Note: Descriptions are shown in the official language in which they were submitted.
- 2 - 20727~2
Field of the IRve~ltiol~
This invention relates to a method of preparing a
printed circuit board by using an aqueous
photosensitive resin composition and a method of
preparing the aqueous photosensitive resin
composition.
Ba~Xaround of the In~ention
Heretofore, in the preparation of a printed
circuit board, generally a photosensitive film is
coated on a laminated board which has been lined with
an electrically conductive metal foil such as a copper
foil. The coated board is then irradiated with
actinic light through a negative and developed. Then,
unnecessary portions of the metal foil, i.e., those
not forming part of the circu~t pattern, are etched
and the photosensitive ilm is stripped. The result
is a printed circuit on the laminated board. The
board itself acts as an insulat~r. The photosensitive
film used in such a method is fairly thick, and
accordingly, causes problems such as decreased
sharpness of the circuit pattern formed after the
irradiation and development, difficulty of uniformly
coating the photosensitive film on the metal foil and
high cost of the photosensitive film. Another method
of preparing a printed circuit board is to coat a
liquid photosensitive resin composition directly on a
substrate and dry it to form a photo-curable coating.
Since the photosensitive resin composition used for
this purpose is dissolved or dispersed in an organic
solvent, the organic solvent will create a problem in
the working environment and accordingly, this method
is hardly acceptable~
3 20727~2
The preparation of a printed circuit board by the
electrodeposition technique has attracted a tremendous
attention in recent years. Such a method not only
requires expensive facilities, but also has a problem
that maintenance of the electrodeposition fluid is
difficult.
Bu~ary of the Invention
It is an object of the present invention to
provide a method of preparing a printed circuit board
by using an aqueous photosensitive resin composition.
The resin image is sharp and has good resistance to an
acidic etching solution after it has been irradiated
with actinic light and developed with water or an
aqueous alkaline solution. Furthermore, significant
cost savings can be had over the electrodeposition
technique, and organic solvents are not required.
Another aspect of the present invention is that
this method of preparing a photosensitive resin has no
adverse effect on the working environment or natural
environment, does not require sa~ety precautions
ayainst fire during the c~ating and drying steps, and
does not require any solvent recovery system.
A method of preparing a printed circuit board in
accordance with the invention comprises the steps of:
(1) coating an aqueous photosensitive resin
composition on an insulating substrate having an
electrically conductive metal layer thereon to
form a photo-curable coating. The aqueous
photosensitive resin composition is made of
(a) a carboxyl group-containing resin having an
acid value of 20 to 500, a number average
molecular weight o~ l,000 at lO0,000 and a
- 4 - ~ ~727
glass transition temperature, ("Tg") of at
least 0C,
(b) an amine compound,
(c) a photo-curable unsaturated compound having
at least two ethylenically unsaturated
bonds,
(d) a photopolymerization initiator and
(e) water as the solvent or the dispersing
medium;
(2) drying the coating;
(3) imagewise irradiating the coating with actinic
light;
(4) developing the irradiated coating with water or
an aqueous alkaline solution; and
(5) etching the portions of the electrically
conductive metal layer other than image portions
with an acidic etching solution.
In another aspect of the invention a method of
preparing an aqueous photosensitive resin composition
is mixing or dispersing
~a) a carboxyl group-containing re~in,
(b) an amine compound,
(c) a photo-curable unsaturated compound and
(d) a photopolymerization initiator in water.
et~ile~ Desari~ion o~ ~he Invent~on
The carboxyl group-containing resin used in the
present invention is any conventional resin having an
acid value of 20 to 500, a number average molecular
weight of 1,000 to 100,000, and a Tg of not less than
0C. When the acid value is lower than 20, its
a~finity to water will be decreased even in the
presence o~ an amine compound, and thus, it is
_ 5 - 2~727~2
difficult to obtain the aqueous photosensitive resin
composition of the present invention. On the other
hand, when the acid value exceeds 500, it will be
difficult to obtain a clear image by development with
water or an aqueous alkaline solution because i~s
affinity to water is too high. When the number
average molecular weight is less than 1,000, the
mechanical strength of the unexposed photosensitive
resin coating will be decreased, and the coating may
be easily damaged in the irradiation step. On the
other hand, when the number average molecular weight
exceeds 100,000, the viscosity of thP photosensitive
resin composition will be remarkably increa~ed. As a
result, the dissolving or mixing step is more
difficult, and also the developing time will be
increased. The Tg of the carboxyl group-containing
resin of lower than 0C tends to increase the
stickiness of the photosensitive resin composition and
causes a problem in the irradiation step.
Resins obtained by copolymerizing acrylic acid or
methacrylic acid with an unsaturated monomer such as a
~meth)acrylic acid ester, styrene, (meth)acrylonitrile
or asrylamide and acid anhydride group-containing
resins such as a styrene-maleic anhydride polymer
whose acid anhydride groups have been ring-opened with
water, an alcohol or an amine can be included in
preferred examples of the carboxyl group-containing
resin of the present invention.
Although any conventional alcohols can be used to
ring-open the acid anhydride groups of the resin, it
is preerred to use a primary or secondary alcohol due
to their reactivity. For example, methyl alcohol,
ethyl alcohol, butyl alcohol, butoxy ethanol and
ethyleneglycol monomethyl ether can be used. Also,
20727~2
primary amines and secondary amines can be used for
this purpose. Examples of such amines include
ammonia; alkylamines such as diethylamine,
monoethylamine, diisopropylemine and diisobutylamine;
alkanolamines such as monoethanolamine and
diethanolamine; alkylalkanol amines such as
dimethylamino ethanol; and alicycilc amines such as
cyclohexylamine.
Preferred ~arboxyl group-containing resins which
can be used in the photosensitive composition of the
present invention have a polymerizable unsaturated
bond in the molecule. Such resins can be synthesized
by any known method, for example, by esterifying part
of the carboxyl groups of the carboxyl
group containing resin with glycidyl acrylate in the
presence of a catalyst. Or, alcohols or amines having
a polymerizable unsaturated bond can be used as the
alcohol or the amine to ring-open the acid anhydride
groups of the above described styrene- maleic
anhydride polymer. Examples of ~3uch alcohols and
amines suitable for such a purpo~;e are hydroxyethyl
(meth)acrylate, hydroxypropyl (meth)acrylate, allyl
alcohol and allylamine.
The photosensitive resin composition of the
present invention also includes an amine compound for
the purpose of dissolving or dispersing the carboxyl
group-containing resin in water. Any conventional
amine compounds can be used for this purpose.
Examples of such amine compounds include alkanolamines
such as monoethanolamine, diethanolamine and
triethanolamine; alkylamines such as triethylamine,
diethylamine, monoethylamine, diisopropylamine and
diisobutylamine; alkylalkanolamines such as
dimethylaminoethanol; alicyclic amines such as
2~727~2
cyclohexylamine; and ammonia. ~mine compounds having
a polymerizable unsaturated ~ond in the molecule are
particularly preferred for such a purpose and examples
of such amine compounds include dimethylaminopropyl
acrylamide, dimethylaminoethyl methacrylate,
diethylaminoethyl methacrylate and allylamine. To
reduce generation of amine odor in the coating and
drying steps, amine compounds having a boiling point
of at least 100C are preferred. The amount of the
amine compound which can be employed in the present
invention is typically 0.2 to 2 mols per mol of the
free carboxyl group of the carboxyl group-containing
resin. The type photocurable unsaturated compound
which can be incorporated in the photosensitive
composition of the present invention i~ one having at
least two ethylenically unsaturated bonds in the
molecule. Examples of such ethylenically unsaturated
compounds include (meth)acrylic acid esters, allyl
compounds, vinyl ethers, vinyl esters and cinnamic
acid esters. Examples o~ the (meth)acrylic acid
esters include epoxy (meth)acrylates obtained by the
reaction of an epoxy resin having two or more
functional groups and a carboxylic acid having an
ethylenically unsaturated bond; urethane
(meth)acrylates obtained by the reaction of a
polyvalent aliphatic isocyanate or a polyvalent
aromatic isocyanate and a monoester of (meth)acrylic
acid with a divalent alcohol; and (meth)acrylates of a
polyvalent alcohol. Examples of tha allyl compound
include diallyl esters of phthalic acid, adipic acid
and malonic acid. Examples of the vinyl ethers
include vinyl ethers of a polyvalent alcohol.
Examples of the vinyl esters include divinyl succinate
and vinyl phthalate. In addition, the so-called
- 8 - 2 ~ 72 7 ~ 2
mono-functional monomers having one ethylenically
unsaturated bond can be used together with the above
described photo-curable unsaturated compound. The
amount of the photo-curable unsaturated compound which
can be used in the present invention is typically 0.2
to 3 times the total weight of the carboxyl
group-containing resin.
According to another embodiment of the present
invention, an aqueous photosensitive resin composition
can be obtained by using a carboxyl group-containing
resin and/or an amine compound which has a
photopolymerizable unsaturated bond instead of or
together with the above described photo-curable
unsaturated compound. Such an aqueous photosensitive
resin composition can form an image when coated, dried
on a substrate and then developed with water or an
aqueous alkaline solution after irradiation with
actinic light, and can form a photo-curable coating
having good resistance to an acidic etching solution.
Any conventional photopolymerization initiators can be
used as the photopolymerization initiator in the
photosensitive composition o~ the present invention.
For example, benzophenones such as benzophenone,
benzophenone methyl ether and Michler's ketone;
~5 benzoins such as benzoin, alpha-methylbenzoin, alpha-
phenylbenzoin, alpha-allylbenzoin, benzoin methyl
ether, benzoin ethyl ether, benzoin isopropyl ether,
benzoin n-butyl ether and benzoin isobutyl ether;
acetophenones such as acetophenone, 2,2-
diethoxyacetophenone, p-tert-
butyltrichloroacetophenone, 2,2-dimethoxy-2-
phenylacetophenone, 2,2-diethoxy-2-p~enylacetophenone
and N,N-diethylaminoacetophenone; benzil; k~tals such
as benzyl dimethyl ketal; anthraquinones such as 2-
- 9 - 2~727~2
methylanthraquinone, 2-ethylanthraquinone, 2-amylan-
thraquinone and 2-aminoanthraquinone; and
thioxanthones such as 2,4-dimethylthioxanthone, 2,4-
diisopropylthioxanthone and 2-chlorothioxanthone can
be preferably used~ The amount of this
photopolymerization initiator to be added in the
photosensitive resin composition is typically 0.10 to
lO~ by weight based on the total weight of the
photosensitive composition.
It is preferred to employ an appropriate
polymerization inhibitor in the photosensitive resin
composition of the present invention. Any
conventional inhibitors can be used as such a
polymerization inhibitor. Preferred examples of
polymerization inhlbitors are phenols such as 2,4-
dimethyl-6-tert-butylphenol and 2,6-di-tert-butyl-p-
cresol; hydroguinones such as hydroquinone,
methylhydroquinone, 1,4-benzo~uinone and hydroquinone
monomethyl ether; and catechols such as tert-
butylcatechol and pyrogallol. The amount of the
polymerization inhibitors which can be used is
typically 0.001 to 5% by weight based on the total
weight o~ the photosensitive resin composition.
Any conventional appropriate surfactants may be
added to improve the dispersibility resins in water.
For this purpose, anionic, cationic or nonionic
surfactants can be used. If desired or necessary, the
resin may be mixed with a known filler such as barium
sulfate, silicon oxide, talc, clay and barium
carbonate; a known coloring agent such as
phthalocyanin green and titanium oxide; a dye; a
leveling agent; an adhesion promotor; thixotropic
agent; and a plasticizer.
The amount of water which can be employed in the
lo- 2~7~7~
photosensitive resin composition is 30 to 90% by
weight based on the total weight of the photosensitive
resin composition, and the total amount of the
carboxyl group-containing resin, the amine compound,
the photo-curable unsaturated compound, the
photopolymerization initiator and, if desired, other
additives which can be employed in the photosensitive
resin composition is 10 to 70% by weight based on the
total weight of the photosensitive resin composition.
The aqueous photosensitive resin composition of the
present invention can easily be prepared by the
following methods which are given for illustrative
purposes and are not meant to limit the invention.
(1) A carboxyl group-containing resin or an acid
anhydride group-containing resin is mixed
with water containing an amine compound and
heated to dissolve or disperse the resin in
water. Then a photo-curable unsaturated
compound and a photopolymerization initiator
are added to the resulting solution or
dispersion, and the solution or dispersion
is mixed and dispersed.
(2) After a carboxyl group-containing resin or
an acid anhydride group-containing resin is
dissolved in a photo-curable unsaturated
compound under heating, a photopolymer-
zation initiator is added to the resulting
solution and then the water containing an
amine compound is blended in.
(3) An acid anhydride group-containing resin and
an alcohol or an amine compound are reacted
with a photocurable unsaturated compound to
ring-open the acid anhydride groups. Then,
a photopolymerization initiator and
20727~2
subsequently, water containing an amine
compound are mixed into the reaction
solution and the solution.
(4) An acid anhydride group-containing resin and
an alcohol or an amine compound having a
polymerizable unsaturated bond are reacted,
if desired, in a photo-curable unsaturated
compound to ring-open the acid anhydride
groups to introduce an unsaturated group in
the resin~ Then, a photopolymerization
initiator and subsequently, water containing
an amine compound are blended into the
reaction solution~
(5) An acid anhydride group-containing resin and
a primary or a secondary amine are reacted
in water to rin~-open the acid anhydride
groups, and then an amine compound to render
the resin easily dissolved or dispersed in
wat~r, a photo-curable unsaturated compound
and a photopolymerization initiator are
added to the reaction solution, and the
solution or dispersion is mixed. These
components which are to be added later may
be previously added in the reaction system
and the ring-opening reaction may be carried
out in the presence o~ these components.
or, an amine compound having a polymerizable
unsaturated bond may be used as the amine
compound to ring-open the acid anhydride
groups and/or as the amine compound to
render the resin easily dissolved or
dispersed in water.
The aqueous photosensitive resin composition o~
the present inventic3n can ba prepared by the methods
- 12 - 20 72 7~2
as described above without using any volatile organic
solvent. However, a small amount, at most 20~ by
weight, based on the total weight of the water, o~ a
volatile organic solvent such as ethanol may be used
to lower the viscosity of the photosensitive resin
composition.
The preparation of a printed circuit board by
using the aqueous photosensitive resin composition of
the present invention can be typically carried out in
the following manner.
The aqueous photosensitive resin composition of
the present invention is coated on a substrate having
an electrically conductive metal layer such as a
copper foil. Coating can be done by any conventional
device such as an ordinary curtain coater, roll
coater, screen coater or electrostatic coater. Any
conventional dryer may be used, if needed. In this
case, since the aqueous photosensitive resin
composition of the present invention contains no
volatile organic solvent or contains a very amall
amount of such an organic solvent, no special measures
for protecting the working environment from fire or
explosion are required, and neither is a solv~-nt
recovery system.
As with any other conventional photosensitive
resist materials, the resist image-forming step is
carried out by the irradiativn of the coating with
actinic light having a wavelength of 200 to 600 nm.
Preferred light sources include a high pressure
mercury lamp, a metal halide lamp, a xenon lamp, a
car~on arc lamp and a chemical lamp. The
developing step after the irradiation can easily be
carried out by an ordinary procedure using water or a
dilute aqueous alkaline solution, for example, a 1~ by
- 13 - 2~727~2
weight sodium hydroxide solution.
The etching step for forming a circuit can be
carried out with an ordinary acidic etching solution
such as an aqueous hydrochloric acid solution of
cupric chloride. A dilute aqueous alkaline solution
such as a 3% by weight sodium hydroxide solution can
be used to strip the resist coating after the etching.
Surprisingly, the aqueous photosensitive resin
composition of the present invention can form an image
when coated and dried on a substrate, irradiated with
actinic light and developed with water or an aqueous
alkaline water resin despite its ability to dissolve
or disperse in water and the presence of an amine
compound. In addition, the irradiated coating has a
good resistance to an acidic etching solution. Since
it does not contain any organic solvent at all or
contains only a very small amount of an organic
solvent, there is no need to provide safety
precautions against fire in the coating and drying
steps. Furthermore, it has no adverse effect on the
working environment or natural environment which might
be caused by organic solvents.
The examples which follow are given for
illustrative purposes and are not meant to limit the
invention described herein. "Part" means "part by
weight" unless otherwise expressly stated.
Ex~pls 1
One hundred parts of an aqueous acrylic resin
(I'CARBOSET XL-27", a product of B.F. Goodrich Co.,
U.S.A., acid value = 80, molecular weight = 40,000) as
the carboxyl gxoup-containing resin, 14.4 parts of
triethylamine as the amine compound and 330 parts of
- 14 - 20727~2
water were mixed and heated at 70C to obtain a
homogeneous and clear solution. Thirty three parts of
trimethylolpropane triacrylate as the
photopolymerizable unsaturated compound, 15 parts of
2,2-dimethoxy-2-phenylacetophenone as the
polymerization initiator and 0.5 part of hydroquinone
monomethyl ether as the polymerization inhibitor were
added to the solution, and then the mixture was cooled
to room temperature with agitation to ~orm an opaque,
creamy aqueous photosensitive resin.
The resin was coated on a laminated board having
an 18 micron copper foil layer using a doctor blade,
and dried at 100C for 5 minutes to give a dri~d film
having a thickness of about 20 microns.
A negative film was tightly contacted with the
dried film with rays from a high pressure mercury lamp
at an exposure energy of 400 mJfcm2, and then,
developed b~ spraying with a 1% by weight aqueous
sodium carbonate solution at 25C to give a resist
film with a clear image showiny a line width as small
as 50 microns.
The copper-lined laminated board having the
resist film was soaked in an etching solution
containing 40 parts of anhydrous cupric chloride, 30
parts of concentrated hydrochloric acid and 50 parts
of water at room temperature for 20 minutes. With the
exclusion of the area of the resist film, the copper
foil was etched and removed. There was no damage to
the resist ~ilm. Furthermore, the laminated board
obtained after the etching was soaked in a 3~ by
weight aqueous sodium hydroxide solution at room
temperature for one minute. As a result, the resist
~ilm could bP easily stripped to give a circuit board.
- 15 - 2~727~2
~x~mpl~ 2
The procedure of Example 1 was repeated except
that 22.3 parts of dimethylaminopropyl acrylamide
were employed instead of the triethylamine to obtain
an opaque, creamy, aqueous photosensitive resin
composition.
When the subsequent coating, drying, irradiation
with light and development were carried out under the
same conditions as in Example 1, a resist image which
had reproduced clearly to a line width of 30 microns
was obtained. In the same manner as in Example 1,
etching and stripping of the resist film after the
etching could be carried out without any problem.
~x .am~
A mixture containing 150 pa:rts of a
styrene-maleic anhydride copolymlsr ('ISMA--lOOo",
styrene/maleic anhydride = 1/1, a product o~ Sartomer
CO. I U~ SoA~ ) ~ 150 parts o~ trimethylolpropane
triacrylate, 54 parts of butyl alcohol, 8 parts of
dimethylolpropane triacrylate, 47 parts of
N-butylbenzene sulfonamide as the plasticizer and 0.5
part of hydroquinone monomethyl ether was heated and
agitated at 80C for 2 hours to obtain a viscous
substance. Four parts of a surfactant ("EMULGEN 903",
a product of Kao K.K., Japan), 20 parts of
2,~.-dimethoxy-2-phenylacetophenone and 35 parts of
ethyl alcohol as the solvent were added to the viscous
substance, and then th~ mixture was cooled to room
temperature. Furthermore, 55 parts of dimethylamino~
propyl acrylamide were added in 300 parts of watex to
prepare a solution. This solution was added to the
- 16 - 2~72~2
above obtained mixture with constant and vigorous
agitation to yield an aqueous photosensitive resin.
The resin was coated on a laminated board having
a 18 micron thick copper foil layer using a doctor
blade, and then dried at 100C for 5 minutes to give a
dried film having a thickness of about 20 microns.
A negative film was contacted with the dried
film, irradiated with rays from a high pressure
mercury lamp at an exposure energy of 400 mJ/cm2, and
then developed with tap water at 25C to give a resist
film having a clear image which showed a line width of
50 microns.
When the copper-lined laminated board having the
resist ~ilm was soaked in an etching solution
containing 40 parts of anhydrous cupric chloride, 30
parts of concentrated hydrochloric acid and 50 parts
of water at room temperature f or 20 minutes, the
copper foil was etched and removed except the area of
the resist film, and there was no damage in the resist
film. Furthermore, when the laminated, etched board
was subsequently soaked in a 3% by weight aqueous
sodium hydroxide solution at room temperature for one
minute, the resist film could be easily striped to
give a circuit board.
~xAmpla 4
The procedure of Example 3 was repeated except
that 85 parts of hydroxyethyl acrylate to ring-open
the acid anhydride groups to introduce a double bond
in the resin were employed instead of the butyl
alcohol to prepare an aqueous photosensitive resin
composition~ When the subsequent coating, drying,
irradiation with actinic light and development with
- 17 - 2~727~2
tap water were carried out under the same conditions
as in Example 3, a resist image which had repro~uced
an image clearly to a line width of 30 microns was
obtained. In the same manner as in Example 3, the
resist film could be etched and stripped without any
problem.
E~nmple 5
A mixture containing 150 parts of a
styrene-maleic anhydride copolymer ("SMA-20001',
styrene/maleic anhydride = 2/1, a product of Sartomer
Co., ~.S.A.), 150 parts of trimethylolpropane
triacrylata, 28 parts of allylamine ~or ring-opening
of the acid anhydride groups in the above described
copolymer to introduce a photopolymerizable
unsaturated bond in the resin, 77 parts of
dimethylaminoethyl methacrylate, 47 parts of
N-butylbenzene sulfonamide as the plasticizer, 0.5
part of hydroquinone monomethyl ether as the
polymerization inhibitor, ~0 parts of
2,2-dimethoxy-~-phenylacetophenone and 300
parts of water was agitat2d at room temperature for 3
hours, and then the mixture was heated and agitated at
80C for one hour to obtain an aqueous photosensitive
resin composition.
The composition was coated on a laminated board
having a 18 micron thick coppar foil layer using a
doctor blade, and then drisd at 100C for 5 minutes to
give a dried ~ilm having a ~hickness of about 20
microns.
A negative film was tightly contacted with the
dried film, and irradiated with rays from a high
pressure mercury lamp at an exposure enargy of 200
- 18 - 2~727~2
mJ/cm2, and then developed by spraying with a 1% by
weight aqueous sodium carbonate solution at 25C to
give a resist film having a clear image with a line
width of 30 microns.
When the copper-lined laminated board formed with
a resist film was soaked in an etching solution
containing 40 parts of anhydrous cupric chloride, 30
parts of concentrated hydrochloric acid and 50 parts
of water at room temperature for 20 minutes, the
copper foil was etched and remo~ed except the area of
the resist film which did not show any damage.
Furthermore, when the laminated, etched board was
soaked in a 3~ by weight aqueous sodium hydroxide
solution at room temperature for one minute, the
~esist film could be easily stripped to give a circuit
board.
