Film-Assisted Shape-Locking Assembly for Complex Freestanding 3D Electronic Architectures

3D electronic architectures offer unique capabilities that are inaccessible to planar electronics because of their out‑of‑plane geometries and omnidirectional interfaces. Mechanically guided buckling assembly enables programmable 3D architectures in diverse, high‑performance materials, yet the elastomer substrate that drives this transformation remains attached, limiting system-level integration and deployment in certain application scenarios. Here, the study presents a film-assisted shape-locking assembly strategy that replaces the elastomer substrate with flexible thin films or flexible printed-circuit boards to lock post-buckled 3D structures while providing a platform for direct electrical interconnection. Nonlinear finite-element analysis quantitatively captures the coupled processes of 3D buckling assembly and thin-film-assisted shape-locking, enabling predictive design across diverse 3D geometries and materials. Multi-step and multi-level assembly using an ordered shape-locking strategy enables complex 3D topologies, with generality demonstrated by dozens of highly complex freestanding 3D structures. Representative applications include two 3D flow sensors, one measuring unidirectional liquid flow in small-diameter tubes and the other resolving airflow magnitude and direction via a trained artificial neural network. This substrate-agnostic approach offers robust mechanical stability and scalable manufacturing while supporting expanded design freedom and integration density, enabling seamless deployment of freestanding 3D electronic architectures in flexible electronics and robotics.