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
1999-07-21
2001-04-17
Hamilton, Cynthia (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Radiation sensitive composition or product or process of making
C430S284100, C430S907000, C430S910000, C430S277100, C522S092000, C522S095000, C522S075000, C522S076000, C522S079000, C522S074000
Reexamination Certificate
active
06218074
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a flexible, flame-retardant, aqueous processable, photoimageable resin composition and a photoimageable element that is flexible after processing and cure. More specifically, the invention relates to a flexible, flame-retardant, aqueous processable, photoimageable resin composition for forming a permanent, protective coating film having excellent properties which can be used for the protection of printed circuitry during its lifetime, and to a multilayer photoimageable element comprising a layer of said composition in combination with a low tack photoimageable resin sublayer and a temporary support film.
The flame-retardant photoimageable resin composition has excellent aqueous developability and yields a cured coating film having good flexibility, ;adhesion, solvent resistance, surface hardness, thermal resistance, electrical insulating properties and Underwriters Laboratory 94VTM-0 flame retardency on flexible polyimide laminates that contain active flame retardants in the adhesive layer, e.g., Pyralux® FR and Teclam® (commercially available from E. I. du Pont de Nemours and Company) and on adhesiveless polyimide laminates. The photoimageable resin composition is suitable for use as a solder resist in the fabrication of printed circuit boards.
DESCRIPTION OF THE PRIOR ART
Photopolymerizable resist materials are known, for example, from U.S. Pat. Nos. 3,469,982 and 3,547,730, which describe a film resist with a sandwich structure in the form of a photopolymerizable layer between a cover sheet and a temporary support. Such a primary film resist can, for instance, be laminated on a copper base, exposed imagewise and developed with organic solvents or aqueous solutions, whereby a defined resist layer is formed. Typically the copper base for a printed circuit board is rigid, with limited flexibility of just a few degrees, such as the conventional copper-clad fiberglass epoxy laminates. More recently, printed circuits are being prepared on highly flexible film substrates to form electronic packages which may be folded and refolded one or more times to fit a specified configuration or a dynamic mechanical operation.
The defined resist layer thus produced can now be selectively etched, electroplated or treated with solder on the substrate. Particularly high demands are placed on photoresist films if they are used as permanent coatings that function as solder resists or masks. In this case, the developed, photopolymerized layer must withstand temperatures up to 300° C. without degradation, loss of adhesion or accumulation of residues contained in or on the molten solder. With the advanced technology of today's printed circuit boards, it is important to have the capability to photoimage a solder mask. According to the current state of the art, such solder masks can be applied by spraying, coating or calendaring liquid compositions on a substrate or also by laminating a dry film on a substrate.
Due to the general adverse environmental impact of organic solvents, aqueous developable photopolymer systems with fast development are now preferred. The use of photopolymer resists with acid functions, primarily carboxyl functions, is known to impart aqueous processability. However, these groups are disadvantageous in many subsequent steps or events. In the case of primary photoresists, delamination of the resist is observed in alkali etching or gold plating and, in the case of solder masks, inadequate environ-mental resistance can occur. Modification of the carboxyl groups with melamine formaldehyde compounds to overcome the named disadvantages is known (EP 01 15 354 and U.S. Pat. No. 4,247,621).
The utilization of polymers containing carboxylic acid groups that are subsequently converted to less reactive and less moisture sensitive species is also known. U.S. Pat. No. 4,987,054 discloses a photo-polymerizable formulation yielding improved properties containing an acid copolymeric binder wherein a copolymer structural unit is the half acid/amide of a dicarboxylic acid. The disclosed formulations are used with conventional rigid printed circuit boards, processed with wholly aqueous alkaline solutions and are storage stable. European Patent Application EP 430,175 discloses a photopolymeric system similar to U.S. Pat. No. 4,987,054.
International Patent Application WO 93/17368 and U.S. Pat. No. 5,536,620 disclose an aqueous processable, photo-imageable, permanent coating composition for printed circuits comprising (a) a cobinder consisting of a low molecular weight amic acid copolymer and a high molecular weight carboxylic acid-containing copolymer, (b) an acrylated urethane monomer component, (c) a photoinitiator system, and (d) a melamine formaldehyde thermal crosslinking agent.
U.S. Pat. No. 5,288,589 discloses a two layer photo-imageable, aqueous processable photoresist containing an amphoteric binder in the layer laminated directly to a printed circuit board thereby providing a permanent coating with improved adhesion throughout the lamination process while maintaining other desirable properties such as storage stability and circuit encapsulation.
However, none of the above-mentioned prior art photoimageable compositions have a sufficient degree of flame retardency.
As the electronic industry is driven towards faster, more reliable and compact devices, there is an increasing need in the printed circuit field for a more flexible, permanent photoimageable coating that can withstand typical manufacturing process conditions, such as molten solder, and which additionally meets established government flammability standards.
SUMMARY OF THE INVENTION
The present invention relates to a flame-retardant, aqueous-processable photoimageable resin composition suitable for forming a flexible permanent, protective coating on a flexible printed circuit board comprising:
(a) a brominated carboxylic copolymer binder formed from (i) a ring-brominated aromatic monomer, (ii) at least one of an alkyl acrylate, allyl methacrylate or non-brominated aromatic monomer, wherein alkyl contains from 1 to 20 carbon atoms, and (iii) an ethylenically unsaturated carboxylic acid monomer said binder having a weight average molecular weight (M
W
) of from 40,000 to 500,000 and containing from 3 to 40% bromine by weight;
(b) a non-brominated low molecular weight copolymer binder having a weight average molecular weight (M
W
) of from 2,000 to 10,000, which is the reaction product of a primary amine with a copolymer formed from at least one ethylenically unsaturated dicarboxylic acid anhydride and at least one ethylenically unsaturated comonomer and containing at least one structural unit A and at least one additional structural unit selected from B
1
, B
2
, and combinations thereof containing carboxyl groups, wherein:
(i) 5 to 50 percent by weight of said low molecular weight copolymer binder is formed from at least one structural unit B
1
, B
2
or combination thereof containing carboxyl groups,
(ii) 50 to 95 percent by weight of said low molecular weight copolymer binder is formed from structural unit A, wherein A, is different from structural units B
1
and B
2
,
(iii) A, B
1
and B
2
have the structures:
wherein R
1
is H, alkyl or aryl; R
2
is H, CH
3
, aryl, —COOR
7
, —CONR
8
R
9
or —CN; R
3
and R
4
independently are H or alkyl; R
5
is alkyl, aryl or aryl which is substituted with primary amino, secondary amino, tertiary amino, hydroxy or ether groups or mixtures thereof; R
6
is —OH or NHR
5
; and R
7
, R
8
and R
9
independently are H, alkyl, aryl or aryl substituted with one or more hydroxy, ester, keto, ether or thioether groups; wherein alkyl in any of the above R groups contains from 1 to 6 carbon atoms;
(c) an acrylated urethane monomeric component containing from 0 to 20% bromine by weight;
(d) a brominated acrylated monomer containing from 10 to 80% bromine by weight with the proviso that (d) is not a urethane monomeric component;
(e) a brominated additive containing from 10 to 85% bromine by weight with the proviso that (e) is not an acr
Dueber Thomas Eugene
Lee Yueh-Ling
Schadt, III Frank Leonard
E. I. Du Pont de Nemours and Company
Hamilton Cynthia
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