The improved ladder production for the Belle silicon vertex detector (SVD2.1)

In autumn 2003 data taking with the new silicon vertex detector SVD2 in Belle started at the KEK-B energy-asymmetric e/sup +/e/sup -/ collider in Tsukuba, Japan. The detector works as expected, however, it was decided to produce replacement ladders for the inner two layers of the vertex detector which are most exposed to the high radiation doses from the beam. The new ladders are not merely reproducing the existing design but include some significant improvements. The readout electronics is designed in a FR4 hybrid board with a new heat transfer scheme in order to dissipate the heat produced in the VA1TA front-end readout chips. The flex circuits that connect the double-sided silicon sensors (DSSD´s) with the hybrid boards were redesigned using a 2-layer technique which improved the production quality and lowered their costs significantly. Production and testing will be finished by the end of 2004 and will provide Belle with spare ladders as well as new expertise for possible future projects like e.g. developments for a high luminosity B-factory.