Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Radiation sensitive composition or product or process of making
Reexamination Certificate
1996-02-05
2002-01-29
Weiner, Laura (Department: 1745)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Radiation sensitive composition or product or process of making
C430S288100, C430S325000, C430S330000
Reexamination Certificate
active
06342332
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to liquid photoimageable resists compositions. More particularly, this invention relates to liquid photoimageable resists compositions having utility in print and acid etching applications used to produce printed circuit boards in the electronics industry.
BACKGROUND OF THE INVENTION
Liquid photopolymerizable compositions can be used in the manufacture of printed circuit boards as photoresists. In typical use, a liquid photopolymerizable composition is applied to a copper-clad substrate through any means commonly used in the art, including roll coating, curtain coating, screen coating or spin coating. The material subsequentially dried and the dried material exposed in certain areas to actinic radiation that preferentially cures the material. The cured material is then washed with a developing solution to remove unexposed material from the copper surface. The exposed copper surface can then be removed in etching solutions leaving the protected area under the cured photopolymerizable composition to form the electrical circuit. Typically photopolymerizable compositions intended as photoresists are preferably designed to keep exposure time and development time to a minimum.
Liquid resist technology is not new. However, recently there has been increased demand for methods to reduce the cost of manufacturing printed circuits through lower materials cost and higher yields. In the past, liquid resist technology was displaced by dry film photoresist due dry-film photoresist's relatively high yields, ease of processing and increased productivity. However, recent developments in dual-sided roller coating and clean room technology has potentially eliminated problems previously experienced with the use of liquid resists.
Liquid-applied resists (in contrast to dry-film application) suffer from many processing problems. These problems include low photosensitivity due to exposure to atmospheric oxygen, poor blocking characteristics, and slow processing when compared to dry film resists. If in overcoming the reduction in photosensitivity due to exposure to atmospheric oxygen, large quantities of inefficient photoinitiators, such as benzophenone, are used other deficiencies in the resists may arise. At high levels, benzophenone acts as a plasticizer to the resist which thereby may effect the physical properties of the applied resist. One affect of increased levels of benzophenone in a resist is an increase in the material's tendency to block. Typically when a resist is used in a commercial setting, substrates are coated with resist and dried. It may be necessary for these substrates to be stacked and stored for a period of time prior to their exposure to actinic radiation. If these substrates are stacked in such a manner so that areas of a panel coated with resist are in contact with coated areas of an adjacent panel and if these materials exhibit a tendency to block, adjacent panels may stick together and transfer material from one panel to another thereby causing circuit defects and yield losses in the final product. To gain antiblocking properties, the previous resists disclose the use of blooming agents and other additives which migrate to the surface of the dried resist detackifying the material.
Also since benzophenone is a relatively volatile material, resists containing relatively large amounts of benzophenone may, upon drying, exhibit a great degree of variability in their photospeed performance. This variability makes it difficult for one to predict the amount of exposure required to cure the resist.
One object of this invention is to provide a liquid-applied resist which exhibits a good balance of photosensitivity and overall physical properties. Another object of this invention is provision of a liquid-applied resist which exhibits a reduced tendency for blocking compared to other liquid-applied resist formulations.
BRIEF DESCRIPTION OF THE INVENTION
The instant invention relates to a resist material comprising:
a) binder,
b) a multifunctional monomer,
c) a photoinitiator, and
d) a solvent;
wherein the photoinitator is present in an amount of greater than about 10% by weight of the material without the solvent. Preferably, the solvent comprises propylene glycol methyl ether acetate.
The binder of the resist material comprises an acrylic polymer. Preferably, the binder is present in an amount of greater than about 60% by weight of the material without the solvent.
Preferably in the resist material, the photoinitiator is present in an amount from greater than 10% to about 17% by weight, more preferably in an amount from greater than 10% to about 11% by weight, more preferably about 11% by weight.
The binder of the resist material without the solvent has a T
g
of about 110° C. or greater, preferably a T
g
of about 110° C. to about 120° C.
The resist material comprising:
a) a binder,
b) a multifunctional monomer,
c) a photoinitator, and
d) a solvent; where the photoinitator is present in an amount of greater than about 10% by weight of the material without the solvent,
wherein the material further comprises a flow modifier, a thermal inhibitor and a dye.
The instant invention also relates to a process for producing a negative resist image on a surface. The process comprising coating a resist material onto a conductor clad laminate surface wherein the resist material comprises; binder, a multifunctional monomer, a photoinitiator, and a solvent; wherein the photoinitator is present in an amount of greater than about 10% by weight of the material without the solvent. The resist material is heated to remove substantially all of the solvent from the resist material to form a dry adherent film. The dry adherent film is exposed imagewise to actinic radiation to form an image, and the latent image is developed to form a negative resist image.
In the process, the resist material may be applied via a roller coater, a screen coater, a curtain coater or a spin coater. Also in the process, resist material is heated above about 93° C. (about 200° F.), preferably about 93° C. to about 107° C. (about 200° F. to about 225° F.) to remove substantially all of the solvent from the resist material to form a dry adherent film.
DETAILED DESCRIPTION OF THE INVENTION
This invention relates to liquid photoimagable resists and provides a material with a sufficient photospeed to be of commercial utility and to be relatively resistant to blocking.
The liquid photoimageable resist of the instant invention comprises a binder, a multifunctional monomer, a photoinitiator and a solvent. Optionally, the liquid photoimageable resist additionally comprises leveling agents, a thermal inhibitors, dyes and the like.
The binder useful in accordance with this invention is prepared from one or more film-forming, vinyl type monomers and one or more alpha, beta ethylenically unsaturated carboxyl group containing monomers having 3-15 carbon atoms, which makes the binder soluble in aqueous media. Examples of useful vinyl type monomers are alkyl and hydroxyalkyl acrylates and methacrylates having 3-15 carbon atoms, styrene, and alkyl substituted styrenes. Examples of useful carboxyl group-containing monomers are cinnamic acid, crotonic acid, sorbic acid, acrylic acid, methacrylic acid, itaconic acid, propionic acid, maleic acid, fumaric acid, and half esters and anhydrides of these acids. The binder has an acid number of about 80 or greater, preferably about 80 to about 160, more preferably about 120 to about 150. A preferred binder comprises an acrylic polymer, more preferably methacrylic acid, methyl methacrylate and ethyl acrylate at a weight ratio of 22.2/64.6/13.2., weight average molecular weight 45,000, acid number 130-150. Other useful binders will be apparent to those skilled in the art.
The binder of the instant invention has a T
g
of about 110° C. or greater, preferably a T
g
of about 110° C. to about 120° C. It is also preferable that the binder is present in the resist at a dry concentration of about 50% or greater, preferably about 50 to about 70%, more prefe
Loo Dekai
Mayes Richard T.
Carmody & Torrance LLP
MacDermid Incorporated
Weiner Laura
LandOfFree
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