Laser-induced crosslinking polymerization of acrylic photoresists

Multifunctional acrylate photoresists have been polymerized within milliseconds by laser irradiation to produce an insoluble polymer network. The polymerization reaction and the insolubilization process were both followed quantitatively by infrared spectroscopy. The most sensitive system consisted of a morpholino-ketone photoinitiator, a triacrylate monomer, and an amino-polyester tetra-acrylate oligomer. An energy as low as 0.1 mJ cm(-2) proved to be sufficient to achieve insolubilization of a 36 mu m thick film upon exposure to a Kr+ laser beam (337 nm) in an inert atmosphere. These highly photosensitive materials are well suited for the manufacturing of printed circuit boards by a laser direct imaging technology. Dry acrylate photoresists were found to be less sensitive than wet photoresists because of severe mobility restrictions in the solid state. A similar drop in photosensitivity was observed when wet acrylate photoresists were exposed to the 488 nm emission of an argon ion laser because of the lower efficiency in radical production of visible photoinitiators. (C) 1997 John Wiley & Sons, Inc.