Tests of a first prototype of the Flexible PCB for the High Granularity Timing Detector at ATLAS

The High Granularity Timing Detector (HGTD) is proposed for the ATLAS Phase II Upgrade to provide precise timing to tracks in the forward region. Each of its modules will be connected to the peripheral electronics via a flexible PCB. A first prototype of this Flexible PCB has been designed and manufactured. The geometrical constraints (thickness $<$ 350 $\mu$m and a maximum length of 750 mm) as well as the electrical requirements (high-speed rate of 1.28 Gb/s and sensor powering up to 1 kV) requires a specific testing plan to check its performance. The Power Integrity (PI) simulation provides the resistance of the dedicated planes for powering and grounding before manufacturing and simulated results are compared to the measured values in the laboratory. The High Voltage insulation of the materials used to fabricate the FLEX cable is also tested. Time Domain Reflectrometry measurements, in order to check the impedance homogeneity of the tracks crucial for Signal Integrity (SI), are performed. Results of the testing of the prototype are presented.