I was recently asked to help evaluate two systems designed to assist in 
    visual inspection of solder connections on board assemblies.  Both use a TV 
    camera and automatic X-Y positioning.  The latter is important help an 
    inspector identify a particular connection of a fine-pitch component that 
    may have fifty or more connections on a side.  One, made by Omron, uses a 
    patented arrangement of three concentric ring lights, each of a different 
    color. The colored reflection pattern allows interpretation of the fillet 
    contour. The other, made by I Systems, uses a motor-driven mirror to allow 
    inspecting connections from any angle, although the TV camera remains 
    oriented to look straight down.
    
    I found things I liked and things I didn't like about each system, and I got 
    to wondering whether there might be other commercially available systems not 
    a whole lot more expensive than these two (say ~ $50K), which we should 
    evaluate as well. In particular, I find that a TV camera results in a poorer 
    image quality than conventional optics, and would recommend just using a 
    microscope, looking at connections at a variety of orientations, if it 
    weren't for three difficulties with fine-pitch parts: identifying the pin 
    number, holding the assembly still enough to interpret what's there, and 
    getting a good view of heel fillets.
    
    Of course, we could try to get our customer to change our acceptance 
    requirements so that a connection that looks OK to the camera is OK, but 
    we're not sure we could do that.  Also, it may not be necessary to identify 
    the exact pin number but only to report the approximate location to help the 
    rework operator to find it.
    
    Comments?
    
    Gordon Davy
    Northrop Grumman ESSD
    Baltimore, MD

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