UV Direct-Writing of Metals on Polyimide

TL;DR

This paper presents a novel UV direct-writing method to fabricate conductive copper micro-patterns on polyimide using a silver seed layer and electroless copper deposition, enabling precise, in-air fabrication on contoured surfaces.

Contribution

Introduces a new UV direct-writing technique combining silver seed layer formation and electroless copper plating on polyimide, allowing accurate, facile patterning in ambient conditions.

Findings

Copper tracks match photomask patterns accurately

Laser writing achieves smaller line widths with good precision

Process works in air and on contoured surfaces

Abstract

Conductive micro-patterned copper tracks were fabricated by UV direct-writing of a nanoparticle silver seed layer followed by selective electroless copper deposition. Silver ions were first incorporated into a hydrolyzed polyimide surface layer by wet chemical treatment. A photoreactive polymer coating, methoxy poly(ethylene glycol) (MPEG) was coated on top of the substrate prior to UV irradiation. Electrons released through the interaction between the MPEG molecules and UV photons allowed the reduction of the silver ions across the MPEG/doped polyimide interface. The resultant silver seed layer has a cluster morphology which is suitable for the initiation of electroless plating. Initial results showed that the deposited copper tracks were in good agreement with the track width on the photomask and laser direct-writing can also fabricate smaller line width metal tracks with good accuracy. The facile fabrication presented here can be carried out in air, at atmospheric pressure, and on contoured surfaces.