Dustfree prepreg and method for making an article based thereon

This invention relates generally to forming of resin-impregnated cloth, and more particularly to forming improved resin-impregnated fiberglass sheets and the resultant sheets which are specially adapted for use in forming chip carriers and the like, and which have improved resistance to generating dust particles during forming operations. A method for coating cloth especially fiberglass sheets with a thermosetting resin and resulting structure is provided. The coating is performed in two steps. In the first step, essentially all of the strands of the fiberglass are coated with the resin/solvent mixture while maintaining at least some of the interstices or openings essentially free of the solvent mixture. This first coating is then partially cured to between about 70% and 90% of full cure. The coated fiberglass with partially cured resin thereon is then given a second coating of either the same or different thermosetting resin mixture which coats the first coating and fills in the interstices between the fibers. This second coating is then partially cured, which advances the cure of the first coating past 80% full cure and results in an impregnated fiberglass cloth structure for use as sticker sheets. During lamination, the first coating acts like an impenetrable insulating sheet, preventing resin displacement and, therefore, preventing glass fiber contact with the conductive planes. The second coating is fluid enough to fill in spaces in the planes and to form the adhesive bond to cores and conductive layers. The structure reduces the tendency of the resin to flake and produce dust during subsequent processing operations.