Development of a Four-Side Buttable X-Ray Detection Module With Low Dead Area Using the UFXC32k Chips With TSVs

Nowadays, single photon counting pixel hybrid detectors are becoming increasingly popular in high-energy physics, X-ray detectors for synchrotron applications, and medical imaging. Readout chips for these detectors usually have the area of a few square centimeters and are designed to be abutted on three sides. However, many applications require large-area detectors without dead areas. The through-silicon vias (TSVs) aim to minimize the dead area and in that way to enable development of four-side buttable large-area detectors. AGH, Krakow, and IZM, Berlin, have undertaken a common effort to apply TSV (via last) technology to the readout integrated circuit called UFXC32k containing a matrix of $128 \times 256$ pixels, with a pixel pitch of $75~\mu \text{m}$ and a total area of 2 cm 2 . The TSVs were applied to the 87 I/O pads located at the bottom of UFXC32k IC. A TSV diameter of $20~\mu \text{m}$ was chosen while the wafers were thinned to $100~\mu \text{m}$ . The redistribution layer and the array of pads for solder bumping were distributed at the bottom side of the chips. Two UFXC32k chips with TSVs were attached to a single, 320- $\mu \text{m}$ -thick silicon sensor and finally, the chip detector modules were attached to low-temperature co-fired ceramic boards. The $2 \times 2$ cm 2 plug-in detector modules were successfully built and tested.