Multi-Board PCB Edge Clearance Guidelines and Panelization Tips
One of the frustrating things about working on a project where your success is dependent upon receiving data from someone else, is when that data is incomplete or incorrect. Perhaps your co-workers didn’t understand what was required of them or maybe they made a mistake. Whatever the reason is, it is going to slow you down.
Not only do you still have to finish your own work, but now you have to finish someone else’s work too. Unfortunately PCB designers often end up being guilty of the same thing when they send a layout out for manufacturing without anticipating the needs of the panelization.
For manufacturing, a PCB design is placed into a larger panel that is designed for the automated assembly processes. Depending on the size of the PCB, the panel will contain one or more instances of that design. Combining multiple smaller boards into one panel increases the amount of boards that can be assembled at one time lowering the manufacturing cost per board.
Proper designing for panelization includes mounting and tooling hole considerations, copper clearance from edges, and the panelization technique involved: v-grooving or tabs. But if the PCB isn’t optimally laid out in the panel during the manufacturing process, it could cause redesigns resulting in delays, fewer boards per panel, and ultimately increase the end cost.
While the manufacturer should always be the expert, PCB designers who understand panelization can help and not hurt the manufacturers during panel creation. One of the most critical areas to watch out for is the multi-board PCB edge clearances between the components and copper to the edge of the board. Those clearances, along with other factors, will have a lot to do with how the panel is created.
Basic Panel and Multi-Board PCB Edge Clearance Guidelines
A printed circuit board in a panel will eventually have to be removed from the panel when the assembly process is complete. With all the layers of copper, dielectric, and core materials that are laminated together in a circuit board as well as the components mounted to it, there is a risk of damage to the board when it is depaneled.
To reduce the chance of damage, panel designs will include features to make board removal easier. These can either be V-grooves scored around the top and bottom board edge, or routing out around the board edge, except for small breakout tabs that are positioned to hold the board in the panel during assembly.
For depaneling, circuit boards with V-grooves will be cut out and boards with breakout tabs will have those tabs broken out. To make sure that there aren’t problems with components close to the board edge during depaneling, there are certain component and copper to board edge clearances that should be followed during PCB design:
Component to Board Edge: A clearance of 0.050 inches should be maintained between the V-groove and components. To avoid interference from the cutting tool, taller components such as large multilayer ceramic chip capacitors should have a 0.125 inch clearance to the edge of the board. Additionally, components with large solder pads should also be placed further away to avoid stress fractures to their solder joints when the board is being depaneled.
Copper to Board Edge: For V-grooved boards, copper should be kept a minimum of 0.020 inches from the score line.
Breakout Tab Clearances:
Component to Board Edge: Because of the possibility of board splintering when broken out, components should be kept a minimum of 0.125 inches from a tab. Taller components should have a 0.250 clearance to a tab.
Copper to Board Edge: Any metal should be kept at least 0.005 inches from the board edge except for where there is a tab. Metal should be kept back 0.125 inches in those locations.
When these clearances aren’t observed during PCB design, the manufacturer’s have to work around these problems or have the PCB design modified. By making sure to incorporate these clearances, PCB designers can help the manufacturer to more easily create the panel. In some cases, panel design is incorporated into the PCB design making sure that the panel standards are followed.
Four PCBs are laid out in a panel ready for assembly
Should PCB Designers Create Their Own Panel Design?
While panelization is a post-process itself, taking into consideration or planning for panelization through your design can be helpful. Preparation of proper stencils due to component needs, and considering through-hole placement are invaluable. Most importantly, PCB designers will be able to make placement and routing decisions with the needs of the panel in mind. There are some other considerations to keep in mind however before jumping into a panel design.
The first thing that must be realized is that each manufacturer may have different panel requirements for their own specific processes. A PCB designer will have to know which manufacturer is being used in order to design the panel according to their specific processes. There are also some very detailed requirements that must be considered when designing a panel:
Board to board clearances.
Panel border widths.
What type of board breakout to use (V-groove or breakout tabs).
Board alignment within a panel.
When and where to use knockouts for panel strength.
How to identify and deal with panel flex and drooping through the assembly processes.
Tooling holes, fiducials, and other miscellaneous requirements.
Just as PCB design is much more complicated than simply throwing a few parts and drawing a couple of lines on the screen, panel design is an art in itself. If the PCB designer understands panelization requirements and has the processes and procedures in place to adequately design a panel, then it could be a great time and cost saver. For the majority of PCB designers however it is best to leave the design of the panel in the hands of those who know best how to do it: the manufacturers.
Don’t let hard work like this get ruined by not preparing the board for panelization
What Can You Do to Help Panelization in Your PCB Design?
Most PCB designers will rely on the manufacturer to create the panels for their boards, but there is still a lot that the designer can do to help:
Work with your manufacturer to understand the needs of their panel and assembly processes and how that ultimately affects the board design.
Design your board with the proper component and copper to edge clearances for the panel.
Make sure that your component placement is optimally aligned for the panel when going through assembly processes such as wave soldering.
Lastly, arm yourself with PCB design tools that have the functionality to give you full control over your design, or even the ability to create a panel design if you choose to. The PCB design tools from Cadence will give you the features and control to do the work that we’ve been talking about. With a multitude of advanced capabilities, Cadence Allegro is the PCB layout tool that you need to handle any design challenge.
If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts.