PCB Panelization

PCB panelization is the process whereby CAM engineers or PCB designers combine multiple PCBs into a single panel to improve manufacturing efficiency. Smaller circuit boards are collectively manufactured as an array, connected together, making them easier to move along the assembly line. Individual circuit boards can be easily separated from the array for packaging or installation into products. Alternatively, a breakaway rail can be added around a single circuit board to increase its width to fit the assembly line. Panelization enhances the utilization of PCB material, reduces PCB costs, and makes automated PCB assembly faster and cheaper.

When performing PCB assembly, the following elements need to be added to the design: breakaway rails, fiducial marks, and tooling holes.

Fiducial marks are small pads placed on the PCB to assist the pick-and-place machine in accurately positioning components during the assembly process. They are often added to the breakaway rails as well. To achieve better assembly results, we recommend following these guidelines for adding breakaway rails, fiducial marks, and tooling holes to your PCB design.

Breakaway Rails

PCB breakaway rails refer to the additional edges added around the PCB to provide space for the SMT processing track and to place panel fiducial marks. They can be added to either two sides (the longer sides rather than the shorter sides) or all four sides of the panel. The width of a breakaway rail should be at least 3mm. You can provide process edges of 5mm, 6mm, 7mm, 8mm, and 10mm. Breakaway rails will increase the cost of the PCB order, so it's better to add the appropriate breakaway rail size based on your PCB design.

Fiducial Marks

Fiducial marks provide common measurable points for all steps in the assembly process, ensuring that the equipment used in assembly can accurately position component footprint. Fiducial marks are crucial for SMT production. In other words, as long as there are surface-mount devices on the PCB, fiducial marks should be placed so that the pick-and-place machine can accurately locate them.

Below are the design guidelines for fiducial marks summarized by PCBWay.

1. Shape: It is recommended to use a solid circle, but other shapes can also be used, as shown in the figure below.

2. Size: The minimum diameter of a fiducial mark is 1.0mm, and the maximum diameter is 3.0mm. It is important to emphasize that all fiducial marks on the same PCB must be of the same size. Engineers are recommended to standardize all designed fiducial marks to a diameter of 1.0mm.

3. Spacing: There needs to be a clear area around the fiducial mark, with a minimum radius of 2R, where R is the radius of the fiducial mark. If a radius of 3R can be achieved, the machine recognition will be better (although it will require more PCB space). Note that there should be no objects (such as copper or silkscreen) within the clear area.

4. Material: Fiducial marks are generally made using bare copper. If soldermask is used, it should not cover the clear area around the fiducial mark.

5. Edge Distance: The edge of the fiducial mark must be at least 5mm from the edge of the PCB (this is the minimum distance required for the machine to grip the PCB) and must meet the spacing requirements.

6. Flatness: The surface flatness of the fiducial mark should be within 15 microns.

7. Contrast: High contrast between the fiducial mark and the PCB substrate provides better recognition.

8. Both the process edges of panelized PCBs and individual PCBs that do not require panelization should have at least three fiducial marks arranged in an L shape, with the diagonal fiducial marks asymmetrical about the center. If four fiducial marks are desired, they can be symmetrically arranged around the center at first, and then shift one mark, this can also achieve poka-yoke (preventing unintentional technical errors by the staff).

9. If components are populated on both sides, each side should have fiducial marks.

10. Single PCBs within a panel should ideally have fiducial marks. If there is no space for fiducial marks on the single PCB, they can be omitted.

Tooling Holes

In PCB design, some holes may seem insignificant, but without these tooling holes, the circuit board may not achieve the expected functionality or even be manufactured correctly. Tooling holes serve the purpose of positioning, aligning, and securing the PCB. They ensure the accuracy and stability of the board material during manufacturing and assembly processes.

Below are the design guidelines for tooling holes summarized by PCBWay:

1. Tooling holes generally require a diameter of 2mm.

2. Tooling holes are typically non-plated through holes.