Negative photoresist compositions for the formation of thick films, photoresist films and methods of forming bumps using the same

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.