Patent ID: 7419769

Claim:
A method of forming bumps, the method comprising the steps of: applying a negative photoresist composition on a substrate of an electronic part to thereby form a resist film as a coating; irradiating the resist film with active light or radiant ray through a mask having a predetermined pattern; developing the exposed resist film; and plating portions from which the resist film has been removed; wherein the negative photoresist composition for the formation of thick films having a thickness of from about 5 μm to about 40 μm, comprising relative to the total 100 parts by weight of the following components (A) through (D) combined: (A) a novolak resin in the range of about 50 to about 95 parts by weight; (B) a plasticizer in the range of about 5 to about 30 parts by weight selected from the group consisting of: (i) an alkali-soluble acrylic polymer containing a constitutional unit derived from a (meth)acrylic acid derivative having an ether bond and an ester bond; (ii) an alkali-soluble acrylic polymer containing about 30 to about 90 weight percent of a constitutional unit derived from a (meth)acrylic acid derivative having an ether bond; (iii) an alkali-soluble acrylic polymer containing about 2 to about 50 weight percent of a constitutional unit derived from a polymerizable compound having a carboxyl group; and (iv) copolymer of 2-methyoxyethyl acrylate, benzyl methacrylate, and acrylic acid made from 65 weight percent 2-methoxyethyl acrylate, 25 weight percent benzyl methacrylate and 10 weight percent acrylic acid; (C) a crosslinking agent in the range of about 1 to 30 parts by weight; and (D) an acid generator in the range of about 0.01 to about 5 parts by weight.