Design of Bus Tapes for the ATLAS Strip End-Cap at the HL-LHC

The ATLAS Phase-II Upgrade will replace the Inner detector with a new all-silicon Inner Tracker (ITk) to accommodate the radiation damage and track density expected at the High-Luminosity LHC (HL-LHC). The all-silicon ITk for the HL-LHC consists of a pixel detector with 5 barrel layers and multiple forward disks at a small radius, and a strip tracking detector at the outermost part with 4 barrel layers and 6-end-cap disks on each side. This contribution presents the design of the flexible circuit (bus tape) for the local support structures of the end-cap region of the strip detector, called petals. The bus tapes provide the electrical interface to common services for all the on-board subsystems including power, control and data interfaces. Connections to external services outside of the petals are carried out through the End-of-Structure (EoS) card using optical fibres and copper wires. The bus tapes are manufactured as a 2-layer printed circuit board using polyimide and adhesive Kapton films, with a total thickness of 185 $\mu$m and a total length of 60 cm. The layout design has been focused on achieving good signal and power integrity while keeping low mass and low thermal resistance. A total of 768 end-cap bus tapes will be produced between 2021 and 2022 for the assembly of 384 petals with 6,912 modules, where each end-cap disk will consist of 32 petals.