Development of a direct metalisation method for micro-engineering
Abstract
This research concentrates on the establishment of a metalisation and micro-patterning
technique that eliminates metal evaporation and/or photoresist molding procedures.
The process design is chosen from the analysis of the broad field of direct metalisation
techniques where novel photocatalysts or photoreducing agents are increasingly
employed to create new processes.
The new photolithographic process in this study introduces two novel photoreducing
agents for additive metal thin film fabrication: methoxy poly(ethylene glycol) and
photosystem I. This work proves the concept of using light energy to directly reduce
metal ions incorporated within an ion-exchanged polyimide substrate to produce metal
thin films. The patterning step can be operated at atmospheric pressure, in a dry
environment, using a coating of the photoreducing agent. This process offers a
significant improvement to prior related work that relied on a water layer to enable the
metalisation. Of particular importance for this process is the influence of light energy
dose and heat treatment, which promote silver nanoparticles growth at the cost of
degradation of the substrate polymer. The investigation was carried out thoroughly by
laser writing experiments for a selected range of laser power and scan speed. To
complement the phenomenon observed in the laser experiments, prolonged UV light
exposure time and heat treatment experiments were carried out to confirm the
hypothesis postulated in this thesis.
The morphology of the silver nanoparticles produced, the changes of the substrate
surface and the adhesion of electroless plating were characterised. Results indicate that
UV irradiation with the energy density required for reasonable production speed causes
inevitable molecular damage to the polymer substrate. Photosystem I was found to be
able to catalyse the production of visually similar silver thin film by light sources in the
blue region. Using a similar light intensity, the exposure time was reduced by an order
of magnitude whilst the degradation phenomenon observed during the UV process
appears to be eradicated. With the fundamentals of the process established in this
thesis, future optimization is suggested for the transition from a proof of concept to
industrial implementation.