A compact computer system board 10 comprises dual on PCB expansion zones 11, 12, expansion connectors 113, 123 which can be connected to expansion boards. Once a expansion board is connected to the expansion connector 113 (123) in the on PCB expansion zone 11 (12) to extent the application of the system 10, a metal housing cover 20 will be mounted above the on PCB expansion zone 11(12). The shield expansion apparatus formed by on PCB expansion zone 11 (12) and metallic housing cover 20 isolates the electromagnetic interference between add-on expansion daughter card and the environment outside of the shield expansion apparatus. The metal housing cover 20 as well as the on PCB expansion zone 11 (12) function as the heat sink of the add-on expansion daughter card inside the apparatus. Dual complete EMI shield expansion apparatuses especially eliminate the cross interference and provide high heat dispassion for the system under the situation when there are two radio frequency application expansion boards installed onto the system board.