Rheological characterization and statistical modeling of resin flow of no-flow polyimide prepreg in rigid-flex printed circuit lamination

Low coefficient of thermal expansion (CTE) prepreg is used, instead of the conventional high-CTE material like acrylic adhesive, as a bonding sheet to improve the reliability of rigid-flex printed circuit (RFPC). No-flow polyimide prepreg is then developed to fulfill the requirement of minimizing resin flow. Thermal characterization of no-flow polyimide prepreg reveals the resin behavior when a heat load is applied. Differential scanning calorimetry analysis reveals the process window when the resin starts to melt and then cure. Rheological tests further help us to observe the change in viscosity when the temperature rises as well as the resin flow effects at different heating rates (HRs). Moreover, a study of design of experiment (DOE) reveals that the HR, pressure and conformal material will have a significant impact on the resin flow of the no-flow polyimide prepreg in RFPC lamination. The combination of the resin behavior and DOE result provides the necessary information to achieve an optimized RFPC lamination process with minimized resin flow.