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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