Electrical and mechanical characterization of carbon nanotube filled conductive adhesive

Electronic assemblies rely heavily on soldering to attach components to the interconnect wiring on printed circuit boards and other types of substrates. In response to environmental legislation, the lead-tin alloys commonly used for soldering are being replaced with lead-free alloys and electrically conductive adhesives. Isotropic conductive adhesives (ICA) filled with metal particles are an alternative to solder reflow processing. ICA materials, however, require up to 80 wt% metal filler to achieve minimum electrical resistivity and the high loading content substantially degrades the mechanical properties of the polymer matrix. Carbon nanotubes (CNTs), a new material based on C60 Fullerenes (Bucky Balls) and graphite rolls have many novel properties. Replacing the metal particles with carbon nanotubes in ICA compositions has the potential benefits of being lead free, low process temperature, corrosion resistant, high electrical conductivity, high mechanical strength and lightweight. In this paper, new conductive adhesives were formulated by adding multiwall nanotubes (MWNT) as filler to epoxy. Different loadings of CNTs and mixing methods were used to make the new conductive adhesives. Contact resistance, volume resistivity, high frequency performance, thermal conductivity and mechanical properties were measured and compared with metal filled ICA and traditional solder paste.