  We report on the construction of a UHV compatible 40 mm active diameter
detector based on micro channel plates and assembled directly on the
feed-throughs of a DN63CF flange. It is based on the charge division technique
and uses a standard two inch Si wafer as a collector. The front end electronic
is placed directly on the air side of the flange allowing excellent immunity to
noise and a very good timing signal with reduced ringing. The important
aberrations are corrected empirically providing and absolute positioning
accuracy of 500 $\mu$m while a 150 $\mu$m resolution is measured in the center.
