surface of a printed circuit board under inspection while
NIR enables imaging underlying layers and associated
Combining these different bands can yield additional
information and make quality control imaging more effective in capturing miniscule defects as well as in meeting other inspection standards.
Polarization is another property of light that can
produce valuable quality control data based on phase
detection, said He. Material attributes that can change
polarization include stress inside a layer and surface
“You can actually detect the thickness of a film, a
transparent thin film,” said He. “You cannot see that
with conventional technology because it’s transparent.”
He predicted that because of such capabilities, polarization imaging will increasingly be part of the standard QC
Advances in processing
Other innovations that could lead to better QC per-
formance involve the use of multiple illumination ap-
proaches, such as bright-field, dark-field and backlight.
These highlight defects differently and make inspection
more productive. Combining these different techniques
has been avoided because each required its own pass,
slowing down the inspection process, said He. To address
this problem, Teledyne Dalsa has developed a camera
that uses different color channels for different lighting
illumination, allowing single-pass scanning.
Such advances are possible, in part, because improvements in silicon have resulted in faster chips that benefit
both image processing and automated decision-making.
This increased capacity has been accompanied by growing expertise on how to best use it, said Brandon Treece,
senior product marketing manager for data acquisition
and control at National Instruments Inc. The Austin-based company supplies image processing software and
Some processors, such as CPUs, require that each operational step in an algorithm executes before the next
can begin. On the other hand, Treece said, an FPGA, or
field-programmable gate array, can execute the first op-
➤ Quality Control
Optical engineering enables rapid inspection of large pieces of glass for small defects.
A seal has multiple bubbles, including one that
breaches air tightness and is a defect.
➤ A subsurface imaging technique based upon
the polarization of light reflected off an object. The polarization of reflected light gives
information about the object’s absorption
properties that traditional intensity sensors
are not capable of obtaining. The characteristics gained through the technique coupled
with computer vision programs can effectively
complete image-segmentation and object orientation tasks, enabling novel techniques for
noninvasive surface and beneath-the-surface
See EDU.Photonics.com for this and other
definitions in the Photonics Dictionary and more
information in the Photonics Handbook.