What are the common problems in PCB circuit board design

　　PCB circuit board design is a complex and rigorous process, and any negligence in any link can lead to board failure, performance non-compliance, or increased costs. The following are common problems in PCB design, classified by category:

　　1、 Layout and structural issues

　　Unreasonable layout planning

　　Module confusion: The distance between the associated circuits (such as MCU and its clock, memory, power supply) is too far, resulting in lengthy wiring, introducing noise and delay.

　　Adjacent thermal and heating elements: If a precision reference voltage source is placed near a power inductor or chip, it can cause temperature drift and unstable performance.

　　Inappropriate interface position: The input/output interface is located in the center of the board, forcing sensitive signal lines to pass through the entire board, making it susceptible to interference.

　　Improper stacking design

　　The distance between the signal layer and the return layer is too far: it leads to an increase in the impedance of the signal circuit and a decrease in electromagnetic compatibility.

　　Incomplete power supply/formation: There are numerous partitions and gaps that disrupt the low impedance return path, causing issues with signal integrity and power supply integrity.

　　Asymmetric sequence: may cause PCB warping during board fabrication or reflow soldering.

　　2、 Wiring related issues

　　Signal integrity issues

　　Impedance discontinuity: The width of high-speed signal lines (such as USB, HDMI, differential pairs) suddenly changes, no reflow through holes are added during layer switching, and right angle wiring causes signal reflection and distortion.

　　The key wiring is too long: clock lines, high-speed data lines, reset lines, etc. are not routed along short paths, which increases the risk of transmission delay and interference.

　　Crosstalk: Insufficient spacing between parallel long-distance lines or lack of isolation with ground wires, resulting in mutual interference between adjacent signal lines.

　　Power integrity issues

　　Power channel bottleneck: The wiring that supplies power to the chip is too thin, or there are high impedance points on the path, resulting in excessive actual voltage drop (IR Drop) to the chip pins.

　　Improper arrangement of decoupling capacitors: too far away from the chip power pin, unable to effectively filter out high-frequency noise. The grounding circuit of the capacitor is too long, causing it to fail.

　　Chaotic power plane segmentation: Different power domains are divided to form "narrow channels" or "islands", which affect current transmission.

　　Basic wiring error

　　Antenna effect: Long and loop free suspended wiring in RF or high-frequency circuits, which becomes a radiation interference source or receiving antenna.

　　Excessive loop area: Especially when the loop area formed by the power supply circuit or signal return path is large, it is easy to radiate or receive electromagnetic interference.

　　Differential pair wiring mismatch: Differential pair wires have inconsistent lengths, uneven spacing, and loose coupling, seriously damaging their ability to resist common mode interference.

　　3、 Power and ground (GND) issues

　　Improper handling of 'land' (common and harmful)

　　The ground plane is severely cut by signal lines, which damages the integrity of the ground.

　　Improper mixing of digital ground and analog ground: Failure to perform segmentation or processing errors after segmentation (such as improper selection of single point grounding position), resulting in digital noise entering the analog circuit.

　　Grounding circuit: Forming multiple grounding paths may cause common mode interference and noise.

　　Design flaws in the power tree

　　Failure to clarify the power on/off sequence of each chip may result in latch up or startup failure.

　　Improper selection or placement of power devices such as fuses, magnetic beads, and inductors can affect the quality and protection function of the power supply.

　　4、 Device and manufacturing related issues

　　The packaging does not match the actual product

　　The mapping error between schematic symbols and PCB packaging pin sequence (especially multi pin chips, connectors, transistors) resulted in the board being completely unusable.

　　The packaging size is incorrect, resulting in components that cannot be soldered or have spacing conflicts.

　　Not considering manufacturability

　　Welding problem: The pad size is too small and the spacing is too close (not in line with the manufacturer's process capability), resulting in difficulty in welding, bridging, or virtual welding.

　　Screen printing issues: screen printing cover solder pads, screen printing too small to recognize, missing or incorrect polarity markings.

　　Test point issue: Failure to reserve test points for critical networks, or test points being obstructed by components, poses significant difficulties for debugging and maintenance.

　　Process edges and positioning holes: Insufficient process edges and positioning holes were reserved during panel design, which affected SMT surface mount processing.

　　5、 Heat dissipation and safety related issues

　　Lack of heat dissipation design

　　High power devices (such as MOSFETs, LDOs, processors) did not consider heat dissipation paths, did not design sufficient copper skin heat dissipation areas, or did not reserve heat sink positions, resulting in device overheating and failure.

　　The thermal sensing element is arranged on the air duct downstream of the heat source.

　　Insufficient safety spacing

　　In high-voltage circuits (such as AC-DC power supply), the electrical clearance and creepage distance between primary and secondary, and between wires and board edges do not meet safety standards, posing a risk of breakdown or fire.

　　Summary and Recommendations

　　The vast majority of PCB design problems stem from "lack of experience" and "inspection omissions". To avoid these issues:

　　Follow the rules: Set strict design rules (line width, spacing, length, topology) for different networks (high-speed, power, simulation) in EDA tools.

　　Modular layout: First, perform functional module division and pre layout.

　　Pay attention to the return path: always consider the return current path of the signal to ensure its smoothness and low impedance.

　　Use inspection tools: After completing the layout, be sure to run the design rule check and electrical rule check.

　　Perform simulation: Perform signal/power integrity pre simulation on critical high-speed circuits and power networks.

　　Communicate with manufacturers: Consult with PCB and SMT factories on their process capabilities and requirements in the early stages of design.

　　Successful PCB design is a balance achieved between electrical performance, mechanical structure, heat management, and manufacturability.