Scalable Fabrication of 3D-Protruded Neural Microelectrodes Using Flexible PCB Technology for High-Fidelity Neural Interfaces

Flexible neural electrodes hold great promise for monitoring electrophysiological activity in the brain, but achieving both fabrication scalability and high signal fidelity remains a significant challenge. Conventional high-performance neural interfaces typically require complex and costly microfabrication processes, while simpler approaches often fail to optimize the electrode–tissue interface. Here, we introduce a scalable, cost-effective platform for fabricating high-performance three-dimensional (3D) neural electrodes using an industrial flexible printed circuit board (fPCB) process. We systematically compare two electrode architectures: (i) recessed microelectrodes with gold (Au) electroless plating, serving as a benchmark, and (ii) 3D protruded microelectrodes formed by tin (Sn) electroplating. To isolate the role of geometry, both electrode types were further functionalized with high-surface-area platinum black (Pt black) and poly(3,4-ethylenedioxythiophene) (PEDOT) coatings. Electrochemical analysis revealed that the Sn-protruded electrodes exhibited lower impedance at 1 kHz and a higher charge storage capacity (CSC) than Au-recessed electrodes. In vivo recordings from the mouse hippocampus further demonstrated that Sn-protruded electrodes achieved a significantly higher signal-to-noise ratio (SNR) and stronger spike amplitudes compared to both bare and coated Au-recessed electrodes. These findings establish 3D protruded electrode geometry as a key determinant of recording fidelity, primarily by reducing the electrode–neuron distance. More broadly, our results demonstrate that the fPCB-based approach provides a rapid, accessible, and scalable route to high-performance neural interfaces, highlighting its potential for widespread adoption in neural engineering.