Variations in brightness and light uniformity can introduce error
into machine-vision systems used in semiconductor wire bonding. A
time-consuming and somewhat unpredictable technique to compensate
for light variations, which involves attaching a diffuser surface
to one side of a machine-vision system’s condenser lens, is
now being replaced by the use of a holographic diffuser/condenser
lens assembly.
Kulicke & Soffa Industries Inc. (K&S), a US producer of
semiconductor-manufacturing equipment, uses ultrasonic technology
to bond gold or aluminum wire to a silicon chip to prepare it for
installation into a printed circuit board. The illuminator in the
machine-vision system in the computerized wire bonder uses LED-generated
light to help govern die alignment and wire placement.
To compensate for LEDs’ inconsistencies in brightness, light
structure and light distribution, K&S has traditionally glass-bead-blasted
and lacquered a diffuser surface to one side of an off-the-shelf
condenser lens. But this process is difficult to control, often
resulting in undesirable lens variations. Now K&S uses a holographic
diffuser/lens optical component to overcome deviations in the software-controlled
LED used in the wire bonder's machine-vision system, leading to
what it says are noticeable improvements in brightness and light
uniformity.
Manufactured by Torrance, Calif.-based Physical Optics Corp., the
new optics assembly in the K&S wire bonder integrates two complex
optical elements – a holographic Light Shaping Diffuser (LSD)
attached by a high-precision process to the plano side of a standard
glass condenser lens.
Reference-point location
The LSD homogenizes and shapes the light before feeding it through
the focusing condenser lens, allowing the wire bonder's pattern-recognition
system to easily locate reference points on the die pad. The holographic
diffuser/lens works with fewer surfaces than the components in the
previous setups and is prealigned. It enables the machine to bond
the tiny wires – typically about 0.001 in. in diameter –
with more precision and accuracy than was possible with the manually
applied diffuser surface.
Based on refraction rather than diffraction, the LSDs used in
the wire bonder homogenize and transmit more than 90 percent of
the LED light, enhancing image quality and machine performance.
These surface-relief holographic elements shape light by precisely
controlling the energy distribution along the horizontal and vertical
axes, allowing engineers to match the light source with the area
requiring illumination. As a result, the diffuser/lens optical component
helps increase the throughput of Kulicke & Soffa’s wire
bonder, while also improving the reliability and quality of the
bonded semiconductors.
Contact: Stan Szczesniak, Kulicke & Soffa Industries Inc, 2101
Blair Mill Road, Willow Grove, PA 19090; (215)784-6000; FAX, (215)784-6850;
Rick Shie, Physical Optics Corp., 20600 Grammercy Place, Building
100, Torrance, CA 90501-1821; (310)320-3088; FAX, (310)320-8067
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