A circuit board assembly is applied to the field of electronic communications technologies to resolve a prior-art heat dissipation problem of a circuit board. The circuit board assembly combines, on a second circuit board, low-speed signals transmitted between a plurality of I/O modules and an IC chip, and then transmits the combined low-speed signals to the IC chip by using a low-speed cable. A low-speed signal sent by the IC chip to the plurality of I/O modules is extended to a plurality of low-speed signals on the second circuit board, and then the plurality of low-speed signals are separately sent to the plurality of I/O modules. This may be applied to a scenario in which a relatively large quantity of electronic components need to be disposed on a circuit board.