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Electrical and Mechanical Properties of Carbon Nanotube Filled Adhesives on Lead Free PCB Surface Finishes
Keywords: Carbon Nanotube Adhesive, Electrical properties, Mechanical properties
Electrically conductive adhesives are attractive alternatives to solder and die attach materials in electronic assemblies particularly in the lead free era. Compared to metal filled conductive adhesives, carbon nanotube (CNT) filled adhesives are lightweight, corrosion resistant, high strength and resistant to metal migration. Previous studies of CNT filled epoxies on bare copper printed circuit boards identified contact resistance as a challenge for surface mount components where pressure was required during curing to lower the average contact resistance. The adhesive we use is a mixture of epoxy epon resin 862, anhydride (MHHPA), catalyst and MWNTs with different loadings ranging from 2% to 8%. Currently, we are repeating contact resistance, volume resistivity, lap shear, die shear and environmental testing of CNT filled epoxy on printed circuit boards with various surface finishes on the copper pads. The surface finishes under investigation are immersion tin, immersion silver and electroless nickel immersion gold (ENIG). The volume resistivity decreases with increased CNT loading, as expected. To date, the mechanical properties (Lap shear and Die shear tests) exceed the test criteria on all surface finishes for all loadings. Contact resistance results vary with loading and surface finish. We are currently investigating the interface between the adhesive, component leads and circuit board pads.
Keerthivarma Mantena, Student
University of Kentucky
Lexington, KY

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