The number of layers of PCB depends on the complexity of the kous Komisyon Konsèy. From the perspective of PCB processing, multi-layer PCB is made of multiple “double panel PCB” through stacking and pressing process. However, the number of layers, stacking sequence and board selection of multi-layer PCB are determined by the PCB designer, which is called “PCB stacking design”.

Factors to be considered in PCB cascade design

The number of layers and layering of a PCB design depends on the following factors:

1. Hardware cost: The number of PCB layers is directly related to the final hardware cost. The more layers there are, the higher the hardware cost will be.

2. Wiring of high-density components: high-density components represented by BGA packaging devices, the wiring layers of such components basically determine the wiring layers of the PCB board;

3. Signal quality control: for PCB design with high speed signal concentration, if the focus is on signal quality, it is required to reduce the wiring of adjacent layers to reduce the crosstalk between signals. At this time, the ratio of wiring layers and reference layers (Ground layer or Power layer) is best 1:1, which will cause the increase of PCB design layers. Conversely, if the signal quality control is not mandatory, the adjacent wiring layer scheme can be used to reduce the number of PCB layers;

4. Schematic signal definition: Schematic signal definition will determine whether PCB wiring is “smooth”. Poor schematic signal definition will lead to improper PCB wiring and increase of wiring layers.

5. PCB manufacturer’s processing capacity baseline: the stacking design scheme (stacking method, stacking thickness, etc.) given by PCB designer must take full account of PCB manufacturer’s processing capacity baseline, such as processing process, processing equipment capacity, commonly used PCB plate model, etc.

PCB cascading design requires prioritizing and balancing all of the above design influences.

General rules for PCB cascade design

1. The formation and the signal layer should be tightly coupled, which means that the distance between the formation and the power layer should be as small as possible, and the thickness of the medium should be as small as possible, so as to increase the capacitance between the power layer and the formation (if you don’t understand here, you can think of the capacitance of the plate, the size of the capacitance is inversely proportional to the spacing).

2, two signal layers as far as possible not directly adjacent, so easy to signal crosstalk, affect the performance of the circuit.

3, for multi-layer circuit board, such as 4 layer board, 6 layer board, the general requirements of the signal layer as far as possible and an internal electrical layer (layer or power layer) adjacent, so that you can use the large area of the internal electrical layer copper coating to play a role in shielding the signal layer, so as to effectively avoid crosstalk between the signal layer.

4. For the high-speed signal layer, it is generally located between two internal electrical layers. The purpose of this is to provide an effective shielding layer for high-speed signals on the one hand, and to limit high-speed signals between two internal electrical layers on the other hand, so as to reduce the interference of other signal layers.

5. Consider the symmetry of the cascade structure.

6. Multiple grounding internal electrical layers can effectively reduce grounding impedance.

Recommended cascading structure

1, the high frequency wiring cloth in the top layer, in order to avoid the use of high frequency wiring to the hole and induction inductance. The data lines between the top isolator and the transmitting and receiving circuit are directly connected by high frequency wiring.

2. A ground plane is placed below the high frequency signal line to control the impedance of the transmission connection line and also provide a very low inductance path for the return current to flow through.

3. Place the power supply layer under the ground layer. The two reference layers form an additional hf bypass capacitor of approximately 100pF/ INCH2.

4. Low-speed control signals are arranged in the bottom wiring. These lines have a larger margin to withstand impedance discontinuities caused by holes, thus allowing greater flexibility.

Can you understand PCB cascade design

▲ Four-layer laminated plate design example

If additional power supply layers (Vcc) or signal layers are required, the additional second power supply layer/layer must be symmetrically stacked. In this way, the laminated structure is stable and the boards won’t warp. The power layers with different voltages should be close to the formation to increase the high frequency bypass capacitance and thus suppress noise.