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This article mainly explains "what are the rules of PCB stack design". Interested friends may wish to have a look at it. The method introduced in this paper is simple, fast and practical. Next, let the editor take you to learn "what are the rules of PCB lamination design"?

Generally speaking, there are two main rules for lamination design:

1. Each alignment layer must have an adjacent reference layer (power supply or stratum)

two。 The adjacent main power layer and stratum should maintain a minimum distance to provide a larger coupling capacitance.

The following is a list of layers from two-layer to eight-layer plates for example explanation:

1. Lamination of one-sided PCB board and double-sided PCB board

For the two-layer plate, due to the small number of layers, there is no problem of lamination. Controlling EMI radiation is mainly considered in terms of wiring and layout.

The problem of electromagnetic compatibility of single-layer and double-layer plates is becoming more and more prominent. The main reason for this phenomenon is that the area of the signal loop is too large, which not only produces strong electromagnetic radiation, but also makes the circuit sensitive to external interference. To improve the electromagnetic compatibility of the line, the easiest way is to reduce the loop area of the key signal.

Key signal: from the point of view of electromagnetic compatibility, the key signal mainly refers to the signal that produces strong radiation and the signal which is sensitive to the outside world. Signals that can produce strong radiation are generally periodic signals, such as clocks or low-order signals of addresses. Signals that are sensitive to interference refer to those analog signals at lower levels.

Single-layer and double-layer plates are usually used in low-frequency simulation designs lower than 10KHz:

1) the power supply wiring on the same floor is in the form of radiation and minimizes the sum of the length of the lines.

2) when walking the power supply and ground wire, get close to each other; lay a ground wire on the edge of the key signal wire, which should be as close as possible to the signal wire. In this way, a smaller loop area is formed and the sensitivity of differential mode radiation to external interference is reduced. When a ground wire is added next to the signal line, a circuit with the smallest area is formed, and the signal current is sure to pass through this circuit rather than other ground wire paths.

3) if it is a double-layer circuit board, you can lay a ground wire along the signal line on the other side of the circuit board, close to the signal line, and the first line is as wide as possible. The resulting loop area is equal to the thickness of the circuit board multiplied by the length of the signal line.

The lamination of two and four layers.

1. SIG-GND (PWR)-PWR (GND)-SIG

2. GND-SIG (PWR)-SIG (PWR)-GND

For the above two kinds of laminated design, the potential problem is for the traditional 1.6mm (62mil) thickness. The spacing between layers will become very large, which is not conducive to the control of impedance, interlayer coupling and shielding, especially the large spacing between power layers, which reduces the plate capacitance and is not conducive to noise filtering.

For the first scheme, it is usually used in the case of more chips on the board. This scheme can get better SI performance, but it is not very good for EMI performance, which is mainly controlled by routing and other details. Main attention: the stratum is placed in the connecting layer of the signal layer with the densest signal, which is beneficial to absorb and restrain radiation, and the plate area is enlarged to reflect the 20H rule.

For the second scheme, it is usually used in situations where the density of the chip on the board is low enough and there is a sufficient area around the chip (placing the required power supply copper cladding). In this scheme, the outer layer of PCB is stratum, and the middle two layers are signal / power layer. The power supply on the signal layer is wired with a wide line, which can make the path impedance of the power supply current low, and the impedance of the signal microstrip path is also low, and it can also shield the inner layer signal radiation through the outer layer. From the point of view of EMI control, this is the best 4-tier PCB structure available.

Main attention: the distance between the mixed layers of the middle two layers of signal and power supply should be pulled apart, the direction of the line should be vertical to avoid crosstalk; the appropriate area of the control board should reflect the 20H rule; if you want to control the wire impedance, the above scheme should be very careful to arrange the wiring at the bottom of the power supply and grounding copper island. In addition, the power supply or copper laying on the stratum should be interconnected as much as possible to ensure the connectivity between the DC and the low frequency.

The lamination of three or six layers.

For the design with high chip density and high clock frequency, the design of 6-layer board should be considered, and the lamination mode is recommended.

1.SIG-GND-SIG-PWR-GND-SIG

For this scheme, this stacking scheme can obtain better signal integrity, the signal layer is adjacent to the connecting layer, the power layer and the connecting layer are paired, the impedance of each alignment layer can be well controlled, and both layers can absorb magnetic lines. And in the case of complete power supply and formation, it can provide a better reflux path for each signal layer.

2.GND-SIG-GND-PWR-SIG-GND

For this scheme, this scheme is only suitable for cases where the device density is not very high, this kind of stack has all the advantages of the upper layer, and the ground plane of the top layer and bottom layer is more complete, so it can be used as a better shielding layer. It should be noted that the power layer should be close to the layer of the non-main component, because the underlying plane will be more complete. Therefore, the performance of EMI is better than the first scheme.

Summary: for the six-layer plate scheme, the distance between the power layer and the stratum should be reduced as far as possible in order to obtain good power and ground coupling. However, although the thickness and layer spacing of 62mil are reduced, it is not easy to control the distance between the main power supply and the ground layer very small. Compared with the first scheme and the second scheme, the cost of the second scheme is greatly increased. Therefore, when we stack layers, we usually choose the first option. When designing, follow the 20H rule and the mirror layer rule

The lamination of four or eight layers.

1. This is not a good lamination method due to poor electromagnetic absorption capacity and large power supply impedance. Its structure is as follows:

1.Signal 1 component surface, micro-take-away line layer

2.Signal 2 internal micro-take-away line layer, better alignment layer (X direction)

3.Ground

4.Signal 3 ribbon line alignment layer, better alignment layer (Y direction)

5.Signal 4 stripline alignment layer

6.Power

7.Signal 5 internal micro-stripper layer

8.Signal 6 micro-stripper layer

2. It is a variation of the third stacking mode. 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.

1.Signal 1 component surface, micro-take-away line layer, good alignment layer

2.Ground formation, good electromagnetic wave absorption capacity

3.Signal 2 stripline wiring layer, good wiring layer

The 4.Power power layer, together with the strata below, form an excellent electromagnetic absorption 5.Ground layer.

6.Signal 3 ribbon wire alignment layer, good alignment layer

7.Power formation with large power impedance.

8.Signal 4 micro-take-away wire layer, good alignment layer

3. The best way of stacking, due to the use of multi-layer reference plane has a very good geomagnetic absorption capacity.

1.Signal 1 component surface, micro-take-away line layer, good alignment layer

2.Ground formation, good electromagnetic wave absorption capacity

3.Signal 2 stripline wiring layer, good wiring layer

The 4.Power power layer, together with the strata below, form an excellent electromagnetic absorption 5.Ground layer.

6.Signal 3 ribbon wire alignment layer, good alignment layer

7.Ground formation, good electromagnetic wave absorption capacity

8.Signal 4 micro-take-away wire layer, good alignment layer

How to choose several layers and how to stack them depends on the number of signal networks on the board, device density, PIN density, signal frequency, board size and many other factors. We should take these factors into consideration. The more the number of signal networks, the greater the device density, the greater the PIN density, and the higher the signal frequency, the design of multilayer board should be adopted as far as possible. In order to get good EMI performance, it is best to ensure that each signal layer has its own reference layer.

At this point, I believe you have a deeper understanding of "what are the rules of PCB lamination design". You might as well do it in practice. Here is the website, more related content can enter the relevant channels to inquire, follow us, continue to learn!

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