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Laser and water-jet manufacturing processes are independently used to cut monolithic and composite ceramics. While these processes offer many advantages over diamond sawing and other abrasive processes, the energy efficiency, precision, cutting speed, and environmental threats remain as barriers to their continued success. This is partly attributed to the material removal mechanisms, which are melting, and subsequent evaporation (laser) and energy-intensive erosive wear (water jet). In this paper, we describe a novel laser and water-jet (LWJ) hybrid manufacturing process that enables the synergistic effects of CO2 laser and pressurized pure water jet, facilitating precise material removal by thermal shock-induced fracture and overcoming the deficiencies listed above. Experiments of the LWJ effects on the cutting of aluminum nitride, an electronic ceramic substrate, are presented. The most exciting results are very narrow kerf dictated by the crack width; the absence of thermally affected zone, slag formation, chemical decomposition; and controlled thermal cracking, implying that the LWJ process is far superior to conventional laser cutting of ceramics. The LWJ process also improved the surface finish while reducing energy losses in the process. The practical realization of the LWJ manufacturing process could be a potential alternative to diamond saw, high-power laser, and high-pressure abrasive water-jet methods for machining hard and brittle ceramics.

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The challenging issues in conventional microfabrication of SiC pressure sensor diaphragms from bulk wafers are low etch rates, thicker (>40 µm) diaphragms, low spatial resolutions, rough surfaces and substantial contamination. In via hole drilling of SiC, the critical concern is the low drilling speed (nm per minute). In this work, femtosecond (fs)-pulsed laser ablation was conducted to overcome some of these deficiencies. Circular diaphragms (0.5 to 1 mm) by trepanning mode and via holes (30-50 µm) by percussion drilling mode were micromachined in 250 µm thick 4H-SiC single crystals using an 800 nm wavelength, 120 fs, 1 mJ Ti:sapphire laser. Pulse energy, number of pulses and scan rate were varied to obtain a high etch rate and high quality features. Results showed that the etch rates are 2-10 µm per pulse, diaphragm thicknesses are 20-200 µm, surface roughness is 1-2 µm Ra and via hole drilling speeds are up to 25 µm per second. The etch depth control was well within ± 1%. High aspect ratio features with excellent spatial resolutions were obtained due to the absence of thermal damages such as a recast layer and contamination. Thus, femtosecond-pulsed laser ablation by virtue of its unique characteristics such as multiphoton ionization and the absence of lattice heating offers high speed, precision and accuracy in micromachining 4H-SiC wafers.

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