U.S. patent number 3,779,758 [Application Number 04/810,378] was granted by the patent office on 1973-12-18 for photosensitive process for producing printed circuits employing electroless deposition.
This patent grant is currently assigned to Photocircuits Corporation. Invention is credited to Joseph Polichette.
United States Patent |
3,779,758 |
Polichette |
December 18, 1973 |
PHOTOSENSITIVE PROCESS FOR PRODUCING PRINTED CIRCUITS EMPLOYING
ELECTROLESS DEPOSITION
Abstract
An adhesive system which provides adhesive compositions to be
applied to an insulating base and form printed images thereon. The
adhesive compositions include agents which render them
photosensitive, and receptive to electroless metals.
Inventors: |
Polichette; Joseph (South
Farmingdale, NY) |
Assignee: |
Photocircuits Corporation (Glen
Cove, NY)
|
Family
ID: |
25203717 |
Appl.
No.: |
04/810,378 |
Filed: |
March 25, 1969 |
Current U.S.
Class: |
430/315; 430/176;
101/467; 430/197 |
Current CPC
Class: |
H05K
3/185 (20130101); G03F 7/00 (20130101); C23C
18/1605 (20130101); H05K 3/387 (20130101); C09J
161/06 (20130101); G03F 7/0047 (20130101); C09J
163/00 (20130101); G03C 1/62 (20130101); G03F
7/04 (20130101); G03C 1/695 (20130101); C09J
163/00 (20130101); C08L 2666/28 (20130101); C08L
2666/28 (20130101); H05K 2203/0709 (20130101) |
Current International
Class: |
C23C
18/16 (20060101); C09J 161/00 (20060101); C09J
163/00 (20060101); C09J 161/06 (20060101); G03C
1/62 (20060101); G03C 1/695 (20060101); G03C
1/52 (20060101); G03F 7/00 (20060101); H05K
3/38 (20060101); H05K 3/18 (20060101); G03F
7/004 (20060101); G03F 7/04 (20060101); G03c
005/00 (); G03c 005/18 () |
Field of
Search: |
;96/49,75,91N,91R,36.2,36,48PD,92,93,36.1 ;117/47A,212,213,217 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
1,064,725 |
|
Apr 1967 |
|
GB |
|
764,959 |
|
Aug 1967 |
|
IT |
|
Other References
Dinaburg, M. S., "Photosensitive Diazo Cpds," The Focal Press, p.
170 relied on, 1964..
|
Primary Examiner: Bowers, Jr.; Charles L.
Claims
What is claimed is:
1. A process for producing printed circuits on an insulated base
which comprises applying to said base a film of a copolymer of
acrylonitrile-butadiene having dispersed therein a catalyst
selected from the group consisting of the salts, oxides or metals
of Groups 1B and 8 of the Periodic Table of Elements including
mixtures thereof and a light sensitive diazonium compound for
enhancing the light sensitiveness of said composition, exposing
said film imagewise to an actinic light source, removing the
unexposed portion of the film with an organic solvent for said film
whereby printed circuit images are formed on the surface of the
base in exposed areas, and immersing the printed circuit images in
an electroless metal plating solution containing the metallic salt
of the metal to be plated and a reducing agent.
2. A process according to claim 1 wherein said diazonium compounds
are selected from the group consisting of p-diethyl-amino-2-ethoxy
benzenediazonium chlorozincate,
4-ethylamino-3-methyl-benzenediazonium chlorozincate,
p-diethyl-amino-2-ethoxybenzene- dizaonium chlorozincate,
4-diethylamino-2-Methyl-benzenediazonium chlorozincate and
p-morpholinobenzene-diazonium fluoroborate.
3. A process according to claim 1 wherein the catalyst is palladium
chloride.
4. A process according to claim 1 wherein the catalyst comprises
palladium chloride in admixture with an epoxy resin and an organic
solvent.
5. A process according to claim 1 wherein the electroless metal
plating solution contains a source of cupric ions.
6. A process for producing printed circuits on an insulated base
which comprises applying to said base a film of a composition which
comprises acrylonitrile-butadiene and a thermosetting phenolic or
epoxy resin having dispersed therein a catalyst selected from the
group consisting of the salts, oxides or metals of Groups 1B and 8
of the Periodic Table of Elements including mixtures thereof and a
light sensitive diazonium compound for enhancing the light
sensitiveness of said composition, exposing said film imagewise to
an actinic light source, removing the unexposed portion of the film
with an organic solvent for said film whereby printed circuit
images are formed on the surface of the base in the exposed areas,
and immersing the printed circuit images in an electroless metal
plating solution containing the metallic salt of the metal to be
plated and a reducing agent.
7. A process according to claim 6 wherein the catalyst is palladium
chloride.
8. A process according to claim 6 wherein the catalyst comprises
palladium chloride in admixuture with an epoxy resin and an organic
solvent.
9. A process according to claim 6 wherein the electroless metal
plating solution contains a source of cupric ions.
Description
This invention relates to an adhesive system whereby a film of
adhesive composition is applied to an insulating substrate to form
printed circuit images thereon. The adhesive composition comprises
agents which render the adhesive layer sensitive to light and
receptive to an electroless metal, e.g., copper.
It is an object of this invention to provide an adhesive system
which is both light-sensitive and receptive to an electroless
metal.
Another object of this invention is to form printed circuit images
with an adhesive composition which is receptive to the deposition
of an electroless metal.
A further object of this invention is to provide an adhesive
composition capable of forming a good bond with an insulating
base.
Heretofore, it has been customary to seed and sensitize insulating
substrata on which it is desired to electrolessly deposit metal,
e.g., copper, by contacting the substrata sequentially with aqueous
acidic solutions of stannous tin ions and precious metal ions,
e.g., palladium, or with a single acidic aqueous solution
comprising a mixture of stannous tin ions and precious metal ions
such as palladium. For example, one such treatment involves
immersing the insulating base material first in an acidic aqueous
solution of stannous chloride followed by washing after which the
substratum is immersed in an acidic aqueous solution of palladium
chloride. In an alternative system, the substratum is immersed in
an acidic aqueous solution comprising a mixture of stannous
chloride and palladium chloride.
Seeding systems are known wherein electroless metal deposition is
initiated on solid particles catalytic to the deposition of
electroless metal and dispersed throughout an organic adhesive
base.
The adhesive system of the present invention represents an
improvement over the seeding and sensitizing systems heretofore
available in that it greatly simplifies the application of printed
circuits on an insulated base board.
Among the advantages of the present system is that a printed
circuit may be provided without altering or deteriorating the base
or insulating base on which the image is printed. With the present
adhesive system there is no need to etch the whole base. The image
may be added to the base only where it is desired or needed.
Another advantage of the present system is that it provides a clean
background for selection of the area where the image may be placed.
Also, with the present system, the insulated base is not tampered
with by mechanical abrasion, chemical etching or with an
overcoating with the adhesive composition.
An important advantage of the present invention is that it provides
a sharp, clear and definable photoprint image. With the present
system, the images may be printed with the lines being as thin as
0.1 millimeters or less, and the spaces in between the lines may
also be 0.1 millimeters or less. This advantage of the present
adhesive system is emphasized in comparison with the prior
silk-screening process where the refinement of the lines could only
be as low as 0.5 to 0.8 millimeters.
Moreover, the adhesives of the present system are curable by light
and thus, the detrimental heat cure cycles may be eliminated which
are necessary in producing images by other systems such as
silk-screening.
The adhesive system of the present invention is also readily
adaptable to a wide variety of substrata and economical. The
present adhesive system in addition to providing printed circuits
may be used to provide various designs including metallic designs,
decorative designs, and the like on a variety of bases.
The present adhesive system includes an adhesive base composition
having dispersed therein a catalyst, e.g. a palladium chloride
catalyst and a sensitizing agent, e.g. a diazonium salt. The
catalyst and sensitizing agent impart desired properties to the
adhesive composition of receptiveness to electroless metals and
light-sensitiveness, respectively.
The adhesive base composition of the present invention will
ordinarily comprise an adhesive polymer or copolymer, an adhesive
resin alone or in combination with a thermosetting resin of the
type described hereinbelow, and solvent material. Typical of the
adhesive polymers which may be used in the present system are
polyvinyl acetal resins, polyvinyl alcohol, polyvinyl acetate,
polyvinyl pyrrolidione, polyamides, polyvinyl butyral natural and
synthetic rubbers, and the like. Preferred for use as the polymer
are acrylonitrile butadiene copolymers, and other polymers
containing ethylenic groups.
The resins which may be used according to this invention include
thermosetting resins such as allyl phthalate; furane; melamine
formaldehyde; phenol formaldehyde and phenol-furfural copolymer,
alone or compounded with butadiene acrylonitrile copolymer or
acrylonitrile-butadiene-styrene copolymers; polyacrylic esters;
silicones; polyesters; and the like.
The adhesive base composition may also include phenolic resins such
as bromo methyl alkylated phenol formaldehyde and thermosetting
phenolics, to reinforce and impart adhesive properties to the
adhesive base compositions. Certain epoxy resins, epoxy-urethane
resins, and urethane resin also may be used to enhance the adhesive
properties of the adhesive compositions.
The adhesive base compositions of the present adhesive system have
dispersed therein an agent which is catalystic to the reception of
an electroless metal dissolved in an organic system which may
comprise one or more organic solvents, one or more organic
polymers, or one or more organic solvents in combination with one
or more organic resins.
The catalytic agent may be a salt or an oxide, or may be any of the
metals of Groups 8 and 1B of the Periodic Table of Elements,
compounds of any of these metals or mixtures of such metals. Salts
or oxides of iron, cobalt, and iridium will ordinarily be used as
the dissolved catalytic agent, with a palladium chloride catalyst
being preferred, i.e. a catalyst identified as PEC-8 according to
the present invention, the preparation of which is described
hereinbelow.
Any organic solvent which is capable of dissolving the catalytic
salts or oxides are used, providing the organic solvent does not
precipitate the adhesive from its solvents.
Preferred catalytic compounds for dissolution in polymers and
solvents of the type described are chlorides, bromides, fluorides,
fluoroborates, iodides, nitrates, sulfates, acetates, and oxides of
the metals and elements described hereinabove. Complexes of
rhodium, iridium, platinum and palladium with stannous chloride are
also suitable catalysts for dissolution in the polymers and
solvents.
According to the present invention the adhesive compositions are
rendered sensitive to light by adding to the adhesive compositions
diazonium compounds, azides, ferrous compounds or bichromate
compounds dissolved in organic solvents as sensitizers.
The diazonium compounds that may be suitably used according to the
present invention include p-diethylamino-2-ethoxybenzenediazonium
chlorozincate, 4 ethylamino-3-methyl benzenediazonium
chlorozincate, p-morpholenobenzenediazonium fluoroborate,
4-Diethylamino-2-methylbenzene-diazonium chlorozincate,
2-butyl-3-diazo-3-pseudoindole, p-amino-N-benzyl-N-ethylbenzene
diazonium chlorostanate, p-Amino-N-benzyl-N-ethylbenzene diazonium
chlorozincate, 3-chlor-4-diethylamino benzene diazonium
chlorozincate, p-diethylaminobenzene-diazonium fluoroborate,
p-diethylaminobenzene-diazonium chlorozincate,
3-diazo-2-methyl-5-phenyl-3-pseudoindole,
3-diazo-2(2-naphthyl)-3-pseudoindole,
3-diazo-5-nitro-2-phenyl-pseudoindole,
3-diazo-2-phenyl-3-pseudoindole, 3-diazoindiazole, 1-diaz-1-benz(e)
indiazole, 3-diazo-5,7-dibromoindiazole, 3-diazo-5-phenylindiazole,
3-diazo-2,4-diphenyl-3H-pyrrolenine,
2-p-chlorophenyl-3-diazo-4,5-diphenyl-3H-pyrrolenine,
2,5-bis(p-chlorophenyl)-3-diazo-3H-pyrrolenine,
2-(4-biphenylyl)-3-diazo-4,5-diphenyl-3H-pyrrolenine,
N-methyl-4'-(3-diazo-4,5-diphenyl-3H-pyrrolenin-2-yl)-benzenesulfonanilide
, 3-diazo-2,4, 5-triphenyl-3H-pyrrolenine, and
4-diazo-2,5-diphenyl-4H-isoimidazole.
The aromatic azide compounds that may be used as a sensitizer
include 4,4'-diazidostibene, p-Phenyl-bis(azide),
p-Azidabenzophene, 4,4'-diazidobenzophenone, and
4,4'-diazidodiphenylmethane.
The organic solvents in which the diazonium compounds, azides, and
other sensitizing compounds are dissolved include diethyl
formamide, dimethyl acetamide, methyl cellosolve,
n-methyl-2-pyrrolidone, dioxane and the like. The sensitizer
compounds are dissolved in organic solvent concentrates to provide
a more uniform distribution of the sensitizer in the adhesive
system. The compounds are added to the solvent and dissolved using
mechanical agitation.
There are certain types of dyes and pigments which have been found
to increase the photosensitizing activity of the diazonium salt in
the adhesive films to light.
The dyes are of a chemical class which include triarylmethane,
anthraquinone, stilbene, xanthene, monazo compounds, e.g.,
Eriocyanine A, Alizarin, Alizarin Blue S, Erythrosin, Eriochrome
Black T, Iosol Greene, and the like.
The pigments include, for example, ammonium ferro-ferri cyanide,
phthalocyamine blue, zirconium silicate, cab-o-sil, aluminum
stearate and the like. The pigments were also found to strengthen
the adhesive film and provide a color contrast on certain types of
base materials.
There are phenolics and epoxy resins which have been found to
impart adhesive properties to the base polymers. The phenolics
include bromo methyl alkylated phenol formaldehyde, oil soluble
heat reactive phenolics, and thermosetting phenolics.
A chlorosulfonated polyethylene elastomer can also be used to
reinforce and impart adhesive properties to the base polymers. The
bromo methyl alkylated phenol-formaldehyde resin may also be used
to improve the photoprintable properties of the adhesive
system.
Typical of the electroless copper solutions which may be used are
those described in U.S. Pat. No. 3,095,309, the description of
which is incorporated herein by reference. Conventionally, such
solutions comprise a source of cupric ions, e.g., copper sulfate, a
reducing agent for cupric ions, e.g., formaldehyde, a complexing
agent for cupric ions, e.g., tetrasodium ethylenediaminetetraacetic
acid, and a pH adjustor, e.g., sodium hydroxide.
Typical electroless nickel baths which may be used are described in
Brenner, "Metal Finishing," November 1954, pages 68 to 76,
incorporated herein by reference. They comprise aqueous solutions
of a nickel salt, such as nickel chloride; an active chemical
reducing agent for the nickel salt, such as the hypophosphite ion;
and a complexing agent, such as carboxylic acids and salts
thereof.
Electroless gold plating baths which may be used are disclosed in
U. S. Pat. No. 2,976,181, hereby incorporated herein by reference.
They contain a slightly water soluble gold salt, such as gold
cyanide, a reducing agent for the gold salt, such as the
hypophosphite ion, and a chelating or complexing agent, such as
sodium or potassium cyanide. The hypophosphite ion may be
introduced in the form of the acid or salts thereof, such as the
sodium, calcium and the ammonium salts. The purpose of the
complexing agent is to maintain a relatively small portion of the
gold in solution as a water soluble gold complex, permitting a
relatively large portion of the gold to remain out of solution as a
gold reserve. The pH of the bath will be about 13.5, or between
about 13 and 15, and the ion ratio of hypophosphite radical to
insoluble gold salt may be between about 0.33 and 10.1.
In the following examples, Epon 1001 is a epoxy resin made by
reacting bisphenol A with epichlorohydrin, having a melting point
of 64.degree.-76.degree.C., and an epoxide equivalent of 450-525.
SP-1055 resin is a heat reactive, bromo-methyl alkylated
phenolformaldehyde resin having a melting point of 135.degree.C.
SP-126 resin is an oil soluble, heat reactive lump form, phenolic
resin, having a melting point of 155.degree. and a specific gravity
of 1.10, SP-6600 resin is a powdered phenolic resin containing 6 to
8 percent hexa and has a melting point of 155.degree.-170.degree.F.
and a specific gravity of 1.15-1.20.
The following example illustrates the method of producing the
palladium chloride catalyst PEC-8.
EXAMPLE 1
642 grams of dimethyl formamide solvent was added to 3685 grams of
an epoxy resin in a reaction vessel. The mixture was stirred until
the epoxy resin was dissolved in the solvent. The mixture was
continuously stirred and heated to a temperature of about
60.degree.C. Then 73.3 grams of palladium chloride was slowly added
to the mixture and stirred and heated to a temperature range of
110.degree. to 120.degree.C. The resulting mixture was stirred at
this temperature for a period of 1 hour. The liquor was a deep
black opaque color. The heat was then removed and the mixture was
continued to be stirred and cooled to approximately 80.degree.C.
Then the material was stored in a non-metallic or a suitably lined
metal drum.
The formulations of photosensitizers of this invention which are
distributed in the present adhesive system are illustrated in the
following examples. The sensitizer salts, i.e., diazonium salts,
are dissolved in organic solvent concentrates to promote a more
uniform method of distribution of the sensitizer in the adhesive
system. The salts are added to the solvent and dissolved by
mechanical agitation.
EXAMPLE 2
Dimethyl Formamide 395 grams p-diethylamino- 2-ethoxy
benzenediazonium chlorozincate 5 grams EXAMPLE 3 Dimethyl Formamide
490 grams 4-Ethylamino-3-methyl- benzenediazonium chlorozincate
6-10 grams
EXAMPLE 4
Dimethylformamide 490 grams p-Morpholinobenzenediazonium
fluoroborate 10 grams
The sensitizers described in Examples 2 through 4 may be combined
with a dye or pigment, and the PEC-8 catalyst. This combination is
then distributed in the adhesive system.
Typical formulations of this combination of the catalyst, dye and
sensitizers are illustrated in the following examples.
EXAMPLE 5
Eriocyanine A 0.1 grams PEC-8 catalyst 2.0 grams Sensitizer of
example 4 50 milliliters
EXAMPLE 6
Iosol Green 0.4 grams PEC-8 catalyst 2.0 grams Sensitizer of
example 4 50 milliliters
EXAMPLE 7
Erythrosin B cert 0.20 grams PEC-8 catalyst 2.0 grams Sensitizer of
example 4 50.0 milliliters
The dyes and pigments together with the PEC-8 catalyst or some
other suitable catalyst may be added to an adhesive base material
prior to the addition of the sensitizer to form the present
adhesive system.
The formulation of various adhesive bases are described in the
following examples.
EXAMPLE 7A
grams Methyl Ethyl Ketone 1600 Acrylonitrile butadiene (Hycar 1431)
380 Phenolic Resin (SP-1055) 20
EXAMPLE 8
grams Ethylene glycol monoethyl ether acetate (Cellosolve acetate)
175 Methyl Ethyl Ketone 150 grams Acrylonitrile-butadiene (Hycar
1431) 36 Pyrogenic fumed Silicon dioxide (Cab-o-sil) 6 PEC-8
catalyst 12 Toluene 50 Oil Soluble Heat Reactive Phenolic resin (SP
126) 15 Thermosetting Phenolic resin (SP-6600) 5 Bisphenol A type
epoxy resin (Epon 1001) 10
EXAMPLE 9
grams Ethylene glycol monoethyl ether acetate 1906.8 Silane Resin
11.8 PEC-8 catalyst 68.1 Pyrogenic fumed Silicon dioxide
(Cab-o-sil) 59.0 Zirconium Silicate 118.0 Acrylonitrile-butadiene
376.0 Thermosetting Phenolic Resin 59.0 Oil Soluble Heat Reactive
Phenolic Resin 177.0 Bisphenol A type epoxy resin 118.0 High Flash
Naptha Solvent 1050.0 Chlorosulfonated Polyethylene 118.0
EXAMPLE 10
Ethylene glycol monoethyl ether acetate (Cellosolve acetate) 175
Methyl Ethyl Ketone 150 Acrylonitrile-butadiene (Hycar 1431) 36
Pyrogenic fumed Silicon dioxide (Cab-o-sil) 6 AuCl.sub. 3 (in 50
grams of N-methyl-2-pyrrolidone) 2.0 Toluene 50 Oil Soluble Heat
Reactive Phenolic resin (SP 126) 15
EXAMPLE 11
Grams Ethylene glycol monoethyl ether acetate 50 Methyl Ethyl
Ketone 200 Acrylonitrile-butadiene 30 Triethanolamine 0.3 Pryogenic
fumed silicon dioxide 1.0 PEC-8 catalyst 3.0
EXAMPLE 12
grams Methyl Ethyl Ketone 2000 Acrylonitrile-butadiene 300 Phenolic
resin (SP-1055) 40 PEC-8 catalyst 40 Ethylene glycol monoethyl
ether acetate 620
EXAMPLE 13
Ethylene glycol monoethyl ether acetate (Cellosolve acetate) 175
Methyl Ethyl Ketone 150 Acrylonitrile-butadiene (Hycar 1431) 36
Pyrogenic fumed Silicon dioxide (Cab-o-sil) 6 AuC 3 (in 50 grams of
N-methyl-2- 2.00 Stannous Chloride pyrrolidone) 1.50 Toluene 50 Oil
Soluble Heat Reactive Phenolic Resin (SP 126) 15
EXAMPLE 14
grams Ethylene glycol monoethyl ether acetate (Cellosolve acetate)
175 Methyl Ethyl Ketone 150 Acrylonitrile-butadiene (Hycar 1431) 36
Pyrogenic fumed Silicon dioxide (Cab-o-sil) 6 AgNO.sub.3 2.0
Toluene 50 Oil Soluble Heat Reactive Phenolic resin 15
The adhesive bases of the type illustrated above and described in
the various examples are then mixed with photosensitizers and
solvents to produce a photosensitive adhesive system according to
this invention whereby a film of adhesive material is applied to
various insulated bases. The formulations of the adhesive systems
are illustrated in the following examples.
EXAMPLE 15
To 100 grams of the adhesive base material of example 9, there was
slowly added 60 milliliters of the photosensitizer of example 2,
i.e. p-diethylamino-2-ethoxy benzenediazonium chlorozincate and 40
grams of a solvent, dimethyl formamide. The sensitizer was added
during mechanical agitation of the adhesive base material and
sufficient time was allowed to assure complete distribution of the
sensitizer. The solid content of the adhesive base was adjusted by
the addition of the solvent to produce the desired film thickness
of the photosensitive adhesive material to be applied to a
base.
A film of the photosensitive material was applied to a base and
allowed to dry and was exposed to ultra violet light. After being
exposed, the undeveloped portion of the film was removed from the
base and a printed circuit image was formed thereon. Then the
printed circuit image was electrolessly plated in a copper
solution. A good bond was obtained between the copper plating and
the adhesive printed circuit image.
The bond was determined by the force required to peel the
electroless copper at a 90.degree. angle from the adhesive image.
The force is measured as the "peel strength" in pounds per inch
width of plated metal removed.
The peel strength of the bond was about 6.0 lbs. per inch width of
the copper removed from the printed adhesive image.
EXAMPLE 16
Another adhesive composition was prepared as described in example
15 which consisted of the following:
Adhesive base of example 11 100 grams Photosensitizer of example 3
35 milliliters Methyl Ethyl Ketone 40 grams
A film of the composition was applied to a base. The film was
exposed to ultra-violet light, developed and electrolessly plated
with a copper solution.
The peel strength of the bond of the plated copper to the adhesive
image was about 7.0 lbs. per inch width. EXAMPLE 17
A third adhesive composition was prepared as described in Example
15, and consisted of the following:
Adhesive base of example 12 100 grams Ethylene glycol monoethyl
ether acetate 30 grams Zirconium Silicate 1.0 grams Pthalocyanine
Blue 0.3 grams Photosensitizer of example 4 50 milliliters
The peel strength of the bond of adhesive image to the plated
copper was about 6 lbs. per inch width.
EXAMPLE 18
A fourth adhesive composition was prepared, and consisted of the
following:
N-methyl-2-pyrrolidone 25.0 grams Zinc chloride 1.0 grams 1, 3, 6
Napthalene tri sulfonic Acid tri sodium salt 0.3 grams Flouboric
acid 1.0 grams 4-Diethylamino-2-methylbenzene- diazonium
chlorozincate 2.0 grams Anionic Wetting Agent 0.3 grams PEC - 8 3.3
grams Aniline Blue (spirit soluble) 0.1 grams Adhesive base of
example 7A 100.0 grams High Flash Naphtha 100.0 grams Methyl Ethyl
Ketone 200.0 grams Pyrogenic fumed Silicon dioxide (cab-o-sil) 3.0
grams
The peel strength of the bond of adhesive image to the plated
copper was about 6 lbs. per inch width.
The photosensitive adhesive material may be applied to a base or
substrate by any conventional means suitable for applying a uniform
coat. The preferred thickness is 0.001 inch. The coating is dried,
such as in an oven set at 45.degree. to 70.degree.C for a minimum
of 10 minutes or until the film is dry to the touch. Films of more
than 0.001 inch may require a longer time in the oven.
After the adhesive film was dried, it is exposed through a negative
or positive circuit pattern using an ultra-violet light source,
e.g., carbon arc, pulsed xenon, mercury lamp. The time for the
exposure depends on the thickness of the adhesive film, the type of
base material and the light source.
Following the exposure cycle of the adhesive film, the printed
circuit image is developed by removing the unexposed portions of
the adhesive film by using a suitable solvent. Such solvents may be
methyl ethyl ketone; 1, 1, 1-trichloroethane; trichlorethylene;
cyclohexanone; or any combination of these solvents.
One method of developing the printed circuit image is the pressure
spray technique. It is particularly effective in removing tenacious
residues caused by the pressure of inert fillers and pigments.
Generally, multiple spray rinses are required to assure a residual
free background for the plating of the electroless metal. For
example, 1, 1, 1-trichloroethane may be used in the first spray
rinse, and isopropyl alcohol or water may be used in a second
and/or third spray rinse.
The developed printed circuit image is then oven dried for about 10
to 20 minutes from 60.degree. to 70.degree.C or until the solvents
are evaporated. Then the developed image is precured for about 1
hour at 160.degree.C before it is ready for electroless metal
deposition.
Before the printed circuit image is electrolessly plated, it may be
activated to remove surface contamination and to open the surface
of the adhesive material to expose the catalytic sites which are
receptive to electroless metal deposition.
The adhesive material, for example, may be activated by being
successively (a) immersed in a chromic-fluoboric acid etchant for
about 5 to 10 minutes, (b) water rinsed for about 5 minutes, (c)
immersed in a sodium bisulfite neutralizer for about 1 minute and
(d) finally rinsed with water for about 5 minutes. The time in the
chromic-fluoboric etchant is dependent on the film thickness of the
photoprinted adhesive material during the immersion period.
The image may be plated with an electroless metal by any
conventional method. For example, the printed circuit image may be
immersed in an electroless copper bath for a period of 1/2 to 1
hour, for complete coverage of the adhesive image with copper. The
length of time in the electroless copper bath is dependent on the
density of the printed circuit pattern and the desired copper
thickness.
The invention in its broader aspects is not limited to the specific
methods, compositions and improvement described herein, but
departures may be made within the scope of the appended claims
without departing from the principles of the invention and without
sacrificing its chief advantages.
* * * * *