Carbon nanotube filled conductive adhesives for aerospace applications

Polymer matrix composites with multi-wall carbon nanotube (MWNT) filler improve the thermomechanical and electrical properties of the host material. The high electrical conductivity of MWNT induces a low percolation threshold in the polymer to produce electrically conductive epoxies at loadings of less than 10 wt% MWNT. Applications of these conductive adhesives address issues such as lead-free environmental legislation, metallic corrosion, tin whiskers, and lightweight electronic assemblies. MWNT filled adhesives are electrically comparable to lead-tin alloys commonly used for soldering and commercial metal filled electrically conductive adhesives. Aerospace applications also require increased strength to weigh ratio, heat dissipation and static charge dissipation. We are currently investigating the dependence of electrical and thermo-mechanical properties on loading, aspect ratio of the carbon nanotubes and various sources of carbon nanotubes. Measurements include DC resistivity, AC parameters, lap shear, laser flash thermal analysis, and volume resistivity. Commercially available isotropic conductive adhesives require up to 80 wt% metal filler to achieve minimum electrical resistivity, however the high loading content degrades the mechanical properties of the polymer matrix. Replacing the metal particles with MWNTs in ICA compositions has the potential benefits of being lead free, low process temperature, corrosion resistant, high electrical conductivity, high mechanical strength and lightweight. Preliminary results show that thermal diffusivity increases with MWNT loading compared to pure epoxy and mechanical strength is improved when compared with metal filled adhesives. Accelerated aging tests in 85C/85%RH are also underway to determine the reliability of the bonds. Carbon nanotubes filled epoxies are suitable for pressure dispensing, spin coating, stencil printing and extrusion for fabrication of structural and electronic assemblies.