The setup for stage 1 of the SVT systems test consists of a single SDD wafer wire-bonded to a fully instrumented SVT hybrid prototype.
The present wafer pool consists of STAR 2.7 wafers, manufactured by SINTEF, as well as STAR 2.8 and STAR 2.9 wafers from BNL. We decided to put together two boards, one with a SINTEF STAR 2.7 wafer and one with a BNL STAR 2.9 wafer. Both wafers were tested independently with the BNL probe station setup. The key measurement was the guard anode current as a function of maximum HV on the wafer. Both wafers exhibited guard anode currents well below 50 micro-amps at 1500 V.
The hybrids were fully instrumented and bonded prototypes, manufactured and bonded by EMTRON. Due to some bonding problems at EMTRON certain hybrids contain non-functional PASA dies. On hybrid 1 twelve out of fifteen dies were functional. The hybrids were fully tested in the SVT electronics laboratory in the BNL Physics Department. The noise level was very stable for all channels and averaged around 5 mV before being connected to the detector.
Both components (wafer and hybrid) were glued onto a E896-SDDA board, which was designed and manufactured by the SVT-OSU group. The board hosts not only the hybrid and the wafer, but also the resistor chain for the external voltage divider, the charge injection inputs and the inputs for HV, LV, and focussing voltage (FV).
The board is about 14 cm by 11 cm, which is considerably smaller than the original STAR motherboards. It is connected to the readout electronics via a 50 pin connector, which carries the signals, LV, FV, calibration and slow controls lines. The board slides into a support structure that can host up to 15 boards for a telescope-like setup to be used in fixed target experiments for measuring hyperons. The structure was designed to fit into the E896 sweeping magnet.
The following assembly steps lead to the instrumented board: a.) the resistor chain and support chips were surface mounted at OSU b.) the voltage linearity of the external chain was tested at V = 1500 V c.) the wafer was epoxied into the wafer cut-out on the board d.) the hybrid was aligned to the wafer with the SVT-NIKON system e.) the hybrid was epoxied to the board f.) the hybrid performance was tested through the board but without bonding to the detector g.) the hybrid was bonded to the wafer h.) the wafer was powered up, a laser signal was injected and read out through the hybrid
The manual hybrid to detector bonding was a good exercise for the anticipated automated bonding during SVT construction. The hybrid to detector distance was held to about 3 mm, comparable to the final SVT component distance. On the hybrid the wire-bonds coming from the wafer anodes share a bond pad with the wire-bonds that connect the PASA die to the hybrid substrate itself. Still, the first bonding attempt turned out to be successful, which demonstrates that the bonding concept for the SVT is feasible.
The following picture shows the fully instrumented and cabled prototype board:E896 board hosting an SVT wafer and a SVT hybrid