Radiation imagery chemistry: process – composition – or product th – Imaged product – Including resin or synthetic polymer
Reexamination Certificate
2002-09-23
2004-06-29
Hamilton, Cynthia (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaged product
Including resin or synthetic polymer
C430S280100, C430S285100, C430S288100, C430S311000, C430S286100, C430S287100, C430S014000, C522S100000, C522S103000, C522S009000, C522S010000, C522S014000, C522S026000
Reexamination Certificate
active
06756166
ABSTRACT:
This application claims priority to Japanese Patent application No. 2001-291324, filed Sep. 25, 2001.
TECHNICAL FIELD
This invention relates to a photosensitive resin composition which is useful in forming an image by a process comprising a step of ultraviolet ray exposure and a step of development using a dilute aqueous alkaline solution, is capable of prolonging pot life, of preventing deposits from being generated in a cured coated film, of widening so-called heat control tolerance (i.e. the controllable range of thermal tolerance relative to the degree of curing of coated film that can be removed on the occasion of developing the unexposure regions at the step of drying the coated film), and is excellent in sensitivity, in heat resistance, in chemical resistance and in electric insulating properties, thereby rendering the photosensitive resin composition suitable for use as a solder resist for producing a printed wiring board.
This invention also relates to a printed wiring board formed by making use of such photosensitive resin composition as mentioned above.
BACKGROUND OF THE INVENTION
The printed wiring board is employed for mounting electronic components on soldering lands of a conductive circuit pattern which has been formed in advance on the substrate of the printed wiring board, wherein all of the circuit regions excluding the soldering lands are covered by a solder resist film as a permanent protective film. By this covering of solder resist film, it becomes possible to prevent the solder from adhering onto regions which are not required to be coated with the solder on the occasion of soldering electronic components to the printed wiring board, and to prevent the conductor constituting the circuit pattern from being directly exposed to air and hence from being oxidized or corroded by moisture.
Conventionally, the solder resist film is formed, in most cases, by a process wherein a liquid composition of the solder resist film is coated on a substrate by means of a screen printing to form a pattern, which is then dried to remove a solvent and cured by means of ultraviolet rays or heating.
Recently however, due to the increasing demands for the enhancement in density (fineness) of wirings of the printed wiring board, a solder resist composition (referred hereinafter also as a solder resist ink composition) is also required to be more excellent in resolution as well as in precision. Under such circumstances, there has been proposed, in place of the conventional screen printing method and irrespective of the kinds of substrate i.e. consumer's use or industrial use, a liquid photosolder resist method (photodeveloping method) which is excellent in registration precision and in covering property of the edge portions of conductive body. For example, Japanese Patent Unexamined Publication S50-144431 and Japanese Patent Publication S51-40451 disclose solder resist compositions comprising bisphenol type epoxy acrylate, a sensitizer, an epoxy compound and an epoxy curing agent. These solder resist compositions are designed to be employed in such a manner that a liquid photosensitive composition is coated all over a printed wiring board, and after the solvent included therein is permitted to volatilize, the layer of the photosensitive composition is selectively exposed to irradiation, unexposed regions of the layer being subsequently removed by making use of an organic solvent to thereby perform the development of the solder resist.
However, the removal of the unexposure regions (development) by making use of an organic solvent necessitates a large quantity of the organic solvent, hence giving rise to environmental contamination or the generation of fire. Particularly, since the influence of the environmental contamination upon human body is high-lighted recently, there have been proposed various countermeasures for solving such problems.
With a view to solve these problems, there has been proposed an alkali-development type photosolder resist composition which can be developed by making use of a dilute aqueous alkaline solution. For example, Japanese Patent Publications S56-40329 and S57-45785 disclose a material comprising, as a base polymer, a reaction product which can be obtained by a process wherein an epoxy resin is reacted with unsaturated monocarboxylic acid to obtain a compound to which a poly-basic acid anhydride is added to obtain the reaction product. Further, Japanese Patent Publication H1-54390 discloses a photo-curable liquid resist ink composition which can be developed by making use of a dilute aqueous alkaline solution, this photo-curable liquid resist ink composition comprising an active energy beam-curable resin which can be obtained from a reaction between a saturated or unsaturated poly-basic-acid anhydride and a reaction product obtained from a reaction between a novolac epoxy resin and an unsaturated monocarboxylic acid, and a photopolymerization initiator.
These liquid solder resist compositions are featured in that carboxylic group is introduced into epoxy acrylate to thereby provide them with photosensitivity and capability of being developed using a dilute aqueous alkali solution. These liquid solder resist compositions are further featured in that they usually include a thermosetting component, e.g. an epoxy resin in general, for thermosetting a coated film of these resist compositions after this coated film is formed into a resist pattern by way of exposure and development, thereby allowing a reaction to take place between the carboxylic group introduced into a side chain of the epoxy acrylate and the epoxy group. As a result, it is possible to form a resist film which is excellent in adhesion, hardness, heat resistance and electric insulating properties. In this case, an epoxy resin-curing agent or a curing promotor is generally employed together with the epoxy resin.
As for the epoxy resin-curing promoter, there are conventionally known various kinds of compounds including melamine.
However, when melamine is incorporated together with epoxy resin into the aforementioned alkali-developing type liquid solder resist composition, defective curing may be caused to occur in the resultant coated film due to the poor compatibility of melamine with epoxy resin, and moreover, the resultant composition would be accompanied with a problem that the pot life thereof is relatively short so that it is impossible to secure the storage stability for a long period of time. Further, if melamine is left unreacted in the cured coated film and left to stand under high temperature and high humidity conditions, the melamine is more likely to be separated on the surface of the cured coated film, thereby not only badly affecting the external appearance of the cured film, but also permitting free moisture to penetrating into a melamine-missing portion to thereby deteriorate the electric insulation of the cured coated film. Moreover, since this deposit is also poor in insulation resistance, the electric insulating properties inherent to the cured coated film is more likely to be obstructed.
Japanese Patent No. 3134037 discloses almost the same photosensitive resin composition as mentioned above except that an organic acid salt of melamine is substituted for melamine. This patent publication also describes that “since the melamine salt according to the present invention has a decomposition temperature ranging from about 120 to 150° C., it cannot be decomposed at a provisional drying temperature, - - - but may be decomposed into melamine and an organic acid on the occasion of thermally curing the coated film by heating it at a temperature ranging from about 140 to 180° C., this melamine thus produced - - - ”. Namely, melamine is caused to generate in the cured coated film to be ultimately obtained, thus making it unavoidable that free melamine is caused to remain in the coated film. Therefore, the photosensitive resin composition disclosed in this Japanese Patent is also incapable of avoiding the aforementioned problem resulting from the deposition of melamine.
With a vie
Miura Ichiro
Ono Takao
Hamilton Cynthia
Tamurakaken Corporation
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