Multilayer PCB circuit board circuit board wiring is an important link in electronic design, it is related to the performance of the circuit, reliability and cost.
1. Multi-layer PCB design process
1.1. Preparation before design
Before starting a multi-layer PCB design, a number of preparations need to be made, including:
a. Determine the function and performance requirements of the circuit, including signal frequency, current size, voltage level, etc.
b. Select the appropriate PCB board, including the thickness of the board, dielectric constant, thermal conductivity, etc.
c. Determine the size and shape of the PCB, and the layout of the components.
d. Understand the relevant design codes and standards, such as IPC-2221, IPC-7351, etc.
1.2. Schematic design
Schematic design is the first step of multi-layer PCB design, which needs to draw the schematic diagram of the circuit according to the function and performance requirements of the circuit, including the symbol of the component and the connection method.
1.3. Component layout
Component layout is the process of placing the components in the schematic onto the PCB, and factors such as the size, shape, and direction of the components need to be considered to achieve a reasonable layout of the components.
1.4. Wiring
Wiring is the most critical step in the design of multi-layer board PCB, which needs to be reasonable according to the flow direction of the signal, the size of the current, the level of voltage and other factors.
1.5. Design inspection and optimization
After the wiring is completed, it is necessary to carry out design inspection and optimization, including checking whether the wiring meets the design specifications, whether there is a short circuit, and whether the signal integrity meets the requirements.
1.6. Production and testing
Finally, the designed multi-layer PCB is delivered to the manufacturer for production, and related tests are carried out to ensure the performance and reliability of the circuit.
2. Multi-layer PCB wiring skills
2.1. Wiring direction
When routing multi-layer PCB, it is necessary to follow certain direction principles to reduce signal interference and improve signal integrity. In general, signal lines should be routed as far as possible along the straight direction, avoiding right angles and acute angles.
2.2. Wiring width
The selection of the wiring width needs to consider the size of the current and the frequency of the signal. For high-current lines, it is necessary to choose a wider line width to reduce resistance and heat generation; For high frequency signals, a narrow line width needs to be selected to reduce parasitic capacitance and inductance.
2.3. Wiring spacing
The choice of wiring spacing needs to consider signal isolation and electromagnetic compatibility. For adjacent signal lines, it is necessary to maintain a certain distance to avoid signal interference; For power cables and ground cables, they need to be as close as possible to improve the stability of the power supply and reduce electromagnetic interference.
2.4. Through hole design
The hole is an important component connecting different layers in the multi-layer PCB, and the size, position and number of the hole need to be reasonably designed. The size of the hole should be selected according to the size of the current and the frequency of the signal, and the position of the hole should be as close as possible to the pad of the component to reduce parasitic inductance and capacitance.
2.5. Ground cable design
Ground wire is an important reference plane in multi-layer PCB, and the layout and connection mode of ground wire need to be reasonably designed. The ground wire should form a complete loop as far as possible to improve the stability of the signal and reduce electromagnetic interference. At the same time, the ground wire should be as close as possible to the power cord and signal line to achieve good signal isolation and power stability.
2.6. Power cable design
The power cord is an important power supply line in the multi-layer PCB, and the layout and connection mode of the power cord need to be reasonably designed. The power line should be as short and thick as possible to reduce resistance and heat; At the same time, the power cord should be as close as possible to the ground wire to improve the stability of the power supply and reduce electromagnetic interference.
3. Signal integrity
Signal integrity is an important index in multilayer PCB design, which is related to the performance and reliability of the circuit. To improve signal integrity, the following aspects need to be considered:
3.1. Transmission line effect
The transmission line effect is the phenomenon that occurs when the signal is transmitted in the PCB, including reflection, distortion, attenuation, etc. In order to reduce the transmission line effect, it is necessary to design the impedance, length and wiring mode of the signal line reasonably.
3.2. Crosstalk
Crosstalk is the mutual interference between adjacent signal lines, resulting in signal distortion and error. In order to reduce crosstalk, it is necessary to reasonably design the spacing, ground wire and shielding of signal lines.
3.3. Clock jitter
Clock jitter is a common problem in digital circuits, which can lead to signal instability and error. In order to reduce clock jitter, it is necessary to reasonably design the routing mode, impedance and terminal matching of the clock line.
3.4. Signal integrity simulation
Signal integrity simulation is an important tool in multilayer PCB design that can help designers predict and optimize signal integrity issues. In the design process, professional simulation software, such as HFSS, ADS, etc., should be used for signal integrity simulation and optimization.
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