CO2 laser micromachined crackless through holes of Pyrex 7740 glass

The drilling of glass through holes with a high aspect ratio is crucial for microsystems application, especially in the inlet/outlet connection of microfluidic devices for biological analysis or for the anodic bonded silicon-glass ones. Traditional glass drilling using mechanical processing and laser processing in air would produce many kinds of defects such as bulges, debris, cracks and scorch. In this paper, we have applied the method of liquid-assisted laser processing (LALP) to reduce the temperature gradient, bulges and heat affected zone (HAZ) region for achieving crack-free glass machined holes. The nominal diameters of circles from 100 to 200 μm were drawn for through glass machining test. Through-hole glass etching can be obtained by LALP for 10 passes of circular scanning in several seconds on conditions of a 6 W laser power, 76 μm spot size and 11.4 mm/s scanning speed. The ANSYS software was also used to analyze the temperature distribution and thermal stress field in air and water ambient during glass hole machining. The higher temperature gradient in air induced higher stress for crack formation while the smaller temperature gradient in water had less HAZ and eliminated the crack during processing. CO2 laser micromachining under water has merits of high etching rate, easy fabrication and low cost together with much improved surface quality compared to that in air.