Online proceedings - EDA Publishing Association

Unfortunately, this fabrication method is slow and
cannot readily be used to produce complex 2D and
3D parts.
TABLE I.
PHYSICAL PROPERTIES OF SAPPHIRE [FROM 1]
11-13
May 2011, Aix-en-Provence, France
Property
Value
Density (kg/m 3 ) 3970
Knoops Hardness (kg/mm 2 )
1800 (║c-axis),
2200 ( ┴ c-axis)
Hardness in Mohs’ scale 9
Young’s Modulus (GPa) 345
Flexural Strength (kpsi) 100
Compressive Strength (kpsi) 425
Poisson’s Ratio 0.29 – 0.30
Optical Transmission (nm) 170-5500
Dielectric Constant
11.53 (║c-axis),
9.35 ( ┴ c-axis)
Resistivity (ohms cm) 10·10 16
Thermal Coefficient (1/°C)
5.41·10 -6 (║c-axis),
4.31·10 -6 ( ┴ c-axis)
Melting Point (°C) 2050
Boiling Point (°C) 2980
Fig.2. SEM image of diamond abrasives on steel wire [3].
One of the very few illustrations known of a sapphire
micropart is a 0.25mm thick sapphire gear wheel
made at Laser Zentrum Hannover, Germany (Fig. 3).
It was used in a fluid sensor and was machined by
multiple passes of higher harmonic 355nm
wavelength radiation from a Nd:YAG laser with a
high peak power intensity of 10 7 – 10 8 W/cm 2 .
Successful machining was attributed to the short
pulse length and superior beam quality [4]. However,
a later publication acknowledged a problem
associated with the effects of laser machining;
namely “Among these undesired effects is the
damaging of the rear side of thin wafers formed while
surface structuring and drilling blind holes” [5].
Fig. 3. A 0.25mm thick sapphire gear wheel made by multiple
passes of 355nm wavelength laser pulses for high precision with
no microcracking (Courtesy of A. Ostendorf and Laser Zentrum
Hannover, Germany) [5]
In an attempt to fabricate crack-free, extremely
durable, optically-clear microcomponents, the authors
have investigated and compared various methods of
fabricating sapphire parts by both non-contact laser
machining [6] and contact diamond machining [7].
II. MATERIALS AND EQUIPMENT
The manufacturing challenge is to fabricate
microparts suitable for use in mechanical watches
and instruments from sapphire discs 31mm in
diameter and 1.2mm thick. Currently, scratch-proof
watch “glasses” are made from sapphire and, very
recently in January 2011, a new design of “seethrough”
sapphire watch dial was advertised in the
horological press. Apertures are stated to have been
fabricated using a laser, but no technical details have
been released, to the knowledge of the authors [8].
In our research, several types of lasers have been
used in order to machine the synthetic c-plane
sapphire disks provided.
As there is a vast range of laser beam machining
systems available these days, collaborations with
specialist laser facilities located in the UK and The
Netherlands were instigated. The collaborating
universities and companies were requested to drill
circular holes of diameters ranging between 0.5 mm
and 3.0 mm, and/or to machine a curve in the
periphery of the disk. Due to the lack of experience in
the machining of 1.2mm thick sapphire samples (such
as those used throughout this project), the laser
technology available for each of the lasers chosen
was applied according to the interpretation of each of
the specialist technicians involved in the machining
processes.
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