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Laser Direct-Writing of Metals on Polyimide Substrates

David Watson, Jack Hoyd-Gigg Ng, Marc Desmulliez, Duncan Hand
A novel packaging solution is being developed at Heriot-Watt University which focused on laser direct-writing of metal tracks, coils and circuits onto flexible polyimide substrates... [read more]

A novel packaging solution is being developed at Heriot-Watt University which focused on laser direct-writing of metal tracks, coils and circuits onto flexible polyimide substrates. This method utilised the range of UV light energy density that induces rapid photoreduction of silver ions which were first ion-doped into the substrates by simple wet chemistry and common precursors. Without exceeding the energy threshold which causes photoetching of the substrates, the continuous-wave 375 nm laser were capable of fabricating narrow silver tracks with line width close to 6 µm with the present optical setup. By configuration of the optical systems, further reduction of the fabricated line width is currently under investigation. Selective electroless plating is then applied onto the silver deposits which are composed of catalytic surfaces of silver nanoparticle clusters in order to obtain conductive metal tracks with higher thickness. Since the direct-writing patterning step can be carried out in air, and no additional coatings, photoresist or evaporation is required on top of the substrate, the fabrication can be carried out on contoured or 3D surfaces provided that the mechanical positioning apparatus was set up for the continuous focusing of the laser beam.

Process steps