Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
1999-10-07
2001-10-02
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
C522S074000, C522S071000, C522S084000, C522S182000, C522S120000, C522S121000, C522S178000, C427S516000, C427S517000, C430S270100, C430S270110, C430S273100, C430S323000, C156S272200, C156S275500, C156S327000, C428S411100, C428S500000
Reexamination Certificate
active
06297294
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method for improving the adhesion of a photopolymerizable composition and the photopolymerized composition formed therefrom to copper. The photopolymerizable composition is useful as a dry film photoresist.
2. Description of the Related Art
Photosensitive compositions particularly useful as photoresists are well known in the prior art. The compositions can be positive-working or negative-working. Particularly useful are negative-working compositions, also known as photopolymerizable systems. The photopolymerizable composition generally contains a polymeric binder, at least one monomeric or oligomeric material capable of polymerizing and/or cross-linking, and a photoinitiator or photoinitiator system. Exposure to actinic radiation initiates the polymerization and/or crosslinking reactions, resulting in insolubilization of the material in developer solvents. The thus formed latent image can then be developed by treating with developer solvent. The photopolymerizable compositions are generally formed as a dry film on a support. The dry film is sandwiched between the support film and a coversheet and stored in roll form.
The photosensitive film is conventionally unwound from a roll and, after the coversheet is removed, laminated to a substrate. The laminated composition is exposed imagewise to actinic radiation, with the support film stripped from the photosensitive composition before or after the exposure step. The exposed film is then treated with developer solvent which removes the unexposed areas of the photosensitive composition to form a resist image of polymeric material. The thus uncovered portion of the substrate can be treated as desired, followed by removal of the polymeric resist image.
For the high resolution desired in the electronics industry today, it is necessary for the resist to be removed cleanly in the development step without leaving any residue on the substrate. The addition of low molecular weight acids to reduce scum and stain formation in aqueous processable photopolymerizable compositions has been disclosed in Covesleskie et al., U.S. Pat. No. 4,510,230. However, in addition to low residue and scum formation, it is also important that the photoresist have good adhesion to the substrate, usually copper. The board with imaged resist is treated with a variety of chemicals during the manufacturing steps, typically etching and/or plating chemistries. Inadequate adhesion of the photoresist to the substrate can result in the chemistries reacting underneath the resist in areas intended to be covered. Thus the quality of the end product is reduced and failures can occur. Photopolymerizable compositions containing benzotriazoles and benzotriazole carboxylic acids have been shown to improve the adhesion of the compositions to substrates in, for example, Hurley et al., U.S. Pat. No. 3,622,334; Weed, U.S. Pat. No. 4,680,249; and Tohda et al, U.S. Pat. No. 4,741,987.
SUMMARY OF THE INVENTION
This invention is directed to a method for increasing the adhesion of a photopolymerizable composition and the photopolymerized composition formed therefrom to a copper substrate,
said substrate presenting at least one surface,
said photopolymerizable composition being adapted for application to said at least one surface for photopolymerizing thereon and comprising (a) a photoinitator system; (b) a nongaseous, ethylenically unsaturated monomer or oligomer; and (c) a preformed macromolecular binder,
said method comprising the step of adding to said photopolymerizable composition 0.01 to 1.0 percent, by weight, of an adhesion promoter, based upon the total weight of the photopolymerizable composition;
said adhesion promoter consisting essentially of a poly-carboxylic acid having 3-6 carbon atoms.
The method results in improved adhesion between copper substrates and photopolymerizable and photopolymerized compositions when the compositions are laminated onto the substrate. The photopolymerizable composition is generally present as a layer between a film support and a coversheet.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Photosensitive compositions used in conjunction with the method of the present invention are particularly suitable for use as photoresists in the formation of printed circuit boards. The compositions have improved adhesion to copper. Other compounds are known to improve adhesion to copper. Examples include benzotriazole and substituted benzotriazoles such as hydroxybenzotriazole, carboxybenzotriazole, etc. The adhesion promoter of the current invention is useful alone or in combination with other adhesion promoters.
In the method of the invention, the adhesion to copper is improved by the addition of an adhesion promotor to the photopolymerizable compositions. The adhesion promoter is an aliphatic poly-carboxylic acid, by which is meant an organic compound having more than one carboxylic acid group. The polycarboxylic acid contains from 3-6 carbon atoms. Examples of suitable acids include malonic acid, and adipic acid. Combinations of acids can be used. A preferred polycarboxylic acid adhesion promotor is succinic acid. The adhesion promoter is present at a level which is effective to improve the adhesion of the composition to copper without adversely affecting the other necessary properties of the photosensitive composition. It is preferred to use the lowest amount possible so as to minimize the amount of added electrolyte to the composition. Generally, the adhesion promoter will be present in an amount of about 0.01 to 1% by weight of the total photosensitive composition; preferably 0.02 to 0.4% by weight.
The photosensitive composition further comprises a photoinitator system, a non-gaseous ethylenically unsaturated monomer or oligomer, and a preformed macromolecular binder.
The photoinitiator system has one or more compounds that directly furnish free radicals when activated by actinic radiation. The system also may contain a sensitizer that is activated by the actinic radiation, causing the compound to furnish the free radicals. Useful photoinitiator systems typically will contain a sensitizer that extends spectral response into the near ultraviolet, visible, and near infrared spectral regions.
Photoinitiator systems are well known and discussions of such systems can be found in, for example, “Photoreactive Polymers: The Science and Technology of Resists” by A. Reiser, John Wiley & Sons, New York, 1989, and “Radiation Curing: Science and Technology” edited by S. P. Pappas, Plenum Press, New York, 1992.
Preferred photoinitiator systems are free radical generating addition polymerization initators activatable by actinic light and thermally inactive at and below 185° C. These include the substituted or unsubstituted polynuclear quinones such as 9,10-anthroquinone; vicinal ketaldonyl alcohols, such as benzoin; &agr;-hydrocarbon-substituted aromatic acyloins, including &agr;-methylbenzoin; Michler's ketone, benzophenone, 2,4,5-triphenyl-imidazolyl dimers with hydrogen donors. Particularly preferred photoinitiators include hexaarylbiimidazoles in association with a hydrogen donor; Michler's ketone and ethyl Michler's ketone, particularly in association with benzophenone; and acetophenone derivatives.
The ethylenically-unsaturated compound is one which is capable of undergoing free-radical initiated polymerization and/or crosslinking. Such compounds are generally known as monomers or oligomers, although polymers having reactive pendant groups can also be used. Such compounds are well known in the art and have been disclosed in, for example, “Light-Sensitive Systems: Chemistry and Application of Nonsilver Halide Photographic Processes” by J. Kosar (John Wiley & Sons, Inc., 1965); “Imaging Processes and Materials—Neblette's Eight Edition” edited by J. Sturge, V. Walworth and A. Shepp (Van Nostrand Reinhold, 1989); and “Photoreactive Polymer—The Science and Technology of Resists” by A. Reiser (John Wiley & Sons, 1989). Typical monomers are: unsaturated esters of alcohols,
E. I. Du Pont de Nemours and Company
McClendon Sanza
Seidleck James J.
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