Disclosed is a method for controlling edge fusion in a laminate
of an aqueous developable photoresist composition sandwiched between
a film support and a protective cover sheet comprising maintaining
the relative humidity below about 20% in the environment surrounding
the laminate, preferentially achieved by packaging the photoresist
with a desiccant in a moisture proof container.
1. An element comprising a laminate of an aqueous developable photoresist
composition sandwiched between a film support and a protective cover
sheet enclosed in a moisture proof container with an amount of dessicant
sufficient to maintain the relative humidity below about 20% inside
2. In a method comprising enclosing in a container a laminate of
an aqueous developable photoresist composition sandwiched between
supporting layers, the improvement comprising enclosing in the container
an amount of desiccant sufficient to maintain the relative humidity
inside the container below about 20%.
3. In an element comprising a laminate of an aqueous developable
photoresist composition sandwiched between supporting layers enclosed
in a container, the improvement wherein the element further comprises
an amount of dessicant enclosed in the container sufficient to maintain
the relative humidity inside the container at less than about 20%.
BACKGROUND OF THE INVENTION
This invention relates to the packaging and storing of aqueous
developable photoresists. More particularly it relates to the reduction
of edge fusion in packaged photoresists.
Aqueous developable photoresists are superior to non-aqueous developable
resists, since aqueous developable photoresists employ water-base
developing and stripping solutions, which avoid the environmental
problems and high costs associated with the organic solvents and
solvent additives needed to develop and strip non-aqueous resists.
Aqueous developable photoresists are typically packaged and stored
in roll form as a laminate of the photoresist composition sandwiched
between a flexible film support and a protective cover sheet. When
packaged in this form the photoresist has a tendency to "cold
flow". U.S. Pat. No. 3867153 hypothesizes that cold flow
is caused by increases in temperature and/or pressure. Cold flow
results in the photoresist oozing out from between successive layers
of the film and cover sheet and fusing on the edge of the roll,
a phenomenon known as "edge fusion". When an edge fused
roll is unrolled, chips of the photopolymer may break off, and some
of the film may delaminate from its support film, which interferes
with proper imaging when the photoresist is exposed and developed.
A fused roll is, therefore, defective and results in increased costs
to either the user, who cannot use the defective portion of the
roll, the seller, who must replace the defective roll, or both.
Preventing edge fusion is, therefore, desirable in cost savings
related to the use and sale of photoresist compositions.
Reducing edge fusion by reducing the temperature surrounding stored
photoresists and by protecting the resists from direct pressure
with improved packaging have not been completely successful, and
Reducing edge fusion is claimed in U.S. Pat. No. 3867153 to have
been achieved by irradiating the edges of the photoresist laminate
and is also claimed by adding specific compounds to the photoresist
composition as shown in U.S. Pat. Nos. 4239849 and 4293635.
However, both of these methods have their disadvantages; significant
cost increases in production result from using either method, and
irradiating makes the photoresist in the radiation exposed edges
hard and, therefore, useless for photoimaging.
SUMMARY OF THE INVENTION
According to the invention, edge fusion is controlled by maintaining
the relative humidity below about 20% in the environment surrounding
a roll or sheets of aqueous or semiaqueous developable photoresist
laminate. A particularly useful and economical way to accomplish
this is by packaging photoresist laminate rolls with a desiccant
in a moisture proof container. This result is unexpected, as the
art has never appreciated the part that moisture plays in cold flow
and edge fusion.
DESCRIPTION OF THE DRAWING
Briefly, the drawing is an exploded view of a unit (4) that, when
enclosed in a moisture proof container, exemplifies a preferred
embodiment of this invention.
In detail, the unit (4) comprises: a roll of photoresist laminate
sandwiched between a film support and a cover sheet (6) mounted
on a cylindrical core (8) having openings (10 12) at its opposing
ends, into which openings (10 12) are inserted bullets (14 16)
of sufficient dimension to provide a friction fit when inserted
into said openings (10 12) said bullets (14 16) projecting from
core support faces (18 20) of perforated support members (22 24)
having desiccant support faces (26 28) opposing said core support
faces (18 20) to which desiccant support faces (26 28) there are
attached, by appropriate known means, dessicant bags (30 32).
DETAILED DESCRIPTION OF THE INVENTION
Aqueous developable photoresists in laminated roll or sheet form
are maintained at below about 20% relative humidity in accordance
with this invention by known methods of humidity control that will
be apparent to those skilled in the art.
In a preferred embodiment of this invention, a desiccant is packaged
in a moisture proof container with a laminated roll of photoresist.
Various methods of packaging the roll with the desiccant will be
apparent to those skilled in the art, such as for example, as shown
in the Drawing.
Desiccant, formulations are well known, and any hygroscopic substance
that does not adversely affect the photoresist is useable in accordance
with the preferred embodiment. Examples of such substances are silica
gel (including silica gel impregnated paper), calcium chloride,
zinc chloride, calcium sulfate, montmorillonite, activated alumina,
asbestos, charcoal, clay, glass wool, kieselguhr, barium oxide,
calcium oxide, calcium bromide, zinc bromide, magnesium chlorate,
copper sulfate, and Type 4A molecular sieves. Other suitable desiccants
will be apparent to those skilled in the art. The desiccant used
in the preferred embodiment is contained in a porous bag or net
that allows moisture to pass through and contact the desiccant.
The amount of desiccant required in the preferred embodiment depends
on such factors as the water absorbing capacity of the desiccant
used, the packaging within which the desiccant and resist are stored,
the humidity in the storage area, the projected storage time, etc.
These and other factors are known, and the amount of desiccant needed
in a particular application will be apparent to those skilled in
The core on which the laminate is rolled in accordance with the
preferred embodiment, as exemplified in the Drawing, is made from
substances well known to those skilled in the art. Suitable cores
are made from wood, metal or molded plastics, such as for example,
polypropylene, polyethylene, ABS plastic, or any nondusting material.
The support members to which desiccant bags are attached in the
preferred embodiment, as exemplified in the Drawing, are made from
the same materials suitable for the cores. Preferably, the caps
are large enough to extend beyond the edges of the roll. The two
caps then form a support from which the roll is suspended in between.
This protects the surface of the roll as well as the edges.
The moisture proof container used in the preferred embodiment is
made from any nondusting material impervious to moisture that can
also, preferably, protect the photoresist laminate from light and
foreign matter, such as dust. Suitable materials are polyvinyl,
polypropylene, ethylene propylene copolymer, cellophane, polystyrene,
low density polyethylene, laminates of aluminum foil and polyethylene
or polystyrene, etc. The container is preferably sufficiently opaque
to protect the laminate from exposure to light. A particularly suitable
container is a sealed, black, low density, polyethylene envelope.
Other suitable materials will be apparent to those skilled in the
Those skilled in the art will be aware of other ways to package
the desiccant with the photoresist laminate in accordance with the
preferred embodiment. What is essential to the preferred embodiment
is that the desiccant and photoresist roll be packaged together
in a moisture proof container.
Whether using desiccant or some other known method of humidity
control in accordance with this invention, humidity is maintained
below about 20% in the area immediately surrounding the photoresist
The photoresist compositions that are protected in accordance with
this invention are aqueous developable photoresists. The term "aqueous
developable" means photoresists that can be developed by water
base solvents, including what are sometimes referred to as semiaqueous
solvents that contain small amounts of water miscible organic solvents,
such as for example, a methyl, ethyl, or butyl ether of ethylene
glycol or diethylene glycol, methanol, or ethanol. A particularly
useful water based solvent is a dilute solution of sodium carbonate.
Other developers are well known to those skilled in the art.
The photoresist compositions of the subject invention essentially
comprise about 10-50 preferably 15-30 weight percent of one or
more addition photopolymerizable monomers, about 35-80 preferably,
40-80 weight percent of a polymeric binder, about 0.001 to 10 preferably
0.01 to 5.0 weight percent of a free radical or photopolymerization
initiator. In addition, minor amounts of background dyes, leuco
(or printout) dyes, adhesion promoters, antioxidants, plasticizers,
fillers, and the like may be optionally included.
The polymerizable monomer may have from 1 to 4 usually 1 to 3
preferably 2 to 3 addition polymerizable olefinic groups. Suitable
monomers include the alkylene and polyalkylene glycol diacrylates
prepared from alkylene glycols having two to fifteen carbon atoms
or polyalkylene ether glycols of one to ten ether linkages. Outstanding
monomers contain ethylenically unsaturated groups, especially vinylidene
groups, conjugated with ester or amide structures. Especially preferred
acrylyl compounds are triethylene glycol diacrylate, tetraethylene
glycol diacrylate, pentaerythritol triacrylate, trimethylol propane
triacrylate and pentaerythritol tetraacrylate. Other suitable monomers
are disclosed in column 3 and 4 of U.S. Pat. No. 4268610 issued
to L. Roos, incorporated by reference herein.
The polymeric binder determines whether or not the photoresist
is developable in water based solvents. The presence of acid groups
on the binder allows the photoresist to be so developed. Typical
polymeric binders are shown in the U.S. Pat. No. 4268610 issued
to L. Roos.
Thermal polymerization inhibitors are known to those skilled in
the art as shown in the U.S. Pat. No. 4268610.
Photoinitiators used in the photoresist compositions are activatable
by actinic light and are thermally inactive below about 185.degree.
C. Typical examples are shown in the U.S. Pat. No. 4268610.
Background and printout dyes may also be included in the photoresists
usable in accordance with this invention. A background dye is a
visible dye which provides good contrast on copper and serves as
an indicator to insure removal of all the unexposed portions of
the resist during the developing step. Blue and green dyes such
as Brilliant Green and Victoria Blue or combinations thereof are
particularly suitable for this purpose. A printout dye is initially
colorless (leuco), developing color only upon irradiation by ultraviolet
light. Some so called printout dyes are initially colored and fade
upon irradiation. Printout dyes facilitate inspection of the patterned
surface for imperfections, if any. However, the dyes must be inert
towards the other components of the photoresist formulations and
must not interfere with the photopolymerization process. Examples
of such dyes are shown in U.S. Pat. No. 4297435 issued to J.
L. Jolly, et. al., incorporated by reference herein.
Adhesion promoting agents include N-substituted benzotriazoles
as described in the U.S. Pat. No. 4268610 . Other adhesion promoting
agents are known to those skilled in the art.
The flexible film support and the protective cover sheet between
which the photoresist is sandwiched in the packaged roll are made
from various materials well known to those skilled in the art. The
film support preferably has a high degree of dimensional stability
to changes in temperature and humidity. In general, the support
has a composition such that there is only a moderate degree of adherence
between the photoresist and the support. Suitable support films
comprise many high polymer substances, such as for example, polyamides,
polyolefins, polyesters, vinyl polymers, and cellulose esters and
have a thickness of from about 0.00025 inch to about 0.008 inch.
If the photoresist is to be exposed through the support film, the
film must transmit a substantial amount of the actinic radiation
used. If the film is to be removed, no such restrictions apply.
A particularly suitable film is a transparent polyethylene terephthalate
film having a thickness of about 0.001 inch. Suitable protective
cover sheets are typically chosen from the same high polymer sustances
used for the support film and have the same variations in thickness.
A cover sheet comprising 0.001 inch thick low density polyethylene
is particularly suitable. The photoresist layer sandwiched between
the support and the cover sheet is generally about 0.0005 to about
0.004 inches thick. Specific applications require specific resist
layer thicknesses that are known to those skilled in the art.
It will be apparent to those skilled in the art that the photoresist
laminate can be packaged as sheets, as well as a roll, in accordance
with this invention.
The following examples further illustrate the instant invention,
but the invention is not limited thereto. All percentages are by
weight unless indicated otherwise.