25 February 2008 Inspection of microchip mounting tolerances by 3D vision
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We have designed and tested a 3D vision system for measuring microchip surface heights relative to a substrate. The microchip is mounted with an adhesive to the substrate. The goal is to check the thickness of the adhesive layer between microchip and substrate before it is encapsuled by a plastic mold compound. This thickness has a significant influence on the reliability and electrical performance of the microchip. The system consists of one camera, a telecentric lens and three semi-transparent mirrors (beamsplitters). Reference patterns on the microchip and the substrate are imaged and illuminated from opposite 45° angles. This yields sets of coordinates which are used to extract the orientation of the chip relative to the substrate. We found that the vertical resolution of the system is greatly influenced by the setup of the image processing system. In principle, the reference patterns are identical for all chips and substrates of a production lot. Thus, the reference needs to be learned only once on a particular chip. With this setup we achieved a resolution of 2 micrometer. On the other hand, if the reference pattern is learned for each chip individually, we achieved a higher resolution of 1 micrometer. However, learning the pattern for each chip individually is time-consuming and may not be applicable for an on-line production inspection system with 2 - 3 chips per second.
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Stefan Behler, Stefan Behler, Martin von Arx, Martin von Arx, } "Inspection of microchip mounting tolerances by 3D vision", Proc. SPIE 6805, Three-Dimensional Image Capture and Applications 2008, 680504 (25 February 2008); doi: 10.1117/12.764830; https://doi.org/10.1117/12.764830

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