Microencapsulated Liquid Metals for the Autonomous Restoration of In-Mold Electronic Circuits

In-mold electronics (IME) is a revolutionary way to form three-dimensional molded films with printed circuitry. However, thermoforming and molding processes inevitably cause microcracks in the printed circuit lines that lower the electronic conductivity. Here, two types of microcapsules containing liquid metals, gallium (Ga) and gallium-indium (Ga-In), in a poly(urea-formaldehyde) shell are synthesized, and their potential as an additive in restoring the conductivity of circuit lines for IME is assessed. Because the microcapsules have good chemical compatibility with Ag paste, they are uniformly distributed in the circuit lines. Tensile test results show that both Ga and Ga-In microcapsules efficiently reduce the resistance increase due to fractured structures after stretching. Nevertheless, incorporating an excess amount of microcapsules results in a fragile matrix in Ag lines, and the aggravated damage causes the resistance to exceed that without microcapsule addition. Compared to the Ga microcapsules, the Ga-In microcapsules perform better in restoring circuit lines, and the reason is discussed.