The need to inspect work carried out in the electronics production line is a vital part of the overall manufacturing process. As component and manufacturing technology develop, so have the number of inspection solutions, from the humble microscope to advanced automated inspection systems.

The development of automated inspection routines has been fuelled, in part, by the changes in electronics manufacturing processes. The transition from through-hole to surface mount configurations has limited the effectiveness of some automated in-circuit test machines. The boards and corresponding pinouts have become smaller and smaller so the need for accurate methods of test and inspection have never been more important.

Printed circuit board (PCB) inspection systems are available in a number of configurations including: automated optical inspection (AOI), automated X-ray inspection (AXI), automated infra-red inspection, and manual optical inspection.

In spite of all the technological developments of automated inspection, there still remains the fundamental reliance on human intervention to program and train the automated inspection system to achieve the level of fault coverage that is required for a particular product. A high quality manual inspection process is essential in the generation and stabilization of an automated inspection program. This is particularly important where a variety of boards are assembled and tested.

Use of manual inspection in today’s industry.
Optical inspection is often used by research and development engineers, especially where the prototypes of boards are inspected for accuracy and design for fit. Quality procedures rely on the experience of engineers and the accuracy of tools for boards to be manually inspected. Often, alongside automated inspection systems, spot checks on production solder quality may be implemented to guarantee automated system accuracy.

With a balance of cost and quality in mind, new components are sourced from competing suppliers, and new suppliers are sourced
to provide new and improved components. When this occurs, it is paramount that these components be checked for quality using
manual inspection.

Ergonomics and manual optical inspection.
The combination of a human operator with a microscope provides a powerful and highly flexible inspection solution for any size of electronics manufacturing operation, yet for many, the issue of operators fatigue and the resulting error provides a real and everyday obstacle.

Both the learning center and demonstration factory at the EMPF have Mantis stereomicroscopes from Vision Engineering (Figure 5-1). The patented “eyepieceless” stereomicroscope is designed to overcome the comfort issues associated with binocular eyepieces. With eyepiece microscopes, the size of the image is around 3mm in diameter. The operator must precisely align their eyes with the eyepieces, otherwise just a small movement of the head will result in a loss of image. The result is that an operator must maintain a rigid and uncomfortable position.

By using “spatial imaging” technology, two separate light paths exit the single viewing lens as twin (stereo) light paths. The large diameter of these exit rays means that operators do not need to precisely align their eyes with the viewing lens in order to see the subject. This bridges the gap between microscopes and bench magnifiers by providing advanced inspection features and ergonomics to improve productivity.

Optical stereo viewers, like the Mantis, provide true linear magnifications up to x20, which are beyond the capabilities of traditional bench magnifiers. They also provide long working
distances for assembly and rework applications. By directing a pool of light directly onto the inspection object, the viewing hood allows the user to work within the ambient working conditions, reducing eye strain. As operators alternate their views from the magnified image to the actual object (especially during rework or when manipulating parts), the long distance to the apparent magnified image eliminates the need for the eyes to refocus each time. In fact, the magnified image is almost the same distance from the operator’s eyes as the actual sample – a tangible advantage in reducing eyestrain and fatigue.

In addition, employing a viewer rather than eyepieces permits a much greater positional head freedom and an upright body posture for the operator, and allows the use of eyeglasses. Operators who require reading glasses, must remove them for microscope viewing and then refocus at a different distance, which quickly leads to eye fatigue. Operators with astigmatism fare worse, removing eyeglasses immediately spoils their vision. The significant ergonomic advantages of the Vision Engineering “eyepieceless” stereomicroscopes contribute to increased production rates and reduced scrap as the operator is able to work longer without experiencing eyestrain and fatigue.

Conclusion.
Manual optical inspection technologies used in parallel to automated processes, maximize the quality of PCBs. The use of an eyepieceless stereomicroscope provides 3-D imaging and improved levels of comfort which helps reduce operator fatigue and increases quality and productivity. The Mantis stereo viewer from Vision Engineering provides high performance for a wide range of precision tasks requiring magnification.

For additional information related to the Vision Engineering stereomicroscopes or to schedule a demonstration at the EMPF, contact Ken Friedman, 610.362.1200 extension 279 or via email at kfriedman@aciusa.org.