The invention relates to a signal transmission method and a motherboard structure (50) used in a base station of a radio system, for example, and comprises printed circuit board units (10-12) communicating with the motherboard structure and communicating with one another by signals. The motherboard structure (50) comprises an optical fibre sheet (40) having optical fibres (41, 42) arranged therein, first converter means (20, 21) receiving from the printed circuit board unit electrical low-power and high-frequency signals, such as clock signals and RF signals. The first converter means convert the received signals into optical signals, and each optical signal is conducted into an optical fibre of its own in the fibre sheet (40). The motherboard structure further comprises second converter means (30, 31) converting the optical signals which have propagated in the fibre sheet (40) back into electrical signals which are conducted to the printed circuit board units after the conversion.