label: Double-Sided PCB,Printed-circuit-board
The next level of complexity is double-sided. Although there are some double-sided FR–2 boards, they are more commonly fabricated with FR–4 material. The increased strength of FR–4 material supports vias better. Doubled-sided boards are easier to route because there are two layers of foil, and it is possible to route signals by crossing traces on different layers. Crossing traces, however, is not recommended for analog circuitry. Wherever pos-sible, the bottom layer should be devoted to a ground plane, and all other signals routed on the top layer. A ground plane provides several benefits:
Ground is frequently the most common connection in the circuit. Having it continuous on the bottom layer usually makes the most sense for circuit routing.
It increases mechanical strength of the board.
It lowers the impedance of all ground connections in the circuit, which reduces
undesirable conducted noise.
It adds a distributed capacitance to every net in the circuit
—helping to suppress radiated noise.
It acts a shield to radiated noise coming from underneath the board
