Modeling of Resin Flow in Reinforced Dielectric Prepregs

Abstract

Manufacturing of printed circuit boards or chip-packaging substrates involves the use of resin-filled reinforcement materials, known as prepregs, to bond together laminates with patterned copper layers and serve as dielectric material. In the circuit board or substrate lamination process, the prepreg sheet is placed on top of the conductive copper patterns and pressure is applied to squeeze the resin out of the prepreg to flow and fill the gaps between the baseboard and the copper as well as drilled holes and vias. The primary processing requirement is for resin to fill all the gaps within reasonable time and pressure limits, before the resin cures to a hardened thermoset material. As the resin flow path may be nontrivial, it is desirable to model resin flow and filling of the gap as a function of applied pressure and lamination press closing rate so that one can successfully manufacture a variety of circuit board designs with different material systems. In this work, we model the flow during the filling of the gaps and justify noteworthy simplifications to provide a solution in closed form. This allows us to relate the material and process parameters such as prepreg thickness and applied pressure to the circuit board design. It also permits prediction of the transient development of gap filling. We illustrate the factors that influence the flow and fill process and discuss their importance. Finally, we analyze the process with typical material and processing parameters and compare it with laboratory scale and industrial experiments.