1 / 16

Electrical and Mechanical Characterization of Carbon Nanotube Filled Conductive Adhesive

Electrical and Mechanical Characterization of Carbon Nanotube Filled Conductive Adhesive. Jing Li, PhD Candidate Dr. Janet Lumpp, Associate Professor Electrical and Computer Engineering Department University of Kentucky. Approach.

ernestoc
Download Presentation

Electrical and Mechanical Characterization of Carbon Nanotube Filled Conductive Adhesive

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Electrical and Mechanical Characterization of Carbon Nanotube Filled Conductive Adhesive Jing Li, PhD Candidate Dr. Janet Lumpp,Associate Professor Electrical and Computer Engineering Department University of Kentucky IEEE Aerospace Conference

  2. Approach • Sn-Pb solder alloys are being replaced with lead free alloys or electrically conductive adhesives. • Typical isotropic conductive adhesives contain up to 80 wt% metal filler with decreased mechanical strength. • Carbon nanotubes in epoxy are conductive at loadings < 5 wt% while maintaining strength of polymer matrix. • CNT properties • Electrical conductivity: 104 S/cm • Current Density: 1013 A/cm2 • Thermal conductivity: 6,600 W/mK IEEE Aerospace Conference

  3. Conductive Adhesives • One or two part polymer matrix + conductive filler (e.g. epoxy + Ag) • Lead free, no-clean, low cure temperature (typically less than 150°C) compared with solder joints • High volume loading (up 80 wt%) ensures electrical continuity but degrades mechanical properties • Isotropic and anisotropic conductive adhesives IEEE Aerospace Conference

  4. Particle to particle contact Flakes, spheres, CNT Single particle contact Metal or metal coated polymer spheres Isotropic vs. AnisotropicConductive Adhesives Fundamentals of Microsystems Packaging, R.R. Tummala, 2001. IEEE Aerospace Conference

  5. MWNT and Epoxy Materials • UK Center for Applied Energy Research • Continuous CVD reactor for growing CNT • 2.5 kg/day production rate of bulk MWNT • Substrates as large as 1400 cm2 • 100 m2/day capacity for arrays • Miller-Stephenson epoxies • Epon Resins 862, 815C • EPI-CURE 3234 IEEE Aerospace Conference

  6. Ultrasonic Dispersion of CNT • Low loadings can be dispersed in epoxy resin by ultrasonication • Viscosity is too high for loadings > 1 wt% Without ultrasonication With ultrasonication IEEE Aerospace Conference

  7. Mixing CNT Filled Resins • Viscosity increases dramatically with CNT loading • Difficult to disperse ultrasonically or mix manually • Air entrained in mixture, non-uniform batches • Planetary mixing - high g, high shear • Mixes higher loadings easily, homogenously • Mixes thoroughly without breaking CNT • De-airs batches, loaded syringes • Screen print or pressure dispense • Test patterns • Bond pads for zero ohm resistors • Area for four point probe • Bond pads for high frequency • Die attach pads IEEE Aerospace Conference

  8. DC Electrical Testing • Daisy chain test pattern • FR-4 printed circuit board • 1 ounce copper, tin plated • 1206 size, 0 W resistors • Average contact resistance • 8 resistors per chain • 8 chains per board • Four point probe • Large printed area Volume Resistivity Solder 1.5x10-5Wcm 0.8 wt% CNT in epoxy 6.4x10-4Wcm IEEE Aerospace Conference

  9. Mixing and DC Electrical Results • Ultrasonic dispersion in EPI-CURE 3234 • Manually mixed with Resin 862 - too viscous for ultrasonication • Resin:Curing agent ratio = 100:15.4 IEEE Aerospace Conference

  10. Mixing and DC Electrical Results • Ultrasonic dispersion in Resin 815C • Manually mixed with EPI-CURE 3234 • Resin:Curing agent ratio = 100:12 • Loading limited to 0.8 wt% • Same preparation • Planetary mixing • Thinner added IEEE Aerospace Conference

  11. Shear area force adhesive Mechanical Testing • Lap shear testing with FR-4 strips IEEE Aerospace Conference

  12. AC Electrical Properties • RT/duroid 5880 Cu clad substrate • Zero ohm resistor • Solder vs. 3 wt% CNT/epoxy • Up to 3 GHz S11 (dB) S21 (dB) IEEE Aerospace Conference

  13. Laser Flash Thermal Analysis • 1 - 5 wt% CNT in Resin 815C epoxy • Molded in cylindrical die, cured, sliced Thermal Diffusivity (mm2/sec) Temperature (C) IEEE Aerospace Conference

  14. Observations • Screen printing leaves a rough surface • Stencil printing and pressure dispensing smoother • Four point probe measurements unreliable • Rough printed surface and excess resin on surface • Measure cut surfaces from laser flash samples • Viscosity and pot life dependent on resin, curing agent and loading • Add solvent (thinner) to resin • Slow cure agent - higher viscosity IEEE Aerospace Conference

  15. Conclusions • Contact resistance is decreased by • Ultrasonic dispersion • Increased CNT loading • Planetary mixing of higher loadings • AC characteristics comparable to solder • 85% retention of epoxy mechanical strength • Thermal conductivity of epoxy increases with CNT wt% IEEE Aerospace Conference

  16. On-going Research • Evaluate cross-linking modification of CNTs • Evaluate full loading range to develop high strength to weight ratio, electrically and thermally conductive polymer materials • Reliability testing of CNT filled isotropic conductive adhesive for microelectronics • Sponsors • Army Research Laboratory (W911NF-04-2-0023) • Kentucky NASA EPSCoR IEEE Aerospace Conference

More Related