Geometry‑Driven Design of Conductive Tracks for Uniform Heating in Thermoformed 3D In‑Mold Electronics

Abstract

Thermoforming enables two-dimensional printed circuits to be converted into three-dimensional (3D) structures for in-mold electronics (IME), enabling electronic functionality to be integrated/embedded directly into molded plastic parts. However, during thermoforming, the substrate and printed conductors stretch and thin unevenly, creating resistance variations that lead to localized heating and reduced current-carrying capacity. This work demonstrates how conductive track geometry can be designed to compensate for these effects. Using screen-printed silver molecular inks on polycarbonate substrates, we compare the electrical performance of flat (two-dimensional, 2D) and thermoformed (3D) tracks and examine how localized widening of tracks in high-elongation regions influences performance. By selectively widening tracks in the elongated regions of thermoformed 3D conductors, resistance becomes more uniform and current-carrying capacity improves by at least ∼20%, approaching those of the analogous 2D tracks. Applying these design principles to compensate for thermoforming-induced changes in track resistance enabled the development of 3D serpentine heaters with a more uniform resistance distribution. The resulting temperature uniformity of the 3D serpentine heater improved from 50% to 74%. These results show that simple geometry modifications can minimize thermoforming-induced resistance variations and provide practical design guidelines for creating reliable 3D-printed electronic circuits for use in IME applications.