How to draw multilayer PCB on altium designer?

4-layer board conventional design: Siganl_1 (Top), GND (Inner_1), POWER (Inner_2), Siganl_2 (Bottom)

6-layer board conventional design: Siganl_1 (Top), GND (Inner_1), Siganl_2 (Inner_2), POWER (Inner_3), GND (Inner_4), Siganl_3 (Bottom).

6 layer PCB stack-up

Advantages:

• Tight coupling of the power and ground layers.

• Each signal layer is directly adjacent to the inner power layer and is effectively isolated from all other signal layers, making crosstalk less likely to occur.

• Siganl_2 (Inner_2) and the two internal power layers GND (Inner_1) and POWER (Inner_3) are adjacent to each other and can be used to transmit high-speed signals. The two inner electrical layers can effectively shield the outside world from the interference of Siganl_2 (Inner_2) layer and Siganl_2 (Inner_2) from the outside world.

Design principle:

• The internal power and ground layers in multilayer boards should be closely coupled to each other (referred to as the inner power layer).

• The high -speed signal transmission layer in the circuit in the multilayer board should be the intermediate layer and sandwiched between the two internal power layers.

• components should preferably be placed on one side. If you need to place components on both sides, in the bottom layer (Bottom Layer) to place though hole type components, it may cause the board is not easy to place, but also not conducive to welding, so in the bottom layer (Bottom Layer) is best to place only SMD components.

• reasonable arrangement of the location and direction of the interface components. In general, as the board and the outside world (power, signal lines) connected by the connector components, connectors usually arranged at the edge of the board, such as serial and parallel port. If placed in the center of the board, it is obviously not conducive to wiring, but also may not be connected because of the obstruction of other components.

• It is best to have a wide electrical isolation strip between high-voltage components and low-voltage components. That is to say, do not place the big voltage level difference components together, so that both conducive to electrical insulation, signal isolation and anti-interference also have a great benefit.

• For components prone to generate noise, such as clock generators and crystals and other high-frequency devices, they should be placed as close as possible to the clock input I/O of the CPU when placed. High-current circuits and switching circuits are also prone to noise, in the layout of these components or modules should also be away from logic control circuits and storage circuits and other high -speed signal circuits, if possible, try to use the control board combined with the power board, using the interface to connect, in order to improve the overall anti-interference ability of the board and work reliability.

• Try to place decoupling capacitors and filtering capacitors around the power supply and chips. The arrangement of decoupling capacitors and filter capacitors is an important measure to improve the quality of the board's power supply and improve the ability to resist interference.

• components number should be arranged close to the edge of the components, uniform size, neat direction, not overlapping with components, vias and pads. Component or connector pin 1 indicates the direction; positive and negative signs should be clearly marked on the PCB and not allowed to be covered; for power conversion components (such as DC/DC converters, linear conversion power supplies and switching power supplies), should be enough space for heat dissipation and installation space, leaving enough space for welding on their perimeter.

Differential pair routing (differential pair routing):

The use of twisted pair cable for signal transmission, one transmits the original signal, the other transmits the signal opposite to the original signal. Different signals are generally connected to external differential signal systems, such as cables, etc.

Advantages: can be a good electromagnetic interference (EMI) solution from the signal line to the outside.

Requirements: 

① Let the signal impedance of each line is half of the impedance of the input differential cable.

② at the receiving end is that both lines are separately to their respective characteristic impedance.

③ two differential signal lines should be of equal length so that they can be within the tolerance of the logic device, generally the difference in the length of the differential signal lines within 500 mil is acceptable.

④ differential lines in the signal impedance can be guaranteed under the tolerance, can switch layer for wiring. (Characteristic impedance only the line width is related, and the line length is not relevant).

RF: emit signal energy to the outside, but there are often reflections, the energy can not be fully accepted, like shouting at the mountain, there will be part of the return.

• Through hole: Thru 1:6 → penetrate 1-6 layers of PCB
  

• Blind hole: Blind 1:2 → connect 1-2 layers of PCB

• Buried hole: Buried2:5 → connect 2-5 layers of PCB