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Printable Sub-200 C nanoCu Solder
Keywords: nanoCu Solder, LEDs, PCBs
At the Advanced Technology Center of the Lockheed Martin Corporation, we have developed a pure copper solder paste material that can be processed below 200 °C. The approach enabled by our controlled fabrication process of Cu nanoparticles, which 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. We found a specific mixture of surfactants that best controls particle size and prevents oxidation. XRD, SEM and HRTEM confirm 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 LEDs onto PCBs using a paste formulated with a consistency very similar to standard SAC solder paste. These results have gotten us a big step closer to drop-in replacement for lead-based and SAC solder. Once fully optimized, the pure copper electrical interface material is expected to produce joints with 10x electrical and thermal conductivity compared to the tin- and lead-based materials currently in use.
Alfred A. Zinn, Senior Staff Member
Lockheed Martin Space System Company
Palo Alto, CA

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