Moving AOI beyond the grey world
Moving AOI beyond the
grey world
by Shoich Rashed, Marantz Business Electronics Europe, Eindhoven, Netherlands
Moving AOI beyond the grey world An AOI system can be qualified as a
Most AOI systems deployed
Most AOI systems deployed in the elec- good machine if it matches its specified
in the electronics assembly tronics assembly industry use greyscale performance indicators: accuracy, sensitiv-
industry use greyscale image image processing to inspect circuit boards ity and specificity values. These values
processing to inspect circuit
and substrates. But some new-generation should be as close as possible to 100%.
boards and substrates.
equipment is taking advantage of colour These performance indicators are the
But some new-generation
imaging engines to extend the depth—quite statistical measures of the performance of
equipment is taking advantage
literally—of the analysis process. The objec- an AOI system by looking into its inspec-
of colour imaging engines
tive is to deliver a more confident result tion results in terms of true positives, false
by dramatically reducing the occurrence of positives, true negatives and false negatives.
to extend the depth—quite
false alarms—arguably the Achilles heel of This means that not only are the amount
literally—of the analysis
modern AOI efficiency. Industry observer of generated false calls or escapes a measure
process. The objective is to
David Hughes looks at the differences and to the quality of the AOI system, but also
deliver a more confident result
likely advantages of getting colourful. the results related to the number of inspect-
by dramatically reducing the Automatic optical inspection for populated ed test points. Another factor of quality
occurrence of false alarms— circuit boards is becoming more of an is the time spent to create a program to
arguably the Achilles heel
imperative for manufacturers looking to achieve the specified performance—this
of modern AOI efficiency.
keep productivity rates high while coping time should be as low as possible.
Industry observer David
with increasingly smaller components and So having the greatest real error detec-
Hughes looks at the differences
denser circuit patterns. Add to this a desire tion and lowest rate of false calls for every
and likely advantages of
to run multiple shifts, or even operate PCB, no matter the complexity and the
continuously 24/7, and it’s clear that the number of the components, and pro-
getting colourful.
inspection process is something that rap- grammed within the shortest time is the
idly moves beyond the capability of human ultimate finish line and a huge leap in the
operators. right direction. The first step to reaching
AOI has a wide range of applica- acceptable performance indicators is to
tions and works on the principle that an accurately describe the component and
optical defect detected requires corrective circuitry under test to the AOI machine.
measures. General advantages include its There are many methods employed to do
contactless measuring capability, its flexibil- this, with different vendors endorsing a va-
ity and its fast programming compared to riety of solutions from learning a captured
electrical test equipment. On the flip side, image (or averaging a succession of images)
the limitations of AOI include the fact that and correlation principles to modelling and
only visible defects can be detected and programming-in details of each component
the occurrence of false alarms precipitated and board topology. More often than not a
by observed visual differences that may be combination of techniques is used to refine
of no detriment to the circuit’s eventual the AOI’s understanding of its inspection
functionality. subjects. This process alone is the subject
a.
b. c. d.
Keywords: Automatic Optical
Inspection, 24-Bit Colour
This paper was originally distributed at the
International Wafer Level Packaging Confer-
Figure 1a. Component in greyscale. 1b. Component in 24-bit colour. 1c. Missing component in greyscale. 1d.
ence, San Jose, California, October 15 - 16,
Missing component in 24-bit colour.
2008.
26 – Global SMT & Packaging – August 2009 www.globalsmt.net
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