Development of an isothermal lubricating layer model for injection pultrusion of electronic prepregs

The current process for manufacturing electronic prepregs uses solvent-based resin systems. Solvents are environmentally unfriendly and contribute to voids in the pre-preg, which are a source of product variability. Prepreg inconsistencies are one of the major sources of scrap on the board shops. To overcome these drawbacks, a solvent-less process is currently being developed in our laboratory. The process is based on the concept of injection pultrusion or continuous resin transfer molding (RTM). The centerpiece of the process is an impregnation die. Glass fabric and resin are fed into the die where fiber impregnation and partial resin cure occurs depending on the material chemo-rheology. The B-staging is finished in an oven located immediately after the die. A key to the success of the process is being able to predict the pulling force. Fabrics used in electronic prepreg manufacturing are relatively fragile; they could be damaged if the pulling force is too high. A model to predict the pulling force, based on the formation of a continuous lubricating layer between the die surface and the moving fabric, has been developed and experimentally tested using model fluids.