NASA EPSCOR: Electrical and Mechanical Characterization of Carbon Nanotube Filled Conductive Adhesives

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. Replacing the metal particles with multiwall carbon nanotubes (MWNTs) can produce ICA compositions with high electrical conductivity and high mechanical strength. Our preliminary results with 0.8 wt% MWNT ultrasonically dispersed in epoxy resin yield a volume resistivity of 6.4 x 10-4 ohm-cm and average contact resistance of 0.82 ohms while retaining 80% of the polymer's shear strength. We are currently evaluating thermoplastic resins, additives and mixing techniques; and measuring AC impedance, thermal conductivity, thermal expansion coefficient, and mechanical properties. Single wall carbon nanotubes (SWNTs) are grown by pulsed laser vaporization at the Johnson Space Center. SWNT and MWNT filled conductive adhesives have the potential benefits of being lead free, low process temperature. lightweight, corrosion resistant, and high strength. The proposed research will evaluate the electrical and mechanical properties of various adhesive formulations and compare results of both SWNT and MWNT fillers. We plan to visit JSC at the start of the project to exchange ideas, review the proposed experiments, identify measurement capabilities and instrumentation available at UK and JSC, and exchange materials. During the experimental work we will communicate by phone and email as needed, but no less than monthly to share results and request advice. A second trip to JSC will be planned for the end of the project to present the final results. Based on the collaborative measurements, shared materials, and experimental results we anticipate at least one joint journal publication. At the second visit we will also discuss opportunities to pursue additional joint funding for nanotechnology research.