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Abstract

For instance, when a washing-free yet low-residue type of flux is coated on a solder resist film, soldering can be carried out while no solder balls remain on a circuit substrate. A photosensitive resin composition comprises a photopolymerizable and photosensitive resin having at least one of a carboxyl group and an onium group, a photopolymerizable reactive diluent, a photopolymerization initiator, a thermosetting component, and an inorganic powder having an average particle size of 2 .mu.m to 20 .mu.m. A cured film thereof is used as a solder resist film for circuit substrate fabrication. A washing-free yet low-residue type of flux is so uniformly coated on the solder resist film that soldering can be carried out in the absence of any solder ball. The resulting film is improved in terms of various properties such as resistance to heat and chemicals by adding the thermosetting component thereto, and is improved in terms of the ability to be developed due to the presence of the carboxyl group and can be developed by use of water alone when the onium group is introduced therein. Circuit substrates can be fabricated with high reliability and high productivity.

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First Claim