How many layers of PCB depends on the complexity of the circuit board, from the point of view of the PCB processing, multi-layer PCB is more than one "double-sided PCB" through the stacking, compression process out of manufacturing. However, the number of layers of multi-layer PCB, the stacking order between the layers and the choice of boards is determined by the circuit board designer, which is known as the "PCB layer stacking design".
Factors to Consider in PCB Layer Stacking Design
A PCB design of the number of layers and layer stacking program depends on the following factors:
1. The cost of hardware: PCB layer number of how much is directly related to the final hardware costs, the more layers of hardware costs are higher, represented by consumer products, hardware PCB for the number of layers generally have the highest limitations, such as laptop products, the number of layers of the motherboard PCB is usually 4 ~ 6, rarely more than 8 layers.
2. High-density components out of the line: BGA package devices as a representative of high-density components, such components out of the line layer number basically determines the number of PCB board wiring layer.
3. Signal quality control: for high-speed signals are more concentrated PCB design, if the focus on signal quality, then it is required to reduce the adjacent layer wiring to reduce crosstalk between signals, then the number of layers of wiring layers and the number of reference layer (Ground layer or Power layer) ratio of the best is 1:1, will cause an increase in the number of layers of the PCB design; on the contrary, if the quality of the signal control is not mandatory requirements On the other hand, if the signal quality control is not mandatory, you can use the adjacent wiring layer program, thereby reducing the number of PCB layers.
4. The schematic signal definition: the schematic signal definition will determine whether the PCB wiring "smooth", the poor definition of the schematic signal will lead to PCB wiring is not smooth, the number of wiring layers increased.
5. PCB manufacturers processing capacity baseline: PCB designers to give the layer stacking design program (stacking method, stacking thickness, etc.), we must fully consider the PCB manufacturer's processing capacity baseline, such as: the processing process, processing equipment capacity, commonly used PCB board models, etc.
PCB stacking design needs to be in all of the above design influences to seek priority and balance point.
General rules of PCB stacking design
1. The ground layer and the signal layer should be tightly coupled, meaning that the distance between the ground layer and the power layer should be as small as possible, the dielectric thickness should be as small as possible, in order to increase the capacitance between the power layer and the ground layer (if you don't understand, you can think of a flat capacitance, capacitance is inversely proportional to the distance between the size of the capacitance).
2. Try not to be directly adjacent to each other between the two signal layers, which is prone to signal crosstalk, affecting the performance of the circuit.
3. for multi-layer circuit boards, such as 4-layer board, 6-layer board, generally require the signal layer as far as possible with an internal electrical layer (ground layer or power layer) adjacent, so that you can use the internal electrical layer of large-area copper cladding to play a shielding role of the signal layer, thus effectively avoiding the crosstalk between the signal layer.
4. for high-speed signal layer, generally to be located between the two internal electrical layer, the purpose of doing so is to play on the one hand to provide an effective shielding layer of high-speed signals, on the other hand, the high-speed signals will be limited to the two internal electrical layer between the other signal layer to reduce the interference.
5. Consider the symmetry of the laminated structure.
6. More than one grounded internal electric layer can effectively reduce the grounding impedance.
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