Oxidation Prevention and Electrical Property Enhancements of Copper-filled Electrically Conductive Adhesives for Electronic Packaging and Interconnection

This paper describes a novel manufacturing process and packaging applications of electrically conductive adhesives (ECAs) incorporated with copper (Cu) powders as electrically conductive fillers for environmentally friendly, low cost, high current capability/low contact resistance and improved reliability. Especially, we have studied isotropic conductive adhesives (ICAs) and anisotropic conductive adhesives (ACAs) using copper fillers for flip chip assembly. We have developed and characterized the Cu-filled ECAs by using an organic functional coating for oxidation prevention of Cu fillers, which are compatible to conventional Ag-filled ICA and Au coated polymer or Ni-filled ACA applications. The effect of the type of organic functional coating materials and the concentration on the electrical conductivity, the thermal stability and the reliability of Cu-filled ICAs were investigated for the potential alternatives of conventional silver-filled ICAs. The surface characteristics of organic functional thin films on copper surfaces such as their hydrophobicity, functionalization and thermal stability were also evaluated to compare the performance of antioxidant behaviors of different organic functional coating materials for Cu-filled ICAs. The low contact resistance and the stable contact resistance of Cu-filled ICA at high temperatures were achieved by addition of optimized concentrations of organic functional coating agents. Improved thermal stability and enhanced reliability of Cu-filled ICAs under high temperature and humidity condition were achieved by using high molecular weight and hydrophobic organic functional coating materials. . The bulk resistivity of ~10^-4 Omegacm of Cu-filled ICAs was achieved by a bimodal filler loading. The most important finding was the enhanced electrical properties of ACA interconnection by use of copper powder coated with an organic functional thin film layer. Three combinations of conductive fillers used in this study, whi- ch include Au-coated polymer ball, Au-coated Ni ball, and organic functional coating treated Cu ball in 5 mum diameter. The treated Cu ball-filled ACA showed the lowest contact resistance, 1.0 times10^-5 Ohm, higher current carrying capability and higher thermal stability of ACA joints compared with the conventional Au-coated polymer ball and Au-coated Ni ball-filled ACAs.