Helix PCBs for the HERA-B Inner Tracker

The HERA-B Inner Tracker, is a Microstrip Gaseous Chamber (MSGC) System. Ten so called superlayers are located at different position in the HERA-B tracking system. Each superlayer consists of several layers of chambers modules, which are tilted by -5, 0 or +5 degree to enable a reconstruction of the point a particle track passes through the detector plane by the strip information of the chambers.

The chambers are read out by Helix128-2.2 and Helix128-3.0 chips. Two chips are mounted on a PCB, three PCBs are connected to an MSGC module, giving a total of 768 channels to be read out. The following picture gives an impression of what an Inner Tracker Superlayer looks like.

This superlayer consists of 6 carbon fibre support layers that carry 2 MSGCs on each side, on opposite quadrants.

The connection between the Helix chip and the MSGC is done via a fanout. A thinfilm ceramic is glued on the PCB and wire bonded to the Helix chip. The thinfilm ceramic contains strips that fanout from 41.4um pitch of the Helix to 220um pitch. This pitch can be z-bonded to a Kapton cable that establishes the connection to the MSGC module. The next picture shows a photograph of the fourfold staggered Helix input bonds.

On trigger layers two MSGCs are mounted on opposite sides of the support plate. The comparator outputs (notCompOut<31...0>) of corresponding channels are ORed via an open drain circuit. For this reason, the lower MSGC is equipped with a so called AS7 type PCB, whereas the upper chamber is equipped with AS8 type PCBs.

The difference between the AS7 and the AS8 is the following:

The AS7 gets power and different control signals (Sclk, Rclk, TrigIn,...) from the backside via a PCB called signal distributor.
These are routed to the AS8 on top of the AS7 via a plug.
The analogue signals of both boards are routed back to the signal distributor board at the rear side of the AS7. Hence the AS8 signals are routed via a plug to the AS7 and then to the signal distributor.
The corresponding notCompOut signals of the chips on the AS7 and AS8 are logically ORed via the open drain output drivers. The drain resistors are located on the AS8 board. Thus the AS7 signal are routed to the AS8 board via plugs in between the boards.
The AS8 board sends the combined comparator outputs to a trigger driver board connected to the rear side of the AS8.

The following picture illustrates the relation between the AS7 and the AS8 boards.

Further pictures of Helix-PCBs can be found here.

Test reports on the PCBs we produced so far, are also available.

Last changes: 99/07/12 by Martin Feuerstack-Raible

If you have comments or suggestions, email Ulrich Trunk