Note: Descriptions are shown in the official language in which they were submitted.
- '1 051~457
This invention relates to processes and compositions
for sensitizing articles to the deposition of metals from
solutions thereof. More particularly, it relates to improved
; means to provide adherent metal layers on non-metallic articles
by treating such articles with a series of media which deposit
catalytically active elements or precursors and contacting
with electroless metal deposition solutions.
Background of the Invention - Sensitizing non-
metallic substrates to the deposition of electroless metal,
e.g., Group IB and VIII metals, i.e., copper, cobalt, nickel
gold, silver and the like, is a key step in the production
of decorative and industriall~ useful metallized objects,
such as name plates, dials, printed circuits,and the like.
This sensitization is conventionally carried out by treating
the substrate either stepwise with precious metal, e.g.,
palladium or platinum, ions in solution followed by a solution
~ of stannous tin or similar ions, or all in one step with a
unitary colloidal suspension of precious metal or with a
soluble complex of precious metal ion, stannous ion and an
anion. This produces a sensitive surace which when immexsed
in a conventional electroless metal deposition bath causes
metal to deposit on all of the sensitized areas thereof.
A number of proposals have been made to carry
out such processes more economically and efficiently:
Chiecchi, U. S. 3,3~9,566 discloses immersion
in a beta resorcylato chromic chloride solution to eliminate
pretreatments such as sealing, sandblasting, etching and the
like. This method still requires the use of a two step,
stannous-palladium subsequent treatment, see, for example,
Schneble, Jr. et al, U. S. 3,403,035 and U. S. 3,033,703.
Moreover, the Werner-type chromium complexes are difficult
to prepare, stabilize and use. In addition, the complex
cb/ - 1 -
~058457
must be polymerized after application and before subsequent
treatment steps.
Bernhardt et al, U. S. 3,547,784 disclose treating
a non-metallic surface with stannous salt then with a silver
salt and then electrolessly plating using processes and
deposition baths for copper, nickel and silver found, for
example, in Schneble, Jr. et al, U. S. 3,527,215 and 3,347,
724. The Bernhardt et al process is conventional and the
point of novelty resides in using aparticular copolymer of
vinyl chloride,which was not easy to metallize up until the
time of the invention.
In a more recent de~elopment, there have been pro-
vided the so-called metal reduction sensitizers, which can
employ base metal ions, followed by treatment with reducing
- solutions or radiant energy, e.g., heat, light and the like,
to produce the sensitized surface.
The metal reduction sensitizing process consists
of coating a surface, preferably one which has been activated
in known ways either to render it permanently polarized and
wettable, or micro-porous, with a reducible metal salt solution~
e.g., CuSO4.5H2O, ~iSO4.6H2O, and the like, then either drain-
ing, semi-drying or completely drying the so-treated surface.
Sensitization is then completed by immersing the surface into
a strongly reducing medium, e.g., a sodium borohydride solution,
during which step the metal salts are reduced to elemental
metal particles. This sensitized surface is then rinsed and
electrolessly plated.
Because thoxou~h rinsing of excess metal salts
before transferrin~ the workpiece to the reducing medium
cannot be practiced, there are numerous difficulties when
dealing with copper clad surfaces ~on other port~ons of the
article). ~insing usually removes all of the metal salts.
cb/ - 2 -
~05845~
Moreover, there is also the problem of drag-over of excess
metal salts into thb reducing medium, and this shortens its
life and also turns it black with atomic metal particles.
Obviously, if a means could be provided to rinse
excess and unwanted metal salts from the surface before immer-
sion in the reducing medium, the above noted problems would
be avoided. In addition, control will be facilitated because
rinsing will provide a positive indication that only those
final catalyticelemental particles which remain are those
which are adsorbed by the surface.
According to the present invention, improvements
are provided in the wettability and adsorptivity of metal
compound media which are used to render surfaces sensitive
to electroless metal depositions. Because of their improved
wettability and adsorptivity, such compositions can be formulat-
ed from base metals or combinations thereof with precious
, .
metals which have performance comparable to traditional expen-
sive and somewhat unstable entirely precious metal-based ~-
sensitizers.
.. ,
In comparison with the prior art techniques, the
instant system provides the following distinct advantages:
~i) more complete rinsing between the first medium
and any subsequent transformation agent can now be tolerated
because of tremendously improved adsorption of any metallic
compound or element in the first medium to the surface;
(ii) "take" or coverage in the electroless metal
bath is wholly uniform and rapid; and
tiii) in the case of activated substrates, metalli
zation within the surface micropores is deep and complete
enhancing bond strength.
Description of the Invention - According to the
present invention, there is provided a process for sensitizing
cb/
1058457
the surface of a non-metallic article for the deposition of
adherent metal from an electroless metal deposition solution
in contact therewith; said process comprising the steps of
(i) adsorbing on said surface a compound of at least one
metal or combination of metals containing an element which
in one of its oxidation states is catalytically acti~e to
electroless metal deposition by contacting said surface with
a first medium comprising an aqueous solution containing a
compound of at least one said metal, ~ii) thereafter treating
said surface with water to decrease the solubility of the
metal compound adsorbed on said wall surface while, at the
same time, removing from said wall with said water unadsorbed
metal compound carried over from said first medium, and (iii)
subsequently to step ~ii), treating said surface with reducing
agents to transfer said metal into a state which is catalyti-
cally active for the electroless deposition of metal, wherein
~- the reduction treatment is carried out in two separate stages,
and using two separate reducing agents.
In a preferred feature of the invention, the agent
or agents in step ~iii) will be reducing agents, such as
borohydrides, e,g., alkali metal borohydrideY, amine boranes,
e.g., dimethylamine boranes, hydrazine hydrate, and others.
If di~ficulty metallizable substrates are used, e.g.,
acrylonitrile-butadiene-styrene ~BS) polymers, in pre~erred
e~bodiments step Ciii~ will be carried out in two separate
stages and employing two separate reducing a~ents. In one
such process, the first reducing agent will be a so-called
secondary reducer, e.g ,formaldehyde, a formaldehyde precur-
sor, dimethyl hydantoin, a stabilized form thereo~, and t~e
3~ e, and the second reducing agent will be a strongt primary
reducer, e,g., a borohydride or an amine borane.
Among the features of this invention are processes
cb~
~058~57
wherein the element or combination of elements are base
metal elements, preferably, copper, nickel, cobalt, iron or
mixtures of any of the foregoing. Under certain circumstances,
molybdenum, vanadium, and lead or mixtures thereof with any
of the preferable elements cited above may also be used.
Preferably, the compound or combination of compounds
in the first medium will be a wetting agent, i.e., it will
seek and affix itself firmly to the surface being treated,
e.g., by electrical attraction or other means. Preferably
also, the first or second medium will comprise a wetting
agent having a polarity which is opposite to the polarity
of at least some of the surface sites of the article to
be sensitized.
~he present invention also contemplates the novel
compositions having the required characteristics, e.g., media
including compounds or combinations which are adsorbable,
transformable, if necessary, and removable in excess by a
second medium, as set forth above.
By way of further illustration, but with no intention
of being bound by any hypothesis, in one embodiment, a first
medium is formed when a copper compound or a nickel compound
or a mixture thereof is mixed with ammonia or amine to form
a copper or nickel complex with ammonia or amine or a mixture
thereof. Not only are ammonia or amines in their own rights
powerful wetting agents, but so are the formed ion complexes.
It appears that such ion complexes behave much like quaternary
; ammonium complexes, i.e., cationically. Such positively charged
(polar~ ion complexes are adsorbed by negative surface sites
on the article to be sensitized.
In another embodiment a dichlorocuprate [I ] ion
complex:
~CuCl~ H+
.
cb~ - 5 -
105~34~'7
is formed by boiling copper chips with cupric chloride in
a large excess of concentrated hydrochloric acid. As in the
ammonia complex case, this compound is highly polar ~polarity
reversed however) and readily attaches to positiYe surface
sites due to its relatively negative charge.
In a further embodiment a complex metal salt, e.g.,
ferrous sulfate ~eSO4) is dissolved in ammonium hydroxide
and this is put onto the surface to be sensitized.
In these embodiments, the rinse of the base with a
second medium will decrease the solubility of the compound
or combination of compounds. In the metal ammonium complex
case, the basic metal ammonium compound is formed; in the
cuprous ion complex case t loss of HCl in the rinse will lead
to decreased solubility. In the soluble iron salt case,
the second medium rinse causes decreased solubilit~.
All three concepts can use a variety of metallic
compounds.
The media can comprise organic and inorganic sol-
vents such as water, alcohols, e.g., methanol and the like,
. . .
ketones, e.g., acetone, methyl ethyl ketone, etc., esters,
e.g., ethyl acetate. Preferably, aqueous media are used.
Media ba~ed on organic systems can be employed,
particularly on resin bearing syste~s such as epoxy. In
one such system, cupric chloride is readily dissolved and
complexed with dimethyl formamide (DMP). ~ resin bearing
surface brought into contact with this solution quickly
adsorbs metal complex. The surface is then rinsed with a
second medium, e.g., water, which removes excess metal complex
(and first medium) and then the surface is next treated with
3~ an agent to convert the metal to a catalytically active state r
such as a solution of sodium borohydride or hydrazine hydrate
dissolved in a suitable solvent, such as DMF.
:
cb~ - 6 -
` ~L058~57
The present invention can be used to sensitize a
wide variety of non-metallic substrates, such as plastic,
e.g., polyepoxides, phenolics, polystyrene, polyesters,
nylons, polyacetals, polycarbonates, and the like, or glass,
porcelain, cloth, paper, compressed wood, and the like.
ABS resins are especially efficiently metallized with a "two-
stage" treatment with reducing agents, as described above
and exemplified hereinafter. The resinous substrates can
be treated in known ways to activate the surfaces prior to
sensitization -- this gives the highest adhesion between
; subsequently deposited electroless metal and the resinous
substrates.
One way to activate resinous bases is to render
them permanently polar and wettable by treatment first with
a pre-activating agent, e.g., dimethyl formamide, dimethyl
sulfoxide, methyl ethyl ketone or mixture of toluene and
-- water, etc., depending on the nature of the resin, then with
an activator such as chromic acid-sulfuric acid, and then with
a reducing agent, such as sodium bisulfite or hydroxylamine
hydrochloride, the result of which is to produce a permanently
polarized, wettable surface.
On the other hand, the surface of the resinous
article can be partially degradable, or be provided with a
surface layer having such properties, or contain degradable
particles, such as rubber particles, and on treatment with
suitable agents, such as chromic acid, or permanganate, is
caused to become microporous and thus activated to adherent
metal deposits.
Any conventional electroless metal deposition bath
useful with conventionally precious metal sensitized surfaces
can be used to deposit metal on the surfaces sensitized accord-
ing to this invention. Generallyl the deposition baths will
.
cb/ - 7 -
.,
10584S~
contain anion of the metal or metals whose deposition is
desired, a complexing agent for the ion, a reducing agent
for the ion and an agent to adjust the bath to an optimum,
predetermined pH. Such baths are amply described in the
patent and textbook literature. See, for example, the patents
cited hereinabove.
Description of the Preferred Embodiments - The
. . ... . . .
following examples illustrate the processes of this invention.
They are not to be construed as limiting.
EX~PL~ 1
. .
An epoxy-slass laminate is provided with holes at
pre-selected locations. The surface is rendered permanently
polarized and wettable by immersion in dimethyl formamide at
80F. for 2-5 minutes, rinsing in water, immersing in a
solution of 100 g./l. CrO3, 250 ml./l. of concentrated sul-
furic acid, balance water, for about 1 minute, immersing
in a 5% solution of NaHSO3 for about 2 minutes, rinsing
thoroughly in cold water, then in hot (160F.) water and
air or oven-drying.
Then the laminate is reverse~masked with a con-
ventional background resis-t and then sensitized by immersion
in and adsorption of a copper compound from a first medium
comprising
CUC12 2H2 34 g./l.
Hydrochloric acid ~37~) 250 ml./l.
2 2 H2O 30 g /l.
Water ~to make~
The so-treated laminate is next rinsed thoroughly
with a second medium comprising cold water to decrease the
; 30 solubility of said copper compound and to remove the excess.
The laminate is next immersed in a water or methanol
solution of 1 gram/liter of sodium borohydride, causing the
cb/ - 8 -
1058457
adsorbed copper compound to be reduced to catalytic sites of
elemental copper.
The sensitized laminate is transferred to an electro-
less copper deposition bath of -the formula:
Cuso4.5H2o 30 g-/l- -~
Rochelle salts150 g./l.
sodium cyanide30 mg./l.
formaldehyde (37%) 15 ml.~l.
wetting agent 1 ml.
sodium hydroxideto pH 13
water (to make)
The conductor pattexn is built up to the desired
thickness, the mask is removed, and the finished printed
circuit board is post cured for 30 minutes at about 320F.
EXAMPLE 2
The procedure of Example 1 is repeated, substituting
- for the first medium, one comprising:
Cu2O 15 g./l.
hydrochloric acid (37%) 300 ~1./1.
NaH2po4.H2o 30 g./l.
water (to make)
Substantially the same results are obtained.
EXAMPLE 3
The procedure of Example 1 is repeated, substituting
for the first ~edium, one comprising:
CUSO4,5H2O 25 g./l.
NiS4 6H2 25 g./l.
~H401I (conc.)200 ml./l.
water (to make)
EXAMPLE 4
~ he procedure of Example 1 is repeated, substituting
for the first medium, one comprising:
cb/ 9
:~05~457
CUS4 5H2 25 g./l.
N~S4 5H2 25 g./l.
NH40H ~conc.~ 200 ml./l.
hydroquinone 2 g./l.
water ~to make)
EXAMPLE 5
The procedure of Example 1 is repeated, substituting
for the first medium, one comprising:
FeS04 20 g./l.
NH4OH (conc.l 200 ml./l.
water ~to makel
E ~ IPLES 6-12
The procedure of Example l is repeated, substituting,
respectively, for the first mediu~, those comprising:
(EXAMPLE 6)
Niso4 .6H20 25 g./l.
NH40H (conc.l200 ml./1.
water ~to make).
`;~ UExAupLE 7 L
CuS04.5H20 25 ~./l.
NH40H (conc. L200 ml./l.
water ~to ma~e1.
~XAMPLE 8
.
Co(C2E302)2 4 225 g./l.
; NX40H ~conc.L200 ml./l.
water Cto makel.
(Example 9)
CuCl lO g./l.
HCl Cconc-) 300 ml./l.
stannous chlor~de . 2H20 30 g./l.
water (to makel.
cb( - 10 -
058457
~EXAMPLE lO)
CuSO4.5H2O 25 g./l.
triethanolamine 40 g./1.
water (to make~
~EXAMPLE lll
The procedure of Example l is repeated, but substitut-
ing for water as the second medium, 1 g. of sodium boro-
~; hydride in lO00 ml. of water (pH 9.5-lO.0).
~XAMPLE 12~
10A combination of metals comprises
CuSO4.5H2O lO g./l.
NiSO4.6H~O 10 g./l.
benzyl trimethyl
ammonium
chloride 10 g./l.
- water (to makel
Substantially the same results are obtained.
~EXAMPLE 13
This example illustrates the use of two separate
reducers in the process of the present invention.
:,
A disc of acrylonitrile-butadiena-styrene terpolymer
~ABS~ is immersed for 5 mlnutes in an alkaline cleaner at 65C.
Oakite ~ 90 or Altrex ~ are illustrative of suitable commercial
materials and trisodium phosphate is also suitable. The
cleaned ABS disc i5 rinsed for 5 minutes in water, t~en the
surface ~s rendered permanently polarized and wettable by
immersion for l minute in ~ solution of 250 ~l.~l. of methyl
ethyl ketone in water, rinsing in water for 3-5 minutes, immer-
sing in a solution of 370 g./l. of chromic acid, 185 ml./l.
o~ concentrated sulfuric acid, 0.5 g./l. of fluorinated hydro-
carbon wetting agent ~3M Company, FC-95~l, balance water,
for about 5-8 minutes, rinsing in water for 1 minute/ immers-
ing in a solution of hydroxyl-amine hydrochloride, 20 g./l.,
c'~ -- 1 1 --
': :
.... . . ,. ~ .
.
1!058457
hydrochloric acid ~37%~, 200 ml./l., balance water, for
about 2 minutes and rinsing thoroughly in water for 5 mlnutes.
Then the activated disc is immersed in a solution
comprising
CuSO4.5H2O 25 g /l.
SO4. H2O 25 g./l.
NH40H ~conc.~ 200 ml./1.
water ~to make)
The so-treated disc is rinsed gently with water
for 1 minute at pH ~5-8) and about 15-20C. to decrease the
solubility of the copper and nickel compounds and to remove
the excess.
The disc is next immersed in a first reducer solution
comprising
formaldehyde (37%~ 100 ml./l.
water (to make)
- for 1 minute, and the excess first solution is drained off
for about 15-30 seconds.
Then the disc is immersed for 5 minutes in a
second reducer solution comprising
sodium borohydride 1 g./l
, sodium hydroxide (50%) 2 ml./l.
deionized water (to make)
(The second reducer is made by adding the NaB~4
to water and mixing for 5 minutes, then adding the ~aOH and
mixing for 5 minutes longer).
The disc which now has catalytic surface sites of
elemental copper and nickel is rinsed for 2 minutes with
water (pH 5.0-8.0).
T~e sensitized disc is transferred to an electro-
less copper deposition bath of the formula:
cb/ - 12 -
'' ' ' ' :
~ 1058457
CUS4 5H2 30 g./l.
Rochelle salts 150 ~./1.
sodium cyanide 30 mg./l.
formaldehyde ~37%) 15 ml./l.
wetting agent 1 ml.
sodium hydroxide to pH 13
water (to make~
Electroless copper builds up to the desired thick-
ness.
(EXAMPLES 14-24)
The procedure of Example 13 is repeated, substitut-
ing for the sensitizing medium described, the media used in
Examples 1, 2, 4-10 and 12, respectively. A~S discs metallized
with adherent electroless copper are obtained.
The invention is not limited to printed circuit
~: boards or to the specific steps and methods described. More-
over, electroless metal baths for depositing any other
conventional metal than copper, e.g., nickel, cobalt, sllver,
; gold, and the like, can be used. Other anions, besides
those exemplified, e.g., phosphates, bromides, fluorides,
fluoborates, etc., can be used with the compound containing
an element which is ultimately the catalytic agent.
-'
-,', . ' '
'
:'`'
cb/ - 13 -
