Patent ID: 7476484

Claim:
A process for producing a solder mask on a printed circuit board, comprising the steps: a) coating of a circuit board with a layer of a photocrosslinkable composition comprising: A1) a linear, crosslinkable polyurethane obtained from monomers comprising i) at least one diisocyanate having 2 to 30 carbon atoms; ii) at least one aliphatic or cycloaliphatic diol having 2 to 30 carbon atoms, to whose carbon chain one or more carboxyl groups have been covalently bonded, and some or all of the carboxyl groups have been esterified with an olefinically unsaturated C 3 -C 8 alcohol or with a glycidyl ester of an olefinically unsaturated C 3 -C 8 carboxylic acid; and (iii) radicals of at least one aliphatic, cycloaliphatic or cycloaliphatic-aliphatic diol, or at least one oligomeric or polymeric oxaalkylene glycol, one polyesterdiol, polycarbonatediol or polylactonediol, or of a diol based on polybutadiene or polyisoprene; A2) an initiator for thermally crosslinking olefinic groups and/or a photoinitiator; and A3) optionally a diluent; b) drying of the layer on the circuit board; c) imagewise exposure of the layer under a negative photomask or by laser inscription; d) treatment of the layer with a developer for removing unexposed parts to produce the solder mask; and e) optionally heat-curing of the solder mask.