A Study on Fabrication of Curved Molded-Interconnect Device Using Thermoresponsive 4D Printing

4D printing is an advanced application of 3D printing with additional shape changes over time, which deforms additively manufactured parts using external stimuli. In this study, a thermoresponsive 4D printing method was developed to fabricate a molded-interconnect device (MID) with a curved shape. For this purpose, a flat MID keypad was designed to contain conductive circuits in a nonconductive plastic base. The flat MID keypad frame was then additively manufactured using a material extrusion (ME)-type 3D printer, by interactively inserting several conductors during the printing process. In ME-type printing, printing paths were programmed to have planar thermal anisotropy and thus induce bending deformation under thermal stimuli. A curved fixture was designed to install a hot air gun and thus guide thermal deformation to have the desired curvature, from which a facile 4D printing method could be developed with high dimensional accuracy and repeatability.