, the test
panels were water rinsed for 1 Nat at 70~F and thereafter
subjected to an aloe aeration treatment for a period of 1 minute at
75F in a 5 percent by volume aqueous solution of fluoboric acid
followed by a water rinse for 1 minute at 70F.
Ike pretreated test panels were thereafter subjected to
an electroless copper plating step for a period of 10 minutes at a
temperature of 140F containing 40 g/l EDNA tetrasodium salt, 4.2
1~2~
g/l cupric chloride, 3 g/l formaldehyde and sodium hydroxide to
provide a pi of about 12.3. A copper deposit of about 45
micro inches was produced.
m e copper plated test panels were thereafter water
rinsed for 1 minute at 70F and immersed m an initiator solution
for a perked of 3 minutes containing 50 Mel palladium chloride
and 1 percent by volume hydrochloric acid. The panels were
thereafter water rinsed for period of 1 minute at 70F.
The resultant test panels were thereafter subject to an
electroless nickel plating step for a period of 2 minutes at 85F
containing 12 g/l nickel chloride hexahydrate, 18 g/l sodium
hypophosphite and 23 g/l citric acid.
The initiation time was about 15 to 20 seconds after the
test panels were immersed in the electrDless nickel plating
solution before a deposition of nickel on the test panels
occurred. Following an electroless nickel plating for 2 minutes
at 85F, about 2 micro inches of nickel deposit was obtained.
EXILE 2
A second series of test panels were subjected to a
replating treatment and electroless copper and nickel plating
sequin ox in accordance with the pro ox dune as described in Example
1 except that 130 Mel of ETA tetrasodium salt was intentionally
added to the palladium initiator solution to simulate a
contamination thereof as may occur in conventional commercial
practice . me test panels upon inversion in the electroless
Lowe a
nickel solution had an initiation time of about 25 seconds before
a nickel deposit kimono ox d.
EXAMPLE 3
A third series of test panels were processed m
accordance with the replating and electroless copper and nickel
plating sequence as previously described in Example 1 with the
exception that 170 my/l of Eta tetrasodium salt was intentionally
added to the aqueous palladium initiator solution. m e test
panels were subsequently immersed in the electroless nickel
plating bath and after a period of 2 aunts immersion time, the
test panels were still totally devoid of any nickel plate. Iris
example demonstrates the detrimental effect of contaminating
ccmplexing agents present in the palladium initiator solution.
EXAMPLE 4
A fourth series of test panels were processed in
accordance with the procedure as described in Example 3 with the
exception that in addition to the 170 Mel of ETA tetrasodium
salt, 170 m3/1 of ferris chloride hexahydrate was added to the
initiator solution. The AS test panels upon immersion in the
electroless nickel plating solution had an initiation time of
about 25 seconds before the nickel plating of the surf ox s thereof
ccronenced. This example illustrates the rejuvenation of an
initiator solution by the addition of a metal ion which had become
impaired due to the preset ox of excessive amounts of oomplexing
agents.
EXEMPT 5
A fifth series of test panels were processed in
accordance with the procedure and employing the solutions as
described in Example 4 with the exception that the concentration
of the ETA tetrasodi~rm salt corplexing agent in the initiator
solution was increased from 170 Mel to 510 Mel in the preset ox
of 170 mg/1 of ferris chloride hexahydrate. Upon immersion of the
test panels in the electroless nickel plating solution, an
initiation period of about 35 seconds was required to effect an
initiation of the nickel deposit on the panels.
EXAMPLE 6
A sixth series of test panels were processed in
accordant ox with the same procedure employing the same compositions
as set forth in Example 5 with the exception that the
con ox nitration of ferris chloride hexahydrate was increased in the
initiator solution from 170 Mel to 300 Mel in the preset ox of
510 Mel of the ETA tetrasodium salt ocmplexing agent. Upon
immersion of the test panels in the electroless nickel plating
solution, an initiation period of only about 20 seconds was
required to effect initiation of the nickel deposit on the test
panels.
While it will be apparent that the preferred elite ens
of the invention disclosed are well calculated to fulfill the
objects above stated, it will be appreciated that the invention is
sup ox tubule to modification, variation and change without
14
ho
departing Fran the proper scope or fair naming of the subjoined
clowns.
