A tiled array of hybrid pixel detectors for X-ray imaging

A prototype multi-chip hybrid was developed, based on tiling together 8 Medipix2 readout chips onto a single silicon sensor with a sensitive area of 28 x 56 mm(2) for a total of about 0.5 Megapixels. A main difficulty of this approach is in the high density of interconnections needed to read out all the circuits in such a tiled array. The amount of connectivity between the readout circuits is drastically reduced by the use of a high-speed serial protocol, allowing the use of Uw-Voltage Differential Signaling (LVDS) at frequencies above 100 MHz. To mount the multi-chip hybrid we are using a new printed-wire-board technology called multi-layer sequential build-up with staggered micro-vias, which allows to accommodate the 128 wire-bonds per chip on a ten layer printed wire board, with smallest feature size of 60 mum line width and 100 mum pitch.