How to panelize PCBs with CAM

What is PCB Panelization?

PCB panelization is the process of grouping multiple printed circuit board designs onto a single panel for manufacturing. Panelizing PCBs offers several advantages:

• Reduces manufacturing costs by producing more PCBs per panel
• Speeds up assembly by allowing multiple PCBs to be populated at once
• Enables more efficient handling, testing, and shipping of finished boards

Types of PCB Panelization

There are two main types of PCB panelization:

1. Tab Routing – Individual PCBs are connected by thin tabs which are cut off after assembly. This is the most common method.

2. V-Scoring – V-shaped grooves are scored between the individual PCBs, allowing them to be easily snapped apart after assembly. V-scoring leaves smoother edges compared to tab routing.

The panelization method used depends on factors like the PCB Size, shape, material, and the capabilities of the manufacturing and assembly facilities being used.

Using CAM for PCB Panelization

Computer-aided manufacturing (CAM) software automates the PCB panelization process. Most PCB CAD tools have built-in or add-on CAM features for panelizing. The general panelization workflow using CAM is:

1. Import the individual PCB design files
2. Define the panel size and material
3. Arrange the PCB array on the panel
4. Add breakaway tabs, fiducial markers, and tooling holes
5. Generate the manufacturing files for the panelized design

Let’s walk through each of these steps in more detail.

1. Import PCB Design Files

The first step is to bring your individual PCB designs into the CAM software. Most CAM tools accept standard PCB file formats like Gerber (RS-274X), ODB++, or IPC-2581.

If your CAM software integrates with your PCB design tool, you may be able to import the native design files directly. This is preferable as it avoids any loss of information in translation to manufacturing file formats.

2. Define Panel Size and Material

Next, set up your panel properties in the CAM tool, including:

• Panel size – Choose a standard panel size offered by your manufacturer, or specify a custom size. Common sizes range from 9″ x 12″ up to 21″ x 24″. The panel size determines how many PCBs you can fit per panel.

• Board material – Select the base material and copper weight for the panel. FR-4 laminate is most common. Make sure to choose a material that is compatible with your PCB manufacturer’s capabilities.

• Board thickness – Specify the thickness of the base material. Standard thicknesses range from 0.031″ to 0.125″. Thicker boards are more durable but also more expensive.

• Solder mask color – Choose the color of the solder mask that will be applied to the panel. Green is standard but other colors are available.

• Silkscreen color – Select the color of ink used for the silkscreen legends on the board. White is most common.

3. Arrange the PCB Array

With the panel properties defined, you can start laying out the array of PCBs on the panel. The CAM software should have tools for importing and placing the PCB designs.

Determine Spacing

First determine the minimum spacing required between boards. This spacing accounts for cutting tolerances and room for breakaway tabs or V-scores. Your PCB manufacturer can provide guidance on minimum spacing based on their equipment capabilities.

Typical spacing between boards might range from 0.5 mm to 2 mm or more. Smaller spacing allows fitting more boards on the panel but requires tighter tolerances in manufacturing.

Optimize Packing

When placing the boards on the panel, experiment with different packing arrangements to maximize the panel utilization. For simple rectangular boards, a straight grid arrangement often works best.

For boards with complex shapes, the CAM tool may have an auto-packing feature that can optimize the placement. Auto-packing rotates and arranges the boards to fit as many as possible on the panel.

Leave room around the perimeter of the panel for rails that secure it during manufacturing. Your manufacturer can advise how much edge clearance to allow.

Panelize in Both Directions

If your boards are small enough, you may be able to panelize them in both the X and Y directions on the panel. This is an effective way to maximize the number of boards per panel and reduce cost.

Boards can also be panelized on both sides of the panel to use both sides. However, this requires extra manufacturing steps and registration controls to ensure proper alignment of the top and bottom layers.

4. Add Breakaway Tabs and Markers

With the panelized PCB layout complete, you now need to add tabs, fiducials, and tooling holes to the panel:

Breakaway Tabs

Breakaway tabs, also known as mouse bites, connect the individual boards together on the panel. The tabs are removed by breaking them off after the boards are assembled.

Tabs are usually made by drilling holes almost all the way through the board along the breakaway edges. CAM tools have automated functions for adding breakaway tabs with customizable spacing and sizes.

Minimize the width of the tabs as much as possible while still providing a secure hold during manufacturing. Tabs that are too big can be hard to remove and leave rough edges. A width around 0.5 mm is typical.

Space the tabs evenly along the board edges, with more tabs on larger/heavier boards. Your PCB manufacturer can recommend an appropriate tab size and spacing for reliable panelization of your design.

Fiducial Markers

Fiducial markers are round copper pads placed on the panel that serve as reference points for aligning the layers during manufacturing.

Global fiducials are placed around the corners of the main panel. Local fiducials are added to each individual board. Use at least 3 global fiducials per panel and 3 local fiducials per board for proper registration.

The CAM software should have tools for automatically placing fiducial markers with industry-standard shapes and sizes. Typical fiducial diameters range from 1 mm to 3 mm.

Tooling Holes

Tooling holes are placed around the edges of the panel to secure it during manufacturing processes. The holes match up with registration pins on the equipment to prevent the panel from shifting.

Tooling holes are typically plated with copper to reinforce the laminate material. Common finished hole sizes are 2.4 mm, 3.2 mm, or 4.0 mm in diameter.

Consult your PCB manufacturer for the recommended tooling hole size, quantity, and placement for your panel size and manufacturing process. The CAM software will have tools for adding tooling holes per the manufacturer’s specifications.

5. Generate Manufacturing Files

The final step is to generate the manufacturing files for the panelized PCB design. This usually involves exporting Gerber files that describe each layer of the board – copper, solder mask, silkscreen, drill data, etc.

Gerber is currently the most widely used format for PCB fabrication data transfer. However, newer formats like ODB++ and IPC-2581 are gaining adoption with enhanced features and better standardization. Check with your manufacturer on their preferred file formats.

In addition to the Gerber files, you will also need to generate a drill file that specifies the locations and sizes of all the drilled holes in the panel – vias, component holes, breakaway tabs, and tooling holes.

The CAM software should have post-processing tools for previewing the generated files in a Gerber viewer. Thoroughly review all the layers for any errors or discrepancies before releasing them to manufacturing.

Zip up the manufacturing files in a single archive to send to the PCB maker. Clearly label the files and include a README with any special instructions or requirements for the build.

Tips for Successful PCB Panelization

Here are some additional tips to keep in mind when panelizing PCB designs:

• Keep boards one-up when possible – If you don’t need huge quantities, keeping the boards individually manufactured can avoid the extra costs and steps of panelization.

• Consider depanelization requirements – Think through how the individual boards will be separated from the panel. Designs that are too thin or have components near the edges can be damaged during depanelization. Leave adequate clearances.

• Follow manufacturer design rules – Each PCB fab house has specific panelization capabilities and design requirements. Follow their design guides and get their approval on your panelized design before starting a production run.

• Test manufactured samples – Before committing to a full production run, have the manufacturer produce a sample panel first. Closely inspect the tabs, routing, and overall quality to catch any issues early.

Frequently Asked Questions

What is the minimum spacing between panelized PCBs?

The minimum spacing between boards depends on the specific manufacturing capabilities of your PCB fabricator and assembler. In general, 1-2 mm spacing is common, but some manufacturers may be able to support down to 0.5 mm spacing for very compact designs. Always consult with your manufacturer for their guidelines.

How thick should the breakaway tabs be?

Tab thickness should be as small as possible while still being strong enough to hold the board in place during manufacturing. A thickness of 0.5 mm is a good starting point, with thicker tabs up to 1 mm for heavier boards. The tab thickness also depends on the overall board thickness. Discuss the optimal tab thickness with your manufacturer based on your design.

How many fiducial markers should I use?

Use at least 3 global fiducial markers around the main panel, and 3 local fiducials on each individual board for proper alignment. More fiducials can be added for very large panels or high layer count boards that require tighter registration controls. Follow the fiducial size and placement requirements from your manufacturer.

What are the most common PCB panelization issues?

Common panelization issues include:
– Spacing violations between boards
– Lack of adequate clearances for rails, tabs, and fiducials
– Poorly sized or unevenly spaced breakaway tabs
– Incompatible drill sizes or inaccurate drill files
– Incorrect layer mapping in the manufacturing files

Catching these issues in the CAM stage is critical to avoid expensive and time-consuming mistakes in production. Always carefully review your panelized design and work closely with your manufacturer to verify that it meets their specifications.

Conclusion

PCB panelization is a crucial step in the process of bringing a circuit board design to mass production. CAM software automates many of the complex panelization tasks, but careful planning and attention to detail is still required for a successful result.

By understanding the key considerations like panel utilization, tab design, fiducial and tooling hole placement, and working closely with your manufacturing partners, you can efficiently panelize PCB designs while avoiding costly mistakes.

As PCB designs continue to push the limits of size and density, effective panelization strategies will be even more important for delivering reliable, high-quality, and cost-effective production results.