Development of a direct metalisation method for micro-engineering
Ng, Jack Hoy-Gig
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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.