RESEARCH AND DEVELOPMENT OF CONDUCTIVE POLYPROPYLENE COMPOSITE FOR ELECTRONIC PACKAGING

Abstract

Volume resistivity of less than 104 ohm.cm is required for typical electrically conductive packages. Conductive polypropylene (PP) packages with the above level of conductivity value can be achieved by a use of carbon black (CB) as conductive filler. To maintain processability of PP with low cost, minimal amount of CB is preferable in the formulated conductive composites. By introducing a second polymer with immiscible or partially miscible nature to the first polymer, and if the conductive filler is localized in one polymer phase, a system of double percolation with minimal filler content can be achieved. In this work, electrically conductive composite packages are prepared from polymer blends of PP and ethylene propylene rubber (EPR) with CB as conductive filler (PP/EPR/CB). PP/EPR mixtures at the weight ratios between 100/0 to 50/50 were blended with CB filler with loadings ranging from 0 to 30 wt% by melt mixing in an internal mixer at 200 oC for 10 min, followed by compression molding at the same temperature. The PP/EPR blends were found to be partially miscible in nature with significant enhancement in percent elongation of the PP and its CB-filled composites. The blends evidently provided a reduced percolation threshold by one half with the obtained electrical conductivity values greater than those of the CB filled PP composites. Scanning electron microscopy has been used to verify the preferential location of the conductive CB particles in EPR domains better than in the PP domains and to reveal the partially miscible blend morphology developed. The obtained tensile and impact properties of conductive composites were also found to provide the values meet those industrial requirements with a competitive material cost. The obtained conductive composites show great possibility of specially designed polymer compositions for electronic package applications.