March, 2015
www.us-
tech.com
An Introduction to Automated Optical Inspection Technology
N
umerous technologies are critical to the effective and efficient production of printed- circuit boards (PCBs) and one of those tech-
Ondrej Simecek, TRI Marketing Department, TRI, Taiwan Resolution is an important parameter to con-
sider when specifying an optical inspection system, since it typically also involves the AOI system
nologies that continues to grow in importance is automated optical inspection (AOI). AOI technolo- gy is rapidly becoming part of quality control in the production of PCBs and PCB assemblies (PCBAs) and knowing some of the basic functions and capa- bilities of AOI systems can help when choosing one of these systems for a production line. As with human vision and optical inspection
practices, AOI systems rely on three essential ele- ments: lighting, distance, and focus. AOI systems are being designed to work with these three elements while operating with increasing speed to aid production efficiency. They are also being designed for enhanced inspec- tion repeatability as components under inspection become smaller and require higher levels of magnification for effective board-level inspections. Effective illumination of the
area on a PCB to be inspected is a critical function for any AOI system. Early AOI systems employed a num- ber of different illumination ap - proaches, including incandescent, flu- orescent, infrared (IR), and ultravio- let (UV) lights. Newer AOI systems use LED light sources; light sources in an AOI system may include white, red, green, and blue LEDs. The angles of the light sources are important since tall components can block light from reaching shorter components on a PCB. Some component features on a PCB or PCBA may require low angle illumination for good visibility, so some applications may require an AOI system capable of providing light from different angles. Proper lighting can contribute a great deal to the opti- cal inspection accuracy possible with a given AOI system.
Focusing on the Camera The camera is a critical part of
an AOI system. AOI systems are available with one or more cameras, although the improved performance possible with a multiple-camera AOI system compared to a single-camera setup comes with a higher price tag. Cameras used in AOI systems range from simple XGA units to high-resolu- tion, multiple-megapixel video sen- sors. An AOI system's cameras may provide monochrome (black-and- white) or color images. The amount of data representing captured images can span a wide range, from mere thousands of data points to millions of data points. Newer cameras are capa- ble of capturing more than 100 frames/second. Of course, such high resolution and fast scanning rates generate massive amounts of data, and this large amount of data must be handled with the proper computing power and processing software. The AOI system or imaging res-
olution determines how much detail it can detect and show. Most current commercial AOI systems operate with imaging resolution that has been set at the factory by the manufacturer for optimized, stable performance, such as 10 or 20µm resolution. A system with 10µm resolution, for example, may use one camera pixel for each 10 x 10µm area of a PCB being exam- ined.
inspection speed, inspection accuracy, and the size of the smallest component that can be analyzed on a PCB or PCBA. System resolution is determined by a combination of the camera's sensor, lens, and dis- tance of the camera from the PCB to be inspected. The resolution of the camera sensor deter-
Different lighting configurations will illumi- nate different features of a PCB or PCBA.
mines the field of view (FOV) provided by the AOI system's imaging resolution. The FOV is that part of a PCB or PCBA included in a single image. An AOI system with a larger FOV allows a PCB to be scanned with fewer images than an AOI system
Continued on next page
Page 87
BE ON THE CUTTING EDGE OF
COMPONENT REWORK WITH METCAL’S NEW SCARAB SITE CLEANING SYSTEM
The cost and complexity of today’s electronic assemblies are forcing manufacturers to reexamine the tools and techniques in operation today. Contactless cleaning of component pads prior to component replacement is a growing trend in the industry. The New Scarab Site Cleaning System ensures accurate and repeatable cleaning of the component pad in one user friendly, single system. The Metcal Scarab System redefines performance and addresses the technical demands presented by component manufacturers today.
www.metcal.com 1 See at NEPCON China, Booth B-1G26
3
11:53 AM
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