Powercell Packaging Using a Structural Electronics Approach

Abstract In-Mold Structural Electronics (IMSE) fabrication is an advanced manufacturing method that integrates electrical functionality into 3D form factors, providing design freedom and device simplification while delivering size, weight, and power (SWaP) advantages over traditional bulky electronics assemblies. IMSE products, for instance those emergent in the automotive industry, are commonly constructed by screen printing circuit patterns onto flat, thermoplastic substrates that are then molded into electronic 3D surfaces. This approach to IMSE requires flowable, electrically conductive inks that suffer from stability and aging problems and do not perform as well as bulk metal conductors. Additionally, the reliance on thermoplastics for IMSE devices precludes their operation in environments of extreme temperature and pressure and limits their durability. We aim to extend the utility of IMSE and thereby increase the potential application space for the technology by integrating more robust materials, namely metal foils for circuitry and moldable thermosets for substrates, into the IMSE manufacturing process. Here we focus on process development for construction of an IMSE powercell package using these new materials, a distinct departure from the human-machine interface devices (buttons and sliders) that dominate current IMSE applications. Adhesive-backed copper foils were laser patterned while adhered to their final substrates with circuit design considerations to accommodate ensuing forming stresses, including serpentine traces and pad migration offsets. We iterated the designs of both circuitry and 3D printed molds for the powercell package, resulting in traces and structures optimized for ease of formability, alignment, and resistance to delamination. For the thermoset substrate material we adapted the chemistry of frontal ring-opening metathesis polymerization (FROMP) of poly-dicyclopentadiene (pDCPD)—a triggerable and energy-efficient curing process—to be compatible with IMSE manufacturing. Addition of the Grubb’s 2nd Generation Catalyst (GC2) in the presence of an inhibitor resulted in pDCPD gel-like materials that could be cast into sheets, patterned with copper foil circuitry, vacuum-formed into 3D structures, and then locked into shape via FROMP autocatalysis at ambient temperatures. However, production of pDCPD gel sheets using this formulation proved inconsistent. Therefore, we developed an inhibitor-free approach using the latent catalyst UltraCat that enabled rapid and reproducible manufacturing of thermoset gel sheets for IMSE. Finally, the formed and FROMP-cured battery cell packages were assembled into functional power devices using standard soldering techniques. These devices displayed minimal damage when subjected to vibrational environments. The development of moldable thermosets in conjunction with forming-tolerant, patterned metal circuitry represents a breakthrough for IMSE that will enable 3D structural electronics’ integration into demanding architectural, automotive, and extraterrestrial applications.