What are PCB Panel Rails? Why Can't Your Design Live Without Them?

August 17, 2025

If you are an electronics enthusiast, hardware engineer, or just starting with PCB design, you may have come across the term "Panel Rails" (also known as grip edges or conveyor edges) in board specifications or manufacturer's工艺 requirements. It looks like an extra strip of blank area on the edge of the board, seemingly wasting material. So, what is its purpose? Why are almost all mass-produced circuit boards inseparable from it? Today, we will delve into this crucial concept.

1.Definition of Panel Rails: More Than Just an Extra Edge

Panel Rails refer to additional blank strip areas added to the sides or periphery of a PCB panel. This area contains no components or traces, and its core purpose is to meet the production needs of automated assembly equipment.

Simply put, it is the "safety zone" and "operation zone" where the circuit board is clamped and transported by machine rails and clamps during automated processes such as SMT assembly, DIP plug-in, and testing.

2.Why are Panel Rails Needed? A Necessity for Automated Production

Imagine what would happen without panel rails:
1.Unable to Secure the Board: The rails and clamps of modern SMT pick-and-place machines need to grip both sides of the board to accurately transport it to the placement position. If the board edges are filled with components, the clamps either cannot grip or will crush the components.
2.Low Production Efficiency: Single small boards without panel rails (especially small-sized ones) cannot be transported stably on the conveyor line, easily causing jams or misalignment, leading to extremely low production efficiency and making mass automated production nearly impossible.
3.Affects Soldering: During wave soldering, the board needs to be driven by chains through the solder wave. Without panel rails to provide clamping points, the chains could damage components on the board edge.

Therefore, the process side serves as a crucial bridge connecting PCB design with modern mass production. According to the official process specifications of well-known PCB manufacturers JLCPCB and PCBWay, they both clearly stipulate that for boards requiring SMT mounting, process edges must be reserved; otherwise, production may not be possible or additional charges may be incurred.

3.Key Design Specifications for Panel Rails

Just adding an edge isn't enough; improper design can also cause production issues. Here are the core specifications summarized from major manufacturers' requirements:
1.Minimum width: It is usually required to be no less than 5mm. Some larger equipment may require a wider (such as 8mm) process edge to ensure the stability and accuracy of clamping. For instance, in the SMT assembly process requirements of JLCPCB, it is explicitly recommended that the width of the process edge be 5mm.
2.Space requirements: Within the process edge range, no components, pads or traces are allowed to be placed. It must be kept absolutely blank to avoid being damaged by the machine's gripper.
3.Mark Point Requirements: This is crucial! To help the pick-and-place machine with precise positioning, fiducial marks must be added to the panel rails.
Quantity: Typically, at least one global fiducial mark is placed on opposite diagonals of the panel rails.
Size: A solid exposed copper circle with a recommended diameter of 1.0mm.
Background: The fiducial mark needs a 1.5mm - 2mm solder mask clearance (solder mask opening) around it, and the background color should provide high contrast with the mark itself (e.g., bright copper color against dark green solder mask) to ensure clear recognition by the camera.
4.V-Cut and Mouse Bites: If using a panel, the panel rails are usually connected to the main board via V-Cut (V-scoring) or mouse bites. V-Cut is more common, but strength needs attention—it must be strong enough not to break during production yet easy to break apart finally.

4.Panelization and Panel Rails: The Perfect Partnership

Panel rails often appear together with the concept of Panelization. To maximize production efficiency, manufacturers often combine multiple identical or different small circuit boards into a large panel.
Panel: The entire assembled large board, including the outer panel rails, used for the production line.
Single Board: The individual functional circuit board.
Process: After the panel completes all SMT, testing, etc., a depanelizer (or manually) separates the individual boards along the V-Cut or mouse bites, and the panel rails are removed, yielding the final individual products.

5. Conclusion

Although panel rails do not participate in any circuit function, they are by no means useless waste. They are:
The "safety belt" of automated production: Protecting components on the board from damage by production equipment.
The "accelerator" of efficient manufacturing: Enabling small-sized PCBs to pass through the SMT production line stably, quickly, and in bulk.
The "reference point" for precise placement: Providing essential optical positioning landmarks for the pick-and-place machine.

Next time you design a PCB and prepare to send it to a factory for manufacturing, remember this unsung "hero behind the scenes." Following the manufacturer's panel rail design specifications will not only ensure your board is produced smoothly but also effectively improve yield, reduce costs, and make your project run smoothly from design to mass production!