
2
Chapter II Main Uses and Scope of
Application of Equipment
2.1 Introduction of AOI
2.1.1 What is AOI
AOI (Automatic Optical Inspection) is a new type of testing technology developing rapidly in
recent years. It is composed of workbench, CCD camera system, electromechanical control and
system software. During inspection, the circuit board to be inspected is first placed on the
workbench of AOI machine, and the inspection program of the product to be inspected is called
out through positioning. The X/Y workbench will send the circuit board under the lens according
to the command of the set program. With the assistance of special light source, the lens will
capture the image required by AOI system and carry out analytical processing. Then the
processor will move the X/Y workbench to the next position to collect and carry out analytical
processing on the next image. Through continuous analytical processing on the image, a higher
inspection speed can be obtained. AOI image processing in essence is to digitize the captured
images, and then compare them with pre-stored "standards". After analysis and judgment, if
defects are found, their position will be prompted, and image characters will be generated for
further confirmation by the operator. Or, the circuit board will be sent to the maintenance
platform for maintenance.
2.1.2 Implementation goal of AOI
AOI used in SMT production line is mainly for the following two targets:
①
Final quality: monitoring the final state of the product when it goes down the production
line. At this time, AOI is usually placed at the end of the production line. In this position, the
equipment can obtain a wide range of process control information.
②
Process tracking: monitoring the production process by using inspection equipment. It is
often required to place the inspection equipment at several positions on the production line to
monitor the specific production conditions on-line and provide necessary basis for the adjustment
of the production process.
2.2 Placement position of AOI
AOI can be arranged at multiple positions of the production line. For its main purposes,
three positions are common:
①
AOI inspection is arranged after solder paste printing: the AOI inspection is arranged after the
solder paste printing, which is a typical arrangement because many defects are caused by poor
solder paste printing. Insufficient solder paste may lead to component loss or open circuit.
②
Before reflow soldering, the inspection equipment should be placed behind the chip for
inspecting the defects caused by the defects of the chip.
③
After reflow soldering, the inspection equipment is placed after reflow soldering, which is the
most common AOI placement position. It can inspect the defective products in all previous
processes to ensure that the final defective products are not used by customers.