Seven steps of PCB layout and wiring and circuit board design skills
PCB layout and routing is a critical step in the circuit board design process, directly affecting the performance and reliability of the circuit. Reasonable layout and wiring can reduce signal interference, improve power distribution and reduce electromagnetic interference. This article will introduce the seven steps of PCB layout and routing, and share some circuit board design skills to help readers better circuit board design.
Before layout and routing, it is necessary to clarify the functions and characteristics of the circuit, including input and output interfaces, signal transmission requirements, power requirements, etc. This helps guide subsequent placement and routing.
2. Select the appropriate PCB size and number of layers
According to the function and characteristics of the circuit, select the appropriate PCB size and number of layers. The proper size and number of layers can meet the layout needs and space constraints of the circuit.
3. Component layout
At the highest level of optimized assembly, design for manufacturability (DFM) rules impose constraints on component layout. If the assembly department allows components to move, the circuit can be properly optimized for easier automated routing. The defined rules and constraints thus affect the layout design. The automatic routing tool will only consider one signal at a time. By setting the routing constraints and setting the layer of the routing signal line, the routing tool can complete the routing as the designer imagined. For example, for the layout of the power cord:
1.In the PCB layout, the power supply decoupling circuit should be designed near the relevant circuits instead of placed in the power supply part, otherwise it will not only affect the bypass effect, but also flow pulsating current on the power line and ground line, causing interference;
2.For the power supply direction inside the circuit, power supply should be taken from the final stage to the previous stage, and the power filter capacitor of this part should be arranged near the final stage;
3.For some main current channels, if the current is to be disconnected or measured during debugging and testing, current gaps should be arranged on the printed wires during layout.
In addition, pay attention to the layout of the regulated power supply, and arrange it on a separate printed board as much as possible. When the power supply and the circuit share the printed board, in the layout, it should avoid the mixed arrangement of the regulated power supply and the circuit components or make the power supply and the circuit share the ground wire. Because this kind of wiring is not only prone to interference, but also cannot disconnect the load during maintenance, and only part of the printed wires can be cut at that time, thus damaging the printed board.
4. Optimize the layout
On the basis of the initial layout, layout optimization is performed. Consider factors such as the shortest signal transmission path, the balance of power distribution, and heat dissipation. At the same time, avoid unnecessary crossing and interlacing wiring to reduce signal interference and electromagnetic radiation.
5. Perform signal integrity analysis
Use signal integrity analysis tools, such as SI simulation software, to evaluate the effect of placement and routing on signal integrity. Check parameters such as timing, noise, and waveform of the signal to ensure that the signal will not be disturbed and lost during transmission and reception on the board.
6.Sixth, power and ground wiring
Arrange power and ground wires reasonably to ensure stable power supply and effective ground wires. Avoid crossing power and ground wires with other signal wires and keep enough distance to reduce mutual interference.
7. Carry out wiring optimization and iteration
According to the results of signal integrity analysis and the actual situation of layout and wiring, the optimization and iteration of wiring are carried out. For the problematic signal lines, adjust and optimize to improve the performance and reliability of the circuit.
8. Board Design Tips
1. Keep signal and power/ground leads separated: try to avoid signal lines and power/ground leads crossing to reduce mutual interference.
2. Use the ground plane layer: In a multi-layer PCB, the use of the ground plane layer can provide a good ground lead and shielding effect, reducing signal noise and electromagnetic interference.
3. Use differential wiring: For high-speed signals, using differential wiring can improve the anti-interference ability and transmission quality of the signal.
4. Consider the issue of heat dissipation: For high-power components, a reasonable layout and heat dissipation design are required to ensure that the temperature of the circuit board is controlled within a safe range.
5. Pay attention to signal spacing and pin spacing: keep the signal spacing sufficient to avoid mutual interference. At the same time, for components with high-density pins, pay attention to the setting of the pin spacing to facilitate wiring and soldering.
PCB layout and routing is a crucial step in circuit board design. The seven major steps include determining circuit functions and characteristics, selecting the appropriate PCB size and number of layers, performing initial layout, optimizing layout, performing signal integrity analysis, conducting power and ground wiring, and performing layout optimization and iteration. At the same time, some board design techniques, such as keeping signal and power/ground leads separated, using ground plane layers, using differential routing, etc., can also help improve board performance and reliability. Through reasonable layout and routing and skill application, the stability, reliability and performance improvement of the circuit board can be ensured.