1. Proposal for the assembly of the PHOBOS ring counters (H.P. 3/20/98) I would like to propose and discuss with you an alternative layout and assembly procedure for the ring counters, namely Bernie’s proposal for the spectrometer in October of last year: A “single-hybrid - single sensor” module layout: –each module would consist of one hybrid –one ring sensor is glued to one hybrid directly –the modules are mounted on the support frame individually –the modules are chained in the readout with short cable going from one module to the next one.

2. My personal Pro’s/Con’s of a single-hybrid/sensor module The positive side of this module layout: –the module assembly would be very simple (and less risky). –the bonding of sensor to hybrid is simple –Each module is a “self-sufficient” unit, which can easily be replace on the ring in case of problems (we –In a failure during assembly or operation we would loose only one sensor and a hybrid without risking working sensors. –We have a lot of flexibility of grouping modules in the readout. The negative side: –modules are chained externally with short (9cm) ribbon cables

3. My “guide-lines” for this layout Position and acceptance of the sensors are not changed A 1 mm clearance between sensors is always maintained The hybrid is as similar as possible to the Octagon hybrid and can be done on PCB’s The modules fit into the existing mechanics The cable length is minimized The readout can be done in groups of 2, 4, or 8 modules in a string.

4. The module layout Single ring counter sensor cut straight along bond pad side PCB hybrid with original octagon layout and line routing Cable input connector Cable output connector to next module Space for line routing input to output connector Aluminum mounting plate Mounting holes Sensor glued along front side of hybrid

5. One Half-Ring First module Forth module in readout Readout cable IN Flat ribbon interconnection cable Support ring supporting individual modules 1mm clearance

6. A possible assembly scheme? Hybrids are glued to Aluminum support plate. Alignment is done by aligning the mounting holes in hybrid and Al plate or via reference marks Chips are glue and bonded; hybrid is tested Sensor is glued to the hybrid: –hybrid is positioned with pins in the mounting holes on a base-board –The sensor is supported on the baseboard (via vacuum) and aligned by two micrometer screws –Sensor is removed from base board; conductive and non-conductive glue applied to the hybrid edge –sensor is place in original position

7. Hybrid and sensor gluing Support area for the sensor on the hybrid (cross-section)