Development of electronic packages from polypropylene/ethylene propylene rubber blends: A double percolation approach

Abstract

Volume resistivity of less than 10⁴ W.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 carbon black is preferable in the 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 were 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 as conductive filler 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. The blends evidently provided a reduced percolation threshold with the electrical conductivity values greater than those of the CB filled PP composites. The percolation threshold of the obtained PP/EPR/CB composites was initially observed at the change in their volume resistivity of about 8 orders of magnitude. To achieve the volume resistivity of 10⁴ W.cm, the CB content in the blend can be reduced at least 50% compared to the composite using neat PP as a matrix. Scanning electron microscopy has been used to verify the preferential location of the conductive particles and to reveal the complex morphology developed. The results presented in this study show the possibility of specially designed polymer compositions for conductive applications.