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Research Papers

Experimental Investigations of Laser Micromachining of Nickel Using Thin Film Micro Thermocouples

[+] Author and Article Information
Hongseok Choi

Department of Mechanical Engineering, University of Wisconsin-Madison, 1513 University Avenue, Madison, WI 53706

Xiaochun Li

Department of Mechanical Engineering, University of Wisconsin-Madison, 1513 University Avenue, Madison, WI 53706xcli@engr.wisc.edu

J. Manuf. Sci. Eng 130(2), 021002 (Mar 07, 2008) (8 pages) doi:10.1115/1.2816021 History: Received June 11, 2007; Revised September 14, 2007; Published March 07, 2008

Laser-material interactions during laser micromachining are extremely complicated. In order to improve the fundamental understanding of the laser micromachining process, it is essential to investigate the complex phenomena and mechanisms of the physical processes within and close to the region of the interaction. Moreover, C-type micro thin film thermocouples with a junction size of 2×2μm2 were fabricated to increase the maximum operation temperature and spatial resolution of sensors. Surface temperature distribution around the laser spot was obtained in the range from 45μmto85μm away from the center of laser spot. The result showed that there was a steep gradient of temperature in the radial direction and a superheated area around the laser spot. Topographical characterizations of laser micromachining with various laser energy fluences were undertaken to correlate the resulting geometry changes with surface temperature measurements. Possible changes of surface chemical composition induced by the laser micromachining process, in particular, oxide formation, were also investigated around the laser spot.

Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

(a) Experimental setup for laser micromachining. (b) Process flow for fabrication of micro-TFTCs.

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Figure 2

(a) 3D image of surface topography obtained by the interferometric profiler: blue color represents areas below the surface. (b) Cross-section profile of the micromachined hole.

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Figure 3

3D image and profile of surface of prepared nickel workpiece (with a silicon nitride thin film on top). (a) 3D image of nickel surface topography. (b) Cross-section profile of nickel surface.

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Figure 4

Design of micro-TFTCs

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Figure 5

(a) Micro-TFTCs fabricated on the Si3N4 thin film layer of the nickel workpiece and (b) magnified image of four micro-TFTCs

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Figure 6

(a) Photograph of micro-TFTCs after selectively etching of the Si3N4 and Ti layers and (b) magnified image of an area near the junctions of four micro-TFTCs.

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Figure 7

Image of micro-TFTCs after wire splicing

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Figure 8

Calibration of C-type micro-TFTCs

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Figure 9

Dynamic response of micro-TFTCs: (a) Transient output signal after laser pulse; (b) Zoom-in view of the transient response

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Figure 10

Temperature distribution in radial direction

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Figure 11

(a) Temperature distribution around laser spot with melting, boiling point, and micromachined area. (b) SEM micrograph of a hole micromachined with a single pulse with a laser energy fluence of 20.37J∕cm2.

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Figure 12

Relationship between laser energy fluence and (a) depth and (b) diameter of laser micromachined holes

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Figure 13

Effect of laser energy fluence on surface temperature at 100μm away from the center of the hole and depth of micromachined hole

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Figure 14

EDS line scans for oxygen and nickel around laser spot micromachined by (a) a single pulse and (b) 14 pulses with a laser energy fluence of 40.74J∕cm2

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Figure 15

SEM micrograph with oxygen distribution from EDS scan

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Figure 16

EDS line scans for oxygen and nickel around laser spot micromachined using 14 pulses with a laser energy fluence of 20.37J∕cm2

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