Best Practices for PCB Panel Design in Manufacturing and Assembly

1. The Importance of a Well-Designed Panel Structure

• If a PCB is not panelised for a pick-and-place machine, assembly
  becomes inefficient and error-prone because the machine relies on
  standardized panel dimensions and fiducials for accurate
  positioning. Irregular-shaped boards, very small PCBs,
  components appearing in the edges of the PCB are especially
  problematic, as they cannot be properly clamped or conveyed, leading
  to misalignment, poor placement accuracy, and increased risk of
  component loss or damage. This often results in slower throughput,
  more manual handling, higher defect rates, and increased
  manufacturing cost.

• Machine Compatibility: The panel must fit within the minimum
  and maximum dimension constraints of the assembly line equipment
  (e.g., solder paste printers, pick-and-place machines, reflow
  ovens). A typical minimum size is around 50mm x 50mm, while maximums
  can reach 330mm x 530mm or more.

• Panel Borders (Edge Rails): A crucial element of any panel is
  the handling edge or border. This is a component-free zone around
  the perimeter of the panel that allows automated machines to
  transport and clamp the board during processing.

The image below illustrates a typical PCB panel layout with a 2×3
array of boards, clearly showing the surrounding handling edge.

2. Common types of PCB panelization include:

1. Tab Routing (Tab + Mouse Bites)
    – Individual
   boards are held together by small tabs with perforated holes; boards
   are snapped apart after assembly.
   Consider
   tab routing when
   your design has an irregular shape or if you need space between your
   boards to allow for overhanging components. Default is to add a 0.1″
   (2.0mm) gap between the boards to allow the router bit to pass
   between them. Small tabs of material will remain to hold the boards
   in place. To make separation easier, add small non-plated holes to
   the tabs called ‘mouse bites’ to perforate the tab. The
   breakaway tab closest to the PCB corner should be located between 10
   mm and 12 mm from the edge to reduce sagging during reflow or wave
   soldering. It is also preferred to have at least one tab per side.
   If the PCB placement is too dense for a Tooling Hole, then it should
   be placed on the breakaway tab. See Figure 3 for the optimized
   breakaway tab solution.

One important aspect is to have a clean edge after the breakaway tab is
removed. Slight inset of perforation is preferred because it provides
an edge which requires little to no additional labor to clean up.
Figure 2 illustrates the perforation location preferences.

2. V-Groove (V-Scoring) – This method involves cutting a
   V-shaped groove into both the top and bottom surfaces of the panel,
   leaving a thin web of material connecting the boards, allowing clean
   separation by snapping; best for straight-edge designs.

3. Solid Routing – Boards are fully routed with no breakaway until final depaneling using a
   router; used for complex or sensitive boards.

4. Frame Panelization
   – Multiple
   boards are placed inside a rigid outer frame, improving handling for
   small or irregular-shaped PCBs.

5. Mixed Panelization
   – Combination
   of V-groove and tab routing in a single panel, depending on board
   geometry.

6. Array Panelization
   – Identical PCBs arranged in rows and columns to maximize panel
   utilization and assembly efficiency.

2. Critical Handling Area and Essential Features

The panel’s edge rails are not just empty space; they are critical
for the successful operation of pick-and-place and screen printing
machines.

• Conveyor Transport: Most SMT (Surface Mount Technology)
  machines use edge conveyors to transport panels down the line. The
  conveyor belts or clamps grip the panel by its edges. A clear, flat
  area is essential to ensure a secure grip and prevent damage to
  components.

• Recommended Dimensions: A minimum border width of 3mm to
  5mm is typically required on at least two parallel sides for
  conveyor transport.

• Component Keep-Out Zone: No components should be placed
  within this handling area. A general rule is to keep components at
  least 3mm to 5mm away from the panel edge to avoid
  interference with conveyor clamps and to prevent damage during
  depaneling.

The handling edge is also the designated location for essential
manufacturing features:

• Fiducial Markers: These are precise copper circles that act
  as reference points for the machine vision systems of pick-and-place
  machines. They ensure accurate alignment of the panel and individual
  boards.

  • Size & Placement: Typically 1.0mm to 3.0mm in
    diameter. A minimum of three global fiducials should be placed in
    the corners of the panel border for overall alignment.

  • Clearance: A clear, solder-mask-free area with a radius of
    at least twice the fiducial’s diameter must surround each marker.

• Tooling Holes: These unplated holes, usually located in the
  corners of the panel border, are used to physically secure and align
  the panel during processes like stencil printing and drilling.

Conclusion

Adhering to these PCB panel design best practices is a critical step
in ensuring a smooth and cost-effective manufacturing process. By
correctly dimensioning the panel, providing a dedicated handling edge
for automated equipment, and incorporating essential features like
fiducials and tooling holes, designers can significantly reduce the
risk of assembly errors and product defects.