Solvent Free Liquid Photoimageable Solder Mask

PROJECT SUMMARY: A novel chemistry is proposed for solder mask coatings on printed circuit boards (PCBs). This chemistry permits 100% solids application, eliminating objectionable solvents. The innovative chemistry uses a hardener blocked with a reactive component. This hardener is added to suitable monomers and oligomers containing acid (COOH) functionality along with photosensitizers and photoinitiators to comprise part A of a two part epoxy resin system. Following mixing and coating, the material is heated to dissociate the blocked hardener, resulting in partial cross linking of the epoxy, forming a tack free (B-Stage) surface. The coating is patternable with UV light which through a free radial photoreaction results in selective polymerization of the coating. The exposed material is developed with a 1% sodium or potassium carbonate water solution. A final heat cycle after developing reacts the residual hardener, acid and epoxy to form the D-Stage final material. This program will demonstrate feasibility of this approach by demonstrating this material on real circuit board blanks at a commercial printed circuit board vendor and subjecting these boards to appropriate electrical tests. This pervassive innovation could eliminate the 6 million pounds/yr. of solvents currently released in the U.S. as a byproduct of PCB fabrication. Anticipated Benefits: Environmentally conscious Printed Circuit Board Chemicals could have a global impact.