8 Layer Impedance Control PCB

Eight-layer boards usually use the following three stacking methods

This is not a good lamination method due to poor electromagnetic absorption and large power supply impedance.

Its structure is as follows:

Signal 1-----------------Component surface, microstrip wiring layer

Signal 2-----------------internal microstrip wiring layer, better wiring layer (X direction)

Ground

Signal 3----------------- Stripline routing layer, better routing layer (Y direction)

Signal 4----------------- Stripline routing layer

Power

Signal 5----------------- internal microstrip wiring layer

Signal 6----------------- Microstrip trace layer

It is a variant of the third stacking method. Due to the addition of the reference layer, it has better EMI performance, and the characteristic impedance of each signal layer can be well controlled:

Signal 1--------------------Component surface, microstrip wiring layer, good wiring layer

Ground stratum--------- good electromagnetic wave absorption ability

Signal 2-------------------Stripline routing layer, good routing layer

Power power layer-----forming excellent electromagnetic absorption with the ground layer

Ground

Signal 3-------------------Stripline routing layer, good routing layer

Power ground layer-----with large power supply impedance

Signal 4 --------------------Microstrip wiring layer, good wiring layer

The best stacking method, due to the use of multi-layer ground reference planes, it has very good geomagnetic absorption capacity.

Signal 1---------------------Component surface, microstrip wiring layer, good wiring layer

Ground stratum-----------good electromagnetic wave absorption ability

Signal 2----------------------Stripline routing layer, good routing layer

Power power laye---------forming excellent electromagnetic absorption with the ground layer below

Ground

Signal 3----------------------Stripline routing layer, good routing layer

Ground stratum-----------good electromagnetic wave absorption ability

Signal 4--------------------- Microstrip wiring layer, good wiring layer

Impedance control for 8 layer pcb

For 8 layer pcb boards, let's explain the stacking and impedance situation from a project we have done before.

As shown in the picture above, this project has made 8-layer boards. For the lamination, three core boards are used (both sides contain copper plates, which can be regarded as a two-layer board). The three core boards have 6 layers. , Stack the prepreg and copper plate on both sides to form an 8-layer board.

Design requirements for trace impedance:

1. The L8 layer of the highlighted part has an impedance of 100 ohms referring to L7

2.The L3 layer of the highlighted part has an impedance of 100 ohms with reference to L2/L4

3.The L8 layer of the highlighted part has an impedance of 90 ohms with reference to L7

4. The L8 layer of the highlighted part has an impedance of 50 ohms with reference to L7

5.The L6 layer of the highlighted part has an impedance of 50 ohms with reference to L5/L7

6.The L3 layer of the highlighted part has an impedance of 50 ohms with reference to L2/L4

7.The L1 layer of the highlighted part has an impedance of 50 ohms with reference to L2

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