Presently, as a solder resist for part of the household grade printed wiring boards and for virtually all the industrial grade printed wiring boards, a liquid developing type solder resist which is to be irradiated with ultraviolet light and then developed to form an image and thereafter finally cured (finish curing) by heating or exposure to light is adopted from the viewpoint of ensuring high accuracy and high density. Further, with consideration for environmental problem, liquid solder resists of the alkali developing type which implement development with a dilute aqueous alkali solution as a developer have come to play the leading role. As such alkali developing type solder resists using a dilute aqueous alkali solution, for example, liquid resist ink compositions including an active energy ray-curable resin produced by the addition of a polybasic acid anhydride to a reaction product of a novolak type epoxy compound with an unsaturated monocarboxylic acid, a photopolymerization initiator, an organic solvent, and an epoxy compound like those disclosed in Patent Literature 1 have been used widely.
From an alkali-developable resist ink composition of the above-described configuration, a cured coating superior in fastness of adhesion, hardness, heat resistance, resistance to electroless gold plating, and electrical insulation property can be obtained via an application step of applying the composition to a printed wiring substrate, a drying step of volatilizing the organic solvent in order to enable contact exposure, an exposure step of contact exposing the dried coating, a development step of removing unexposed parts of the coating exposed in a desired pattern, by alkali development, and a thermal cure step for obtaining sufficient coating characteristics. The steps each have a significant role, and if even one of the steps is out of the proper specification conditions of a solder resist, a resulting coating will fail to have sufficient characteristics. For example, generally during exposure to light, a tool, called photomask, which is a polyethylene terephthalate (PET) film or glass having a desired pattern drawn thereon is placed on a dried coating, the pressure of an exposure environment is reduced for preventing the photomask from shifting in position during the exposure or oxygen inhibition during photoreaction, and the exposure is performed with the dried coating being in contact with the photomask under pressure. One probable problem with the exposure is the sticking of the photomask to the dried coating which will occur at the time of peeling the photomask after the completion of the exposure. One conceivable cause for the sticking is poor dryability to finger touch (the degree of tackiness) of the dried coating.