Note: Descriptions are shown in the official language in which they were submitted.
~ 176118
SPECIFICATION
Background and Description of the Invention
. _ _
The present invention generally relates to the
treatment of metal substrates so as to render them catalytic
to subsequent electraless deposition of metals thereonto,
and is especially well suited to the electroless deposition
of nickel, cobalt, or polyalloys containing nickel and/or
cobalt onto copper that had previously been plated onto a non
conductive substrate in an electronic circuitry pattern. In
an important embodiment of this invention, printed wiring
boards are prepared which are less likely to develop electrical
short circuiting problems than plates prepared without the
use of these catalytic solutions.
Copper-plated circuits tend to oxidize, making it
highly desirable to overplate the copper with a more durable
metal to thereby enhance the circuits' corrosion resistance,
20 abrasion resistance, and solderability or~ bondability to
aluminum or gold wire by ultrasonic means or the like, while
at the same time maintaining or enhancing adequate conductivity.
Early procedures for providing overplatings included electro-
plating techniques which require electrically connecting each
individual circuit of the printed wiring board to a current
source. While electroless overplating does not require such
inefficient handling techniques, and avoids other drawbacks
of electroplating such as non-uniformity of coating at board
locations relatively remote from the power source and exposed
30 copper at the electrode connection sites, it has been found
~ 176~1~
that such electroless overplatlngs do not readily adhere
to copper or copper alloys.
When electrolessly overplating the copper circuitry
of a printed wiring board or a printed circuit board with a
nickel-phosphorus or nickel-boron deposit, general im-
provement has been found to be attained by dipping copper
clad boards into a bath of an activator without rinsing in
order to coat the copper clad board with a slightly alkaline
film prior to nickel overplating in a slightly acidic electro-
less nickel bath. Activators known to be useful in thisregard include a bath having dimethylamine borane to activate
reduction of nickel onto the copper. A serious drawback of
this procedure is that it activates the entire board including
the insulating portions thereof to also activate the reduction
of nickel onto portions of the board that are not in the
circuitry pattern for carrying current, which leads to short
circuiting or bridging, especially when the insulating portions
have metal specks therein which serve as sites for plating
initiation and bridging between specks and between specks and
portions of the circuitry.
It is believed that one important reason for the un-
desirable plating in the non-circuitry portions is the fact
that it is not possible to rinse the plate after treatment
with such activators primarily because such a rinsing step
would simply remove essentially all of the activator ~efore
it has had a chance to enhance the subsequent electroless step.
Copper specks are often embedded into the surface of the
board and they typically can not be seen by the human eye.
Specks that re~ain on the board at the time it is over-
plated with nickel or the like serve as sites for electroless
~ ~76~1~
metal deposition at locations that are not within the
circuitry pattern and which can eventually lead to short
circuiting of the circuitry.
Another approach that has been taken in attempting
to improve the electroless overplating of nickel or the
like onto copper clad boards includes the use of baths hav-
ing materials, known generally as catalyzing agents, w~ich
operate to make the copper surface more receptive to the
electroless deposition of metals thereover. A known catalyz-
ing agent is a palladium chloride dip which, although it
effectively catalyzes the copper, has been found that adhesion
between the copper and the subsequentlY electrolessly de-
posited metal is tenuous; and, as a result, when circuits made
in this manner are subjected to rugged mechanical handling,
or heat shock such as that developed during dip soldering,
there is a tendency for the conductive layer to crack or pop
free of the non-conductive base, thereby disrupting the circuit.
Discussions relative to catalyzing agents are found in
Schneble et al ~.S. Patent No. 3,226,256 and Weisenberger U.S.
Patent No. 3,431,120.
It has now been discovered that certain formulations
perform quite effectively as catalyzing agents in order to
enhance the adhesion of nickel, cobalt, or polyalloys of
nickel and/or cobalt over copper surfaces, especially those
copper surfaces found onprinted wiring boards for use in
preparing printed circuitry, while at the same time permitting
a procedure whereby these catalyzing agents in conjunction with
a rinse will enhance overdeposition only upon the metal carry-
ing components of the circuit board to the exclusion of other
metal imbedded in the board.
These results are achieved in accordance with the
present invention basically by employinq catalyzing formulations
~ ~7~118
that include nickel or cobalt and a source of a secondary,
inhibitor-type of metal such as tin, molybdenum, copper or
tungsten, together with a reducing agent. Such catalyzing
formulations can be applied to a copper surface and rinsed
to form a catalytic film for enhancing electroless over-
plating in a bath that deposits nickel or cobalt, either
alone or in combination with other metals, onto the
circuitry pattern but discourages overplating onto portions
of the board not within the circuitry pattern.
Accordingly, an object of this invention is to pro-
vide improved electrolessly plated products.
Another object of the present invention is to pro-
vide a product having improved adhesion of an electrolessly
deposited metal over copper, copper alloys, or the like.
Another object of this invention is to provide
products produced with an improved catalyzing agent.
Another object of the present invention is to
provide an improved product which exhibits enhanced adhesion
and simultaneously allows for rinsing just prior to electro-
less overplating for reducing the tendency to bridge or
short circuit.
Another object of the present invention is a
product having a catalytic surface on plated copper, which
surface can be subsequently treated by electroless deposition
of nickel, cobalt, and/or polyalloys including either~
Another object of this invention is to provide an
improved product produced by a bath including a catalyzing
agent which includes nickel or cobalt and tin, molybdenum,
copper or tungsen together with a reducing agent.
These and other objects of the present invention
will be apparent from the following detailed description,
~ 1 7~
taken in conjunction with the accompanying drawings wherein:
The Figure is a generally schematic view depicting
a production flow in accordance with this invention and
products at various stages of production.
Catalyzing agents in accordance with this invention
are, in general, polymetallic formulations of deposition-
enhancing nickel and/or cobalt metal, and of secondary or
inhibitor-type metals such as tin, molybdenum, copper and
tungsten. As such, these catalyzing agents are related to
the electroless polyalloy plating formulations shown in
Mallory U.S. Patent No. 4,019,910. Typically, the formu-
lations will be put to use within an aqueous bath which also
includes a reducing agent for electroless baths.
Any of these metals can be added as soluble salts,
salts of low solubility within the particular electroless
bath system in which they are intended to be used, esters, or
substantially any other source suitable for electroless
systems. In an important aspect of this invention, boron
is added to the system as a third metal by means of a
boron-containing reducing agent.
Suitable salts of nickel or cobalt include sulfates,
chlorides, sulfamates or other anions compatible with these
electroless systems. These same anions usually provide an
-- 5 --
~ ~7~1~8
acceptable source of salts of the secondary metals, including
for example stannous chloride, stannous fluoroborate, sodium
stannate, cuprous chloride, cuprous sulfate, and cupric salts,
although it is preferred that these secondary metals be
provided in the form of ester complexes of polyhydric compounds
which are prepared by conventional techniques involving reaction
between an oxyacid and a polyhydric acid or alcohol. The oxyacids
are generally inorganic acids of the particular metal cation,
for example, the tungstic, molybdic or boric acids. Representati~e
of the polyhydric acids or alcohols which may be employed
are carboxylic acids or alcohols which contain at least two
hydroxy groups and from about four to about fifteen carbon
atoms per molecule. Typical polyhydric compounds include acids
such as tartaric, gluconic, or glucoheptonic acid, or alcohols
such as mannitol, 2,3-butanediol or 1,2,3-propanetriol. Of
these various polyhydric compounds, the carboxylic acids are
generally preferrfd, and a particularly suitable one is gluco-
heptonic acid. The ester complexes may also be, and in certain
instances preferrably are, in the form of a polyester, that is
as ester complex formed by reacting two or more mols of the
oxyacid with one mol of the polyhydric c~mpound.
Ester complexes of these general types are forMed
and are generally believed to exist in aqueous solution as
a complex equilibrium mixture where the cation of the oxyacid
forms one or more ester linkages either with two hydroxyl
groups of the polyhydric compound or with one hydroxyl group
and one carboxylic acid group when the polyhydric compound is
an acid, for example glucoheptonic acid. Such an ester complex
has been found to be quite stable when used within baths pre-
pared with the catalyzing formulations.
l ~7611~
Catalyzing baths for use in connection with the
catalyzing agent formulations of this invention will usually
include a reducir.g agent for the cations in the bath. While
reducing agents such as hydrazine may be used, it has been
found to be most advantageous if the reducing agent is a
boron compound whereby boron cations are provided to the
system and assist in forming the catalyzing film, together
with the nickel or cobalt and the secondary rnetal. Various
boron-containing compounds can be used;they are preferably any
of those employed as reducing agents in electroless nickel
or cobalt plating baths. Typical examples include boron
hydrides, amine boranes or lower alkyl substituted amine
boranes such as dimethyl-or diethyl-amine borane. Generally,
of the various boron compounds which may be employed, the
alkylamine boranes are preferred, particularly dimethylamine
borane.
In general, when these various agents are combined
with water and formulated into a catalyzing bath, the total
bath will usually be alkaline although slightly acidic baths
can be put to ractice, a typical pH range being between 5.5
and 13, preferably between about 8 and about 11. Operating
temperatures are between room temperature and the boiling
temperature of the bath, a typical temperature range being
between about 20 and 100C. These baths are, in general,
capable of operating as electroless polyalloy plating baths;
their catalyzing function is achieved in part by using
relatively low concentrations of active ingredients and by
limiting the time period during which the article being sub-
jected to the catalyzing agent remains within the bath. Very
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~ i 7~ l g
generally, active ingredient concentrations about one-tenth
those of plating baths can be formulated. The time period is
such that the catalytic agent will form a coating to the extent
that the surface is "nucleated", typically with a tertiary
polyalloy; in order to provide a film that is not necessarily
observable to the unaided eye but which will perform as catalyzing
agent even after rinsing a substrate that had been immersed
in the bath. Generally, catalyzing bath immersion will continue
for between about 10 to 90 seconds, usually no more than 60
seconds, at approximately 0.1 mil/hour, the most appropriate
time and rate depending upon the particular catalyzing system
being used, the temperature of the bath, the pH of the bath,
and the precise make-up of the material being overplated.
Plating baths prepared with formulations according to
this invention may, if desired, contain conventional bath
additives which are commonly employed in electroless plating
baths. Included a!re bath stabilizers such as sulfur contain-
ing compounds, for example thiourea, as well as pH regulators
, such as an acid or a base, complexing agents for the metal
~0 ions maintained within the bath, such as ethylene diamine
tetracetic acid, potassium pyrophosphate or polyamines, or
sulfide ion controllers such as lead. Buffering agents can
also be added to add to the pH stability of the bath.
In proceeding with the method according to this in-
vention, a metal substrate that is not normally receptive to
electroless nickel or cobalt plating baths is rendered
catalytic whereby nickel or cobalt can be electrolessly de-
posited thereover. Not only does the method include catalyz-
ing a surface and improving adhesion between the nickel or
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~ l761~
cobalt and the overcoated metal, but also it allows for
rinsing after application of the catalytic coating in order
to enhance the quality of products produced thereby.
As an aid for illustrating this invention, reference
is made to the Figure, which generally depicts the catalyzing
and overplating of a copper clad board, generally designated
11, that had been prepared by conventional plating techniques
to plate about 1/4 ounce of copper per square foot of plating
area. These conventional plating techniques prepare a copper
clad board by a process which includes removing copper from
a plate 12 at those locations that are not within a circuitry
pattern 13, which, in general tends to leave copper specks or
particles 14 lying on the surface of plate 12 and often em-
bedded into that surface.
Typical conventional techniques (not depicted) can
include adhering copper to the plate, for example an expoxy
fiberglass plate, at which stage procedures such as
drilling holes 15 can be proceeded with, and this can be
followed by laying down a resist and plating copper onto the
board. The copper plating can be entirely electroless, but
the length of time needed to plate a suitable thickness is
shortened if an electroless copper deposition is followed by
an electrodeposition of copper. Then, by etching, lifting-
off, or the like, the copper that had been plated onto the
non-circuitry portions of the plate 12 is removed in order to
leave an isolated circuitry pattern to form the copper clad
board 11.
Conventional further treatment that is not depicted
can include cleaning the copper clad board in a mildly
_ 9,
~ ~761l~
alkaline detergent bath ~or on the order of about five minutes
at an elevated temperature that will not damage surfactants
in the bath. After rinsing with water to remove residual
carry-over, the plates are often either mechanically scrubbed
or are dipped in an etching agent such as ammonium persulfate
at a concentration of about 1 pound per gallon in order to
etch off surface oxides and render the copper more active for
subsequent deposition, which step would typically be followed
by rinsing with tap water or the like. Next, a copper clad
plate would usually be acid dipped as insurance that any
residual surface materials are removed and in order to re-
activate the copper. A mineral acid bath, such as 10~ sulfuric
acid, or a dry acid salt such as sodium bisulfate salts can
be used, followed by rinsing for about one minute with, for
example, deionized water. Even if every one of these further
treatments are conlducted on the copper clad board 11, the
residual specks or particles of copper remain on the plate
portion 12 off of the circuitry pattern 13.
Copper clad board 11 is treated with the catalyzing
agent in accordance with this invention, with the general
objective of forming a catalyzing film thereon to, generally
speaking, nucleate the copper surface with what may be in the
nature of a monomolecular layer. Typically, this treating
step will include immersing the board 11 into a bath 16 having
the catalyzing agent according to this invention. This
treating step should not be of such a length that electroless
plating actually occurs, but should be of a duration adequate
to pxovide a catalytic coating of the board as shown at 17.
When the bath immersion technique is used, a typical suitable
time period will be between about 10 and 60 seconds, the exact
--10--
l ~76118`
time that is most suitable depending upon the particular
catalyzing systems being used, the temperature of the bath,
the pH of the bath, the reducing agent used, and the make-
up of the copper clad board.
The catalyzing treatment time is also dependent some-
what upon the temperature of the bath in which the catalyzing
agent is used, with typical temperature ranges being between
about 20C. to substantially boiling, or about 100C., pre-
ferred temperatures ranges therewithin varying somewhat de-
pending upon the particular reducing agent included within thebath.
After treatment with the catalyzing agent, the board
17 is subjected to a rinsing step, illustrated in the Figure
by spray nozzle 18, although any means or method for rinsing
may be used, such as running through a water bath for a very
short period of time. This rinsing step will not significantly
affect the catalytic surface formed by the catalyzing agent at
the circuitry pattern 13 or the particles or specks of metal 14,
but the rinsing step does wash away all of the plating solution,
especially that on the insulator board 12, which is not nucleated
or catalyzed, only the metal portions having been nucleated. It
is possible to then pass the rinsed board 17 into subsequent
baths, even those having hypophosphite, which is not possible when
activator solutions such as dimethylamine borane are used instead
of catalyzing agents of this invention~
It has been found that the catalyzing agents, when
used according to the method of this invention, can be combined
with this subsequent rinsing step in order to obtain a result
that catalyzes plating on the circuitry pattern by nucleating,
30 or providing active sites thereon, while at the same time
avoiding enhancement of deposition, typically discouraging
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I i7611~
deposition, at those locations on the surface of the board 12
that are not within a circuitry pattern 13. As a result, after
the catalyzing agent films are electrolessly plated over with
nickel, cobalt, or polyalloys including either or both, the
electroless overplating is selectively deposited onto only the
nucleated metal and does not spread onto the insulator board
by way of forming plated bridges between specks and/or the
circuitry pattern, which undesirable spreading out or extending
is otherwise started at and encouraged by the specks within
0 a catalyzed board environment provided by other systems. In
this way, a finished printed circuit or wiring board can be made
with precisely overplated circuitry pattern, one that does not
have substantial excess deposits outside of the pattern which
can and often do lead to short circuiting within the circuitry
pattern and a generally undesirable increase in the conductivity
of the board 12 outside of the pattern.
Rinsing solutions suitable for use in the rinsing step
will typically be aqueous, and the rinsing step itself should
be long enough to significantly reduce the effect of catalyzing
0 agent that had been placed onto the non-circuit portion during
the immersion step. The maximum rinsing time desired will be
determined by convenience and economics in general, there being
a point at which lengthy rinsing times will become expensive.
On the whole, lengthy rinsing will not reduce the extent that
the surfaces are catalyzed since it is the surfaces themselves
that are transformed rather than a rinsable fllm being placed
thereon. The catalytic surface will be removed only by etching
off or otherwise removing the copper or the like from the board.
Multiple rinsing can be carried out, and the rinsing can be
in a still bath, under a running bath, or the like. Rinsing
times will vary somewhat depending upon the overall make-up
of the plates, the materials, other physical
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conditions, and whether the rinsing solution is running or
still, typical ti~es generally ranging between about 2
seconds and about 45 seconds for each rinse. The preferred
rinsing times will depend upon the catalyzing agent being
used, the extent to which the catalyzing agent has adhered
to the copper prior to rinsing, and the solventizing ability
of the particular rinsing agent being used. Usually, a
cool water rinsing agent, such as tap water or deionized
water at ambient temperature, is preferred primarily because
`10 of the ready availability and low cost of water. If desired,
wetting agents could be added, provided they do not interfere
with the subsequent electroless plating.
Once rinsing in accordance with this invention has
been accomplished, the selective electroless plating step
is ready to be carried out ~atalytic flims formed in ac-
cordance with the preceeding steps are especially receptive
to electroless deposition of nickel plating or cobalt plating
within any number of baths, such as nickel-phosphorous baths,
electroless cobalt plating baths, or pollyalloy type baths,
including ones listed in U.S. Patent No. 4,019,910. The
rinsed board 17 is electrolessly plated in a conventional
manner, such as within a plating bath 19, whereby an over-
coated layer 20 is added to the copper circuitry pattern 13
in order to form an overcoated circuit board 21, shown in the
Figure emerging from the bath 19, which has substantially no
overplating deposits that are not within the precise circuitry
pattern 13, except for any specks 22 that had been catalyzed
and overplated but not spread out or expanded into a bridging
or short circuiting path, the specks 14 and 22 being illustrated
in exaggerated size for drawing clarity.
-13-
- ~ ~7~118
Included withln the electroless plating bath 19 can be a
source of nickel cations or cobalt cations, a source of other
metal cations when polyalloy deposition is to be accomplished,
a pH regulator, a reducing agent, a complexing agent, water, bath
stabilizers, sulfide ion controllers, or other suitable bath
ingredients. Details concerning many of these various ingredients
and the conditions suitable for such baths are discussed in U.S.
Patent No. 4,019,910. Also, a typical nickel-phosphorus electro-
less plating bath usually would form a binary coating having be-
10 tween about 88 to 95 weight percent nickel and between about 12
to 5 weight percent phosphorus.
If desired, especially when preparing printed circuit
boards of high quality, it is possible, usually after one or more
rinsing steps, to plate over the overcoating of nickel, cobalt, or
polyalloy with another metal, such as gold, in order to enhance the
solderability and corrosion resistance of the circuit. When final
plating is completed, the substrate formed by this invention, such
as a printed cireuit or wiring board, will be allowed to dry or will
be dried aecording to any desired drying procedure.
While there is no desire to be bound by any theory concerning
the operation of this invention, it is believed that the inclusion
of metals generally accepted as being inhibitors, especially in
the case of the molybdenum, tungsten or tin secondary metals,
cooperate with the plating enhancement abilities of the nickel or
eobalt within the eatalyzing agent to render eatalytic the other-
wise non-catalytic surfaces, especially copper circuitry patterns.
30 The combination of the nickel or cobalt with the inhibitor-type
secondary metals is believed to bring about the catalyzing properties
attained by this invention by nucleating the otherwise non-catalytic
surface and thus render the surface itself catalytic rather than
merely lay a film over such surface that will be washed off during
-14-
'
~ ~7611$
a subsequent rinsing step. It is believed that this particular -
combination within the system of this invention enhances the
deposition efficiency of the system to the extent that a
catalyzing surface is actually formed from a surface that
previously was non-catalytic. Once such a catalytic surface
is formed, it is possible to electrolessly plate thereover
because the overplating reaction is thereby encouraged, the
catalyzed surface being much more favorable to deposition
thereover than the original non-catalytic surface, especially
when such overdeposition is that of a polyalloy. The components
of the system cooperate with each other to efficiently
utilize the attributes of each to the extent that the system
will succéssfully transform a non-catalytic surface into a
catalyzed one.
As far as the mechanism by which the catalyzing agent
itself renders the circuitry pattern more receptive to over-
plating, it is believed that galvanic initiation plays a part
in instituting the overplating surface. In a general sense,
the catalyzing agent transforms the copper surface to the
extent it is rendered catalytic for the subsequent overplating
step. The ultimate result is a preferential catalyzing of the
copper within the circuitry pattern.
It is believed that the results attributable to the
inventionare enhanced by including boron within the sensi-
tizing agent formulation, which inclusion can be most readily
accomplished by using a boron-containing reducing agent.
1 176118
It is also possible that physical attributes of the various
materials involved in the process contribute to this effect.
An immersion within the catalyzing agent bath wets all of
the board, but the surface textures of the board within and
out of the circuitry pattern are different, which would in-
dicate that the effects of the subsequent rinsing step on
the make-up of the catalyzing agent left on the board will
be different too.
Baths incorporating the catalyzing agents according
to this invention are typically alkaline. It is believed that
operating with pH any lower than about 5.5 can lead to bridg-
ing or plating in between portions of the circuitry pattern,
and a pH that is too high, say above about 13, would be un-
necessarily severe. The preferred pH range is between about
8 and about 11. The concentration of the deposition-enhancing
metals such as nickel compounds within a bath according to
the invention can be between about 0.001 and about 0.3 mol/liter,
usually between about 0.002 to about 0.125 mol/liter. A
typical range for the secondary metals such as the tin com-
pounds within such baths is between about 0.001 to about 0.5
mol/liter, generally between about 0.002 and about 0.250
mol/liter. Reducing agent concentrations such as those for
dimethylamine borane can be between about 0.001 and about 0.2
mol/liter, usually between about 0.002 and 0.1 mol/liter. The
upper limits of the various constituents are determined by
economics~and solubility, and the lower limits by minima~
effectiveness.
While the Figure and this specification deal primarily
with the preparation of printed circuit boards, the invention
is suitable for use whenever it is desired to catalyze a metal
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! ~76118
surface, particularly a cop~er surface, ~or su~sequent
overpla~ing with nicXel, cobalt, or ~olvalloys including
same. Eventual end uses for proaucts ~roducea according to
this invention incluae boaras lor carrying electrical
circuit components within games, watcneS, or ~gnetic memory
aevices in computer-type applica~ions. These ~ay be in the
Iorm of 2-sided printed etched hoards which can have plating
thraugh holes therein. The following ex~m~les are o~rered
to illustrate the present invention:
E X A M P L E 1
Nickel - Mol~baenum - B~ron
-
A catalyzing agent immersion bath was prepared to
include 0.01 mol/liter molybaenum ester of ~luconic acid,
0.0~ mol/liter nickel sulfate, 0.1 mol/liter poiassium
p,yrophosphater which is a buffer and complexing agent, and
0.~04 mol/liter dimethylamine borane reducing agent. The
operating p~ was 9.O, and the operating temperature was
gO~C. ~his bath formed an a~herent catalytic ~ilm on copper
alloys that was then overplated with electroless nickel.
Printe~ circuit boards were preparea and exhibite~ an en-
hanced adhesion between the copper ana its nickel-containing
overcoaiing. ~he use of printea circuits thus prepared were
found to be more consistently iess susceptible ~o aeveloping
short circuits during use.
E X A M P L E 2'
- Nickel - ~ungs~en - ~oron
~ no~her catalyzing b~th was pre~ared a~d used
generally in accoroance wi~h ~xamp~e 1, tnis c~-talyzing
aaent ~ath including 0 00~ mol/liter tun~sten ester of
I ~7611~
glucoheptonic acid, 0.02 mol/liter nickel sulfate, 0.05
mol/liter potasium pyrophosphate, 0.04 mol/liter dimethyl-
amine borane, with the balance of the bath being essentially
water. The bath was operated at a pH of 9.0, and the
operating temperature was 40C.
E X A M P L E 3
Nickel - Tungsten - Boron
Another bath that had been prepared and is suitable
for use as a catalyzing agent bath includes 0.2 mol/liter of
a tungsten ester of glucoheptonic acid, 0.1 mol/liter of
nickel sulfate, O.g6 mol/liter of dimethylamine borane and
1 ppm of thiourea. The operating conditions were a pH of
9.6-and a temperature of 90C., and the catalytic film pre-
pared thereby should include 77.4 weight percent nickel, 20.0
weight percent tungsten, and 2.6 weight percent boron.
E X A M P L E 4
Nickel ~ Tungsten - Tin - Boron
Another suitable catalytic agent bath includes
deionized, carbon treated and filtered water containing 0.2
mol/liter tungsten ester of glucoheptonic acid, 0.1 mol/liter
nickel sulfate, 0.025 mol/liter stannous chloride, 0.06
mol/liter dimethylamine borane, and 1 ppm of thiourea, the
operating temperature being 90C and the pH being about 7.5.
- ~his bath produces a catalytic film believed to be analyzable
as 77.9 weight percent nickel, 16.0 weight percent tungsten,
4.2 weight percent tin, and 1.9 weight percent boron.
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1 .~ 76l l g
. E X A M P L E 5
Nickel - Tin - Boron
A suitable catalytic plating aqueous bath includes
0.1 mol/liter of nickel sulfate, 0.1 mol/liter of stannous
chloride, 0.06 mol/liter of dimethylamine borane, 0.2 mol/liter
of potassium pyrophosphate, 1 ppm of thiourea, and O.l mol/liter
of a diboron ester of glucoheptonic acid, which was pre-
pared by charging approximately 2 mols of boric acid and 1
mol of sodium glucoheptonate into an esterification vessel
containing about 600 milliliters of water as a solvent,
followed by stirring while maintaining the temperature at
about 25C for 30 minutes, after which it was diluted to a
final volume of 1 liter with additional water. This bath
produces a catalytic film which has been analyzed in thicker,
plating, operations as 92.8 weight percent nickel, 6 1 weight
percent tin, and 1.1 weight percent boron.
E X A M P L E 6
.
Nickel - Molybdenum - soron
An aqueous catalyzing agent bath was produced to
include 0.001 mol/liter of a molybdenum ester of glucohep-
tonic acid, 0.1 mol/liter of nickel sulfate, 0.06 mol/liter
of dimethylamine borane, and 0.3 mol/liter of lactic acid,
the operating pH being 10.0, and the operating temperature
being 90C. This bath produces a catalytic film which has
been analyzed in thicker, plating, operations as 79.8 weight
percent nickel, 20 weight percent molybdenum, and 0.2 weight
percent boron.
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! ~ 7~
E X A M P L E 7
Nickel - Molybdenum - Copper - Boron
A catalyzing agent bath was prepared by adding the
following to deionized, carbon treated and filtered water:
0.001 mol/liter of molybdenum ester of glucoheptonic acid,
0.1 mol/liter of nickel sulfate, 0.000~ mol/liter of copper
sulfate, 0.06 mol/liter of dimethylamine borane, and 0.3
mol/liter of lactic acid. The operating temperature was
90C and the operating pH was 10. This bath has been
analyzed to produce a coating of 77.87 weight percent nickel,
20 weigh percent molybdenum, 1.8 weight percent copper, and
0.33 weight percent boron.
E X A M P L E 8
Nickel - Tin - Boron
A tin-containing catalyzing bath is prepared by
adding to water 0.001 mol/liter of nickel ion, 0.02 mol/liter
of sodium stannate ~tetravalent) complex of gluconic acid,
and 0.02 mol/liter of dimethylamine borane. A very similar
bath is prepared when 0.002 mol/liter of dimethylamine borane
is included therein.
E X A M P L E 9
Nickel - Tin - Boron
Another useful catalyzing agent bath includes 0.001
mol/liter of the stannate ester of glucoheptonic acid, 0.1
mol/liter of nickel sulfate, 0.06 mol/liter of dimethylamine
borane, and 0.3 mol/liter of lactic acid, with the'operating
temperature being 90C and the operating pH being 10Ø
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E X A M P L E 10
Cobalt - Tungsten - Boron
A complexing agent aqueous bath for subsequent
cobalt overcoating has 0.2 mol/liter ofthe tungsten ester of
slucoheptonic acid, 0.1 mol/liter of cobalt sulfate, 0.06
mol/liter of dimethylamine borane, and 1 ppm of thiouréa.
The operating pH is about 9.6 at a temperature of about 90C,
coating analysis being about 81 weight percent cobalt, 18
weight percent tungsten and 1 weight pexcent boron. After
application of a catalyzing film with this bath, subsequent
cobalt overplating can be accomplished by using a similar
bath.
E X A M P L E 11
Cobalt - Molybdenum - Phosphorus
Copper catalyzing bath can be prepared including 0.1
mol/iiter of molybdenum ester of gluconic acid, 0.1 mol/litèr
of cobalt sulfate, and 0.28 mol/liter of sodium hypophosphite.
An operating pH is 10.0, and an operating temperature is 90C,
the film to be prepared having about 92 9 weight percent
cobalt, 1.1 weight percent molybdenum, and 6 weight percent
phosphorus. If desired, the bath formulation is useful for
coating over this catalytic coating after rinsing with cold
water, typically including increasing the plating rate to
about 0.2 to 0.3 mil/hour and reducing the pH to an acidic
level.
E X A M P L E 12
Cobalt - Tin = Boron
An aqueous catalyzing agent bath can be prepared to
include 0.1 mol/liter of cobalt sulfate, 0.2 mol/liter of a
sodium stannate complex of gluconic acid, and 0.~ mol/liter of
dimethylamine borane. The operating temperature is 60C at
a pH of about 7.
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E`X A M P L E 13
After any of one of the catalyzing agent baths of
Examples 1 through 9 have been used to prepare a catalytic
film on a copper substrate which remained in the bath for
about 45 seconds, and after that film has been rinsed with
water twice for 15 second time periods, nickel can be
electrolessly plated thereover using an aqueous bath having
0.1 mol/liter of nickel sulfate, 0.2 mol/liter of citric
acid and 0.17 mol/liter of sodium hypophosphite. The operating
pH is between about 4.5 and S.0 at a temperature of 90C, and
o the plating rate is about 10 microns/minute which usually con-
tinues for about 10 to 20 minutes. The overplating is generally
complete, no bridging or coating over of copper specks on the
board being observable.
E X A M P L E 14
After copper clad substrates are immersed in any of
one of the catalyzing agent baths of Examples 1 through 9
for about 45 seconds; to prepare a catalytic film thereon,
and after that film has been rinsed twicewith running water,
a nickel overplating can be electrolessly formed thereover at
about 40~C and a pH of 5.0 using an aqueous bath having 0.1
mol/liter of nickel sulfate, 0.25 mol/liter of succinic acid,
and 0.04 mol/liter of dimethylamine borane. This was followed
by two running water rinses and further overplating with an
electroless gold bath at 63C and at a plating rate of about
1 micron/minute.
While in the foregoing specification certain embodi-
ments and examples of this invention have been described in
detail, it will be appreciated that modifications and
variations therefrom will be apparent to those skilled in
this art. Accordingly, this invention is to be limited only
by the scope of the a2pended claims.
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