Why Should PCB Tracks Not Be Laid Out at Right Angles?

Why Should PCB Tracks Not Be Laid Out at Right Angles?

In the intricate world of printed circuit board (PCB) design, every detail matters. One of the fundamental principles that designers adhere to is avoiding the use of right-angle tracks. While it may seem like a minor aesthetic choice, this practice is rooted in a combination of electrical, mechanical, and manufacturing considerations. This article explores the various reasons why PCB tracks should not be laid out at right angles.

Electrical Performance Considerations

Signal Integrity: Right-angle tracks can introduce discontinuities in the signal path, leading to signal reflection and degradation of signal integrity. When a signal encounters a sharp corner, it is forced to change direction abruptly, causing the signal wavefront to spread out, resulting in distortion.

Impedance Mismatch: PCB tracks have a characteristic impedance, which is determined by their dimensions, material properties, and surrounding structures. Right-angle corners can disrupt the impedance continuity, leading to impedance mismatches. These mismatches can cause reflections and standing waves, further degrading signal performance.

Electromagnetic Interference (EMI) and Radio Frequency Interference (RFI): Sharp corners can act as antennas, radiating unwanted electromagnetic energy. This can lead to EMI and RFI issues, affecting the performance of nearby components and circuits.

Mechanical Durability

Stress Concentration: Right-angle corners are points of high stress concentration. During the manufacturing process, as well as during the operational lifetime of the PCB, these corners are prone to cracking and damage due to the concentrated stresses.

Flexibility: In flexible PCBs, right-angle corners can restrict the flexibility of the board, limiting its bending radius and potential for conformal applications.

Solderability: Sharp corners can also affect the solderability of components, as the solder may not flow smoothly into the joints around corners with sharp edges.

Manufacturing Considerations

Etching Accuracy: During the etching process, the acid or chemical used to remove unwanted copper can have difficulty penetrating sharp corners evenly. This can result in uneven track widths and thicknesses, affecting electrical performance.

Drilling Accuracy: When vias or holes need to be drilled near right-angle corners, the drill bit can be deflected by the sharp edge, causing positioning errors and potentially damaging the board.

Automated Inspection: Right-angle corners can be challenging for automated optical inspection (AOI) systems to detect and analyze defects accurately. This can increase the risk of undetected issues in the PCB.

Design Practices to Avoid Right-Angle Tracks

To mitigate the issues associated with right-angle tracks, PCB designers employ various techniques:

Use 45° or Curved Corners: Replacing sharp right-angle corners with 45° angles or curved corners can significantly reduce the impact on signal integrity and impedance continuity.

Increase Track Width: Increasing the track width at the corners can help distribute the stress more evenly and reduce the risk of cracking.

Use Teardrops: Teardrop-shaped extensions at the ends of tracks near vias can improve the strength of the joints and reduce the risk of cracking during thermal cycling.

Consider Routing Algorithms: Advanced routing algorithms in PCB design software can help avoid sharp corners automatically, optimizing the track layout for electrical and mechanical performance.

Conclusion

In PCB design, avoiding right-angle tracks is not just a matter of aesthetics; it is a critical aspect that affects the electrical, mechanical, and manufacturing performance of the board. By understanding the underlying principles and adopting appropriate design practices, PCB designers can create boards that are more reliable, efficient, and cost-effective. With the increasing complexity of modern electronics, adhering to these principles becomes even more crucial for ensuring the overall success of a product.