Note: Descriptions are shown in the official language in which they were submitted.
1077643
Organic coatings and materials whose surfaces
may be provided with electroless metal deposits having
commercially acceptable adhesion, that is, peel strengths
of at least seven pounds per inch of width, have hereto- :
fore fallen into two distinct categories according to the
method of preparing them and the requisite chemical
treatment for insuring sufficlently adherent electroless
metal plating on them.
A first type includes such products as platable
grades of ABS and polypropylene, the adhesives disclosed
in Stahl et al U.S. Patent No. 3,625,758, issued
December 7, 1971, and epoxy/phenolic blends with poly-
butadiene, such as the Beiresdorf technical materials.
Materials of this first type typically contain a dispersed
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~ 1 107764 '
~- 1 ¦ phase of butadiene or acrylonitrile butadiene agglomerates
2 ¦ within a matrix of materials such as epoxy/phenolic blends.
8 ¦ The material of the dispersed phase of such substrates is
4 I readily degraded by o~idizing agents, such as chromic or
6 I permanganate solutions, while the matrix phase is less
6 ¦ reactive to such agents. Following chromic or permanganate
7 ¦ treatment, the substrate surface is microporous, resulting in
8 ¦ greatly increased surface area, and is suitable for further
~¦ processing in known electroless metal plating procedures.
10¦ Substrates of this type, i e., heterogeneous, dispersed
11 I phase-matrix phase materials, have previously been prepared
12 ¦ by masticating prepolymer of the dispersed or reactive phase ~
¦ material in solvent down to the desired molecular weight or ~-
1~ ¦ chain length, and then blending the mast~cated prepolymer
15 I with t~e cont~nuous phase or matrix phase materials in copious
16 I amounts of solvent. Such substrate materials normally comprise
17¦ from 65 to 80 weight percent solvent prior to their application
18¦ to base substrates as coatings, and, following solvent
i91 evaporation, typically comprise about 60 weight percent of
' I unsaturated rubber as the dispersed phase and about 40 weight
¦ U l percent of a thermosetting plastic matrix.
. æ. ¦ A second general type of resinous substrates, such as
23 epoxy and polysulfone, includes materials having an otherwise
2~ homogeneous single phase but with areas of differing crosslink
density. Forming a microporous surface on such substrates
; 26 requires a mandatory step preceding oxidation: polar and
a7 stxained sites that are selecti~ely attacked in the-oxidation
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i ' I 1~77643
1 ¦ step must be created, usually by contacting the homogeneous
2 1 substrate with a strong organic solvent, to permit preferential
3 ¦ attack at areas having a lower density of crosslinks.
4 It is the object of this lnvention to provide improved
processes for forming substrates for adherent metallization
6 ant improved substrates for the elec~roless deposition of
7 metals thereon.
8 It was believed that if a diphase material could be
9 ~ormed as a result of micro phenomena, rather than as a
result of physically masticating prepoiymer of a degradable
lt material and then effecting a dispersion of this material in
12 a matrix of a second material by blending, the diphase material
13 would be more uniform and the process for making it would
14 be more efficient.
Polymers having ethylenic unsaturation, i.e., double
16 bonds that are not of the resonant or benzene-type and that
li will participate in chemical reactions in a fashion analogous
18 to the double bond in ethylene, are relatively susceptible
19 to oxidative degradation, especially compounds having con~u-
gated touble bonds. Polymers having essentially no ethylenic
2t unsaturation are rela~ively resistant to oxidation. According
22 to the invention, totslly liquid mixtures having at least two
Z3 liquid constituents are polymerized to yield a diphase polymer,
24 with at least one of the constituents being a liquid precu~sor
of a polymer having ethylenic unsaturation and with at least
26 one li~uid precursor Df a polymer having essentially no `
27 ethylenic unsaturation.
28 The precise fonm or the liquid precursors is not critical.
29 Thus, they may be monomeric, dimeric, or even longer in chain
3 - _
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¦¦ 10776 3 IL
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1 ¦ length, so long as they remain liquid, wlll form the requisite
2 ¦ mixtures with each other, and will polymerize to yield diphase
3 ¦ polymers according to the invention.
¦As detailed below, liquid mixtures of the sort iUst des-
cribed may be polymerized to yield materials that comprise a
dispersed phase rich in polymer having ethylenic unsaturation
7 and a continuous phase rlch in polymer having essentially no
ethylenic unsaturation, with a polymer having conjugated double
9 bonds being preferred for the dispersed phase. When such a
polymeric material is contac~ed in known fashions with, for
Il example, chromic or permanganate solutions, the portions rich
12 in ethylenic unsaturation are preferentially attacked and de-
1 13 graded, resulting in a microporous structure interconnected by
14 portions rich in polymer having essentially no ethylenic
IS unsaturation.
16 Substrates according to the invention include surfaces
i of the heterogeneous type, some of which require only
18 oxidati~e treatment to increase the surface area of the
substrate by rentering it microporous ant some of which
require pre-treatment with an organic solvent.
21 A heterogeneous, dispersed phase-matrix phase type of
substrate may be obtained as described herein with the followin
23 advantages over the previously known heterogeneous substrates:
24 no tèdious and energy-consuming mastication and blend~ng
procedures are required and far less solvent is necessary,
26 thereby decreasing cost, energy consumption in meeting drying
i requirements, and waste of materials.
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1C1 77643
Whether heterogeneous substrates requiring only
oxidation treatment to render the surfaces microporous
are desired or those requiring pretreatment with an
organic solvent prior to oxidation are preferred, subs-
trates resulting from processes described below are
generally obtained in a more efficient fashion than
previously known substrates and impart enhanced proper-
ties to finished metallized articles.
In a preferred embodiment of the invention,
heterogeneous surfaces comprising an unsaturated rubber-
rich phase dispersed in a continuous phase of thermo-
setting resin are formed by taking advantage of micro
phenomena, rather than by effecting a physical dispersion
as in the previously known process. A totally liquid
mixture is formed of at least two constituents: one of
the two minimum ingredients must be a liquid which, upon
polymerization, will yield an unsaturated rubber suscep-
tible to oxidative degradation; the other minimum ingred-
ient must be a ~iquid which, upon polymerization, will
yield a thermosetting resin that is relatively impervious
to oxidation. And finally, the liquid mixture must, upon
polymerization, result in separation of the two polymer
products to a sufficient extent to form a diphase solid
con8isting of a di6persed phase rich in unsaturated rubber
and a continuous phase rich in resin.
In order to provide a suitable platable surface ; ~ -
for the deposition of electroless metal, it is also
necessary that the resultant surface be adherent to the
metal. And if the overall objective is the formation of
printed circuit boards, the final product having the
metallized surface must be capable of high temperature
performance, for example to
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~ 77643
ermit soldering operations.
Experimental work specifically directed to the use of the
invention in making printed circuit boards has demonstrated
that the preferred embodiment may be achieved by using as one
component a highly polar liquid precursor that will polymerize
to yield a rubber having ethylenic unsaturations and a highly
functional liquid precursor of a thermosetting resin as a
second component. As a general rule, it has been found that
combinations of lower polarity unsaturated rubber precursors
and low functionality resin precursors lead to polymer products
exhibiting unreliable adhesion to electroless metal or inferior
high temperature performance, rendering them unsuitable in
printed circuit applications. Combinations of lower polarity
unsaturated rubber precursors and resin precursors of high
functionality tend to result in a lack of compatibility of
the two components, which is usually manifested by unacceptable
separation.
I have found that certain liquid mixtures comprising
liquid carboxyl-terminated acrylonitrile butadiene, having also
carboxyl groups randomly dispersed along the chain length or
amine -terminated acrylonitrile butadiene, such as B.F. Goodrich's
ATBN; highly functional liquid epoxies, such as epoxy novolacs
or cycloaliphatic epoxies or mixtures thereof; and, optionally,
liquid phenolic novolac yield, upon polymerization, improved
resinous surfaces for later adherent metallization in electroless ---
metal deposition baths.
In one particular aspect the present invention provides
a process for producing a diphase polymeric surface for the
adherent electroless deposition of metal thereon, the two
phases consisting of a dispersed first phase rich in polymer
having ethylenic unsaturation and a continuous second phase
rich in polymer having substantially no ethylenic unsaturation,
,
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10i77643
lid process comprising the steps: (a) admixing at least two
liquid constituents, the first of said constituents comprising
a liquid precursor of a solid polymer having ethylenic unsat-
uration and the second of said constituents comprising a liquid
precursor of a solid polymer having substantially no ethylenic
unsaturation; and (b) polymerizing the admixture of step (a) to
yield a solid, two phase polymerization product comprising a
dispersed phase rich in the polymerization product of said first
constituent and a continuous phase rich in the polymerization
product of said second constituent.
In another particular aspect the present invention
provides a process for producing a diphase polymeric surface
for the adherent electroless deposition of metal thereon, the
two phases consisting of a dispersed first phase rich in a
polymer having ethylenic unsaturation and a continuous second
phase rich in a polymer having substantially no ethylenic
unsaturation, said process comprising the steps: (a) forming
a liquid mixture comprising two liquid constituents, the first
said constituent being a liquid precursor of a solid polymer
having ethylenic unsaturation consisting of from about 45 to
; about 65 percent by weight of a highly polar liquid carboxyl- .. : -
terminated acrylonitrile-butadiene having carboxyl groups
: dispersed along the chain length, and the second said constituent
being a liquid precursor of a solid polymer having substantially .
no ethylenic unsaturation consisting of from about 20 to about
40 percent by weight of at least one component selected from -
the group consisting of liquid novolac resins and liquid
cycloaliphatic epoxy resins; and (b) polymerizing the admixture :
of step (a) to yield a solid, two phase polymerization product : :
comprising a dispersed phase rich in the polymerization product
of said first constituent and a continuous phase rich in the
polymerization product of said second constituent.
-6a-
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~077643
In a further particular aspect the present invention
provides an article for the electroless deposition of adherent
metal thereon from an electroless metal deposition bath, in
which at least a portion of the surface of said article has
been coated with a layer of two-phase polymer susceptible to
oxidative attack, said polymer comprising a dispersed phase
rich in the polymerization product of a first liquid constituent
comprising a liquid precursor of a solid polymer having
ethylenic unsaturation, and a continuous phase rich in the
polymerization product of a second liquid constituent comprising
a liquid precursor of a solid polymer having substantially no
ethylenic unsaturation. .
In yet a further particular aspect the present invention
provides an article for the electroless deposition of adherent
metal thereon from an electroless metal deposition bath, in :
which at least a portion of the surface of said article has
:; been coated with a layer of a two-phase polymer susceptible to :
.i
oxidative attack, said polymer comprising a dispersed phase
; rich in the polymerization product of a first liquid constituent
comprising a liquid precursor of a solid polymer having ethylenic
unsaturation consisting of from about 45 to about 65 percent
by weight of a highly polar liquid carboxyl-terminated
acrylonitrile-butadiene having carboxyl groups dispersed along
the chain length, and a continuous phase rich in the polymer-
ization product of a second liquid constituent comprising a
liquid precursor of a solid polymer having substanti.ally no
ethylenic unsaturation consisting of from about 20.to about 40
percent by weight of at least one component selected from the
group consisting of liquid novolac resins and liquid
cycloaliphatic epoxy resins.
The figures are scanning electron microscope photomicro-
graphs obtained at the magnification and tilt indicated for each
specimen and illustrate the grain structures, or surface charac-
.
-6b-
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1~776~3
teristics, of the substrates.
Figure 1 shows an untreated, heterogeneous
substrate according to the invention;
Figure 2 is a photomicrograph of a preferred
prior art heterogeneous substrate, also untreated;
Figures 3 and 4 illustrate a Figure 1 surface
following chromic treatment in the known fashion;
Figure 5 is a Figure 2 surface following chromic
oxidation;
Figures 6 and 7 are Figure 1 surfaces following
oxidative attack by contacting with permangana~e
solution; and
Figure 8 is a Figure 2 surface that haæ been
permanganate treated. -
The content of the carboxyl acrylonitrile
butadiene in the liquid mixture may vary from about 45 to
about 65 weight percent of the mixture. Significantly
more than 65 weight percent generally results in a
polymer that is overly rubbery and weak. Significantly
less than 45 we~ght percent content renders the resultant
polymers almost totally resistant to oxidation agents
presently preferred by practitioners. The preferred -
content of this component is from about 50 to about 60
; weight percent.
The highly functional epoxy content of the liquid
mixture may range from about 20 to about 40 weight percent.
Suitable epoxies include liquid epoxy novolacs and liquid
cycloaliphatic epoxies having a high functionality, or
mixtures of such epoxies.
Phenolics may optionally be included in the
liquid mixture. A preferred liquid phenolic resin is
phenolic
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` ~ ~ I ; 1077643 L
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1 ¦ novolac, and it may be present in amounts ranging from
2 ¦ zero to aboue 35 weight percent.
8¦ Utilization of the liquid mi::tures described to form
~¦ resinous surfaces for adherent me~allization requires their
~¦ polymerization. This is preferably achieved through the
G¦ addition of a catalyst, curative, accelerator or mixture
7 thereof to the liquid mixture. Preferred agents inclute
8 dicyandiam~de, menthane diamine,
~ N,N,N',N'- tetramethylbutanediamine, and stannous octoate.
Polymerizable mixtures according to the pr~eferred
11 embodiment will typically consist of about~85 weight perc~t
12 solids, with the remainder attributable to minor solvent
13 content of the ingredients and catalyst. A preferred method
14 of forming polymerized substrates from the liquid mixtures
16 includes the step of curtain coating a base with the liquit
16 prior to polymerization, and I have found that reducing the
17 sol:~ds content to about 70 weight percent facilitates this
18 processing step. Where the curtain coating step is used,
i9 my yreferred solvent is ethylene glycol monomethyl ether
~: A 20 (methoxyethanol), such as methyl-Cellosolve~
21 Forming the initial liquid polymerizable mixture
22 containing from about 45 to about 65 weight percent
23 carboxyl-terminated acrylonitrile butadiene, also having
24 carboxyl groups along its chain length, from about 20 to
2~ about 40 weight percent of highly functional epoxy novolac
26 or cycloaliphatic epoxy or a mixture thereof, and from zero
27 to about about 35 weight percent phenolic novolac may be
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1 1(~776
1 conveniently done at room temperature or with slight warming
2 to facilitate mixing.
8 The above-described mixtures may be utilized in any
4 number of ways to provide polymeric surfaces for adherent
~ metallization. The entire article may be formed of
6 polymerization products according to the above, or the
7 article to be metal plated may be provided with just a
8 surface coating of such polymers.
9 If the articles to be metallized are to be provided with
a layer of the disclosed polymers, such layers may be applied
11 to a base in many ways. Two basic options include: applying
12 the liquid mixture diree~ly to the base and then precuring
13 the mixture prior to conducting the metal de~osition process;
1~ and forming thin precured sheets from the liquid mixture for
later lamination to the article to be metallized. For
16 example, panel size articles (typically about two square
17 feet in area), including laminates, may be coated with the
18 liquid mixtures by, for example, curtain coating, roller
19 coating or dip coating. The mixtures may then be cured or
1 20 polymerized by heating, for example via infrared or in a
1 21 convection oven. Sheet size laminates (typically about
22 twelve square feet in area) are most efficiently provided
23 with a coating of such materials by forming precured sheets
24 of a polymer, for exemple by coating and precuring the
2$ mixture on a release sheet, and then laminating the polymer
a~ with a base material.
_9~
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1C~77643
If polymeric surfaces according to the invention
are to form a layer on a base of a different material,
fully cured layers of the polymer preferably have a
minimum thickness of about 0.75 mil and a maximum thick-
ness of about 1.5 mil, ~ith a preferred thickness of about
1 mil. In contrast with the previously known platable
surface coatings, which have low solids - high solvent
contents and will provide a final 1 mil-thick coating
over about 300-350 square feet of base material per
gallon, the low solvent of the instant polymeric coatings
permits coverage in the amount of 850-950 square feet of --
base per gallon per mil.
Diphase polymeric surfaces formed according to
the instant invention may be rendered microporous by,
e.g., chromic or permanganate treatment, and then seeded
according to known procedures to render them catalytic to
electroless metal deposition baths. Alternatively, the
polymers may include a filler that is autocatalytic to
electroless metal deposition baths and the seeding step
may be eliminated, such as is taught in U.S. Patent ~o.
;~ 3,779,758, issued December 18, 1973.
Regarding all of the data below, the test sarnples
were precured for one hour at 160C prior to electroless
; metal processing and postbaked for one hour at 160C
following adherent metallization.
Unless otherwise noted, as for Tables II and III,
infra, all weight percents herein regarding constituents
that enter into the resultant polymer are with respect
to the basic liquid mixture, i.e., the weights of other
ingredients such as catalysts, solvents and the like are
not included. With respect to Tables II and III, all
weight percents are based upon the total weight of each
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10776~3
system given.
Table I sets forth the compositions of the basic
liquid mixtures for each of the seven examples described
below.
TABLE I
~ CO~PONENT EXAMPLE
; (wt.%)
I II III IV V VI VII
carboxylated acrylonitrile
butadiene60 60 60 60 61 61 45
epoxy novolac40 40 40 40 -- -- 22
cycloallphatic epoxy-- -- -- -- 25 25 --
phenolic novolac-- -- -- -- 14 14 33
The examples of Table II illustrates applications
of the invention that result in polymeric substrates that
may be rendered microporous according to known methods
without prior treatment with a strong organic solvent.
All component concentrations are in weight percents.
Surfsces formed of polymers from mix~ure according to
Examples ~ and IV require a seeding step prior to adherent
metallization, while polymeric surfaces according to
Examples II and III are catalytic to electroless metal
deposltion without seedin8.
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1 TABTE II
2 .
3 CCMPONENT EXAMPLE
4 I ~I III IV
5 carboxylated acrylonitrile ~
6 butadiene (B.F. Goodrich CTB ~ 52.3 50.8 54.2 55.7
epoxy novRlac (Dow Chemical
8 DEN 43~ . 34.8 34.0 36.1 37.1
'. 9 .
- 10 flow promoter (Raybo 1 ~ 0.7 0.7 0.7 0.7
11 catalytic filler (PEC-8~ --- 2.6 2.7 ---
12 catalyst (solution A*) 12.2 11.9 --- ---
13 catalyst (solution B**) --- --- 6.3 6.5
_
*Solution A **Solution B
16 component wt.% com~onentwt.Z
dicyandiamide 11.9 tioyandiamide 21.4
j 17 dimethylformamide 66.7 menthane diamine78.6
silicone resin (Dow~;~ , .
, 18 Corning DC No. 21 ~ 17.8
r~ 19 N,N,N',N'-tetramethyl ,
butanediamine 3.u
.
21 The examples of Table III are directed to the use of
22 mixtures from which polymers yielding surfaces that should
23 be treated with a strong organic solvent prior to oxidation
are derived. Polymers from mixtures according to Examples
26 V and VII yield platable surfaces that require seeding, while
27 surfaces of polymers from mixtures according to E~ample VI
28 do not reauire a seeding step prior to adherent metallization.
1 29 Again, all component concentrations are in weight percent.
.- , . .
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-~ I 1077643
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I I TABLE III
2 1 COMPONENT EXAMPLE
4 ¦ cycloaliphatic ep (Union ~
I Carbide ERL 423 ~ . 24.0 23.3 ---
I carboxylated acrylonitrile
8 I butadiene (B.F. Goodrich CTB ~ 60.0 58.3 44.25
¦ phenolic novol~c (Monsanto ,
I ChemicaI P9~ 14.0 13.6 33.2
11 ¦ epoxy novolac (Dow Chemical DEN 438~ 22.1
12 1 latent catalyst (stannous octoate) 2.0 1.9 ___
3 ¦ catalytic filler (PEC-8~ 2.9 ___
l accelerator (N,~,N',N'-tetramethyl
15 ¦ benzyldiamine) --- --~ 0.45
16 1
18 1 Figure 1 is a cured and untouched surface of a
19 1 heterogeneous polymeric substrate according to the invention.
The photomicrograph shows .he surface as it appears under a
21 scanning electron microscope and the conditions indicated.
22 Figure 2 is a photomicrograph of a cured and untouched known
23 surface according to U.S. Patent No. 3,625,758. The surface
24 was prepared by blending masticated acrylonitrile butadiene
rubber prepolymer with an epoxy/phenolic mixture. A comparison ~ :
27 of Figures 1 and 2 shows that diphase surfaces resulting from
processes according to the lnvention present a more uniiorm
28 appearance than the previously known heterogeneous surfaces.
i 29
. :
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~ 1~776~3
Figures 3 and 4, at 2000 and 7000 magnification,
respectively, show surfaces of the Figure 1 type follow-
ing oxidation in chromic solution according to known
procedure, while Figure 5, at 7000 magnification, shows
a prior art surface as shown in Figure 2 following the
same chromic treatment. As is evident from comparison of
Figures 3 and 4 with Figure 5, diphase surfaces according
to the present invention result in a relatively well-
ordered, honeycomb-like microporous structure following
chromic treatment, while the oxidized diphase surface
according to U.S. Patent No. 3,6259758 exhibits a much
more randomly mlcroroughened and microcracked appearance.
The differences are attributable to the fact that
surfaces according to the methods here disclosed include
- a low and narrow-range molecular weight unsaturated
component, while the diphase polymer surfaces of U.S.
Patent No. 3,625,758 have a very large molecular weight
distribution of the dispersed phase rubber, because of
the chain length and the dispersion being effected phys-
ically.
The unsaturated polymer component of mixtures
according to the inventior. and the other components
polymerize to yield a dispersed phase rich in polymer
having ethylenic unsaturation within a continuous phase
or matrix rich in polymer having substantially no
ethylenic unsaturation. Because the dispersion is
effected by micro phenomena, rather than masticating
and blending on a macro scale, the chain length and
distribution of the dispersed phase are much more uniform
than with previously known heterogeneous surfaces. As
indicated by the photomicrographs of the figures, the
matrix polymer is much less susceptible than the areas
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107~643
rich in unsaturated polymer to oxidative degradation,
resulting in a well-ordered microporosity.
Figures 6 and 7 illustrate platable surfaces
according to the invention following permanganate treat-
ment of a Figure 1 type surface, while Figure 8
illustrates the prior art, Figure 2 type surface follow-
ing contacting with a permanganate solution. Again,
the honeycomb-like result following oxidative attack of
the surfaces of the present invention may be compared to
the generally microroughened and microcracked surface
resulting from previously preferred hetarogeneous surfaces
for adherent metallization in electroless metal deposition
baths.
Typical micropore diameters following oxidative
attack on the polymeric surfaces described range from
about 1000 A to about 45,000 A, with the majority having
t diameters in the range of from about 6000 A to about
18,000 A. The depth of penetration varies widely up to
about 0.3 mil.
Surfaces resulting from polymers formed from the
disclosed preferred embodiments typically produce peel
st.engths on the order of ~3 pour.ds per ilLch of width
following known electroless metal deposition procedures.
Previously known heterogeneous systems for the
electroless deposition of metal thereon would exhibit
rather sharp attenuation of peel strengths with increased ~-
oxidation treatment time, while metallized polymeric
surfaces according to the invention yield a relatively
flat peel strength response curve: a five minute oxida-
tion treatment yielded a peel strength of about 13 pounds
per inch of width and a twenty minute treatment resulted
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1077643
in a peel strength of about 15 pounds per inch of width.
Electrolessly metallized diphase surfaces of the
sort disclosed are also remarkably heat resistant. There
was no evidence of blistering, even on large areas
(1" x 3" samples), when articles having metallized poly-
meric surfaces according to the invention were dip
soldered for 20 seconds at 260C. Repeated application
of a soldering iron (up to twelve repetitions) had no
blistering effect and evidences an excellent repair
capability for such surfaces in printed circuit applica-
tions.
Resinous surfaces of the instant invention are
widely useful in known electroless metal deposition
processes.
For those polymers for which pretreatment prior
to activation is suggested, in order to provide polar -~
and strained sites that will be more readily attacked by ~-
the oxidizer, contacting with strong organic solvents
according to known methods is preferred.
Known oxidizing agents and methods such as
chromic, chromic/sulfuric and permanganate treatments
may be utilized~
Where a catalytlc filler has been incorporated
into the polymeric surface in known fashions, no seeding ~ -
step iæ required.
If a seeding process is desired, known processes,
such as the typical stannous chloride/palladium chloride
methods, may be employed.
- Plating of the instant resinous surfaces may be
achieved with a variety of metals according to known
procedures, including, but without limitation, copper -~
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(Zeblisky et al U.S. Patent No. 3,095,309, issued
June 25, 1963), nickel (Brenner Metal Flnishing,
November 1954, pages 68-76), and gold (Brookshire U.S.
Patent No. 2,976,181, issued March 21, 1961).
:
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