To obtain the subject composition with excellent processability for e.g. fine blind via holes by incorporating an alkali-soluble curing resin with specific two kinds of particulate substance so as to compatibilize its impact resistance, heat resistance, flame retardancy and electrical insulation reliability and others with one another.

This composition is obtained by incorporating (A) an alkali- soluble curing resin composition [pref. comprising a carboxyl-bearing alkali- soluble (meth)acrylic polymer, a polymerizable compound having at least one C=C unsaturated double bond, an ultraviolet polymerization initiator, a ultraviolet polymerization sensitizer, and a thermal polymerization-initiator] with (B) a particulate substance <1 μm in size consisting of a carboxy-contg. elastic polymer (e.g. a crosslinked acrylic rubber), and (C) a 2nd particulate substance 1-10 μm in size consisting of a benzoguanamine-based resin (e.g. a benzoguanamine-formaldehyde condensate); wherein the amounts of the components B and C to be compounded are pref. 5 -40 wt.% and 10-40 wt.% based on the whole composition.