A substrate assembly is provided, including a first substrate and a circuit substrate. The first substrate comprising an edge. An active element layer is disposed on the first substrate. A plurality of first electrodes are disposed on the first substrate and between the edge and an edge of the active element layer, and arranged along a first direction. At least one of the plurality of first electrodes is electrically connected to the active element layer, a first register mark is disposed on the first substrate. The circuit substrate is partially overlapping the first substrate in a vertical projection direction, a plurality of second electrodes is disposed on the circuit substrate.