Thin-Film Eddy Current Sensors for Proximity Detection in Smart Capillary Pick-and-Place

The eddy current sensor is a representative nondestructive sensing technique that enables sensitive interrogation of the conductive object surface in close proximity. Here, we propose an eddy current-based proximity detection strategy using a micropatterned inductor fabricated on a thin-film substrate (25 μm thickness) for integration as a smart, in situ inspection modality in advanced capillary pick-and-place systems. Notably, the eddy current sensing mechanism exhibited small sensitivity to liquids, allowing successful proximity detection during capillary pick-and-place operations. Our new suggested sensor consists of a copper inductor micro-fabricated on one side of a thin polyimide film surface, while the other side is roughened in nanoscale by argon plasma treatment. This new design offers several advantages: (1) enhanced eddy current induction efficiency enabled by thickness reduction, achieving an inductance change of up to 54.7% upon copper contact; and (2) facile release of lightweight objects due to reduced surface adhesion during the pick-and-place process. We verified the electrical and eddy current sensing characteristics of the micropatterned inductors via experiments and finite element simulations. We then further explored the in situ sensing capability during capillary pick-and-place operation by measuring the impedance change over time. The decreased adhesion of the plasma-treated polyimide surface was verified by atomic force microscopy and supported by an analytical model. We envision that this approach provides a promising strategy for advanced manufacturing applications requiring high reliability and nondestructive in situ monitoring during pick-and-place operations.