Authors: A. Zinn, R. Stoltenberg
Affilation: Lockheed Martin Space Systems Company Adv. Technol. Center, United States
Pages: 71 - 74
Keywords: nanocopper, lead-free solder, solder-free electronics
The Advanced Technology Center of the Lockheed Martin Corporation developed a copper-based electrical interconnect material that can be processed at 200 °C, dispensed using 75 micron size syringe tips and has shown electrical & thermal conductivity approaching that of bulk copper. The controlled Cu nanoparticle fabrication process takes advantage of the rapidly increasing melting point depression as the particle size decreases to the nanoscale. The readily scalable synthesis of Cu nanoparticles uses a low cost solution-phase chemical reduction approach. XRD, SEM and HRTEM confirmed the formation of stable Cu nanoparticles less than 10 nm in size and the effectiveness of the surfactant mixture to prevent oxidation. We have demonstrated assembly of fully functional LED test boards Cu nanoparticle paste with a consistency similar to standard solder and a tap density of around 6g/ccm. Further improvements have led to the assembly of an operational small camera board with a 48 pad CMOS sensor QFN chip. The fused material shows decent tensile strength. Once fully optimized, the pure copper electrical interface material is expected to produce joints with 10x electrical and thermal conductivity compared to tin-based solders currently in use and a bond strength comparable to that of eutectic SnPb.