Effect of Bed Temperature on the Laser Energy Required to Sinter Copper Nanoparticles

Copper nanoparticles (NPs), due to their high electrical conductivity, low cost, and easy availability, provide an excellent alternative to other metal NPs such as gold, silver, and aluminum in applications ranging from direct printing of conductive patterns on metal and flexible substrates for printed electronics applications to making three-dimensional freeform structures for interconnect fabrication for chip-packaging applications. Lack of research on identification of optimum sintering parameters such as fluence/irradiance requirements for sintering of Cu NPs serves as the primary motivation for this study. This article focuses on the identification of a good sintering irradiance window for Cu NPs on an aluminum substrate using a continuous wave (CW) laser. The study also includes the comparison of CW laser sintering irradiance windows obtained with substrates at different initial temperatures. The irradiance requirements for sintering of Cu NPs with the substrate at 150–200°C were found to be 5–17 times smaller than the irradiance requirements for sintering with the substrate at room temperature. These findings were also compared against the results obtained with a nanosecond (ns) laser and a femtosecond (fs) laser.