Laser Direct Structured 3D Circuits on Silicone

Silicone rubber is a biocompatible elastomeric polymer, with great potential for mechanical and biologic sensing applications, if electrical circuits can be reliably integrated. Laser direct structuring is a bottom-up circuit fabrication process, whereby copper is chemically grown on laser exposed regions of a modified substrate, promoting adhesion by laser roughening the circuit tracks. In this Research Article, we successfully demonstrate this process using superflexible biocompatible silicone (30 hardness on Shore 00) with copper chromite additive, cast into both 2D planar and 3D contour substrates. A horseshoe pattern circuit, meander and Hilbert fractal inductors, and a 3D hemispherical helix trace are fabricated and tested. The range of laser power and copper chromite concentration are explored. Mechanical testing is performed to determine breakage strain and elastic modulus. Material stiffness and trace peel strength are shown to increase with copper chromite concentration. Peel strength is measured to be very high, from approximately 1 to 5 kN/m, depending on dopant loading. With high adhesion and conductivity, the simple laser-writing process presented here enables high-quality circuit integration into elastomeric silicone.