Eight-layer boards usually use the following three stacking methods.
The first stacking method:
The first layer: component surface, microstrip routing layer
The second layer: internal microstrip routing layer, better routing layer
The third layer: stratum
The fourth layer: stripline wiring layer, better wiring layer
The fifth layer: stripline wiring layer
The sixth layer: power layer
Seventh layer: internal microstrip routing layer
Eighth layer: microstrip routing layer
It can be seen from the above description that this stacking method has only one power layer and one ground layer, so the electromagnetic absorption capability is relatively poor and the power supply impedance is relatively large, which makes this method not a good stacking method.
The second stacking method:
The first layer: component surface, microstrip wiring layer, good wiring layer
The second layer: formation, better electromagnetic wave absorption capacity
The third layer: stripline wiring layer, good wiring layer
The fourth layer: the power layer, which forms excellent electromagnetic absorption with the underlying stratum
The fifth layer: strata
Layer 6: Stripline wiring layer, good wiring layer
The seventh layer: formation, with a large power supply impedance
The eighth layer: microstrip wiring layer, good wiring layer
It can be seen from the above description that this method adds a reference layer, which has better EMI performance, and the characteristic impedance of each signal layer can be well controlled.
The third stacking method:
The first layer: component surface, microstrip wiring layer, good wiring layer
The second layer: formation, better electromagnetic wave absorption capacity
The third layer: stripline wiring layer, good wiring layer
The fourth layer: the power layer, which forms excellent electromagnetic absorption with the underlying stratum
The fifth layer: strata
Layer 6: Stripline wiring layer, good wiring layer
The seventh layer: formation, better electromagnetic wave absorption capacity
The eighth layer: microstrip wiring layer, good wiring layer
The third stacking method is the best stacking method, because this method uses a multi-layer ground reference plane and has very good geomagnetic absorption capacity.
Let's explain from a previous project - the lower stack and impedance.
This project is to make 8-layer boards. In terms of lamination, three core boards are used (both sides contain copper boards, which can be regarded as a two-layer board). Three core boards have 6 layers, and the two sides are stacked again. The upper prepreg and copper plate can constitute an 8-layer board.
The stacking method of PCB eight-layer board
Trace impedance design requirements:
1. The L8 layer of the highlighted part refers to L7 to make an impedance of 100 ohms
2. The L3 layer of the highlighted part refers to L2/L4 to make an impedance of 100 ohms
3. The L8 layer of the highlighted part refers to L7 to make an impedance of 90 ohms
4. The L8 layer of the highlighted part refers to L7 to make an impedance of 50 ohms
5. The L6 layer of the highlighted part refers to L5/L7 to make an impedance of 50 ohms
6. The L3 layer of the highlighted part refers to L2/L4 to make an impedance of 50 ohms
7. The L1 layer of the highlighted part refers to L2 to make an impedance of 50 ohms
