Design suggestions for multi-layer pcb boards

2019-11-14 20:12:08 Juding Circuit Technology

Design suggestions and examples of multi-layer pcb board: description and requirements of pcb board design (4, 6, 8, 10 layers):

A: The surface and surface are complete ground planes (shield).

B: No adjacent parallel wiring layers.

C: All signal layers are as close as possible to the ground plane.

D: The key signal is adjacent to the ground layer and does not cross the partition.

4-layer pcb board:

Option 1: There is a ground plane under the component surface, and the key signal is preferentially placed on the TOP layer. As for the layer thickness setting, there are the following suggestions: 1: Meet the impedance control 2: The core board (GND to POWER) should not be too thick to reduce, ground The distributed impedance of the plane; the decoupling effect of the power plane is guaranteed.

Solution 2: Defect 1: Power supply and ground are too far apart, and the power plane impedance is too large. 2: The power supply and ground plane are extremely incomplete due to the influence of component pads. 3: The signal impedance is discontinuous because the reference plane is incomplete.

Option 3: Similar to scenario 1, for the case where the main device is in the BOTTOM layout or the critical signal is underlying.

6-layer pcb board

Solution 3: One signal layer is reduced, and one internal power layer is added. Although the available wiring level is reduced, the pcb design solution solves the defects common to the first and second solutions.

Advantages: 1: The power and ground layers are tightly coupled. 2: Each signal layer is directly adjacent to the inner layer, and is effectively isolated from other signal layers, and crosstalk is less likely to occur. 3: Siganl_2 (Inner_2) and two inner 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 layers can effectively shield the external interference to the Siganl_2 (Inner_2) layer and the interference of the Siganl_2 (Inner_2) to the outside world.

Solution 1: Four layers of signal layers and two layers of internal power/ground layers are used, with more signal layers, which facilitates the wiring work. Defect: 1: The power and ground layers are separated far apart and are not fully coupled. 2: The signal layer Siganl_2 (Inner_2) and Siganl_3 (Inner_3) are directly adjacent, and the signal isolation is not good, and crosstalk is likely to occur.

8-layer pcb board

10-layer pcb board

to sum up:

1. The key signal layer of the pcb design should be adjacent to the ground. GND should be adjacent to the power to reduce the power plane impedance.

2. Do not adjacent between signal layers to increase the isolation between signals to avoid crosstalk.

3. The signal layer should be adjacent to the ground plane as much as possible, and the adjacent layers should not be wired in parallel.

4. For the transmission line, the top layer is analyzed by the microstrip line model, and the inner signal layer is modeled by the strip line. The signal layers on both sides of the 6 layer/10 layer / 14 layer / 18 layer substrate are preferably software.

5. If there are other power sources, take the thick line first in the signal layer and try not to divide the electric ground. The high-speed line is best to go inside, and the top layer is easily affected by external temperature, humidity, and air, and is not stable.