Magnet-actuated loading of magnetic conductive high-viscosity droplets

The dispensing resolution of high-viscosity magnetic conductive adhesives is essential for the bonding of magnetic components. Here, a novel magnet-actuated loading method based on transfer printing is proposed. The core of the loading method is the forming and breaking of a cone-shaped liquid bridge. The complete loading process is simulated using a computational fluid dynamic technique. With the homemade device and electromagnetic needle-stamp, the loading process is experimentally investigated. According to the results, magnetic flux intensity, viscous force, and surface tension together dominate the formation of the cone-shaped liquid bridge from an adhesive film. For the formed cone-shaped liquid bridge, its geometry size is dominated by magnetic flux intensity, which is controlled by the variation of the initial distance between the needle-stamp and the adhesive film. As the initial distance decreases, the top area of the liquid bridge on the needle-stamp correspondingly increases and the adhesive effect on the needle-stamp gradually strengthens. After the liquid bridge breaking, the volume of loaded droplets adhering to the needle-stamp gradually increases from about 0.11 to 1.41 nL with the standard deviations less than 0.08. Moreover, these loaded droplets are transferred to the substrate by the microforce feedback, and a transferred droplet with a minimum area of about 0.01 mm2 is obtained. The presented method gets rid of the limitation of submicron needle-stamps, realizes the loading of sub-nL high-viscosity droplets, and has great potential in microdispensing and other related techniques.