For the ATLAS experiment a new Silicon tracker is necessary for the High-Luminosity Upgrade of the LHC. The main building block for the strip tracker is a module which consists of a silicon sensor, readout ASICs and a hybrid PCB. Up to 28 modules are placed on long substructures. An End-of-Substructure (EoS) card provides common connections for data, commands and power to the off-detector systems. Prototypes has been developed based on the GBTx and GBT-SCA chip family and SFP+ optical links to understand the design issues, the behavior of the EoS and the detector level integration. Presented will be the design of the electronics, the exercised tests for electrical behavior, mechanical deformation and thermal behavior.