Photoresist composition and printed circuit boards and packages made therewith

A photocurable composition which is useful as a permanent resist in the manufacture of printed circuit boards and packages of such boards comprises a multifunctional epoxidized resin, a reactive diluent, a cationic photoinitiator and, optionally, an exposure indicator, a coating aid and a photosensitizer.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates generally to photoresist compositions and more 
specifically to photoresist compositions for use in the manufacture of 
printed circuit boards and packages of printed circuit boards. 
2. Prior Art 
Printed circuit boards and their manufacture using photoresists as negative 
masks during conductive metal plating processes are not new. 
Printed circuit board designs using a "permanent" resist are also known. A 
permanent resist is a negative plating mask which is not removed from the 
printed circuit board substrate after plating, but rather becomes a part 
of the printed circuit board structure. Permanent resist printed circuit 
boards are described, for example, in U.S. Pat. No. 3,982,045 issued Sept. 
21, 1976 to Kukanskis. 
Attempts to manufacture useful permanent resists and printed circuit boards 
and packages using such a resist have uncovered a number of difficulties. 
One such difficulty is that there has not heretofore been available a 
UV-sensitive photoresist material which can be coated onto a substrate at 
cross-sectional heights of at least about 0.0015 inch and which will 
resist delamination in response to temperature cycling. 
One reason for the desirability of printed circuit boards of the permanent 
resist design is that they will present a relative smooth surface if the 
pattern of conductive material and the pattern of photoresist material 
have substantially the same cross-sectional height. However, in the past 
there has not been available a photoresist material capable of being 
coated onto a substrate to a cross-sectional height of at least about 
0.0015 inch and of maintaining that height without delamination during 
processing and use. 
It has also been a problem that permanent resist materials which were 
previously available tended to delaminate from substrates after 
temperature cycling. There has been a need in the printed circuit board 
industry for a permanent resist material which will not delaminate after 
temperature cycling. 
The delamination problems have also tended to frustrate commercialization 
of packages containing permanent resist printed circuit boards. There is a 
need for a permanent resist material which will enable the manufacture of 
packages containing two or more permanent resist printed circuit boards 
which will not delaminate in response to temperature cycling. 
SUMMARY OF THE INVENTION 
It is, therefor, an object of the present invention to overcome the 
disadvantages of the prior art. 
It is another object of the present invention to provide a composition 
which is curable to a resinous material and which, prior to curing, can be 
coated onto a substrate to a thickness of at least about 0.0015 inch in a 
layer which is non-brittle and non-distortable. 
It is a further object of the present invention to present a composition 
which is useful as a permanent resist on printed circuit boards. 
It is still another object of the present invention to achieve a resist 
material which will not easily delaminate from an epoxy resin-containing 
substrate in response to temperature cycling. 
It is also an object of the present invention to achieve a material which 
is capable of imagewise curing in response to imagewise exposure and of 
subsequent development with a chlorinated solvent. 
It is yet another object of the present invention to enable to manufacture 
of packages of at least two permanent resist printed circuit boards, which 
packages will resist delamination. 
These and other objects are accomplished by the present invention which, in 
one aspect, is a photocurable composition comprising: 
(a) an epoxyfunctional resin which is capable of being cured by the action 
of a cation-producing photoinitiator: 
(b) a reactive diluent for (a) which is soluble in developing solvents for 
photoresists; 
(c) a cationic photoinitiator; 
(d) optionally, an indicator which changes color in response to radiation 
and which can crosslink with (a) during curing; 
(e) optionally, a coating aid; and 
(f) optionally, a photosensitizer; wherein (a) comprises at least about 65 
wt. % of the resin solids and is dissolved in a suitable solvent, (b) 
comprises from about 10 to about 35 wt. % of the resin solids, (c) is 
present in an amount of from about 2 to about 6 parts per 100 parts by wt. 
of resin and is dissolved in a suitable solvent, (d) is present in an 
amount of from 0 to about 5 wt. % resin solids, (e) is present in an 
amount of from 0 to about 0.5 parts per 100 parts resin and (f) is present 
in an amount of from 0 to about 1 wt. % based on the weight of the resin 
solids. 
In another aspect, the invention relates to a printed circuit board which 
comprises an epoxy resin-containing substrate on which is disposed an 
imagewise pattern of the cured composition described above. A package of 
at least two such printed circuit boards cured in layered configuration is 
also contemplated by the present invention. 
In yet another aspect, the invention relates to a method of making the 
composition described above which comprises the steps of: 
(1) dissolving (a) in a solvent which will dissolve substantially all of 
(a) which is not partially crosslinked in an amount which will comprise at 
least about 65 wt. % of the resin solids in the composition; 
(2) filtering the solute from step (1) to remove any partially crosslinked 
(a); 
(3) adding from about 10 to about 35 wt. % resin solids of (b) and from 
about 2 to about 6 parts per 100 parts resin of (c) with stirring; and, 
optionally, 
(4) adding a suitable solvent to adjust the viscosity of the composition to 
from about 600 to about 2,000 centipoise. 
In still another aspect, the present invention relates to an improvement in 
a method of making a printed circuit board which comprises the steps of: 
(A) coating a photocurable resin composition onto a substrate; 
(B) exposing the coating on the substrate to an imagewise pattern of 
radiation to which the composition is responsive in an amount sufficient 
to at least partially cure the composition, which imagewise pattern is the 
negative image of a desired printed circuit pattern; 
(C) developing the exposed composition with a solvent which will dissolve 
the non-exposed areas of the coating; 
(D) advancing the cure of the developed imagewise coating; and 
(E) depositing a conductive material on the portions of the substrate which 
are not covered by the developed imagewise coating in order to form a 
partially cured printed circuit board construction; 
wherein the improvement comprises, in step (A), the coating of the 
composition of Claim 1 onto an epoxy-containing substrate to a thickness 
of at least about 0.0015 inch and the additional step of: 
(F) further curing the construction of step (E) to a point at which the 
coefficient of thermal expansion in the z axis of the fully cured 
imagewise coating and the epoxy resin-containing substrate are 
substantially the same.

DETAILED DESCRIPTION OF THE INVENTION 
It has been discovered that the composition of the present invention, 
described above, which is curable in response to imagewise radiation, can 
be coated onto a substrate at thicknesses of at least about 0.0015 inch in 
a non-brittle, non-distortable layer, thus overcoming one problem of the 
prior art as described above. 
It has also been discovered that the composition can be fully cured such 
that when curing takes place in contact with an epoxy resin-containing 
substrate the coefficient of thermal expansion of the substrate and the 
cured composition will be substantially the same in the z axis, thus 
overcoming the delamination problem of the prior art described above. 
It has also been discovered that printed circuit boards comprising the 
permanent resist composition of the present invention can be fully cured 
in layered configuration to form a package which resists delamination. 
The composition of the present invention requires as component (a), an 
epoxyfunctional resin which is capable of being partially cured to a 
resinous state by the action of a cation-producing photoinitiator. Curing 
is by a ring opening addition reaction of epoxy moieties which is 
initiated by cations produced when the photoinitiator is struck by 
activating radiation. Such reactions are already well known in the resin 
technology. 
Any useful such epoxyfunctional resin may be employed in the present 
invention. However, in order to function satisfactorily, the resin should 
have at least two epoxy groups, and preferably more. 
Good results have been obtained using an octafunctional epoxidized novalac 
as (a), and such a resin is preferred. The octafunctional epoxidized 
novalac is commercially available from Celanese Resins under the tradename 
SU-8. It will be readily apparent to one of ordinary skill in the resin 
technology that other such multifunctional epoxy containing resins will be 
useful in the present invention. Such other useful resins are within the 
intended scope of the appended claims. 
Component (a) should be present in an amount of at least about 65 wt. % 
resin solids. The solvent in which (a) is provided, such as a ketone, is 
not taken into account when determining the concentration of (a). 
Concentrations of (a) of less than about 65 wt. %, when coated on 
substrates, form coatings which are too soft to be useful. It is preferred 
that (a) be present in an amount of from about 78 wt. % resin solids to 
about 83 wt. % resin solids. Concentrations of (a) of less than about 78 
wt. % begin to form coatings which, when cured, are softer than is 
preferred. Concentrations of (a) greater than about 83 wt. % have been 
found to result in cured coatings which are undesirably brittle. 
Component (b) may be any reactive diluent which is effective as a 
plasticiser for (a). Reactive diluent, as used herein, is understood to 
mean a diluent which will react or crosslink with (a) during curing. 
Suitable materials are, for example cycloalaphatic epoxides, although 
other suitable reactive diluents will readily come to mind to those of 
ordinary skill in resin technologies. Such other materials are within the 
intended scope of the appended claims. 
Good results have been obtained using cycloalaphatic epoxides such as 3,4 
epoxycyclohexylmethyl-3,4 epoxycyclohexyl carboxylate and 
7-oxabicyclo(4.1.0)heptane-3-carboxylic acid, 
7-oxabicyclo(4.1.0)hept-3-glmethyl ester. Such materials are commercially 
available from Ciba Geigy under the tradename CY 179 and from Union 
Carbide under the tradename ER 4221. 
Component (b) should be present in a concentration which will constitute 
from about 10 to about 35 wt. % of the resin solids in the composition. It 
has been found from experimentation that if less than about 10 wt. % of 
(b) is present the resulting cured composition will be undesirably brittle 
and that if more than about 35 wt. % is present the resulting cured 
composition will be undesirably soft. 
A preferred range of (b) is from about 12 to about 17 wt. % of the resin 
solids, depending on the relative softness or brittleness which is desired 
in the final composition. 
Component (c) may be any photoinitiator which produces cations acids upon 
exposure to radiation. The cations must be produced in amounts sufficient 
to cause curing of (a). 
One group of cationic photoinitiators which are useful in the present 
invention as component (c) are triarylsulphonium salts. The use of such 
salts as photoinitiators is known from, for example, U.S. Pat. No. 
4,245,029, issued Jan. 13, 1981, to Crivello. 
One suitable such photoinitiator is a product available from General 
Electric Company under the tradename UVE 1014, which comprises a mixture 
of triarylsulphonium hexafluoro antimonate and thio phenoxy triaryl 
sulphonium hexafluoro antimonate in a propylene carbonate solvent. It will 
be readily apparent to those of ordinary skill in the resin curing 
technology that other such cationic photoinitiators will be useful in the 
present invention and are within the intended scope of the appended 
claims. 
Component (c) should be present in the composition of the present invention 
in an amount of from about 2 to about 6 parts (not counting the solvent) 
per 100 parts of resin. It has been found from experimentation that 
concentrations of (c) less than about 2 parts per 100 parts of resin will 
result in a composition which takes undesirably long to cure upon exposure 
to radiation. 
It has been observed that concentrations of (c) greater than about 6 parts 
per 100 parts resin results in a composition which is not developable by 
chlorinated solvents. When the composition of the present invention is to 
be used as a photoresist in the manufacture of printed circuit boards it 
is important that portions of the composition which are not struck by 
radiation be dissolvable in chlorinated solvents in order to develop the 
pattern of the cured, radiation struck portions. 
Optionally, the composition of the present invention may include an 
indicator (d) to help determine which portions of the composition, have 
been struck by radiation. Any useful such indicator which will crosslink 
with (a) during curing can be incorporated. One suitable indicator which 
has been used is epoxidized trishydroxyphenylmethane, which is 
commercially available from Dow Chemical under the tradename XD 7342. It 
will be readily apparent to those of ordinary skill in the resin curing 
technology that any such indicator may be used and that all useful such 
indicators are intended to be within the scope of the appended claims. 
Component (d), may be present in amounts of from 0 to about 5 wt. % of 
resin solids. The trishydroxyphenylmethane indicator described above 
changes color when it has been struck by radiation of the wavelength which 
will cause the composition to cure. Thus, technicians working with the 
composition can tell which portions of the composition should be cured. It 
has been observed that amounts of (d) greater than about 5 wt. % cause the 
cured image to lose resolution and increase the photoexposure time 
undesirably. 
A second optional component (e) is a surfactant coating aid. The purpose of 
the coating aid is to produce an even thickness of film across a surface 
and to prevent defects in the an end product, such as a printed circuit 
board which might be caused by non-wetting of the surface. Any useful such 
coating aid my be employed. One suitable coating aid is a non-ionic 
surfactant (a fluorinated hydrocarbon) available from the 3M Company under 
the tradename FC 430. It will be readily apparent to those of ordinary 
skill in the coating technology that any suitable such coating aid may be 
used and will be within the intended scope of the appended claims. 
Component (e) may be present in amounts up to about 0.5 parts per 100 parts 
resin. It has been observed that higher concentrations of the surfactant 
coating aids results in a coated composition which is undesirably 
slippery. 
A photosensitizer (f) is also an optional component. Any photosensitizer 
which is useful to cause the photoinitiator to absorb more light is 
suitable. Good results have been obtained using anthracene, perylene and 
mixtures thereof, although other useful photocatalysts may come to mind to 
those of ordinary skill in the resin curing technology. 
The first step in making the composition of the present invention is the 
pre-dissolving of component (a) in a suitable solvent. Any solvent which 
will dissolve any of (a) which is not partially crosslinked can be used. 
Useful solvents have been found to be methyl isobutyl ketone, methyl ethyl 
ketone and mixtures thereof, although other suitable solvents will readily 
come to mind to those of ordinary skill in resin technologies. The amount 
of solvent used should be at least enough to dissolve the desired amount 
of non-partially crosslinked component (a) 
It is important to the eventual use of the composition as a photoresist in 
the manufacture of printed circuit boards that the second step of 
filtering any partially crosslinked (a) from the solute be accomplished. 
If this step is not accomplished, portions of the unexposed composition 
will not be soluble in some chlorinated solvents, and the photoresist 
material will not be as easily developable. 
Filtering through a 10 micron porous membrane filter has been found to be 
adequate for the preparation of a composition which will be useful as a 
photoresist. 
After filtering, from about 10 to about 35 wt. % resin solids of (b) and 
from about 2 to about 6 parts per 100 parts resin of (c) are added with 
stirring. The sequence of addition is not critical, and any method of 
stirring can be used. 
As an optional step, additional solvent may be added in order to adjust the 
viscosity of the composition. The composition of the present invention may 
have any viscosity; however, when it is intended for eventual use as a 
photoresist in the manufacture of printed circuit boards, it is desirable 
that the composition have a viscosity of from about 600 to about 2,000 
centipoise. Although any suitable solvent may be used for adjusting the 
viscosity, it is preferable to use a solvent which is at least similar to 
the one used to solubilize (a). 
A photocatylist (f) may be added as an optional component when (b) and (c) 
are added. As described above, the photocatylist can be added in amounts 
up to about 1 wt. % of the resin solids 
Optional components (d) and (e) may also be added to the composition with 
components (b) and (c). The addition of optional component (d) has been 
observed to increase the required stirring time of the composition. 
As has been indicated above, the composition of the present invention is 
useful as a permanent photoresist on a printed circuit board. In such use 
composition 1 is coated on substrate 2 in FIG. 1. Best results are 
obtained when the substrate is a partially cured epoxy resin-containing 
material such as epoxy resin coated glass cloth, commonly known as 
pre-preg in the printed circuit board technology. The composition, when 
fully cured, substantially matches the coefficient of thermal expansion of 
such a substrate, which is also fully cured, in the z axis between about 
.degree. C. and 100.degree. C. to minimize delamination during use. As 
used herein, substantial matching of the coefficient of thermal expansion 
of the epoxy resin-containing substrate and the composition of the present 
invention means that in the z axis the relative difference between the 
expansion of the composition and the substrate over 100.degree. C. is less 
than about 300 micro inches per inch per .degree.C. 
The process of using the composition as a permanent photoresist begins with 
the step of coating the composition onto such a suitable substrate. The 
method of coating is not critical and may be by any suitable technique, 
many of which are known to those of ordinary skill in the coating 
technology. However, it is an important advantage of the composition of 
this invention that it can be coated to thicknesses of 0.0015 inch and 
greater. Coatings of such thicknesses are important in the manufacture of 
printed circuit boards having permanent resist designs. The discovery of a 
material which can be coated to such thicknesses overcomes a serious 
problem of the prior art in the industrialization of the permanent resist 
technology, as discussed above. 
For example, the composition may be placed directly on a substrate by a 
wiping or doctoring technique or by the use of a coating nozzle. However, 
a more preferred method is to first coat the composition onto a carrier 
medium, such as Mylar film, and then to remove solvent by heating or 
heating in the presence of vacuum until a coating of the desired thickness 
has been achieved on the carrier medium. An advantage of this preferred 
method of coating is that the layer of composition on the carrier medium 
can then be stored until it is needed for use on a substrate. The rheology 
of the composition on the carrier medium, after some of the solvent has 
been dried off is such that the carrier medium can be rolled for 
convenient storage. The non-brittle, non-distortable nature of a layer of 
the present composition is important in enabling the use of a carrier 
layer. The parallel plate T.sub.g of the composition should be between 
25.degree. C. and 40.degree. C. in order for the carrier layer method of 
coating to work well. In this preferred method, component (d) has been 
found useful in helping achieve the T.sub.g range mentioned above. 
In this preferred method of coating the composition on the substrate, the 
composition is transferred from the carrier medium to the substrate by the 
use of a heated nip roller arrangement or by the use of a heated vacuum 
laminator. Both such techniques are well known in the coating technology. 
After lamination of the coating to the substrate, the carrier medium is 
stripped away, although stripping does not have to take place at once. The 
coated substrate can be stored with the carrier medium still covering the 
coating, if desired. 
After the carrier medium is removed, or alternatively after doctor blade 
coating, the coating on the substrate is exposed to an imagewise pattern 
of radiation 3 to which it is responsive. The composition described above 
is responsive to ultraviolet radiation having a wavelength of less than 
about 500 nm in an amount sufficient to cause the release of Lewis or 
Bronstead acids from component (c). It has been observed that good results 
are obtained when the radiation provides at least about 200 milli Joules 
of energy to the coating. 
If optional component (d) is present in the composition, it will change 
color in the radiation-struck areas so that a technician can inspect the 
pattern of exposure. In the manufacture of printed circuit boards, the 
exposure is typically a negative image of the desired conductive circuit 
pattern. A colored pattern in the composition, when it is used as a 
photoresist as described above, will indicate at least partial 
crosslinking in the colored areas. 
The exposed coating is subsequently developed by exposure to a suitable 
solvent. A suitable solvent is one which will solubilize non-crosslinked 
or non-partially crosslinked component (a), but which is incapable of 
dissolving crosslinked or partially crosslinked component (a). The most 
typical solvents for use in developing photoresists after exposure are 
chlorinated solvents, such as 1,1,1-trichloroethane. The particular 
solvent used is not critical to the invention. Other useful solvents will 
come to mind to those of ordinary skill in the printed circuit board 
manufacture technology, and such solvents are within the intended scope of 
the appended claims. 
The development of the exposed composition will leave an imagewise coating 
of partially crosslinked composition on the surface of the substrate. 
After development the cure of such an imagewise coating 4 in FIG. 2 is 
advanced in order to further harden it and to enhance its subsequent use 
as a resist in metal plating baths. Advancing of the cure of the imagewise 
resist pattern is accomplished by applying either heat or light energy. At 
least about 2 Joules of light energy to which the composition is 
responsive has been found to be sufficient for this step. Alternatively, 
heating the substrate and imagewise coating to at least about 100.degree. 
C. for at least about 10 minutes has been found to provide sufficient 
energy to advance the cure of the imagewise resist coating. 
A conductive material 5 in FIG. 3 is then deposited on substrate 1 in the 
areas not masked by the imagewise photoresist coating 4. Deposition of 
conductive material 5, which is normally copper, is usually accomplished 
by use of an electroless metal plating bath, which may be followed by use 
of an electorlytic metal plating bath. By operation of the baths, the use 
of which are well known in the printed circuit board manufacturing 
technology, a conductive metal is deposited on the substrate in the areas 
not protected by the imagewise photoresist pattern so that a pattern of 
conductive material is deposited on the substrate in a positive image of a 
desired printed circuit. 
It is sometimes desirable that the resist material then be removed from the 
printed circuit board to leave the conductive pattern on the substrate. 
However, in other applications, it is desirable for the resist to remain 
on the printed circuit board. In such uses, the photoresist material is 
known as permanent resist and such printed circuit boards are known as 
permanent resist printed circuit boards. 
When permanent resist is desired, the imagewise composition may be further 
cured after the step of depositing the conductive material. Further curing 
is normally done by heating because of the impractability of supplying 
sufficient energy as actinic radiation. Good results have been obtained in 
the present invention by heating the printed circuit board to at least 
about 175.degree. C. for at least about an hour. 
It is an important advantage of the composition and method of the present 
invention that, after such further curing, the composition will have a 
coefficient of thermal expansion in the z axis which is substantially the 
same as that of epoxy resin-coated glass cloth which is normally used as a 
substrate for printed circuit boards. This advantage overcomes serious 
problems of delamination of permanent resists, as is described above. 
A printed circuit board manufactured by the process described above and 
using the composition of the present invention is intended to be within 
the scope of the present invention. Such a circuit board may be of the 
permanent resist design, and, as such, will have the advantage of a 
reduced tendency to delaminate because of the substantial similarity of 
the coefficient of thermal expansion in the z axis of an epoxy 
resin-containing substrate and the resist material 
A package 6 of FIG. 4 of two or more permanent resist printed circuit board 
constructions 7 and 8 may be made by further curing them together under 
pressure, sometimes with an enclosing layer 9. Enclosing layer 9 should 
preferably be of partially cured epoxy resin containing material so that 
it will more readily match the curing characteristics of the other 
components of package 6, although any useful material can be employed. 
Further curing of package 6 should be done under a pressure of from about 
200 to about 500 psi and preferably at about 300 psi. It should be 
understood that packages of more than two layers of constructions such as 
7 and 8 are contemplated. 
The invention is illuminated and illustrated in its various aspects by the 
following examples, which are not intended to be limiting. 
EXAMPLE 1 
Eighty-eight g. of SU-8, which is an octafunctional epoxidized novalac 
available from Celanese Resins, was mixed with 100 g. methylethyl ketone 
and filtered using 10 micron filter paper before 12 g. of CY 179, a 
cycloalaphatic epoxide available from Ciba Geigy, was added with stirring. 
4.0 g. of UVE 1014, a triarylsulphonium salt (50% solution) available from 
General Electric, was added in yellow light. 
The resulting composition was coated onto a partially cured epoxy resin 
coated glass cloth substrate using a doctor blade and checked for 
thickness at various locations using a micrometer. Average thickness was 
about 0.0018 inch with a variance of plus or minus 0.0003 inch. Parallel 
plate rheology was used to determine that the T.sub.g of the coated 
composition was 40 -43.degree. C. (+/-3.degree. C.). 
Imagewise exposure of the coating was made using an Oriel 560 UV generator 
and a Stouffer resolution guide, after which the coating was developed 
with 1,1,1-trichloromethane to reveal a crosslinked pattern of resist 
corresponding to the UV radiation struck areas. Cure of the resist pattern 
was advanced by baking in an oven at 100.degree. C. for 10 minutes. 
The resist imaged substrate was immersed in a Shipley electroless plating 
bath until a conductive layer was built up on the portions not protected 
by the substrate. The resist was observed to remain intact. The 
construction was further cured in an oven at 175.degree. C. for one hour 
before the resist was tested on a Perkin Elmer thermomechanical analyzer 
(TMA) to determine change in the z axis during cycling between 0.degree. 
and 100.degree. C. Test results indicated less that 100 
microinches/inch/.degree.C. change. Multiple cyclings over a period of 
time failed to cause delamination. 
EXAMPLE 2 
The procedure of Example 1 was repeated using 80 wt. % resin solids SU-8 
and 20 wt. % resin solids CY 179 to form a composition which was suitable 
for coating on a substrate with a doctor blade, but which had too low a 
T.sub.g (about 20.degree. C.) to use in the carrier layer coating 
technique. Once coated, the material functioned substantially as in 
Example 1. 
EXAMPLE 3 
The procedure of Example 1 was repeated using 88 wt. % SU-8 and 12 wt. % CY 
179 to form a composition which could be coated onto a substrate using a 
doctor blade but which was too brittle (T.sub.g 45.degree. C.) to be used 
in the above described carrier layer coating technique. Once coated by the 
doctor blade technique, however, the composition functioned substantially 
as in Example 1. 
EXAMPLE 4 
The procedure of Example 1 was followed using 65 wt. % resin solids SU-8 
and 35 wt. % resin solids CY 179 to achieve a composition having a T.sub.g 
of 20.degree. C. and not being useful in the carrier layer coating method. 
However, after coating on the substrate with a doctor blade, the material 
functioned substantially as in Example 1. 
EXAMPLE 5 
The procedure of Example 1 was followed using 85 wt. % resin solids SU-8 
and 15 wt. % resin solids CY 179. The resulting material had a good 
hardness, but was found to distort substantially and was not useful in the 
carrier layer transfer method. The composition functioned substantially as 
the composition of Example 1 after coating on a substrate with a doctor 
blade. 
EXAMPLE 6 
In this comparative example, 70 wt. % resin solids SU-8 was used with 10 
wt. % resin solids XD7342, an epoxydized trishydroxyphenylmethane 
available from Dow Chemical Co., and 15 wt. % resin solids CY 179 was used 
in the procedure of Example 1. The resulting composition, which had a 
T.sub.g below 25.degree. C. was not soluble in chlorinated solvents and 
could not be developed. 
EXAMPLE 7 
The procedure of Example 1 was followed using 80 wt. % resin solids SU-8, 5 
wt. % resin solids XD7342 and 15 wt. % resin solids CY 179. The 
composition had a T.sub.g of 35.degree. C. and was capable of being coated 
onto a Mylar film using a doctor blade, dried to remove solvents and then 
coated onto a substrate using a heated nip roller. The composition 
performed substantially the same as did the composition of Example 1. 
EXAMPLE 8 
The procedure of Example 1 was followed except that the optional components 
listed below were added in the amounts shown to produce the results shown: 
(a) fluorinated hydrocarbon. 0.5 parts/100 parts resin solids. smoother 
coating achieved. 
(b) fluorinated hydrocarbon. 1 parts/100 parts resin solids (comparative 
example). smooth coating, but oily resin surface. 
(c) perylene. 0.5 parts/100 parts resin solids. 75% less UV radiation 
required for imagewise exposure. 
(d) anthracene. 1 part/100 parts resin solids. 34% less UV radiation 
required for imagewise exposure. 
EXAMPLE 9 
The procedure of Example 1 was followed except that the resin/solvent 
solution was not filtered in this comparative example. Upon development, 
it was observed that undeveloped deposits of partially crosslinked 
material remained in the non radiated areas. 
EXAMPLE 10 
The procedure of Example 1 was followed except that before further curing, 
two such constructions were layered together and enclosed on the side 
having the exposed patterns of circuitry with a partially cured epoxy 
resin containing substrate material to form a package. Further curing of 
the package was then accomplished at 175.degree. C. for one hour while the 
package was subjected to a pressure of about 300 psi. 
The procedure was repeated at 150, 200, 500 and 700 psi. No delamination 
and acceptable TMA results (below 300 microinches/in/.degree.C.) were 
noted for samples further cured at 200 psi and 500 psi. At 700 psi image 
distortion was noted and at 150 psi insufficient adhesion between layers 
was noted. 
The present invention has been disclosed in the above teachings and in the 
accompanying drawings with sufficient clarity and conciseness to enable 
one skilled in the art to make and to use the invention, to know the best 
mode for carrying out the invention and to distinguish it from other 
inventions and from what is old. Many variations and obvious adaptations 
of the invention will readily come to mind and these are intended to be 
contained within the scope of the invention as claimed below.