Almost all modern ICs require multiple supply voltages to operate, making power integrity one of the biggest problems in electronic product design. Many times, analog ground and digital ground are kept separate on the board to avoid induction of noise from one part of circuitry to another. It is impossible to assign a separate layer for each of the power planes. Even if the designer could somehow have an individual layer for each power net, it would unnecessarily increase the number of vias used or make the board unnecessarily complicated and susceptible to noise and board failure. Also, having more layers in the stack up increases the manufacturing cost of the board. more