Quasi-Monolithic All-in-One TEG-PCM Systems: Reducing Thermal Interfaces via Multilayer PCB Technology

Engineering systems increasingly demand multifunctional and energy-efficient integration within constrained volume and energy budgets. One promising solution is the monolithic integration of components and functions to minimize occupied volume and simplify control interfaces. Paraffin-based phase change material (PCM) actuators provide high mechanical work density and can be coupled with thermoelectric generators (TEGs) for multifunctional operation. However, their dynamic response is typically constrained by the intrinsically low thermal conductivity of PCM materials. This work introduces a quasi-monolithic fabrication method for a fully integrated TEG-PCM system combining standard four-layer printed circuit board (PCB) technology and CNC milling. By constructing the system as a quasi-monolithic block, thermal interface materials are considerably reduced, thereby diminishing parasitic thermal resistance and promoting faster heat transport from the TEG to the PCM cavity. The system is fabricated using CNC milling with high depth resolution enabled by an electrical sensing-via structure. Experimental validation shows a 76% improvement in displacement rate (15.03 µm/s) at half the input power (1 W) compared to a conventional hybrid-assembled TEG-PCM actuator system consisting of a commercial TEG and an aluminum PCM container. The exploitation of the PCM as a thermal flux modulator for energy harvesting has been preliminarily investigated; considering the measured 5 K temperature difference sustained during a simulated short “day–night” cycle, an estimated open-circuit voltage of ∼13.5 mV is expected to be retrieved under load-match conditions. The actuator is compatible with PCB-based power management and thermal routing, enabling scalable incorporation into compact microsystems and multifunctional MEMS devices.