How PCB Panelization Can Improve Your Manufacturing Process
PCB panelization is the art of organizing multiple boards on a single panel in order to manufacture more efficiently. From soldering, to component assembly, and even testing, fitting multiple boards into a standardized array is a surefire way to make production faster and more cost-effective.
In order to reap the benefits of PCB panelization, there are a few things you should be aware of before you send your Gerbers to your local fabrication house. Here are some tips and tricks you can use to make the most of PCB panelization in your designs.
Know your fab house’s preferred panel sizes
If you’ve never worked with a fabrication house before, it can seem a bit daunting approaching a third party to handle one of your designs. Different manufacturers will have different limitations regarding what size boards or panels can fit on their conveyors.
Most assembly lines can’t directly process boards less than 2.0 inches wide. For smaller boards, some degree of panelization is a must, so you may as well get your money’s worth and decide how many boards you want to fit in a single panel.
A good rule of thumb is to use 18 x 24 inch panels with ½ inch perimeter of clearance for handling double-sided boards (1 inch for multilayer boards). Alternatively, if your board is too small for a conventional conveyor belt, and you do not need many boards fabricated, it may make sense to use a 2 x 2 inch panel to contain a single layout.
At the end of the day, it’s not about quantity but efficiency. The goal is to minimize the amount of wasted material from any given panel. Pick a standard panel size and fit enough boards to utilize at least 80% of the available space. Do what makes economic sense for your PCB needs.
Understand how fiducial marks work
One thing that often gets overlooked by new PCB designers is those little copper pads that you’ll sometimes see towards the edge of a PCB or panel. Fiducial marks may not serve any functional purpose to a circuit, but they’re essential for any manufacturing process that relies on computer vision for automation.
Process automation machines such as the pick-and-place machine don’t see the way we do. They need a little help via fiducial marks to use as a point of reference to help them precisely recognize where an object rests within 3D space. Fiducial marks help assembly machines know if a given PCB’s alignment and orientation is correct. They are a hard requirement for surface mount assembly machines.
Here are some best practices for fiducial marks:
Copper pads should be circular and 1 to 2 mm in diameter.
Create it in the copper layer for positional accuracy (since copper layer is applied in one operation, it’s a good reference point for the whole board).
Provide ample clearance between the pad and vias, traces, etc.
Copper pad must be bare to help with contrast (do not coat with soldermask or silkscreen.
Note the danger of symmetry when placing fiducial marks. 3 marks is recommended by IPC-7351b-3-10 because orientation is clear to machine. 2 marks can also work as long as they are staggered. Don’t make the mistake of placing four marks, one on each corner of the panel or board. This will make it difficult for the machine to distinguish orientation on a bare board, leading to manufacturing errors.
Keep depaneling stress free
When done correctly, panelization mitigates the risk of damage due to mechanical stress from the assembly line. However that does not mean mechanical stress has been eliminated from production entirely. Some depanelization methods are riskier than others. Here’s a quick overview of the options that are available to you.
Breakaway tabs or mousebites are often the cheapest and most practical cost-wise for board designs. However they also pose the most risk of damage due to mechanical stress when popping PCBs out of a panel.
V-scoring involves cutting a “v” shaped groove into the top and bottom of a panel along the edges of the board. The individual boards can be separated along the v-groove by applying pressure by hand or via a fixture. V-scoring is fast but only for rectangular boards.
Routing involves depaneling boards via a machine called a depaneling router. Similar to a wood router, it uses a drill bit to mill the edges of the PCBs to remove them from a panel. While you’re less likely to break a board or component as with tabs or scoring, vibrational stresses from the bit can damage sensitive components.
Laser cutting is the best depaneling technique for designs with tight tolerances and unusual shapes. It produces the lowest mechanical stress of any depaneling technique. It’s also the most expensive option.
Design for panelization from the start
The best way to avoid headaches and complications during manufacturing, is to factor panelization into their designs from the beginning. Modern PCB software lets you design multi-board arrays complete with depanelization clearances and fiducial marks all within a single Gerber file you can send to your manufacturer. A little planning goes a long way.