The electromagnetic compatibility analysis of multilayer PCB boards can be based on Kirchhoff's law and Faraday's law of electromagnetic induction.
Based on the above two laws, we conclude that the following basic principles should be followed in the delamination and stacking of multilayer printed boards:
1 The power plane should be as close as possible to the ground plane and should be below the ground plane.
2 The wiring layer should be arranged adjacent to the image plane layer.
3 Power and formation impedance are lowest. Wherein the power supply impedance Z0 = where D is the distance between the power plane and the ground plane. W is the area between the planes.
4 A strip line is formed in the middle layer, and a microstrip line is formed on the surface. The characteristics of the two are different.
5 Important signal lines should be close to the ground.
Stacking and delamination of PCB boards
1 two-layer board. This board can only be used in low speed designs. EMC is relatively poor.
2 four-layer board. The stacking order is as follows. The different stacking advantages and disadvantages are explained below.
A case should be the best case of a four-layer board. Because the outer layer is the ground layer, it has a shielding effect on EMI, and the power layer is also reliable close to the ground layer, so that the internal resistance of the power source is small, and the best suburban fruit is obtained. However, the first case cannot be used when the density of the board is relatively large. Because of this, the integrity of the first layer cannot be guaranteed, and the second layer signal will become worse. In addition, this structure cannot be used in the case where the power consumption of the whole board is relatively large.
The B case is the most common way we usually use. From the structure of the board, it is not suitable for high-speed digital circuit design. Because in this configuration, it is difficult to maintain a low power supply impedance. Take a plate of 2 mm as an example: Z0 = 50 ohms is required. The line width is 8 mils. The thickness of the copper foil is 35 цm. Thus the middle of the signal layer is 0.14mm between the ground and the ground. The formation and power layer are 1.58mm. This greatly increases the internal resistance of the power supply. In this structure, since the radiation is spatial, it is necessary to add a shield plate to reduce EMI.
In case of C, the signal quality on the S1 layer is the best. S2 is second. It has a shielding effect on EMI. However, the power supply impedance is large. This board can be used when the power consumption of the whole board is large and the board is the source of interference or close to the source of interference.
3 six-layer board
A case is one of the common ways, and S1 is a good wiring layer. S2 is second. However, the power plane impedance is poor. Pay attention to the influence of S2 on the S3 layer when wiring.
In case B, the S2 layer is a good wiring layer, at the S3 level. The power plane impedance is better.
In case of C, this is the best case of a six-layer board, and S1, S2, and S3 are all good wiring layers. The power plane impedance is better. The fly in the ointment is that the wiring layer is one layer less than the first two cases.
In the case of D, in the six-layer board, although the performance is better than the first three, the wiring layer is less than the first two. This situation is mostly used in the backplane.
4 eight-layer board
Eight-layer board, if there are 6 signal layers, it is best to use A. However, this arrangement is not suitable for high speed digital circuit design. If it is 5 signal layers, it is best to use C. In this case, S1, S2, and S3 are all good wiring layers. At the same time, the power plane impedance is also relatively low. If it is 4 signal layers, it is best to use B in Table 3. Each signal layer is a good wiring layer. In these cases, adjacent signal layers should be routed.
5 ten-layer board
If there are 6 signal layers in the ten-layer board, there are three stacking sequences of A, B, and C. The A case is the best, the C type is the second, and the B case is the worst. Other cases not listed are worse than these cases. In the case of A, S1, S6 are better wiring layers. S2, S3, S5 second. In particular, it should be pointed out that the reason why A is the same as C and A is better than that of C. The main reason is that in the case of C, the distance between the GND layer and the POWER layer is determined by the distance between S5 and GND. This does not necessarily ensure that the GND layer and the POWER layer have the lowest power plane impedance. The case of D should be said to be the best stacking order of the ten layers. Each signal layer is an excellent wiring layer. E and F are mostly used for the backboard. Among them, the shielding effect of F is better than that of E. The downside is that the two signal layers are connected, and attention should be paid to the wiring.
In short, the layering and lamination of PCBs is a complicated matter. There are many factors to consider. But we should remember the features we are going to accomplish and the key factors that are needed. In this way, we can find a layered and laminated sequence of printed boards that meet our requirements.