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What causes a PCB short circuit?
In addition, there is a netlist that lists the connections between components in an electronic circuit. Netlist mismatches can lead to short circuits or other problems on the PCB. This fault can be identified in the Gerber files when performing engineering review using a CAM application.
What causes PCB short circuits?
Here are some common causes of PCB short circuits.
1. External Contamination
Short circuits are often caused by external contamination of the board after prolonged operation in the intended environment. Contact with substances during board assembly can also lead to short circuits. Causes include:
● Insufficient cleaning, including flux residue
● Salt accumulation after contact with water
● Contact with conductive dust or metallic debris
● Growth of copper dendrites between closely spaced conductors
Enclosing the PCB in a waterproof housing protects it from moisture and debris, but may not prevent short circuits caused by no-clean flux residue. These residues have some conductivity and may become more conductive over time.
2. Internal CAF Growth
Internal conductive anodic filament (CAF) growth is a significant cause of printed circuit board (PCB) short circuits. This is because contaminants typically do not enter the inside of a PCB once the board is constructed. However, electrochemical reactions within the inner layers can lead to short circuits. In short, this is a phenomenon that occurs within the inner layers of a PCB, potentially causing unintended connections between conductive traces or layers.
Over time, electrochemical reactions within the inner layers of a PCB (often influenced by factors such as humidity, temperature, and electrical bias) can lead to the formation of conductive anodic filaments. These filaments represent tiny conductive pathways that bridge the fiberglass bundles within the PCB laminate.
Therefore, to mitigate short circuits related to CAF, you must take various measures to minimize the presence of conductive contaminants, ensure proper insulation, and design the PCB to reduce the likelihood of filament formation. These preventative measures are crucial for improving the reliability and safety of electronic devices and systems.
3. Stencil Contamination/Oversize and Misalignment
During the manufacturing of a PCB, solder paste is applied to the component pads and vias. The design is then put into a wave soldering/reflow soldering production line, causing the solder paste to melt and form an electrical connection from the component to the PCB. Misalignment when applying solder paste to component leads can cause a short circuit between two leads on a component. Misalignment can cause leads to connect adjacent pads or solder to bridge between two leads.
The size of the PCB pads may now be aligned with the stencil used to apply the solder paste, which may have aperture sizes. If the aperture is too large, the solder paste and resulting solder joint may spread to multiple pads. If the aperture is too small, the solder joint may not consistently reach the lead, resulting in a weak connection. The pad sizes in the package and the component lead sizes may not match.
4. Undetected Design Errors
In some cases, design errors can lead to short circuits. If a thorough PCB design review is not conducted before production, the final printed circuit board assembly (PCBA) may have short circuits and fail to operate as intended.
Additionally, there is a netlist, which lists the connections between components in an electronic circuit. Netlist mismatches can cause short circuits or other problems in the PCB. This fault can be identified in the Gerber files when using a CAM application for engineering review.
Furthermore, if the CAM department finds issues, they will send the project back to you with details on what needs to be corrected. This may involve adjusting the design files to fix the errors.
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