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ATLAS ITk

Production of pixel modules and quality control of flexible PCBs

We are currently assembling and testing around 200 production modules, equipped with the front-end chip version RD53C (ITkPixV2) based on the developments made by the RD53 Collaboration, for the Outer Barrel region of the ATLAS ITk (Fig. 1).

Schematic of ATLAS ITk Pixel detector
Fig. 1: Schematic of the location of modules in the ATLAS ITk Pixel detector. The Outer Barrel region is highlighted in blue.

 

In preparation for the module production phase, our group designed and built a dedicated setup for testing modules electrically (Fig. 2) and simulating thermal stress of the modules, and a dedicated cleanroom was set up to assemble modules in a dust-free environment. The production of pixel modules was successfully trained using silicon dummy, prototype and preproduction modules. It is important to reach highest precision during the assembly (Fig. 3) and to ensure that the modules are of best quality regarding their dimensions and electrical and thermal properties after each assembly step.

Wirebonds
Fig. 2: Siegen's setup for testing up to four modules electrically. A series of electrical tests is performed in dry air conditions, at room temperature and at -15 °C.

 

Wirebonds
Fig. 3: Precisely placed wirebonds with 25 μm thickness connect the flexible PCB with the silicon sensor. Around 700 wires are placed on each module using a high-precision wirebonder.

 

In addition to module assembly and testing, Siegen also performs the quality control of all 2000 flexible PCBs (flexes) needed for the German Outer Barrel pixel module cluster. The members of this cluster are Bonn, Göttingen and Siegen. During this quality control, we control if the flexes produced in industry fulfill stringent requirements on the electrical performance and on the dimensions required for building good production modules.