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
2000-08-04
2002-03-26
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
C430S285100, C522S084000
Reexamination Certificate
active
06361924
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to aqueous photosolder resist compositions which can be alkali developed, and also to solder resist films formed from the compositions.
2. Description of Related Art
Solder resist compositions are generally used in the form of liquid dispersions which are applied, in the form of coatings, onto substrates such as printed circuit boards. Images are transferred to the coatings by a sequence of light exposure and development. Their curing levels are further increased by the subsequent exposure to heat or light. The compositions for use in the formation of such solder resist films are typically solvent-borne. The use of a solvent is not desirable from an environmental point of view. This has led to the need to develop water-borne or aqueous solder resist compositions.
Japanese Patent Laying-Open No. Hei 5-100427 (1993) discloses active energy radiation-curable resins prepared by partially reacting &agr;-olefin having 6 or more carbon atoms with maleic anhydride, reacting the product with a compound having an unsaturated double bond and a hydroxyl group in a molecule, and then neutralizing the product with an alkaline substance to render it water-dispersible. It also discloses aqueous photosolder resist compositions containing a compound having at least one epoxy group.
Due to the incorporation of a glycidyl-form epoxy group which has a tendency to deactivate in an aqueous medium, the disclosed aqueous photosolder resist compositions suffer from the reduced stability when stored in the form of a liquid mixture containing a principal resin and a curing agent. This problem is attributed to the glycidyl group which is caused to react while the compositions are stored or dried. Its reaction also leads to reductions in various properties, e.g., reduces developability and heat resistance as a result of failure to form uniform films. Also, some compositions, in spite of their aqueous form, release solvent odors to adversely affect working environments. Other deficiencies include pattern defects after development and heat resistance reduction, as a result of insufficient dispersion stability of inorganic fillers.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an aqueous photosolder resist composition which is free from solvent odors and has satisfactory storage stability and excellent heat resistance.
The aqueous photosolder resist composition of the present invention contains:
(A) an aqueous solution prepared by neutralizing a resin containing a free-radically polymerizable group and a carboxyl group with a base;
(B) an inorganic filler;
(C) a photocurable mixture containing (c-1) a multifunctional acrylic monomer, (c-2) a compound having a cyclic ether group other than a glycidyl group and (c-3) a photoinitiator; and optionally
(D) an aqueous solution prepared by neutralizing a free-radically polymerized substance having an acid value of 130-230 mgKOH/mg with a base.
The aforementioned cyclic ether group other than a glycidyl group may be an alicyclic epoxy or oxetane group, for example. The aforementioned resin preferably has a free-radically polymerizable group content of 5×10
−4
−1×10
−2
mole/g and a carboxyl group content (i.e., acid value) of 30-200 mgKOH/g, more preferably of 30-130 mgKOH/g. The molar ratio of carboxyl groups present in the aqueous solutions (A) and (D) to cyclic ether groups, exclusive of glycidyl groups, present in the photocurable mixture (C) may be 1.3/0.7-0.7/1.3, for example.
The aqueous photosolder resist composition of the present invention may further contain a coloring pigment. The inorganic filler is contained preferably in the amount of 5-60 parts by weight, based on 100 parts by weight of solids in the aqueous photosolder resist composition. The solvent, if used, is contained preferably in the amount of not above 20 parts by weight, based on 100 parts by weight of solids in the composition.
The solder resist film of the present invention can be formed according to the following procedure: The aqueous photosolder resist composition of the present invention is coated on a substrate, dried at 50-90° C., exposed to an active energy beam through a mask so that it is photocured in a patterned region. The resulting resist coating is developed by removing its unexposed region with the aid of an alkaline cleaner, and then exposed to heat at 140-170° C. to increase a cure level of the previously photocured region.
DETAILED DESCRIPTION OF THE INVENTION
Detailed explanation will be now given concerning the aqueous photosolder resist composition of the present invention which contains (A) an aqueous solution prepared by neutralizing a resin having a free-radically polymerizable group and a carboxyl group with a base; (B) an inorganic filler; (C) a photocurable mixture (C) containing (c-1) a multifunctional acrylic monomer, (c-2) a compound having a cyclic ether group other than a glycidyl group and (c-3) a photoinitiator; and optionally (D) an aqueous solution prepared by neutralizing a free-radically polymerized substance having an acid value of 130-230 mgKOH/mg with a base.
(A) Aqueous Solution Prepared by Neutralizina a Resin Containina a Free-Radically Polymerizable Group and a Carboxyl Group with a Base
A first component incorporated in the aqueous photosolder resist composition of the present invention is obtained by neutralizing a resin containing a free-radically polymerizable group and a carboxyl group with a base. The resin contains at least one free-radically polymerizable group and at least one carboxyl group in a molecule and preferably has a free-radically polymerizable group content of 5×10
−4
−1×10
−2
mole/g and a carboxyl group content (i.e., acid value) of 30-200 mgKOH/g.
The free-radically polymerizable group content of below 5×10
−4
mole/g may lead to the insufficient cure level and accordingly to the reduced heat resistance of the resulting resist. If the free-radically polymerizable group content exceeds 1×10
−2
mole/g, an undesired proportion thereof may be left remained in the resulting resist. The carboxyl group content of below 30 mgKOH/g may result in the reduced alkaline developability. If the carboxyl group content exceeds 200 mgKOH/g, the dissolution of the exposed resist coating region may also result. It is more preferred that the free-radically polymerizable group content is in the range of 1×10
−3
-5×10
−3
mole/g and the carboxyl group content is in the range of 30-150 mgKOH/g. The carboxyl group content is still more preferably in the range of 30-130 mgKOH/g, most preferably in the range of 70-110 mgKOH/g.
The aforementioned resin containing a free-radically polymerizable group and a carboxyl group preferably has a number average molecular weight within the range of 1,500-25,000. If the number average molecular weight is below 1,500, the insufficient heat resistance may be imparted to the resulting resist. If it exceeds 25,000, it becomes difficult for the resin to be dispersed in water.
The type of the aforementioned resin containing a free-radically polymerizable group and a carboxyl group is not particularly specified. Such a resin can be prepared, for example, by reacting a compound having plural epoxy groups with a compound having a free-radically polymerizable group and a carboxyl group, such as acrylic acid, and then allowing the hydroxyl groups produced as a result of the reaction to react with acid anhydride.
Various compounds can be used for the compound having plural epoxy groups. Examples of such compounds include aromatic polyepoxy compounds represented by the following structural formulas 1
a-
1
c
, as described in Japanese Patent Publication No. Hei 7-103213, and epoxides represented by the following structural formulas 2
a
and 2
b
and obtainable by reacting condensation products of phenols and phenolic hydroxyl-containing aromatic aldehyde with epihalohydrin, as described in Japanese Patent
Fujita Minoru
Namba Osamu
Okajima Keiichi
Yabuuchi Naoya
Hamilton Cynthia
Nippon Paint Co. Ltd.
Townsend & Banta
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