Direct Printing of 1-D and 2-D Electronically Conductive Structures by Molten Lead-Free Solder

This study aims to determine the effects of appropriate experimental parameters on the thermophysical properties of molten micro droplets, Sn-3Ag-0.5Cu solder balls with an average droplet diameter of 50 mu m were prepared. The inkjet printing parameters of the molten micro droplets, such as the dot spacing, stage velocity and sample temperature, were optimized in the 1D and 2D printing of metallic microstructures. The impact and mergence of molten micro droplets were observed with a high-speed digital camera. The line width of each sample was then calculated using a formula over a temperature range of 30 to 70 degrees C. The results showed that a metallic line with a width of 55 mu m can be successfully printed with dot spacing (50 mu m) and the stage velocity (50 mm.s(-1)) at the substrate temperature of 30 degrees C. The experimental results revealed that the height (from 0.63 to 0.58) and solidification contact angle (from 72 degrees to 56 degrees) of the metallic micro droplets decreased as the temperature of the sample increased from 30 to 70 degrees C. High-speed digital camera (HSDC) observations showed that the quality of the 3D micro patterns improved significantly when the droplets were deposited at 70 degrees C.