Absorber-Free Quasi-Simultaneous Laser Welding For Microfluidic Applications

Absorber-free laser transmission welding is a novel welding technique which enables joining of polymers with the same optical properties. As no absorber is needed, this method is especially predestined for the encapsulation of transparent polymers for life science applications such as microfluidic devices. Due to the high welding seam densities and lengths of microfluidic devices, it is crucial to keep the thermal stress low in order to avoid the formation of cracks and distortions. On top of that, a melt flow into the channel structures has to be avoided to ensure the correct operation of the device. Therefore, a precise energy deposition into the interface during the welding process has been the subject of research for many years. One promising approach is a quasi-simultaneous welding technique where the laser beam is guided along the welding contour multiple times at high feed rates of up to several m/s. In the present work, a welding process is developed to encapsulate microfluidic devices by using this technique. In order to avoid heat accumulation, the welding contour was divided in several segments. By defining an irradiation sequence for each segment, a homogenous heat distribution on the sample can be achieved.