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
1991-11-18
2001-01-30
Chapman, Mark (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Radiation sensitive composition or product or process of making
C522S025000, C522S031000, C522S049000, C522S053000, C522S101000, C522S102000
Reexamination Certificate
active
06180317
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to a cationically polymerizable epoxy resin system having photoinitiators added thereto, and which resin system has improved rheological and also photoimaging properties, and more particularly, is suitable for use with epoxy-glass laminate circuit boards which have been cured with dicyandiamide.
BACKGROUND OF THE INVENTION
There are many different instances where photoimagable compositions are utilized in various industrial processes. In one particular process a photoimagable composition is utilized as a solder mask by applying the composition to the underlying printed circuit board. Thereafter photolithographic techniques are employed to reveal various underlying structures on the board while masking others so that solder may be applied by various solder applying processes to the exposed structures. During the solder applying process the solder will adhere to the exposed underlying components and be prevented from adhering where the remaining material operates as a solder mask.
It is necessary that the solder mask material be formulated such that it can be applied by the appropriate methods; for example curtain coating, a preferred method, requires certain rheological properties for effective coating. Further, the solder mask must have the properties of providing efficient transmission of the light or other exposing radiation so as to photolyze the photoinitiator through whatever thickness of material is applied. Also, of course, if the material is to be used as a solder mask, the solder mask must possess appropriate physical and chemical properties to withstand the application of the solder material without significant deterioration, degradation or loss of adhesion to the underlying substrate and maintain its coverage over the portions of the board wherein solder is to be masked. If it is to be used for other purposes, such as an etch resist, other properties may be required.
There have been many prior art proposals for different photoimagable compositions including many that use epoxies. Examples of these are found in the following U.S. Pat. Nos. 4,279,985; 4,548,890; 4,351,708; 4,138,255; 4,069,055; 4,250,053; 4,058,401; 4,659,649; 4,544,623; 4,684,671; 4,624,912; 4,175,963; 4,081,276; 4,693,961; and 4,442,197. All of these patents show various resins and photoinitiators for use in photoimageable compositions many of which are useful as solder masks. However none of them teach or suggest the specific composition of the present invention.
Good photopatternable formulations which permit high resolution fine line photopatterning have been disclosed in the parent application Ser. No. 07/318,536, which issued as U. S. Pat. No. 5,026,624. However, these formulations may not be suitable for use on epoxy-glass laminate circuit boards, which are cured with dicyandiamide. It has been found that certain coating formulations demonstrate poor image resolution when applied to epoxy-glass laminates cured with dicyandiamide. It is desirable to have a liquid photoimagable coating which may be used as a solder mask, containing epoxy resin cured with photosensitive cationic initiators which demonstrate good image resolution when applied to epoxy-glass laminates, cured with dicyaniamide.
SUMMARY OF THE INVENTION
According to the present invention, an improved photoimagable cationically polymerizable epoxy based coating material demonstrating good image resolution, even when applied to epoxy glass laminates, cured with dicyandiamide, is provided. The material includes an epoxy resin system comprising between from about 10% to about 90%, preferably about 28% to about 57% by weight of a polyol resin which is a condensation product of epichlorohydrin and bisphenol A, having a molecular weight of between about 40,000 and about 130,000; and from about 10% to about 90%, preferably about 43% to 72% by weight of an epoxidized glycidyl ether of a brominated bisphenol A having a melting point of from about 90° C. and to about 110° C. and a molecular weight of between about 600 and about 2500. Optional resins may be added to the system to increase the photospeed and/or to control the rheology. To this resin system is added about 0.1 to about 15 parts by weight per 100 parts of resin of a cationic photoinitiator capable of initiating polymerization of said epoxidized resin systems upon exposure to actinic radiation. Optionally, a photosensitizer in an amount of up to about 10 parts by weight may be added to enable/enhance exposure at other wavelengths. The resin system, exclusive of the photoinitiator and sensitizer, being further characterized by having an absorbance of light in the 330-700 nm region of less than 0.1 for a 2.0 mil film.
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Allen Robert David
Day Richard Allen
Glatzel Donald Herman
Hinsberg William Dinan
Mertz John Richard
Chapman Mark
Hogg William N.
International Business Machines - Corporation
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