Precision Welding of Microfluidic Seams, Repeatability of 10 µm

Microfluidics are gaining in significance because they offer an increasing number of biological analysis opportunities, especially in areas like lab-on-a-chip. German laser welding equipment manufacturer LPKF has a laser system that enables the creation of completely new product layouts for this component.

The functional zone in a microfluidics unit generally consists of planar surfaces. The lower component has channels created by hot stamping. The upper cover is placed on top to seal the channel structure. The channels are so fine that the capillary forces dominate and gravitational forces can be ignored.

Laser welding has established itself as the technology of choice for creating the highly precise join between the upper and the lower components. It can combine the two parts without damaging the sensitive channels with interfering particles, melt blow-out or additives.

The LPKF PrecisionWeld is reportedly able to create weld seams with a thickness of only 100 µm. Positioning repeatability is 10 µm. It has been said that this level of precision has never been achieved before by any technology in this field. This is achieved constructively by mechanically decoupling the housing from the processing compartment.

The system has a scanner system to guide the laser beam, as well as a positioning table. This expands the effective working area to 320 mm x 320 mm. An integrated camera system allows the detection of specially applied fiducial marks or uses the geometrical elements of the component. This allows compensation for tolerances in the component and in the component holder.

With the LPKF PrecisionWeld, parts can be joined using the classic transmission laser welding technology as well as the new LPKF ClearJoining technology. In transmission laser welding, the two parts to be joined have different absorption properties, for example a laser-absorbing basal unit has a clear cover plate. The laser beam passes through the laser-transparent upper component but is absorbed when it hits the lower part, so that the energy in the light is converted to heat and melts the plastic. A moderate joining pressure is applied which promotes thermal conduction into the upper part to produce a reliable and precise weld seam. This technology has established itself as transmission laser welding. 

Because it has a laser wavelength of 1,940 nm, the LPKF PrecisionWeld is also capable of joining two transparent components. This takes advantage of the new LPKF ClearJoining technology: at this wavelength, most technical polymers absorb enough of the light to melt at high energy densities. The laser beam is focused very precisely on the welding horizon to apply the energy where it is required to create a weld—without additives.

The system also has an automatic focus setting which identifies the surface of the component and automatically adjusts the focus to the optimal position.