3D AOI is achieved by using a variety of techniques, such as stereo vision, point clouds, and 3D triangulation. Image acquisition, analysis, and image processing are the main functions of 3D AOI systems. Image acquisition involves image sensing, representation of image data, and digitization. Image processing is the modification and preparation of the pixel values of a digital image in order to produce a more suitable form for subsequent operations. The photo shows a typical optical structure of a machine vision system. The commonly four-angel projection design for the AOI System is used to minimize the shadow area.
The optical system using a light controller comprised of a reflective spatial light modu lator (e.g. LCoS) able to illuminate an area of the circuit board from a single distinct direction and adjust the pattern, where no macroscopically moving parts are required to adjust the pattern.
3D AOI systems are used to increase performance of industrial inspection, where accuracy and efficiency can be improved by more complete automation of the inspection process. JDC provides service for different customized applications, including machine vision. With our small pixel pitch and high fill factor, Jasper’s LCoS devices target diverse applications, ranging from phase modulation, diffractive optical elements, and other “structured light” applications.
Jasper Display Corporation (JDC) liquid crystal on silicon (LCoS) devices can be utilized as a spatial light modulator to facilitate 3D automated optical inspection (AOI). Features include:
- JDC LCoS has micro-displays for both amplitude and phase modulation schemes, with field rates over 1 KHz.
- JDC LCoS (production HD) devices feature 2 million pixels, support for 60 frames per second video input, and have high pixel processing rates, e.g. 2M pixels x 720 frames/sec.
JDC LCoS has the advantages of precise control of the multi-level phase modulation (our unique modulation method allows 8 bits of control for 256 RMS voltage levels).
Automated optical inspection (AOI) is an automated visual inspection of printed circuit board (PCB) (or LCD, transistor) manufacture where a camera autonomously scans the device under test for both catastrophic failure (e.g. missing component) and quality defects (e.g. fillet size or shape or component skew). It is commonly used in the manufacturing process because it is a non-contact test method. It is implemented at many stages through the manufacturing process including bare board inspection, solder paste inspection (SPI), pre-reflow and post-reflow as well as other stages.
AOIs for a PCB board with components may inspect the following features:
- Area defects
- Component offset
- Component polarity
- Component presence or absence
- Component Skew
- Excessive Solder Joints
- Flipped component
- Height Defects
- Insufficient Paste around Leads
- Insufficient Solder Joints
- Lifted Leads
- No Population tests
- Paste Registration
- Severely Damaged Components
- Solder Bridges
- Volume Defects
- Wrong Part
AOI can be used in the following locations in the SMT lines: post paste, pre-reflow, post-reflow, or wave areas.
Bare PCB inspection
AOI for a bare PCB board inspection may detect these features:
- Line width violations
- Spacing violation
- Excess copper
- Missing pad – a feature that should be on the board is missing
- Short circuits
- Hole breakage – a drilled hole (via) is outside of its landing pad
- Wrong mounting components identified
The triggering of a defects report may be either rule based (e.g. no lines on the board should be smaller than 50μ) or CAD based in which the board is locally compared with the intended design.
This inspection is much more reliable and repeatable than manual visual inspection.
In many cases, smaller circuit board designs are driving up the demand for AOI vs in-circuit testing.