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December, 2014
Combining 2D and 3D AOI: The Most Effective Inspection
By Kevin Garcia, Nordson YESTECH
technology (SMT) manufacturing environment. Growing trends to - wards the use of smaller compo- nents, more advanced component packaging, finer lead pitches, and higher printed-circuit-board (PCB) densities increases the need for AOI. It provides a way to inspect for com- mon defects, such as missing or wrong components, incorrect compo- nent orientation, poor solder quality, and lead bridging. Coplanarity issues are also prevalent on smaller chip components (i.e. 01005), leaded de - vices, and BGA packaged devices. In order to attain the highest
A
level of quality assurance (QA), high- precision AOI capability is essential. Combining AOI methods, using both two-dimensional (2D) and three- dimensional (3D) inspection strate- gies, is proving to be the most effec- tive solution for thorough inspection coverage in today’s advancing manu- facturing environments. Before exploring the latest 3D
AOI technology, it may help to under- stand widely accepted 2D AOI systems that have been in use for many years. Technological advancements have enabled 2D AOI to be come wide- spread, if not mandatory, at most SMT manufacturing plants. There are sev- eral key factors to take into account when considering 2D AOI:
3D processed image captured with Nordson Yestech’s FX-940 3D AOI system.
the optics of the AOI system. The use of a telecentric lens allows for a consistent magnification across the entire field of view (FOV). An AOI system should be equipped with
tion (compared to a system with a larger FOV) which will lead to an increase in cycle time. The proper camera and optics configuration should be determined based on the
utomated optical inspection (AOI) has become an essential tool in today’s surface-mount-
l Camera/Optics. Pixel counts, opti-
cal and digital magnification are important factors that determine the capabilities of an AOI system. The pixel size is determined by the properties of the imaging sensor (i.e., a 9.0 MegaPixel camera) and
enough magnification to provide the required resolution for accurate image processing. A tradeoff, howev- er, is that higher magnification results in reduced FOV. A smaller FOV means that additional images must be captured during an inspec-
size of the components to be inspect- ed, the complexity of the assemblies to be inspected, and the cycle-time considerations.
l Lighting. Multiple lighting direc-
tions and colors allow for improved image quality and ensure the identi- fication of various defect conditions. Today’s advanced AOI systems are commonly equipped with multiple- tiered, multicolored, programmable light-emitting-diode (LED) lighting. This results in a consistent uniform image within the FOV, with enhanced contrast and stability.
For many years, 3D inspection
has been commonly used for the inspection of solder paste depositions on PCBs. In recent years, 3D inspec- tion technology has been emerging more and more on AOI systems. 3D AOI methods serve as an effective tool for volumetric and coplanarity inspections. These inspection meth- ods can provide details on the height information of lead tips, BGAs, chip components, reflowed solder fillets or, essentially, critical dimensional information on any height-sensitive component. The common methodology used
in most 3D AOI systems is Moiré 3D phase-shift image processing. In this application, multiple projectors are used to digitally project multiphase digital fringe patterns (i. e., vertical lines) on a specified FOV. A 2D cam-
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