Dielectric properties of highly filled thermoplastics for printed circuit boards

In this study, highly filled high-temperature thermoplastics (polyethersulfone [PES], polyphenylensulfide, polyetherimide [PEI], and polyetheretherketone [PEEK]) are used as insulating substrate for printed circuit boards (PCBs). Talc has been added to the thermoplastics to adjust their coefficient of thermal expansion (CTE) to the CTE of the copper circuits, thus reducing the possibility of failure of the PCB owing to thermal stress. The dielectric properties of the substrates were analyzed between 10 MHz and 1 GHz, depending on filler fraction and water absorption. An increase of filler fraction resulted in an increase of dielectric constant epsilon. As expected, the absorption of water molecules led to an increase of both tan and epsilon. Moreover, the combination of filler and absorbed water resulted in a strong increase of the dielectric loss factor at low frequencies. Finally, theoretical approaches with fitting parameters could be employed to precisely describe the measured properties between 0.8 and 1 GHz. This study shows that most of the materials investigated here, namely highly filled PPS, PEI, and PEEK, are suitable for high-frequency PCB applications. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013