Nanosecond pulsed laser transmission welding of cyclic olefin copolymer

Laser transmission welding (LTW) is a technique for joining a transparent polymer to an opaque polymer. This paper presents the results of nanosecond pulsed laser (1064 nm) transmission welding of cyclic olefin copolymer (COC). COC has a wide range of applications in biological, biomedical, membrane, and semiconductor fields. LTW has advantages over conventional adhesive and thermal-based methods of bonding. These include precision sealing and minimised heat affected zone, which makes this process favourable for bio-applications. The effect of laser processing parameters, such as the laser pulse energy and the laser scan speed, on the weld morphology as well as on the bonding strength was studied via cross-sectional optical microscopy and lap shear tests. The lap-shear strength of laser bonded COC substrates achieved lap-shear strength of 0.15 N mm⁻² to 0.5 N mm⁻² which is comparable to the strength found in adhesive bonded substrates. These studies provide novel insights into the welded region at the interface of the two materials and demonstrate the impact of laser parameters on the weld seam width and bond strength. Leak tests were performed on laser welded fluidic channels and no leakages were detected. Further, the analysis of lap-shear tests demonstrates that laser welding produces joining strengths similar to those of adhesive-bonded COC. The joining interface area for laser welding is in general smaller than that of adhesive bonding, which potentially can enable more design freedom and capacity for accommodating complex functionalities on a singular COC-based device.