This thesis examines various direct metallization methods for microelectronics and
advanced manufacturing. The reason for this lies in that these methods do not require
vacuum-based metal evaporation, complex equipment or multi-lithographic steps. They
also eliminate copper waste, as they require no etching, and the need of toxic materials
and inert gases. Novel direct metallization methods have been developed for insulating
substrates such as glass, silicon, polydimethylsiloxane, thermoplastic polyurethanes and
liquid photosensitive acrylic resins.
The thesis starts with the investigation of a direct metallization method of the modified
photosensitive 2-diazo-2H-naphthalen-1-one (DNQ)-novolac polymer. This was
achieved through mixing a positive photoresist with silver salt. Silver ions were
thermally reduced to silver nanoparticles inside the polymeric matrix, which allowed a
deposition of the electroless copper onto the nanocomposite. This method resulted in the
electroless copper films of 0.44 ± 0.05 μm in thickness and (1.6 ± 0.4) ✕ 107 S/m in
conductivity.
Due to the growing interest in using 3D printing for fabricating electronics, another aim
of this thesis is to examine the metallization of newly developed 3D printable
thermoplastic polyurethanes. This was carried out by loading polyurethanes with silver
ions through an ion exchange mechanism. Surface-modified polyurethanes were
exposed to a blue light in order to photo-reduce silver chloride to silver nanoparticles.
The photo-reduced silver nanoparticles served as catalysts for the deposition of
electroless copper, which resulted in a sheet resistance of (139.4 ± 7.2) mΩ/☐.
Being able to modify the liquid photosensitive resin that is used for digital light
processing (DLP) 3D printing made it more favorable for use in direct metallization. It
was modified with AgClO4 before printing. Once the 3D printed structure was
immersed into electroless copper solution, silver ions acted as catalysts for copper
deposition. The resultant electroless copper reached a conductivity of
(0.29 ± 0.05) ✕ 107 S/m. The interchanged printing with the modified and unmodified
resin allowed a selective metallization in which the former was coated with the
electroless copper, while the latter was left unaffected
