Powderblasting is a flexible, cost-effective and accurate technique to create fluidic channels and interconnections. Because of the use of a lithographic mask position accuracy is very good, within 2 µm. Feature size accuracy is about 25µm. Layout and design of the holes and channels can be very flexible.
First of all, the design of the channels and holes is transferred onto the glass by means of photolithography: a photoresist film is laminated on the glass and the mask with the design is positioned above the film. The film is then illuminated with UV light through the mask. Illuminated areas willl be removed from the glass during development.
Powder blasting process
The wafer is now powderblasted. During the exposure of the wafer to the powder the areas not covered by film are etched, while the covered areas deflect the powder. The etch rate and depth can be controlled by controlling the time and particle speed.
With sophisticated powderblasting equipment the glass substrate with the developed film can be processed. By processing by lithography and powderblasting, the complexity of the design is irrelevant (when the design meets the tolerances) and only one mask is needed when processing more substrates.
Shape and rougness
Shaped wells can be round or rectangular. The sides of the wells will not be completely vertical, but sloped at an angle of 70 degrees (tolerance depending on specifications). Well shapes can be round, rectangular or triangular.
The average roughness of the channels will be between 0.8 and 2.5 µm, also depending on the process chosen.
After the powderblasting process, the substrate can be bonded to another glass or silicon substrate. As the surfaces of the powderblasted substrate remain undamaged, polishing the surface is not necessary.