Roughening surface of a substrate

The surface of a substrate is roughened by providing a substrate which comprises a resinous material and an inorganic particulate material; and etching a surface of the substrate to selectively etch the resinous material and thereby produce the roughened surface.

DESCRIPTION 
1. Technical Field 
The present invention is concerned with a method for roughening the surface 
of a substrate and is particularly concerned with a substrate which 
comprises a resinous material. The present invention is especially 
concerned with roughening the surface of so-called prepreg substrates. 
2. Background Art 
A number of fiber reinforced plastics are used commercially for various 
purposes. Articles such as sheets, tapes, or fabrics wherein fibers are 
impregnated with a resin such as an epoxy resin or an unsaturated 
polyester resin are referred to as "prepreg substrates". One important use 
of prepreg substrates is to provide a surface upon which a pattern of an 
electrical conductor can be provided to obtain circuit boards or circuit 
cards. The desired pattern of the electrical conductor can be provided by, 
for instance, electroless plating of metal such as copper and nickel onto 
the substrate. Such technique is well-known in the prior art. For 
instance, an electroless or autocatalytic copper plating bath usually 
contains a cupric salt, a reducing agent for the cupric salt, a chelating 
or complexing agent, and a pH adjustor. Moreover, if the surface being 
plated is not already catalytic for the deposition of the desired metal, a 
suitable catalyst is deposited on the surface prior to contact with the 
plating bath. Among the more widely employed procedures for catalyzing a 
substrate is the use of a stannous chloride sensitizing solution and a 
palladium chloride activator to form a layer of metallic palladium 
particles. 
After the substrate is sensitized with the catalyst or seeder, the desired 
circuit pattern is defined by conventional photosensitive processes. For 
instance, a photosensitive material such as a negative photoresist can be 
applied to the substrate and then, by use of a mask, the photosensitive 
material is subjected to light of suitable wavelength to cause 
crosslinking or curing thereof. Next, unexposed photosensitive material is 
removed by treating with a chemical such as methylchloroform in areas 
where the circuitry is to be plated. The areas in which the photosensitive 
material is removed are those areas where the circuitry is to be plated. 
After this, the metal such as nickel or copper is plated, preferably by 
electroless plating onto those preselected areas of the dielectric 
substrate which do not contain the photosensitive material. The metal is 
coated to the desired thickness of the circuitry. 
However, in order to provide adequate adhesion of the catalyst and of the 
photosensitive material to the dielectric substrate, an irregular surface 
can be created on the dielectric substrate which, in turn, provides for 
improved bonding sites for the subsequently plated additive metal. A 
commonly used method to create an irregular surface on the dielectric 
substrate is a process which has been referred to as a sacrificial metal 
layer process. 
Briefly, such process includes laminating a sheath or film of a metal such 
as copper, nickel, or aluminum onto the surface of the dielectric 
substrate. The metal film is then stripped or etched completely from the 
substrate prior to application of any circuitry. This technique creates an 
irregular surface on the dielectric substrate which, in turn, provides the 
improved bonding sites for the subsequently plated metal. The film which 
is laminated to the substrate is textured and, during the lamination, the 
resinous material of the prepreg flows, generating the reverse image of 
the textured surface. Upon wet chemically etching-off the metal film, the 
reverse texture topography of the film is exposed in the prepreg. 
A disadvantage of this process is the requirement of employing a wet 
chemical etching process. The disadvantages which accompany wet chemical 
etching processes include control of the etching composition, requirements 
of caution in handling the compositions, and care in disposal of spent 
etchants and relative high cost involved. In addition, wet chemical 
processing can lead to loss in insulation resistance due to residual ionic 
contaminants from the wet chemical process. 
An alternative way to fabricate circuit boards involves encapsulating 
insulated wires in an adhesive. The resulting circuit board is generally 
termed an encapsulated wire circuit board. Encapsulated wire circuit 
boards are commercially available under the trade designation "Multiwire" 
which is owned by the Kollmorgen Corporation. The encapsulated wire 
technique is shown in U.S. Pat. Nos. 4,097,684 to Burr; 3,646,772 to Burr; 
3,674,914 to Burr; and 3,674,602 to Keough. 
U.S. patent application Ser. No. 392,996 filed June 28, 1982, by Varker, 
entitled "High Density Encapsulated Wire Circuit Board", disclosure of 
which is incorporated herein by reference, describes a technique for 
making an encapsulated wire circuit board wherein the insulated wires are 
firmly bonded to a relatively thick layer of copper which is covered by a 
layer of prepreg. The 
expansion and contraction of the board during thermal cycling is controlled 
by the copper and, therefore, there is not any significant amount of 
unpredictable variations in the dimensions of the board. Holes can be very 
accurately drilled at precise locations in such boards. In the technique 
shown in said Varker application, insulated wires are bonded to a 
substrate utilizing a heat curable adhesive so that after the adhesive is 
cured, the wires can not move relative to the substrate. 
U.S. patent application Ser. No. 392,998 filed June 28, 1982, entitled 
"Process for Making an Encapsulated Circuit Board and Products Made 
Thereby", by Grant, et al., disclosure of which is incorporated herein by 
reference, describes an improvement of the circuit board and process 
described in said Varker application. The Grant, et al. application 
describes the fabrication of an encapsulated wire board using a 
photosensitive such as a photo-curable adhesive material. In the technique 
described in the Grant, et al. patent application, the wires are laid in a 
photosensitive adhesive, this adhesive is exposed to light, thereby curing 
the adhesive and firmly bonding the wires to the substrate. The Grant, et 
al. patent application describes the use of the material described in U.S. 
Pat. No. 4,169,732 to Shipley. 
However, in order to enhance the adhesion of the photosensitive material to 
the prepreg, an irregular surface can be created on the surface of the 
prepreg. A commonly used method to create an irregular surface on the 
dielectric prepreg substrate is the sacrificial metal layer process 
discussed hereinabove. The disadvantages of the wet chemical etching 
process are also discussed hereinabove. Accordingly, it would be desirable 
to provide a roughening process which does not require wet chemical 
etching and does not have the disadvantages associated with wet chemical 
etching. 
SUMMARY OF THE INVENTION 
The present invention makes it possible to provide good adhesion of the 
photosensitive material to the dielectric substrate. In addition, the good 
adhesion of the photosensitive material made possible by the present 
invention can be achieved without employing a sacrificial metal layer. In 
addition, such good adhesion of the photosensitive material can be 
achieved without employing wet chemical processing and the various 
undesirable aspects associated with wet chemical processing. 
The present invention provides a method for roughening the surface of a 
substrate. The present invention includes providing a substrate which 
comprises a resinous material and an inorganic particulate material. The 
substrate is etched by a method which selectively etches the resinous 
material, thereby providing a roughened surface. The resinous material is 
removed while inorganic particulate material remains and is left exposed. 
The surface topography of the surface of the substrate will assume the 
features such as particle size and shape of the exposed inorganic 
particulate material. 
BEST AND VARIOUS MODES FOR CARRYING OUT THE INVENTION 
The substrate, roughened in accordance with the present invention, 
comprises a resinous material which can be thermoplastic or thermosetting 
and, particularly, those thermoplastic and thermosetting polymers which 
are useful in preparing dielectric substrates useful in the preparation of 
integrated circuit modules such as high density circuit boards. Typical 
thermosetting resinous materials include epoxy, phenolic based materials, 
and polyamides. Such materials are usually molded articles of the resinous 
material along with a reinforcing agent such as being a glass-filled epoxy 
or phenolic based material. Examples of some phenolic-type materials 
include copolymers of phenol, resorcinol, and cresol. Examples of some 
suitable thermoplastic polymeric materials include polyolefins such as 
polypropylene, polysulfones, polycarbonates, nitrile rubbers, and ABS 
polymers. The preferred polymeric materials employed in accordance with 
the present invention are the epoxy resinous materials. Typical epoxy 
resins include the bisphenol A type resins obtained from bisphenol A and 
epichlorohydrin, resinous materials obtained by the epoxidation of novolak 
resins produced from a phenolic material such as phenol and an aldehyde 
such as formaldehyde with epichlorohydrin, polyfunctional epoxy resins 
such as tetraglycidyldiaminodiphenyl methane, and alicyclic epoxy resins 
such as bis (3,4-epoxy-6-methyl-cyclohexylmethyl) adipate. The most 
preferred epoxy employed is of the bisphenol A type. 
In accordance with the present invention, it is essential that the 
substrate also include an inorganic particulate material such as 
SiO.sub.2, CaCO.sub.3, Al.sub.2 O.sub.3, CaO.sub.2, SiC, and CaF.sub.2. 
The preferred inorganic particulate material is silica (SiO.sub.2). In 
addition, the inorganic particulate material can be a mixture such as 
talc, clay, siliceous stone, diatomaceous earth, pyrosclerite, fluorite, 
dolomite, sericite, kaolin, and glass. 
The most preferred inorganic particulate materials include all forms of 
silica such as fused silica, available under the trade designation 
Cabosil, and hollow silica particles including hollow glass beads. 
In addition, if desired, the inorganic particulate material can contain an 
additional coating or coupling agent in order to enhance adhesion of the 
subsequently applied metal, such as copper, to the substrate. Suitable 
coupling agents include those containing amine functionality. Examples of 
such coupling agents include silanes having the general formula: 
##STR1## 
wherein R' is a hydrocarbon radical and preferably, an alkyl radical of 
1-6 carbon atoms and R is an amine-substituted alkyl radical in which the 
alkyl groups have from 1-6 carbon atoms. Examples of some commercially 
available silanes are Union Carbide A-1100 (gamma amino propyl trimethoxy 
silane); and Union Carbide A-1120 (N-beta(aminoethyl)-gamma-amino propyl 
trimethoxy silane). 
Such coupling agents can be provided onto the inorganic particulate 
material by vapor deposition. 
The inorganic particulate material is preferably an aggregate of fused 
spherical particles and has an aggregate size of about 0.002 to about 10 
microns, and most preferably, about 0.01 to about 1 micron. 
The amount of the inorganic particulate material is about 1% to about 10% 
by weight, and preferably, about 4% to about 8% by weight of the total of 
the resinous material and inorganic particulate material. 
The epoxy resinous compositions also can contain accelerating agents and 
curing agents, as well-known in the art. Examples of suitable curing 
agents include polyamines, primary, secondary, and tertiary amines, 
polyamides, polysulfides, urea-phenol-formaldehyde, and acids or 
anhydrides thereof. In addition, suitable curing agents include Lewis acid 
catalysts such as BF.sub.3 and complexes thereof. 
In the preferred aspects of the present invention the epoxy composition 
containing the inorganic particulate material is used in combination with 
reinforcing fibers such as glass fibers. The compositions containing 
fibers are usually prepared by impregnating the fibers with the above 
epoxy composition. The amount of the epoxy composition containing the 
inorganic particulate material when combined with the fibers is usually 
about 30% to about 70% by weight and preferably, about 55% to about 65% by 
weight of the total of the solids content of the epoxy composition and the 
fiber glass. 
After combining with the reinforcing fibers, the composition is cured to 
the B-stage and molded to the desired shape, such as a sheet. When sheets 
are employed, the thickness is usually about 1.5 mils to about 8 mils, and 
preferably, about 2 mils to about 3 mils. The curing to the B-stage is 
generally achieved by using temperatures of about 80.degree. C. to about 
110.degree. C. and for times of about 3 minutes to about 10 minutes. 
The substrate can then be laminated onto another supporting substrate as is 
generally practiced in the art. For instance, the bonding of the substrate 
containing the inorganic particulate material to an underlying substrate 
for use in integrated circuit modules or high-density circuit boards can 
be carried out by pressing together a sheet of the substrate containing 
the inorganic particulate material and a dielectric substrate material 
such as glass in a preheated laminating press at a predetermined pressure 
and temperature as, for example, about 200 psi to about 500 psi and 
preferably, about 250 psi to about 300 psi and at about 180.degree. C. The 
time of the pressing operation is variable, depending upon the particular 
materials employed and the pressure applied. About 1 hour is adequate for 
the above conditions. 
One surface of the substrate containing the inorganic particulate material 
is subjected to an etching process which selectively etches the resinous 
material in the substrate, leaving inorganic particulate material exposed 
to thereby produce a roughened surface. The surface topography assumes the 
features such as particle size and shape of the exposed inorganic 
particulate material. 
The preferred etching processes are the so-called "dry etching processes" 
such as plasma etching, sputter etching, and reactive ion etching. This 
eliminates the need of requiring wet chemical processing. The most 
preferred etching process is a plasma etching process which involves 
filling an evacuated reaction chamber with a gas whose constituent ions 
and/or radicals are chemically reactive such as CF.sub.4 in admixture with 
O.sub.2. The volume ratio of the CF.sub.4 to O.sub.2 is usually about 4:96 
to about 65:35. The best results, as far as uniformity is concerned, are 
obtained from volume ratios of CF.sub.4 to O.sub.2 of about 5:95 to about 
60:40. The surface which is to be etched is introduced into the reaction 
chamber, along with the reactive gas. The reactive gas is usually 
disassociated, forming radicals, positive ions, and/or negative ions by 
coupling radio frequency power to the plasma by a capacitive or inductive 
coupling. It is believed that the disassociated radicals and/or ions then 
chemically interact with the surface to be etched. In such a process the 
substrates are positioned either on a ground plane or at the same 
potential as the plasma gasses. 
A typical plasma etching process for a surface area of about 2000 square 
centimeters per side of substrate can be carried out at a pressure of 
about 500 millitorr, a total gas flow of 1 standard liter per minute, 
radio frequency power of 2.5 kilowatts, radio frequency of 13.56 
megahertz, and about 5 minutes of on time for the radio frequency. 
Using the above conditions, the etch rate of the substrate is usually 
between about 300 angstroms and about 700 angstroms per minute, while that 
of the inorganic particulate material is only about 1 angstrom to about 10 
angstroms per minute. It is desirable to provide ratios of etch rates of 
the resinous material to the inorganic particulate material of at least 
about 100:1, and preferably, at least about 500:1. 
In an encapsulated circuit board process, the wires are laid in a 
photosensitive adhesive, such as one described in U.S. Pat. No. 4,169,732 
and the adhesive is cured by exposure to actinic light. This results in 
firmly bonding the wires to the substrate. Suitable photosensitive 
compositions comprise: 
(a) reaction product of monoethylenically unsaturated carboxylic acid and a 
bisphenol A-diglycidyl ether epoxide 
##STR2## 
(b) reaction product of a monoethylenically unsaturated carboxylic acid and 
an epoxidized novolac of the formula: 
##STR3## 
(c) the ratio of a:b is from about 1:4 to about 4:1; 
(d) polyethylenically unsaturated compound; and 
(e) photo-initiator. 
Examples of .alpha.,.beta. ethylenically unsaturated carboxylic acid used 
to provide the above reaction products are acrylic acid, methacrylic acid, 
and crotonic acid. Component (a), above, can be liquid or solid, depending 
upon the molecular weight which generally ranges from about 
3.times.10.sup.2 to about 10.times.10.sup.4. The n in the above formula 1 
generally varies from about 0.2 to about 100, and preferably from about 
0.2 to about 25, and most preferably up to about 10. 
The relative amounts of monoethylenically unsaturated acid to the 
diglycidyl ether--bisphenol A epoxide usually employed is sufficient to 
react stoichiometrically with about 25 to about 100 percent, and 
preferably about 25 to about 75 percent of the epoxide functionality of 
this epoxy. The most preferred amount is about 75 percent. 
Component (b), above, can be a liquid, semi-solid, or solid, depending upon 
its molecular weight. Epoxy polymers wherein m is 1.5 to 3.5 are 
commercially available and are generally suitable. 
The relative amount of the monoethylenically unsaturated acid to the 
epoxidized novolac polymer is such as to react stoichiometrically with 
from about 25 to about 100 percent of the epoxide functionality of the 
novolac resin and preferably with about 25 to 75 percent of the epoxide 
functionality. The most preferred amount is about 75 percent. 
The relative amounts between the two epoxy constituents is from about 1:4 
to about 4:1, preferably is about 1:3 to about 3:1, and most preferably is 
about 1:1. 
The relative amounts of the combination of epoxides in the composition are 
generally from about 20 percent to about 75 percent. 
The composition may include a relatively minor amount (e.g., up to about 
10% of the total epoxy component) of a relatively high molecular weight 
bisphenol A-epichlorohydrin type polymer or phenoxy polymer of the 
formula: 
##STR4## 
wherein p is usually about 25 to about 100. Some commercially available 
phenoxypolymers include Eponol 53, Eponol 55, and Epon 1009. 
The polyethylenically unsaturated compounds employed in the compositions 
are capable of reacting upon exposure to ultraviolet light and should 
contain terminal ethylenic groups. Such compounds include unsaturated 
esters of polyols and especially esters of the methylene carboxylic acid 
such as the polyethylene glycoldiacrylates and trimethylol propane 
triacrylate. The relative amount of the polyethylenically unsaturated 
compound employed is usually from about 0.5 percent to about 40 percent 
and preferably from about 1 percent to about 20 percent. 
The compositions further include a photo-initiator or sensitizer. Many such 
materials are well-known to the prior art. Examples of some suitable 
photo-initiators include anthraquinone and substituted anthraquinones, 
such as the alkyl substituted or halo substituted anthraquinones including 
2-tert-butylanthraquinone. The photo-initiator is employed in amounts 
sufficient to sensitize the composition to ultraviolet light and is 
generally from about 0.1 percent to about 10 percent and preferably from 
about 0.1 percent to about 5 percent. 
In addition, the compositions, when desired, can include an organic 
non-reactive diluent to facilitate the coating operation. Examples of 
suitable solvents include cellosolve acetate, methyl carbitol, butyl 
carbitol, methylene chloride, and ketones such as methyl ethyl ketone. 
When employed, the diluent is present in an amount sufficient to provide 
compositions having a viscosity between about 100 centistokes and about 
1700 centistokes. 
The range of light exposure, time, and intensity for a typical 
photo-processable coating may be ascertained from the following typical 
conditions: 
30 inches from a high-pressure, short-arc, mercury lamp manufactured by 
OSRAM GMBH, Germany, Model HBO, 500 watts, for a period of about 2 minutes 
to about 20 minutes. 
Concerning an electroless coating process, after the roughening pursuant to 
the present invention, generally the substrate is then catalyzed by, for 
instance, a two-step activation procedure using stannous chloride in 
hydrochloric acid, followed by a dip in palladium chloride in hydrochloric 
acid or by a one-step procedure employing a tin-palladium hydrosol. In 
addition, it may be desirable to subject the catalyzed board to an 
accelerating solution of, for instance, a dilute solution of suitable acid 
or alkali. 
For a discussion of various seeder compositions and processes of applying 
same, attention is directed to U.S. Pat. Nos. 3,099,608; 3,632,388; and 
4,066,809; disclosures of which are incorporated herein by reference. 
After sensitization, the desired circuit pattern is defined by conventional 
photoresist processes. For instance, a negative photosensitive material is 
applied to the substrate and then, by use of a mask, the photosensitive 
material is subjected to light of suitable wavelength to cause 
crosslinking or curing of the photosensitive material. Then, unexposed 
photosensitive material is removed by treating with a chemical such a 
methylchloroform in areas where the circuitry is to be plated. 
Examples of some photosensitives employed include negative or 
photohardenable polymerizable compositions of the type suggested in U.S. 
Pat. Nos. 3,469,982; 3,526,504; 3,867,153; and 3,448,089; and published 
European Patent Application No. 0049504, disclosures of which are 
incorporated herein by reference. Polymers from methylmethacrylate and 
from glycidyl acrylate and/or from a polyacrylate such as trimethylol 
propane triacylate and pentaerythitol triacrylate are commercially 
available from E. I. du Pont de Nemours and Company under the trade 
designation "Riston". 
Examples of some negative photosensitive materials employed are from 
polymethylmethacrylates such as those commercially available from E. I. du 
Pont de Nemours and Company under the trade designation "Riston T-168". 
"Riston T-168" is a negative photoresist material from 
polymethylmethacrylate and crosslinkable monomeric units such as from 
trimethylol propane triacrylate. A detailed discussion of preparing a 
negative resist from polymethylmethacrylate, trimethylol propane 
triacrylate, and trimethylene glycol diacetate can be found in Example 1 
of U.S. Pat. No. 3,867,153. 
It has been found in accordance with the present invention that the 
mechanical adhesion of the photoresist to the substrate is significantly 
improved. 
Next, a metal such as copper or nickel is plated onto the substrate in the 
desired pattern. The metal can be plated by an electroless process. 
Examples of suitable electroless plating processes can be found in U.S. 
Pat. Nos. 3,844,799 and 4,152,467, disclosures of which are incorporated 
herein by reference.

The following non-limiting examples are presented to further illustrate the 
present invention: 
EXAMPLE 1 
Glass fibers are impregnated with a composition of 50% solids in 
methylethylketone of a composition containing about 85 parts by weight of 
Araldite 8011, about 15 parts by weight of ECN 1299, about 5 parts by 
weight of benzyldimethylamine, and about 5 parts by weight of Cabosil M-5. 
Araldite 8011 is a diglycidyl ether of tetrabromo bisphenol A having a 
weight per epoxide of about 455 to about 500, a melting point of about 
70.degree. C. to about 80.degree. C., a bromine content of about 19 to 23 
weight percent, is 100% solids, and is available from Ciba Geigy. ECN 1299 
is an epoxidized ortho-creosol formaldehyde novolak having a molecular 
weight of about 1270, a weight per epoxide of about 235, a melting point 
of about 99.degree. C., an epoxide functionality of about 4.4, and is 
available from Ciba Geigy. Cabosil M-5 is available from Cabot 
Corporation, has a surface area of about 200.+-.25 square meters per gram, 
and are colloidal silica particles sintered together in a chain-like 
formation. The relative amount of the epoxy composition to the fiberglass 
is about 60% by weight of the total composition based upon solids. 
The prepreg is cured to the B-stage by heating at about 80.degree. C. to 
about 110.degree. C. for about 6 to 7 minutes. 
The B-stage cabosil-filled sheet is laminated onto an epoxide substrate at 
300-500 psi pressure, at about 175.degree. C.-180.degree. C. for about 
one-half hour to about 2 hours to provide a fully cured Cabosil-filled 
epoxy surface of about 2-3 mils thick. The Cabosil-filled epoxy surface is 
then etched by a plasma etching process. The composite is placed in a 
reaction chamber which is then evacuated and filled with a gas containing 
5 parts by volume of CF.sub.4 and about 95 parts by volume of O.sub.2. The 
pressure in the reaction chamber is about 500 millitorr and the gas is 
introduced into the reaction chamber at a flow rate of about 1 standard 
liter per minute. The gas is disassociated by coupling radio frequency 
power of about 2.5 kilowatts to the plasma and is continued for about 5 
minutes. 
Adhesive tests are performed by laminating under vacuum, at a temperature 
of about 76.degree. C., a photosensitive adhesive to the above plasma 
etched prepreg. The pressure-sensitive adhesive is from a composition 
prepared in accordance with Example 1 of U.S. Pat. No. 4,169,732 (i.e., up 
to the disclosure therein concerning exposure), disclosure of which is 
incorporated herein by reference. 
The adhesion tests are performed using a modified Z-axis cross-pull 
technique. The interface bond is generated by laminating at 76.degree. C. 
in vacuum so as to produce a cross. The sample is then rigidly mounted on 
a test fixture. The test fixture is then mounted on a tensile testing 
machine which measures the load necessary to separate the two 
perpendicularly laminated strips. The average maximum load from a series 
of 9 tests is about 6.3.times.10.sup.2 Newtons (N).+-.0.8.times.10.sup.2 
N. 
COMISON EXAMPLE 2 
Example 1 is repeated, except that the prepreg is prepared from the same 
epoxy composition without the presence of the Cabosil and instead of being 
plasma etched, the surface is roughened by a sacrificial metal layer 
process including wet chemical etching off of the metal film. The average 
maximum load for about 10 samples is about 4.0.times.10.sup.2 
N.+-.0.5.times.10.sup.2 N. The maximum load is somewhat increased when the 
method of bonding the pressure-sensitive adhesive is a hot-roll laminating 
process employing a temperature of about 120.degree. C., rather than the 
vacuum laminating at about 76.degree. C. The results achieved are an 
average maximum load of about 4.9.times.10.sup.2 N.+-.0.4.times.10.sup.2 
N. 
EXAMPLE 3 
Example 1 is repeated, except that the method of bonding the 
pressure-sensitive adhesive to the etched prepreg is a room temperature 
high pressure (about 200 psi) technique. 
The following results are obtained: 
Max. load (.times.10.sup.2 N)/3.6.times.10.sup.2 mm.sup.2 sample area 
6.4 
6.5 
7.7 
COMISON EXAMPLE 4 
Example 2 is repeated, except that the method of bonding the 
pressure-sensitive adhesive to the prepreg is a room temperature high 
pressure (about 200 psi) process. 
The results are as follows: 
Max. load (.times.10.sup.2 N)/3.6.times.10.sup.2 mm.sup.2 sample area 
5.6 
6.8 
A comparison of the results from Example 3 to those of Example 4 shows that 
the process of the present invention provides as good as, or better, 
adhesive bonding characteristics, as achieved by the more complex prior 
art techniques involving chemical etching. 
EXAMPLE 5 
A plasma etched prepreg as obtained in Example 1, is immersed into a bath 
of about 0.05 grams of Reten per 100 ml of an 8% HCl aqueous solution for 
about 3 minutes. The substrate is then washed with deionized water and 
dried with air. Next, the coated substrate is immersed in a bath of about 
1.5 grams per liter of PdCl.sub.2, about 100 grams per liter of 
SnCl.sub.2, and about 280 milliliters per liter of 37% HCl at about 
65.degree. F. for about 3 minutes. The substrate is then air-dried. A 
photoresist, available under the trade designation "Riston T-168", being 
obtained from polymethylmethacrylate and a cross-linkable monomeric unit, 
such as trimethylol propane triacrylate, is laminated by a hot-roll 
laminator at about 110.degree. C. and a pressure of about 10 to about 15 
psi. The photoresist is then subjected to imaging radiation through a mask 
and developed in 1,1,1-trichloroethane. 
The substrate is then immersed in a copper electroless additive plating 
bath for about 20 hours. The electroless plating bath contains about 10 
grams per liter of CuSO.sub.4 -5H.sub.2 O, 35 grams per liter of ethylene 
diamine tetraacetic acid dihydrate, 0.25 grams per liter of GAFAC RE-610, 
14 milligrams per liter of sodium cyanide, and 2 milliliters per gram of 
37% aqueous HCHO. The specific gravity of the plating bath is about 1.07, 
the pH is about 11.7 by the addition of NaOH, and the temperature of the 
bath is about 73.degree. C..+-.5.degree. C. The oxygen content of the bath 
is maintained at about 2.5 ppm to about 3.5 ppm. The gas flow rate is 
about 12 SCFM. In addition, the plating racks are continuously agitated 
during the plating. 
After the plating, the remaining photoresist is stripped by dissolving in 
methylene chloride. 
The peel strength of the copper plating, as tested with a tensile testing 
machine, is about 1.5 grams/mil of line width of adhesion; whereas, the 
specification of the peel strength for commercial purposes is only 1 
gram/mil of line width. Peel strengths for certain optimized sacrificial 
metal techniques of about 3 grams/mil have been achieved, but such 
optimized techniques are much more complex and costly to carry out.