Passive device assembly for accurate ground plane control is disclosed. A passive device assembly includes a device substrate conductively coupled to a ground plane separation control substrate. A passive device disposed on a lower surface of the device substrate is separated from an embedded ground plane mounted on a lower surface of the ground plane separation control substrate by a separation distance. The separation distance is accurately controlled to minimize undesirable interference that may occur to the passive device. The separation distance is provided inside the passive device assembly. Conductive mounting pads are disposed on the lower surface of the ground plane separation control substrate to support accurate alignment of the passive device assembly on a circuit board. By providing sufficient separation distance inside the passive device assembly, the passive device assembly can be precisely mounted onto any circuit board regardless of specific design and layout of the circuit board.