Photosensitive Ink Composition for Screen Printing and Method of Forming Positive Relief Pattern with Use Thereof

Abstract

Disclosed is a photosensitive ink which can form a coated film that is excellent in insulation properties, heat resistance, low warping, low elasticity and adhesion with the substrate, when used as an ink for screen printing, and with which clogging of the screen, bleeding, blur, chipping and the like are unlikely to occur even when the screen printing is repeatedly carried out, so that which has an excellent ease of handling in printing. The ink composition comprises 100 parts by weight of an organic solvent-soluble polyimide block copolymer(s), and 1 to 100 parts by weight of a photoacid generator(s). The polyimide block copolymer(s) and the photoacid generator(s) are dissolved in an organic solvent. The polyimide block copolymer(s) contain(s) in its molecular skeleton a diamine having a siloxane bond, and an aromatic diamine having a hydroxyl group(s) and / or carboxyl group(s) at ortho-position with respect to an amino group.

Description

TECHNICAL FIELD[0001]The present invention relates to a photosensitive ink composition for screen printing and method of forming positive-type relief pattern using the same.BACKGROUND ART[0002]Flexible printed circuit boards such as FPC, TAB and COF are conventionally manufactured as follows: First, a laminate in which a desired circuit pattern is formed is produced by laminating a photosensitive film or coating and drying a photosensitive resin on “polyimide film / adhesive / copper foil”, and exposing and developing the resultant. Thereafter, an insulative protective film (coverlay film) is coated or a thermosetting paste is coated and cured on the surface of the copper circuit pattern formed.[0003]However, as a printed circuit meeting the recent demands of compaction and weight saving of electronic devices, flexible printed circuit boards are attracting attention and their use is now being widened. Especially, with the compaction and densification of packaging by increasing the numbe...

AI Technical Summary

Benefits of technology

[0019]An object of the present invention is to provide a photosensitive ink which can form a coated film that is excellent in insulation properties, heat resistance, low warping, low elasticity and adhesion with the substrate, when used as an ink for screen printing, and with which clogging of the screen, bleeding, blur, chipping and the like are unlikely to occur even when the screen printing is repeatedly carried out, so that which has an excellent ease of handling in printing.Means for Solving the Problems

[0020]The present inventors intensively studied to discover that a photosensitive polyimide resin composition comprising a photosensitive polyimide block copolymer containing in its molecular skeleton a diamine having a siloxane bond(s), and an aromatic diamine having a hydroxyl group(s) and / or carboxyl group(s) at ortho-position with respect to an amino group exhibits an excellent ease of handling in printing when used as an ink for screen printing, thereby completing the present invention.

[0022]By the present invention, a photosensitive ink was provided which can form a coated film that is excellent in insulation properties, heat resistance, low warping, low elasticity and adhesion with the substrate, when used as an ink for screen printing, and with which clogging of the screen, bleeding, blur, chipping and the like are unlikely to occur even when the screen printing is repeatedly carried out, so that which has an excellent ease of handling in printing.

Problems solved by technology

However, these resins used in the paste have a rigid structure, and there are problems in that in cases where they are applied to a thin substrate, the substrate after curing largely warps, and the cured film lacks suppleness and has poor flexibility.

However, in cases of thin circuits wherein the width of the wiring is 80 μm or less, and the intervals between wirings are 80 μm or less, it is difficult to completely embed an adhesive in the irregularities between the wirings.

With the progress of miniaturization of the wiring in the flexible printed circuit boards, the method in which the coverlay film after forming the holes at the terminals of the circuit or the joint portions with other parts is subjected to positioning with the flexible circuit board (FCCL) having a formed circuit pattern has problems in that the method has a limited ease of handling and a limited positioning precision, and the production yield is low.

By this method, although the positioning precision is very high, there is a drawback in that holing is time-consuming and the costs of apparatus and running thereof are high.

However, as a solvent for preparing a varnish or paste, a high boiling nitrogen-containing solvent such as N-methyl-2-pyrrolidone is used, so that curing at a high temperature of not lower than 200° C. is required, which brings about a problem that thermal deterioration of electronic parts occurs.

Further, there in also a problem in that in cases where the paste after being coated on a substrate is left to stand for a long time, whitening of the coated film due to moisture absorption and formation of voids occur, and the handling conditions are complicated.

It is necessary to heat the formed coated film at a high temperature of 240° C. to 350° C. In the imidization reaction, the fact that the shrinkage of the formed polyimide resin is large is a big problem in processability, and especially, it is difficult to mold the resin as a protective layer with a precise pattern on a semiconductor wafer or the like.

Further, since the solvent used in the ink is NMP, DMF or the like with a high moisture absorption, problems that the polyamic acid is likely to precipitate due to the moisture absorption by the varnish, that whitening occurs in printing, that clogging of the screen occurs, and so on occur, so that continuous printing is difficult.

For decreasing the elastic modulus, expensive diamines having dimethylsiloxane bonds are used as the starting material, which is disadvantageous from the viewpoint of economy.

Further, there are problems in that with the increase in the amount of the modifying siloxane, the adhesiveness with the sealing material, solvent resistance and chemical resistance (solder flux resistance), as well as PCT (Pressure Cooker Treatment) resistance are degraded.

Since the polyimide is solvent-soluble, there is a problem in that the composition has a poor chemical resistance.

In addition, there are practical problems in that the composition is likely to dry during screen printing, and as a result, clogging of the screen mesh occurs so that the formation of a pattern becomes very difficult.

However, the compositions are especially poor in ease of handling in printing, when viewed from the point of developing the use as an ink for printing.

However, the polyimide is obtained by reacting the acid dianhydride and the diamine in the presence of a catalyst in an organic polar solvent containing as a major component N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide or the like, and they have problems of whitening in printing, clogging of the screen sheet and so on, so that the compositions are especially poor in ease of handling in printing, when viewed from the point of developing the use as an ink for printing.

However, Patent Literature 13 does not disclose or suggest a photosensitive resin composition which exhibits excellent properties when used as a ink for screen printing.

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