Characterization of Laser Sintering of Copper Nanoparticle Ink by FEM and Experimental Testing

In the last few years, inkjet printing of functional materials for electronics applications has been studied intensively, and significant progress has been made in developing ink materials and deposition techniques. Though sintering, the process of turning liquid nanometallic ink into its final and functional form, has also been studied, the traditional convection-oven-based heat treatment yet remains the common sintering method. High process temperature and long process time both limit the usability of inkjet printing as they restrict the selection of substrate materials and consume most of the overall fabrication time. Several sintering methods have been studied as alternatives for thermal sintering, but so far none of them have been widely adopted. We studied laser sintering of copper nanoparticle ink to gain an understanding of the process and the main variables affecting it. Laser sintering was also studied by thermal modeling, and the results are used to explain the behavior of process. Process parameters comprised substrate material and thickness, application of an insulator layer on top of the silicon wafer, laser scanning speed and optical power, and thickness of the printed structure. Comparison of modeling and test data shows that though the temperature of the printed structure can be used to plan the sintering process, it alone cannot explain the test-based conductivity results.