Filtering device is made of polymer material perforated with multiple holes, and is installed in the flow of liquid to collect contamination. Using precise laser micromachining up to 30% of material is removed in active filter area. Special holes geometry assures that mechanical stiffness of material is adequate to maintain filter integrity through the life time of the filter. Polyimide materials like Kapton, Apical and Upilex are used due to excellent mechanical properties, low moisture absorption and compatibility with Excimer laser micromachining.
Excimer laser machining of polymers for the filtering devices has couple key advantages comparing to machining using chemical etching or mechanical drilling. Unlike chemical etching , excimer laser machining allows to create holes pattern with holes diameter smaller than the thickness of material. Existing limitation on holes diameter of the holes pattern is the taper of excimer laser machined holes (4.5 to 8 degrees), and characteristics of the projection lens used for machining. Practically, holes diameter can be as small as 2 um. Proper choice of laser beam shape and characteristics of the projection lens allows to machine couple thousand holes simultaneously. None of the other type of laser machining system including galvo steered triple frequency YAG or small frame Excimer laser can give this type of efficiency and quality of the holes. Fig.1 shows fragment of the filtering device.
Usually, size of the holes is defined at the holes exit side where diameter is smaller. Entrance hole diameter could be easily calculated from material thickness and taper. Tolerance on the holes diameter is usually +/-3um (3 sigma). Optical inspection with automated vision inspection system at magnification 500X is used to control machined area for holes diameter, pitch and absence of holes overlapping in the stitching area.
After pattern of holes is machined, the final filter is cut out using galvo based YAG system equipped with vision system to provide true position tolerances of the tooling holes location to filtering holes within .002″ (3 sigma).
Cleaning procedure is used to eliminate soot, residue and static build- up.
Laser machining and optical inspection take place in temperature control room and final operations (cleaning and packaging) are performed in class 100 clean room environment.