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The need to inspect work carried out in the electronics production line is a vital part of the overall manufacturing process and as component and manufacturing technology has developed, so have the plethora of inspection solutions, from the humble microscope through to advanced automated inspection systems. Today, the introduction of sophisticated quality methodology has become more that just aworking requirement. The development of automated inspection routines has been fuelled in part by the changes in electronics manufacturing processes. Firstly the departure from through-hole components to surface mount components meant that traditional in-circuit tests no longer had the electrical connectivity to provide high levels of fault coverage. It has further been accelerated by the use of smaller and smaller geometry devices forcing the requirement for a high connection count automated solution. PCB inspection systems come in a number of guises: automated optical inspection (AOI); automated X-ray inspection (AXI); automated infra-red inspection; manual video and manual optical inspection – positioned at post paste, post place, post solder and finished goods stages. With all of the technological developments of automated inspection solutions, there 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 programs. 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. At this point automated routines have not been programmed and with no defect history, quality procedures rely on the experience of their engineers and the accuracy of the tools allowing them manually inspect the boards. Often, alongside automated inspection systems there will be spot checks on production solder quality. This will usually be implemented to stringent quality procedures making sure the boards are being inspected by the automated systems consistently. With a balance of cost and quality always in mind, new components are often sourced from competing suppliers and new suppliers are often sourced to provide new and improved components. When this occurs, it is paramount that these components are checked for quality and this can only achieved by inspection, where often manual inspection is preferential. Where bespoke boards are designed and manufactured, optical inspection is an ideal solution where a large investment of automated inspection is not always necessary. Manual inspection systems come in a number of guises, ranging from simple bench magnifiers to high resolution video cameras, but the humble stereo microscope has become the mainstay of manual inspection solutions, primarily since whilst the resolution of video systems has increased dramatically over the decade, they are only able to present 2D images to the operator. However the design of the microscope dictates that operators must sit in an uncomfortable position, often for prolonged periods, which can result in operator fatigue, leading to a risk of error. Ergonomics and manual optical inspection
Where manual optical inspection is required, a high level of ergonomics is essential to maximize comfort to operators, minimizing associated fatigue from a strained body posture, optimizing both accuracy and productivity. Traditionally, optical microscopes have two eyepieces, look like a microscope and act like a microscope. The resulting 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 errors provides a real-life and everyday obstacle. Vision Engineering’s patented optical technology is designed to overcome the fundamental problem of a conventional microscope – the small image that exits from the microscope eyepieces. With ‘eyepiece’ microscopes, the size of the image exiting the eyepieces (the exit pupil) is around 3mm in diameter. This means that 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 an operator fixed rigid in and uncomfortable position. ‘Eyepieceless’ technology enlarges the imageexiting the microscope eyepieces (figure 1). Vision Engineering’s patented range of stereo inspection microscopes utilize two different types of optical technology to overcome the comfort issues associated with binocular eyepieces. The Mantis utilizes ‘Spatial Imaging’ technology where two separate light paths pass through its patented optics, exiting the single viewing lens as twin (stereo) light paths. The large diameter of these exit rays means that users do not need to precisely align their eyes with the viewing lens in order to see the subject (figure 2). This bridges the gap between microscopes and bench magnifiers by providing advanced inspection features and ergonomics to improve productivity in the production environment. Optical stereo viewers like the Mantis provides true linear magnifications up to x20, which are beyond the capabilities of traditional bench magnifiers, typically around 2.5 dioptres (x1.5 true magnification), and also provides long working distances for assembly and rework applications. By directing a pool of light directly onto the inspection object, the specifically-designed viewing hood allows the user to work within the ambient working conditions, reducing eye strain. The second type of technology used by Vision Engineering to optimize ergonomics is the sophisticated Dynascope viewing head used on the Lynxx – an advanced stereo zoom microscope. This patented optical technology utilize a 148mm diameter multilenticular (multi-lens) disc surface comprising of over 3.5 million individual lenticules (lenses), each measuring just 70 microns in size (figure 3). The Dynascope disk spins at 3,400rpm to merge the millions of individual optical paths into a smooth, expanded stereo image with a generous depth of focus and a wide field of view. In use, the multilenticular disc serves to expand the intrinsic pupil of the system. The resultant image is reflected through the field lenses to the operator’s eyes and the high resolution image is projected onto a large viewing area formaximum viewing comfort. As operators frequently alternate their views from the magnified object 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 (figure 4). In fact, the magnified image is almost exactly the same distance from the operator’s eyes as the actual sample is - a tangible advantage in reducing eyestrain and fatigue. In addition, employing a viewer rather than eyepieces permits much greater positional head freedom and an upright body posture for the operator, plus allows the use of spectacles. Operators who require reading glasses remove them for microscope viewing and must then refocus at a different distance, which again quickly leads to eye fatigue. Operators with astigmatism fare worse: removing spectacles immediately spoils their vision. The significant ergonomic advantages contribute to increased production rates and reduced scrap as the operator is able to work longer without experiencingeyestrain and fatigue. Conclusion
It is optical inspection technologies such as those just discussed, that when used in parallel to automated processes, maximizes the quality of PCBs. Manual inspection plays an important role alongside automated systems or where automated systems are not a cost-effective option and since technology is constantly changing and components are evolving, optical inspection provides a magnified view for engineers so they can apply their expertise and knowledge to individual case-by-case scenarios and imperfections. Colin Wells, Vision Engineering Ltd. Figure 1 Figure 2 Figure 3 Figure 4 About the author:
Colin Wells is the International Product Manager at Vision Engineering Ltd. He can be reachedat colin.wells@visioneng.co.uk. | 
