Chemical Machining of Microscopic Holes and Grooves in Glass

This technique overcomes disadvantages of conventional macro- and micromachining.

A technique for making precise, microscopic holes and grooves in glass workpieces has been invented. The technique differs from both (1) traditional macroscopic mechanical drilling and milling and (2) conventional micromachining that involves etching through photolithographically patterned masks. The technique can be used, for example, to make holes between 20 µm and 1 mm in diameter.

The technique involves wet chemical etching, but unlike in conventional micromachining, the etch is localized. As shown in the figure, a hole in a glass workpiece is formed by use of a nozzle that contains at least one delivery channel and at least one return channel for the flow of an etchant fluid. Both channels open out to the tip of the nozzle. By use of a pressure pump at the far end of the delivery channel and/or a suction pump at the far end of the return channel, the etchant fluid is made to flow across the tip of the nozzle. The flowing etchant dissolves and carries away the glass along the flow path in the tip region. Unlike in conventional machining, the surface of the workpiece does not become roughened by abrasion, and there is no contamination by particles of workpiece material.

The shape and width of the resulting hole or groove is determined by the size and shape of the nozzle. As etching proceeds, the nozzle is either moved deeper into the workpiece to deepen the hole or else moved laterally (along the surface of the workpiece) to lengthen the groove. The nozzle can be fabricated, to the required precision, by use of photolithography and deep trench etching. The movement of the nozzle can be automated easily with computerized control. The precision of the movement, and thus of the final product, can be as high as 1 µm; such a level of precision has been demonstrated in robotic equipment commonly used in micromachining in a clean room.

This work was done by Kirill Shcheglov and William Tang of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com/tsp under the Manufacturing & Prototyping category.

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