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
1998-12-28
2002-06-04
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
C430S311000, C430S331000
Reexamination Certificate
active
06399277
ABSTRACT:
This invention relates to a photosensitive thermosetting resin composition, more specifically to a novel photosensitive thermosetting resin composition which is useful as a solder resist for a printed wiring board, and a process for forming a solder resist pattern by coating the photosensitive thermosetting resin composition, carrying out drying by a dryer at a constant temperature, exposing the composition selectively through a film on which a predetermined pattern is formed, with active rays, developing an unexposed portion and further carrying out heating.
The present invention relates to a photosensitive thermosetting resin composition which is suitable as a solder resist having excellent adhesion property, water-soluble flux resistance, water resistance, moisture resistance, electric characteristics, photosensitivity, resolution property, soldering resistance, chemical resistance, solvent resistance and whitening resistance and also has adhesion property on a rust preventive used for protecting the circuit of a printed wiring board.
According to the present invention, it becomes possible to cope with attachment of gas to surrounding apparatuses caused by gas generation which is a problem when a printed wiring board is produced, and environmental problems, etc. caused by gas generation.
In general, a printed wiring board has been used frequently for incorporating electronic parts compactly. The printed wiring board is obtained by etching a copper foil clad on a laminate along a circuit wiring, and electronic parts are arranged at predetermined places and soldered. A solder resist is used in a step prior to soldering of electronic parts to such a printed wiring board, and a film is formed on the entire surface of a circuit conductor except portions on which electronic parts are to be soldered. Such a film not only functions as an insulating film which prevents soldering from being attached to unnecessary portions when soldering is carried out, but also functions as a protective film which prevents corrosion caused by oxidation and moisture when a circuit conductor is exposed directly to air, so that the film is indispensable. In the prior art, such solder resists have been formed by screen printing them on substrates and setting them by UV rays or heat. These solder resists for industrial use have been disclosed in, for example, Japanese Patent Publication No. 14044/1976.
As a material for public welfare obtained by paying attention to productivity, a rapid-setting UV ray-setting type material as disclosed in, for example, Japanese Patent Publication No. 48800/1986 has been used mainly. However, for the purpose of realizing high density, a printed substrate has tended to be made finer and larger in quantity and made into one board, its level has been heightened at remarkable speed, and a mounting system has been shifted to surface mounting technology (SMT). Accompanied with a finer printed substrate and SMT, also in a solder resist, demands for high resolution property, high precision and high reliability have been increased, and there have been proposed from a screen printing method to a liquid photoresist method which is excellent in positional precision and coating property of a conductor edge portion, for both of a substrate for public welfare and a substrate for industrial use.
For example, in Japanese Unexamined Patent Publication No. 55914/1982, there have been disclosed dry film type photo-sensitive solder resists which comprise urethane di(meth)acrylate, a specific linear high molecular weight compound and a sensitizer. When these dry film type photo-sensitive solder resists are used for a high density printed wiring board, soldering resistance and adhesion property are not sufficient.
As an active energy ray-setting material which can be developed with alkali, there have been disclosed materials using, as abase polymer, a reaction product obtained by reacting an epoxy resin with an unsaturated monocarboxylic acid and further adding a polybasic acid anhydride thereto in Japanese Patent Publication No. 40329/1981 and Japanese Patent Publication No. 45785/1982. In Japanese Unexamined Patent Publication No. 243869/1986, there has been disclosed a liquid solder resist composition which uses a novolak type epoxy resin, has good heat resistance and chemical resistance and can be developed with a dilute alkaline aqueous solution. However, in the above solder resist composition, depending on a combination of a polybasic acid anhydride, an epoxy resin and an epoxy resin-setting agent to be reacted to make the composition soluble in an alkaline developing solution, thermosetting proceeds at the time of drying after coating a resist, whereby development failure occurs, or electrolytic corrosion and discoloration of a copper foil surface are caused. Further, there are limitations that electric characteristics are bad due to influence by a carboxylic acid generated by reacting a polybasic acid anhydride, heat resistance and adhesion property are poor when the amount of an epoxy resin which is a thermosetting component used for obtaining characteristics as a solder resist is small, and it is difficult to carry out development with a dilute alkaline aqueous solution when the above amount is large. Moreover, the above solder resist composition has problems that setting by UV rays is slow to require a long exposure time, and sufficient soldering resistance has not yet been obtained.
In order to solve these problems, in Japanese Unexamined Patent Publication No. 50473/1995 and Japanese Patent Publication No. 17737/1995, there have been disclosed solder resist compositions comprising a novolak type epoxy resin, particularly a cresol novolak epoxy resin-esterified acid adduct, a sensitizer, an epoxy compound, an epoxy-setting agent, etc. However, these solder resists have poor photosensitivity, so that for the purpose of improving photosensitivity, the amount of a polymerizable vinyl monomer is increased, or the amount of a photopolymerization initiator is increased. In the former case, tackiness is worsened, so that sticking of a film and attachment of a resist occur to cause peeling. In the latter case, although photosensitivity is improved by increasing the amount of a photopolymerization initiator to be added, there is a problem that an unreacted substance is sublimated at the time of exposure or postcure to foul a substrate or pollute environment. For the purpose of protecting the environment of the earth, a method in which various kinds of parts are soldered on a printed wiring board and then washed has come into question. From the point of protecting environment, a flux to be used for solving these problems is subjected to washing with water in place of washing with a solvent, and water-soluble fluxes and non-washing type fluxes have been used. Many of these fluxes are strongly active and have caused a problem in soldering resistance of a solder resist, so that improvement of resistance of the resist has been demanded. Further, surface mounting is used in a soldering method, and electroless gold plating is carried out or rust preventive treatment is carried out for the purpose of preventing oxidation of a printed wiring board. There is a problem of peeling of a resist, caused by these treatments carried out before coating a resist or after forming a resist. Further, since a printed wiring board has high density, the surface treatment method of a substrate has been shifted gradually from mechanical polishing to chemical polishing, so that a demand for adhesion property on rust preventive treatment has been increased. With respect to characteristics of a resist, due to a demand for high density of a printed substrate, there have been higher demands for resolution property, electric characteristics, etc. Existing solder resists which comprise a cresol novolak type epoxy-modified resin as a main component are not sufficient and also have a problem in reliability.
With the aim of solving the problem mentioned above, Japanese Patent Kokai Hei 8-41150 has disclosed a solder resist co
Ido Toyoyuki
Nojima Yasuharu
Hamilton Cynthia
Lyon & Lyon LLP
Vantico Inc.
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