Comparison of methods for measuring flow of resin in electrical laminating prepregs

In the complex process of constructing a printed circuit board, the control of the initial prepreg production is critical. The currently used methods to characterize prepreg performance involve some assessment of resin reactivity and prepreg flow. This paper compares the results of using a method of flow measurement based upon the rheological performance of B-staged resin during cure, with those generated using more conventional methods of prepreg flow evaluation. An empirical analysis is presented which indicates that the rheological measure is much less dependent upon the process variable of resin content, and may therefore be regarded as an intrinsic measure of flow. The observations of this study are summarized in terms of the implications of the proposed approach for setting specifications for prepreg flow according to the conventional methods of flow measurement. In this regard, once the “B-staged” prepreg has been characterized by rheological indexing to meet the requirements of a particular press cycle, then effective prepreg production process control may be achieved through accurate monitoring of dust gel time and resin contents