Photosensitive resin composition and circuit substrate employing the same

A photosensitive resin composition which is prepared by combining 1 to 20 parts by weight of a photopolymerization initiator as an essential component with respect to 100 parts by weight of a siloxane-containing polyamic acid resin containing 50 to 80 mol % of a structural unit represented by the following formula (1), 5 to 30 mol % of a structural unit represented by the following formula (2), and 5 to 30 mol % of a structural unit represented by the following formula (3):

• wherein
• Ar represents a tetravalent tetracarboxylic acid residue in which carboxyl groups are removed from an aromatic tetracarboxylic acid, R1 represents an alkyl group having 1 to 6 carbon atoms or phenyl group, R2 represents an alkylene group having 2 to 6 carbon atoms or phenylene group, l represents a number of 0 to 10, R3 represents a divalent group or a direct bond, R4 represents a group represented by CH2═CH—R6—, R6 represents a direct bond, an alkylene group having 1 to 6 carbon atoms, or a phenylene group, R5 represents a divalent diamine residue in which an amino group is removed from a diamine compound, except in the case of the divalent diamine residue being diamine residues in the formulae (1) and (2), and m, n, and o represent abundant molar ratios of the respective structural units, where m is in the range of 50 to 80, n is in the range of 5 to 30, and o is in the range of 5 to 30.