Brothers, what is the biggest fear when designing a PCB? It’s not about routing issues, but rather when the board comes back and you power it on—there’s a “bang” or it simply doesn’t work! Those who understand know the feeling.
Today, I will summarize the major pitfalls in PCB layout that I have encountered, seen, and heard over the years. These are lessons learned at a cost, and after reading, you can save a lot on board fabrication and perhaps even some hair!
1. No Capacitor at Power Input—Powering On is Like Opening a Mystery Box
Situation: At the power input, the power chip is directly connected without adding any filtering capacitors.
Consequence: The board works intermittently, has poor anti-interference capability, and plugging in a USB can cause a reboot.
Avoiding the Pitfall: The first step when power comes in is to connect a 10uF-100uF electrolytic capacitor in parallel with a 0.1uF ceramic capacitor for stability.
2. Crystal Oscillator Far from Chip—Clock Signal “Limping”
Situation: Thinking that the crystal oscillator and two small capacitors take up space, they are casually placed in a corner of the board.
Consequence: The long routing of the clock signal is prone to interference, leading to system instability or even failure to oscillate.
Avoiding the Pitfall: The crystal oscillator must be placed right next to the chip’s clock pin, with routing kept as short and direct as possible, and ground isolation underneath.
3. Decoupling Capacitors “Playing Hide and Seek”—Chip Lacks Power
Situation: Assuming that having a capacitor at the power input is sufficient, no decoupling capacitors are placed near each chip’s power pins.
Consequence: When the chip switches at high speed, the instantaneous current supply is insufficient, causing voltage fluctuations and inexplicable resets.
Avoiding the Pitfall: There must be a 0.1uF (or the value recommended in the chip manual) decoupling capacitor between each IC’s power and ground pins, and the closer, the better!
4. Connectors “Anti-Human”—Wiring is All Guesswork
Situation: The schematic looks good, but the wire sequence is defined chaotically, or the connectors are too close to components, making plugging and unplugging extremely difficult.
Consequence: Production testers will “thank” you, and you may also easily plug in the wrong way.
Avoiding the Pitfall: Simulate the wiring process during layout, leave enough operational space, and clearly label the wire sequence.
5. Ignoring Heat Dissipation—Chip Becomes a “Little Heater”
Situation: High-current chips (like LDOs or motor drivers) are placed directly on the board without leaving space for heat dissipation or vias.
Consequence: The chip overheats, efficiency drops, and it may stop working due to thermal protection.
Avoiding the Pitfall: Under heat-generating chips, lay down a large area of copper and create thermal vias connecting to the back ground plane to aid in heat dissipation.
6. Forgetting to Round the Board Corners—Sharp Edges Like a Knife
Situation: The board has four sharp corners that could cut open a box.
Consequence: Scratches on hands, packaging, and potential safety hazards.
Avoiding the Pitfall: After finishing the board outline, habitually round the corners to enhance both aesthetics and safety.
7. Line Width Too Arbitrary—High Current Causes “Meltdown”
Situation: Power lines are routed as thin as signal lines.
Consequence: When carrying high current, the wires heat up, causing excessive voltage drop, or even burning out.
Avoiding the Pitfall: Use a line width calculator based on current size, and ensure power lines are sufficiently thick!
8. High-Frequency Signal Routing “Twists and Turns”—What is Signal Integrity?
Situation: USB, differential signals, clock lines, etc., are routed in a convoluted manner, and layer changes are made without adding return ground vias.
Consequence: Poor signal quality leads to errors in high-speed data communication.
Avoiding the Pitfall: Prioritize routing high-frequency critical signal lines, keeping them as short as possible, minimizing vias and bends, and implementing impedance control when necessary.
9. Components Too Close—Soldering is a “Micro-Sculpture” Art
Situation: To make the board compact, surface mount capacitors and resistors are crammed tightly together.
Consequence: Difficulties in soldering during production, leading to solder bridges, and repairs become a nightmare.
Avoiding the Pitfall: Consult the PCB manufacturer about their process capabilities during layout, and maintain sufficient spacing between components.
10. Forgetting to Perform DRC—Confidence is at its Peak
Situation: After finishing the board, it looks good, and you send it directly for fabrication.
Consequence: Various basic errors like unconnected traces and insufficient spacing lead to the entire board being scrapped.
Avoiding the Pitfall: Before sending for fabrication, be sure to run a DRC check! This is the cheapest and most effective “insurance.”
In conclusion:
PCB design is an experience-based task, and encountering pitfalls is a necessary part of growth. I hope that the pitfalls I have experienced can pave a smoother design path for you!
What memorable pitfalls have you encountered? Feel free to share in the comments so we can all avoid them together!