Contents

• Highlights
• The Context: What Makes Panelization for Assembly Challenging
• The Core Technologies (What Actually Makes It Work)
• Ecosystem View: Related Boards / Interfaces / Manufacturing Steps
• Comparison: Common Options and What You Gain / Lose
• Reliability & Performance Pillars (Signal / Power / Thermal / Process Control)
• The Future: Where This Is Going (Materials, Integration, Ai/automation)
• Request a Quote / DFM Review for Panelization for Assembly (What to Send)
• Conclusion

Highlights

• Mechanical Stability: How edge rails and connecting tabs prevent sagging during reflow.
• Separation Methods: The trade-offs between V-scoring (linear, efficient) and Tab-routing (flexible, stress-prone).
• Fiducial Strategy: Why global and local fiducials are non-negotiable for fine-pitch assembly.
• Material Utilization: Balancing the cost of waste material against the efficiency of throughput.
• Depanelization Stress: Protecting sensitive components like MLCCs from micro-fractures during the breakout process.

The Context: What Makes Panelization for Assembly Challenging

On the surface, panelization seems like a simple geometry problem: fit as many rectangles as possible onto a larger rectangle. However, in the context of modern electronics manufacturing, it is a complex optimization challenge involving competing physical forces and economic constraints.

The primary challenge is mechanical rigidity versus ease of separation. The panel must be stiff enough to travel through solder paste printers and reflow ovens without warping or sagging, which would cause printing defects or tombstoning. Yet, it must also be weak enough at specific points to allow the individual boards to be separated (depaneled) after assembly without damaging the circuitry.

Furthermore, miniaturization has complicated the landscape. As PCBs shrink to fit into wearables and IoT devices, they become too small to be handled individually by standard conveyor systems. APTPCB (APTPCB PCB Factory) often advises clients that handling a 20mm x 20mm board individually is inefficient and risky; panelization provides the necessary physical interface for the machinery.

Finally, there is the issue of component overhang. Connectors that protrude beyond the board edge require specialized panel designs with "knock-out" areas or strategic spacing, complicating the layout and reducing material efficiency.

The Core Technologies (What Actually Makes It Work)

To navigate these challenges, engineers rely on a specific set of design techniques and manufacturing technologies.

1. V-Scoring (V-Cut)

This is the most material-efficient method. Two rotating blades cut a "V" groove into the top and bottom of the panel, leaving a thin web of material (usually 1/3 of the board thickness) to hold the boards together.

• Pros: Zero spacing required between boards (unless there are overhanging parts), providing the highest material utilization.
• Cons: Only works for straight lines; the web must be uniform; requires a specialized depaneling machine (pizza cutter style) to avoid stress.

2. Tab Routing (Mouse Bites)

For non-rectangular shapes or boards with hanging components, tab routing is essential. A router bit cuts the board outline, leaving small tabs of material to hold the PCB in place. These tabs are perforated with small holes (mouse bites) to facilitate breaking.

• Pros: Can handle complex shapes (circles, L-shapes); allows for component overhang.
• Cons: Requires spacing between boards (typically 2.0mm - 2.5mm), increasing waste; leaves a rough edge ("nubs") that may require sanding.

3. Tooling Holes and Fiducials

The panel is not just a carrier; it is a precision fixture.

• Tooling Holes: Non-plated holes (usually 3.0mm or 4.0mm) located in the panel corners (edge rails). These secure the panel during testing (ICT) or stencil alignment.
• Fiducials: Copper markers (usually 1.0mm circles) that provide optical reference points for the pick-and-place machine. Global fiducials align the whole panel; local fiducials align specific fine-pitch components like BGAs.

For complex projects involving Rigid-Flex PCB technology, panelization becomes even more critical. The flexible sections are flimsy and require a rigid frame (often part of the waste material) to keep the entire assembly flat during the SMT process.

Ecosystem View: Related Boards / Interfaces / Manufacturing Steps

Panelization does not exist in a vacuum; it dictates the success of downstream processes.

Stencil Printing and SMT The flatness of the panel is paramount here. If a panel has too much "spring" due to poor tab placement, the board will bounce during component placement, leading to missing or misaligned parts. Large panels (e.g., 500mm x 500mm) are prone to sagging in the center. To counteract this, APTPCB engineers may recommend adding vertical stiffening rails or increasing the tab density in the center of the array.

Reflow Soldering During reflow, the entire panel is heated to over 240°C. The thermal mass of the waste rails can affect the temperature profile. If the rails are solid copper while the boards are sparse, the edges might heat up slower than the center, causing uneven soldering. Conversely, heavy copper planes in the boards and empty FR4 rails can lead to warping (bow and twist) as the materials expand at different rates.

In-Circuit Testing (ICT) Automated test fixtures use "bed of nails" probes to test the electrical integrity of the assembly. These fixtures rely on the tooling holes in the panel rails for alignment. If the panelization is inconsistent—for example, if the tooling hole location shifts by 0.1mm between batches—the test probes may miss their targets, causing false failures.

See our SMT/THT Assembly capabilities to understand how panel design influences throughput.

Comparison: Common Options and What You Gain / Lose

When designing a panel, the choice between V-score and Tab routing is often the first major decision. It impacts cost, edge quality, and component safety.

Reliability & Performance Pillars (Signal / Power / Thermal / Process Control)

The reliability of the final product is heavily influenced by how the panel is designed and subsequently separated.

Stress Management and Component Placement

The most common failure mode related to panelization is the cracking of Multi-Layer Ceramic Capacitors (MLCCs). When a board is snapped out of a panel manually or using a guillotine cutter, the PCB substrate bends. This bending moment is transferred to the solder joints. If a ceramic capacitor is placed too close to a V-score line or a mouse bite, and oriented parallel to the cut, the flexion can crack the capacitor body.

• Rule of Thumb: Keep sensitive components at least 3.0mm to 5.0mm away from the separation edge.
• Orientation: Orient components perpendicular to the V-cut line to minimize stress.

Thermal Balance and Warpage

As mentioned, the copper distribution on the panel rails matters. To prevent warping, manufacturers often add "copper thieving" (dots or grid patterns of copper) to the waste rails. This balances the copper density across the panel, ensuring that the rails and the PCBs expand and contract at similar rates during the thermal excursions of reflow soldering. This is particularly vital for Mass Production where consistency is key.

Acceptance Criteria

For a panel to be considered "production-ready," it must meet specific criteria:

Feature	Requirement	Reason
Edge Rails	Min 3.0mm - 5.0mm width	Fits standard SMT conveyor belts.
Fiducials	3 per panel + 3 per board	Ensures alignment even if the panel is loaded backwards.
Tooling Holes	Unplated, 3.0mm+	Electrical isolation for test fixtures.
Board Spacing	0mm (V-cut) or 2.0mm (Route)	Accommodates the cutting tool width.

For detailed design rules, refer to our DFM Guidelines.

The Future: Where This Is Going (Materials, Integration, Ai/automation)

As components become smaller and boards become thinner, traditional "snap-off" panelization is reaching its limits. The mechanical shock of breaking a tab is simply too high for ultra-fine-pitch BGAs or fragile MEMS sensors.

Request a Quote / DFM Review for Panelization for Assembly (What to Send)

When submitting data for assembly, clear communication about panelization preferences prevents costly delays. If you do not provide a panel drawing, the manufacturer will create one based on their standard practices, which might not align with your specific component constraints. To ensure the best results with APTPCB, please include the following details in your Quote Request:

• Single Unit vs. Panel: Explicitly state if you are supplying a single PCB file (requiring us to panelize) or a pre-panelized Gerber file.
• X-Out Allowance: Can we use panels that contain defective boards (marked with an "X")? Allowing X-outs significantly reduces PCB fabrication costs.
• Rail Width: Specify if your assembly line requires specific rail widths (e.g., 5mm, 7mm, 10mm).
• Fiducial Requirements: Detail the size and shape of fiducials required by your pick-and-place machines.
• Component Overhang: Highlight any components that extend beyond the PCB edge so we can design the rails to accommodate them.
• Depanelization Method: Specify if you plan to use a V-cut machine, router, or manual separation.
• Special Markings: Indicate if you need unique serial numbers or barcodes printed on the waste rails.

Conclusion

Panelization for assembly is a critical bridge between PCB design and successful manufacturing. It transforms a fragile, individual circuit board into a robust, production-ready format capable of withstanding the rigors of high-speed assembly and thermal processing. By understanding the trade-offs between V-scoring and tab routing, and by planning for the mechanical stresses of depanelization, engineers can ensure higher yields and lower costs.

As manufacturing moves toward higher densities and more fragile materials, the collaboration between the designer and the assembly house becomes even more vital. Whether you are prototyping a new IoT device or scaling up for mass production, a thoughtful panel design is the foundation of a smooth assembly process. Visit our PCB Fabrication Process page to learn more about how we handle these critical steps.

Related links

• Rigid-Flex PCB
• SMT/THT Assembly
• Mass Production
• DFM Guidelines
• Quote Request
• PCB Fabrication Process