Evaluation of carbon-filled polymer composites for future base substrate and integral resistor applications

Future packaging with multi-layered high-density wiring and direct-chip-attach requires substrates having superior thermomechanical properties such as no CTE mismatch with the attached IC chip and high stiffness. Various novel polymer composites were evaluated in this work and compared to the conventional FR-4 substrates in order to assess their candidature for future base substrate applications. Carbon cloth, milled fibers and nanofibers have many attractive properties such as negative CTE, high modulus and were hence pursued in this work. The manufactured carbon-polymer composites showed CTE in the range 2-3 ppm/K and significant improvement in stiffness (50 GPa at only 36 vol. % loading). In related work, polymer composites with carbon black and conductive carbon nanofibers were evaluated for embedded resistor applications. Resistivities in the range of 0.2 - 1.5 Ohm cm were obtained. These composites show lot of potential for future electronic packaging applications both by simplifying the build-up process and eliminating the underfill materials.