If you have double-sided design experience, designing multi-layer is not difficult.
First of all, you have to divide the stack-up structure, in order to facilitate the design, it is best to substrate as the center, to both sides of the symmetrical distribution, adjacent to the signal layer between the electrical isolation.
For the transmission line, the top and bottom layer using microstrip line model analysis, the internal signal layer stripline model. 6 layers / 10 layers / 14 layers / 18 layers on both sides of the signal layer is best to use software simulation, more trouble.
6 layers / 10 layers / 14 layers / 18 layers and other substrates on both sides of the signal layer, there is no electrical isolation, you need to pay attention to the vertical alignment of the adjacent layers and to avoid the exchange loop.
If there are other power supply, give priority to take a thick line in the signal layer, try not to divide the electrical ground.
Second, ask the manufacturer for the specs (dielectric constant, line width, copper thickness, board thickness) for impedance matching. These specs do not have to calculate (manufacturers may not be able to do), should be provided by the manufacturer. With these specs, you can calculate the line width, line spacing (3W), line length, then you can start drawing a board.
Multilayer PCB has blind holes, buried holes, vias, you can easily wiring, but the price is expensive. Sometimes it is necessary to reduce the board thickness so that the PCI slot can be inserted. However, the dielectric material does not meet the requirements. In this case, non-uniform boards can be used variably, for example, the middle 14 layers and the edge 2 layers.
High-speed line is best to take the inner, top and bottom easily affected by external temperature, humidity, air, not stable. If you need to test, you can test the test leads to lead. No more flying lines, seclusion fantasy, multi-layer no longer need to "hands-on ability," because the line and high-frequency, can not fly, the line is very dense and can not drill. Develop the habit of working on paper to ensure a successful system board, otherwise, destroy it locally.