Characterization of carbon nanotube filled conductive adhesive

In response to environmental legislation, the lead-tin alloys commonly used for soldering are being replaced with lead-free alloys and electrically conductive adhesives. Lead-free alloys usually require higher reflow temperatures than the traditional lead-tin alloys, which can impact the assembly yields. Isotropic conductive adhesives (ICA) are an alternative to solder reflow processing, however, ICAs require up to SO wt% metal filler to achieve minimum electrical resistivity. The high loading content degrades the mechanical properties of the polymer matrix and reduces the reliability and assembly yields when compared to soldered assemblies. Carbon nanotubes (CNTs) have many novel properties and these properties make if possible to provide electrical conductivity for the polymer matrix while maintaining or ei'en reinforcing the mechanical 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, multiwall nanotubes (MWNTs) with different dimensions are mixed with epoxy. The relationships among MWNT's dimension, volume resistivity and viscosity of the composite are characterized. Different loadings of CNTs, additives and mixing methods were used to achieve satisfying electrical and mechanical properties and pot life. Different assembly technologies such as pressure dispensing, screen and stencil printing are used to simplify the processing method and raise the assembly yields. Contact resistance, volume resistivity, high frequency performance, thermal conductivity and mechanical properties were measured and compared with metal filled ICA and traditional solder paste.