During 2000 the importance of the visual inspection test has increased dramaticaly as implant breaks and damaged bias resistors were clearly observed during the tests done at Cavendish Labs early in the year. During the meeting at Cavendish Labs on 23/11/00 it was decided that all detector testing institutes should have microscopes which can resolve these defects clearly. In order to reduce handling of the detectors it was also decided that the microscope should be fitted onto the probe station on which the other tests are performed.
Models from Nikon, Meiji, Olympus and Mitutoyo were demonstrated at Sheffield and Rutherford Labs. All the compound microscopes produced good images but it was difficult to see whether a custom mount would allow them to be used on the probe station.
Image from the Leica microscope currently fitted to the probe station.
The best image from a stereo microscope.
To find which microscopes would fit a 3D model was made using Autocad 2000 of the two most likely candidates: The Mitutoyo FS60 and Nikon Modular focusing unit.
The shorter (13.8mm) working distance of the Nikon means that the probe card holder has to be removed from beneath the probe station platform. A conservative 15mm clerance was left between the underside of the probe station platform and device being probed. The device is represented by the dark blue block. The result is a very tight fit, so much so that the model of the microscope was not completed. Only the nosepiece , lenses and focusing block are shown. The 2x lens does not have a long enough working distance to be used with this setup.
This microscope has a much longer working distance (20.5mm) and a 1 to 2x zoom. The situation with a manipulator only is clearly much better than with the Nikon. The body of the Mitutoyo is also shorter than that of the Nikon making it easier to mount and producing a smaller moment on the sliding mount.
The probe card facilty on the probe station can be retained after a small modification. The modification involves removing the angular adjustment mechanism for the probe card which takes up an additional 10mm in the vertical plane. The nearest lens can be seen clashing with the prober platform in the picture where the modification has not been made.
Picture: Using probe card without modification.
Picture: Using probe card with modification.
