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With inspection, a problem can be corrected, and the substrate rescued, at the most inexpensive point in the process.
"Keep your eyes on the road and your hands upon the wheel." - The Doors
Controlling the surface-mount assembly process entails knowing what each sub-process is doing (or not doing) and being able to rectify any problems. In-process inspection should be implemented at each phase of the assembly process: post-print, post-placement and post-reflow. But who inspects circuit boards?
Inspection: Who Needs It?
My company did a market analysis for a client in 1992, and we surveyed the industry regarding inspection. All key segments of the industry, including telecommunications, computers and peripheral, industrial control, medical, automotive and, yes, even military, were sampled. The study was limited to North America, but was representative of trends in Europe and Asia. The study revealed that less than 15 percent of the industry was using inspection in the surface-mount assembly process at any stage of the process. Much of the inspection was post-soldering and accomplished manually by using some sort of magnification device.
Less than 5 percent were doing any sort of post-print inspection. Again, the few who were smart enough to undertake inspection were usually having the stencil printer operator audit his or her work visually. Still, this type of inspection was better than nothing, which was what the majority of assemblers were doing. At this time, both Speedline MPM and DEK were offering onboard 2-D post-print inspection systems. CyberOptics had just introduced their Sentry 3-D post-print inspection system. Needless to say, no one was clamoring for inspection processes.
The study further revealed that the reluctance to invest in inspection was not generated by manufacturing and process engineering. Management,...