Fabrication of mechanically reliable micrometric scale conductive pattern by direct pattern transfer using UV photopolymer penetration

Abstract

A mechanically reliable micrometric scale conductive wire fabrication method was developed using silver paste. In order to increase the bonding strength between silver particles, a method was developed for filling the space between particles with UV photopolymer. The UV photopolymer covers the top of a mold filled with silver paste, after which vacuum forces are generated by the evaporation of the solvent in the silver paste and the density difference between the UV photopolymer and the solvent. This results in the penetration of UV photopolymer into the silver paste. The UV photopolymer fills the interparticle air gaps inside the silver paste and positively modifies the mechanical strength of the conductive pattern. A conductive wire with a minimum line width of 10 µm was successfully fabricated on a polyethylene terephthalate film using silver paste with a particle size of 300 nm. The height of the wire is defined by the penetration depth of the UV photopolymer into the silver paste, which is a function of the resting period between applying the UV photopolymer coating and UV illumination to induce UV photo-polymerization. The penetration affected the spreading of the silver paste, resulting in favorable resistance values. A numerical analysis of the UV photopolymer penetration depth was done for validation and was consistent with the experimental results. The developed method enables large-area replication of micrometric scale conductive wire on a flexible substrate using a simple process and instrumentation with improved conductivity per unit area.