PCB007 Magazine

PCB-Mar2018

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54 PCB007 MAGAZINE I MARCH 2018 The difficulty with manual inspection is the operator's field of view, lighting, ambient dis- tractions and memory retention of the tomes of information they need to review of any giv- en PCB on demand. Not surprisingly, that de- mand can change mid-order, requiring the op- erator to immediately change focus to a whole new PCB, many times with absolutely differ- ent requirements! It can be overwhelming, to be sure. The AVI uses sophisticated CCD multicol- or cameras with detection resolution down to 5 microns. Coupled with LED multi-chan- nel lighting, the capture effectiveness is im- pressive. Now with this technology we also achieve predictability and repeatability. AVI is driven by your CAD/CAM data so observance variance is removed. Of course, when the ma- chine is set up for the specific PCB, fine-tuning can be accomplished to allow for manufactur- ing tolerances. In Figures 1 and 2 we can see the display screen on an AVI machine. The CAM represen- tation is shown vs. the actual board topogra- phy. From here on out, it is predictable and re- peatable. One can calculate with favorable ac- curacy how many panels or square feet (de- pending on how you calculate throughput) will be produced. It is not uncommon to see throughput ~400 sf/hr. Remember, the AVI is looking for multiple imperfection possibilities simultaneously. Ex- posed copper, land violations, annular ring, solder mask imperfections/violations, missing features, and even surface discoloration are all simultaneously screened. As noted previous- ly, defects found are visually displayed to the inspection technician. Non-conforming prod- uct is segregated from conforming so that re- view can be performed on the non-conform- ing product. Remember, we are not making the decision as to whether the product is initially conforming or not. CAD/CAM is driving the inspection along with allowed manufacturing tolerance. Here is our predictability and repeat- ability coming back into play. Suppose, due to manufacturing constraints, the job has to change immediately. If a repeat job, we just load the saved program and we are inspecting within minutes. Different re- strictions on the new job? No problem. AVI al- ready knows the requirements and moves right on with inspection. If a new job, it must be set up only once, saved and production moves on. Now back to the automation vs. human ar- gument. We are not replacing the human fac- Figure 1: AVI display.

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