Microwave Processing of Thin Sheet Materials

Accomplishments of this project included inventing and optimizing the applicator design using finite-element modeling and experimental testing; design, specification, and installation of a prototype prepreg system; formulating flame-retardant, water-based resins suitable for circuit board manufacture; characterization of solvent and water evaporation; and the fabrication of circuit cards from microwave-processes, water-based resins.
These accomplishments resulted from a multi-faceted team effort. Prior to designing the microwave applicators, a computer modeling program was chosen and implemented. This finite element model was the key tool for developing the understanding necessary to invent and optimize applicators that would provide the necessary uniformity in prepreg heating. In parallel, a prototype prepreg tool was designed and built to specifications. This tool was itself a significant technical challenge because it had to be not only safe and compact for installation in a research laboratory, but it also had to be a good model for a manufacturing tool. A third parallel effort was directed towards developing water-based resins for prepreg manufacture. Because one of the main advantages of microwave processing is its ability to efficiently heat aqueous mixtures; a key goal of this project was to formulate water-emulsified resins as alternatives to the conventional, solvent-based prepreg resins. This achievement required testing many candidate mixtures to find one that would process properly and meet a long list of specifications for printed circuit cards. An important related effort was the characterization of solvent and water evaporation in prepreg processing. Evaporation must occur in a controlled manner to avoid defects in the prepreg from bubbling. A computer model for the drying process was adapted and implemented. This model gave the necessary insights which guided the final culmination of all these efforts - the first successful processing of the degree of cure across the web demonstrated that the prepreg was uniform and within specifications, prototype circuit cards were prepared by conventional lamination and copper etching.