For application to synthetic resin parts and to the fabrication of microfluidic devices made of cyclo-olefin polymer (COP), an adhesiveless bonding technology was developed: photo-activation bonding. A Xe excimer lamp irradiating vacuum ultraviolet (VUV) light of 172 nm wavelength was used as a light source for COP surface modification. The surface modification procedure is extremely simple. A COP plate placed in air with atmospheric pressure is irradiated with the VUV light. Based on VUV photochemistry assisted with atmospheric oxygen, a modified layer including large amounts of polar functional groups (-OH, -CHO, -COOH, etc.) is formed on the COP plate. The VUV-modified COP plates were bonded at a low temperature through attractive interactions between the modified layers on the COP plates without deforming the plates' preformed microstructures. A strength test of bonding was conducted to elucidate the effects of surface modification and bonding conditions such as VUV-irradiation distance (d VUV ), VUV-irradiation time (t VUV ), bonding pressure (P B ), bonding temperature (T B ), and bonding time (t B ).
A photochemical process was applied to form an active surface layer on cyclo-olefine polymer (COP) for improved immobilization of palladium. A Xe excimer lamp irradiating vacuum ultraviolet (VUV) light of 172 nm wavelength was used as a light source for surface modification. COP samples placed in dry air with atmospheric pressure were irradiated with VUV light. Because of the dissociative excitation of oxygen molecules, atomic oxygen species were generated along with ozone molecules formed through the following chemical reactions of the oxygen atoms. These active oxygen species served as oxidants for COP surface modification. Based on VUV photochemistry assisted with oxygen, known as the oxygen-amplified VUV process, an oxidized COP layer with thickness of several tens of nanometers was formed on each COP sample. The layer, which contained highly concentrated hydrophilic functional groups such as -OH, -CHO, and -COOH, functioned as an adsorbing site for palladium catalysts. Consequently, this technique has been found to be effective as a pre-treatment of Ni-P electroless plating. Electroless Ni films with sufficient adhesion to pass the cross-cut tape test were deposited on the VUV-modified COP substrates. Direct patterning without photolithography has been demonstrated for fabricated Ni micropatterns.
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