Circuit Board Assembly Inspection
Based on an original publication by O.C. White
Beyond the Naked Eye
Some circuit board assembly defects, such as surface board damage, misaligned components and soldering flaws, can easily be seen with the naked eye; others require more sophisticated equipment.
Visual inspection (about 80% accuracy) still serves as a primary way of inspecting completed printed circuit boards (PCBs). Highly trained inspectors look for many things when examining PCBs and know how to spot small flaws the untrained eye may miss. They also may be able to compare a series of matching boards side by side to identify defects. Not all defects, however, can be seen with the naked eye and with components becoming smaller and smaller, inspection requires more sophisticated equipment, like the microscope, to view miniaturized parts and assemblies.
The Basics of Quality
Eye fatigue, ergonomics and how much the inspection equipment can be adjusted and positioned factors greatly into quality inspections, as does sufficient magnification and proper illumination. When starting to think about inspections, begin with a well-trained operator and proper equipment. Experienced operators know what to look for when inspecting and having the proper equipment, including lighting, will not only help guarantee a quality inspection but also lessen operator fatigue.
From Eyes to Scopes
Knowing the kind of application the microscope will be used for will help determine the type of microscope needed. Do you want a bench-type microscope or one that can handle a boom and articulated arm? Microscopes can be built out piece by piece or be purchased pre-assembled with common components and accessories designed to fit a variety application purposes such as assembly, rework and inspections.
Another big decision will be to determine if you need a binocular-stereo or trinocular microscope. Common binocular microscopes have two eyepieces and show images via a single high-power objective lens. The image looks flat and 2-dimensional.
Binocular-stereo microscopes also have two eyepieces (essentially two microscopes with separate optical paths) and show an image for the left and right eye from different angles creating a 3-dimentional image.
The trinocular microscope has a third eyepiece or port where a digital or video camera can be fitted. The captured image(s) can then be viewed or shared as needed, e.g., over the internet, or for training
From Fluorescents to Fiberoptics
Light and illumination used during inspections play a key role when looking through a microscope at an object. Providing the right type can help the operator see the object clearly and reduce eye fatigue, a major factor in worker comfort and quality outcomes.