failure can be detected, the smaller the likelihood of refuse device manufacturing. Because of
component down-scaling and increasing in density, optical inspection is now only possible
with the help of machine vision as opposed to manual inspection.
2. Rise of the AOI systems
Manufacturing electronic devices necessitates the constant controlling and inspection of the
product. Previously, ICT was the main appliance used for this purpose. It inspected electronic
components (e.g. resistor, capacitor etc.), checked for shorts, opens, resistance, capacitance and
other basic quantities. Finally, it checked the proper operation of the whole circuit to show
whether the assembly had been correctly fabricated. It operated by using a bed of measure-
nails type test fixtures, designed for the current PWB and other specialist test equipment. It
had the following disadvantages. As the dimensions of components were shrinking and the
emplacement density was increasing, the positioning of the test-points became increasingly
difficult. Beds of measure-nails are also relatively expensive and they are PWB-specific. This
problem was however, partially solved by using flying-probe ICT systems (but at the expense
of speed). Another disadvantage of ICT was that only finished product could be examined. It
was able to detect failures but not to prevent them. It is also was not suitable for inspecting the
quality of various assembling technologies. A further disadvantage was also in the case of
functional testing. Extra measurement procedures had to be developed to ensure the enhance‐
ment of the quality of the manufacturing process.
Previously, the quality of solder joints had only been verified by manual visual inspection
(MVI). The disadvantage of manual inspection, which at best was subjective, was that the
tolerance limits were narrower than used in automated machines. A magnifying glass could
help for a while, but as the mounting number of components per unit area exceeded the
capabilities of manual testing, this option was already proving to be difficult or not even
applicable as described in [1]. Because of the rapid development of digital computing, machine
vision and image processing, it was obvious that it was becoming necessary to automate the
process with the help of various high-resolution cameras, novel lighting devices [2], illumi‐
nation techniques [3]-[5] and efficient image processing algorithms. Such state-of-the-art
devices and solutions are described in detail in the following books: [6]-[8].
In cases where the manufacturing of large quantities of precise and high quality products takes
place, the capabilities of production appliances can only be used effectively if the inspections,
after various technological sequences are automated (in-line), are fast and reliable. As a result,
the automatic optical inspection or testing appliances has been developed to replace manual
inspection. The words, Automated Optical Inspection imply that when used in the manufac‐
turing and assembly of PWBs, the nature of the inspection process itself, using digital machine
vision and image processing, will give objective results.
AOI inspects bare and mounted PWBs automatically and uses optical information. It is faster,
more accurate and cheaper than manual inspection. In preparing the parameters for such
Materials Science - Advanced Topics
388
Manymanuals.com
Manymanuals.de
Manymanuals.fr
Manymanuals.it
Manymanuals.pl
Manymanuals.cz
Manymanuals.es
Manymanuals-pt.com
Comentarios a estos manuales