Implementation of a shadow mask for direct writing in abrasive jet micro-machining

Abrasive jet micromachining uses a jet of high-speed particles to erode a wide variety of materials. Since the air driven jet is highly divergent, the edges of the desired features are usually defined using a mask which is attached to the surface of the target material. This paper presents an alternate technique using shadow masks that can be moved over the surface, thus allowing direct writing of features on the surface. This eliminates the additional cost and time of fabricating and attaching traditional masks. The technique was used to machine straight channels in borosilicate glass, and their quality was compared to those machined using traditional clamped masks. The channels machined using the shadow mask were found to be approximately 10% wider than those machined using clamped masks up to an aspect ratio of approximately 0.5. Under these conditions, the shadow mask channels were bounded on the edges by lightly-eroded, frosted regions approximately 60 μm wide. The effects of nozzle standoff, shadow mask standoff, particle size and mask thickness on the frosted regions and the channel width were studied. To create a direct-writing device, a crossed arrangement of two mutually perpendicular sets of shadow masks was used to generate arbitrarily curved paths. These crossed shadow masks resulted in less frosting than did the parallel masks.