I’ve tried my hand at model building a few times. Whether it’s Japanese mechs or fantasy orcs, I’ve always had fun putting together the sets and painting them, even if the result rarely looks as good as the front of the packaging. The model pieces are attached to thin plastic rods to sit flat and prevent the set pieces from rubbing against each other during transit; builders can either break the pieces out of the set roughly with a little torque or use a hobby knife for a cleaner break that prevents bits of plastic that can remain attached after separation.
If PCBs and panels are analogous to the set pieces in their plastic housing, then PCB mouse bites would be like additional perforations at the connecting material. Because the value of electronics far outstrips that of a plastic model (although the latter can get quite expensive), it’s essential to have a clean board breakaway during depanelization to prevent damage. These holes have to be precisely located and dimensioned, and yes, they resemble the nibbling left behind by a mouse.
Comparing PCB Mouse Bites and V-Grooves
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What Are PCB Mouse Bites?
A mouse bite in a circuit board is part of the manufacturing panel used to fabricate and assemble the circuit board. Circuit boards are typically laid out in a manufacturing panel by a PCB contract manufacturer using their Computer-Aided Manufacturing (CAM) systems. The panel gives the fabricator and the assembler more board material for handling during manufacturing, which is critical for smaller boards. Panels are usually of uniform size, and the board design usually affords different configurations within the outline of the panel. A panel makes it easier to manufacture a board, but multiple boards in the panel are all for processing at nearly the same cost as a single board.
Once the circuit boards have completed their fabrication and assembly processes, separation from their panels in a process called “depanelization” is necessary. Depanelization is accomplished by cutting the boards out along pre-scored lines known as “V-grooves” or breaking them out. Boards require break out and routing around their outlines to separate them from the panel and are only held in place by small tabs of material. These “breakout tabs” are removed, freeing the board from its manufacturing panel.
The tabs have small holes drilled into them, making breaking out the PCBs easier and reducing the boards’ stress. With each tab broken along the line of the holes, the remaining material resembles a “mouse-bitten” appearance that requires smoothing. Next, we’ll examine these mouse bite holes to determine their recommended sizes and dimensions.
Locations, Sizes, and Mouse Bite Dimensions
The holes used for the breakout tabs can vary, but most manufacturers will use five holes in a breakout tab with the following dimensions:
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The mouse bite hole sizes and spacings appear random to minimize the cleanup required after breaking the board out of the panel. While a smaller hole would take less effort to smooth out, it would also require drilling more holes and leaving more bulk material. However, If the holes are too big, the board has larger “mouse bites” that need smoothing. The placement of the holes within the breakout tab is also essential. The goal is to drill them closer to the edge of the PCB to reduce the amount of leftover tab material for removal.
The placement of the breakout tabs around the board outline also has some constraints to keep in mind:
- There need to be enough tabs to support the board fully in the panel during PCB assembly operations.
- Avoid using too many tabs to save time, effort, and wear on the router bits.
- Avoid placing the tabs near sensitive components or circuitry areas more susceptible to breakout stresses on the board.
- Locate tabs with at least 0.125 inches of clearance to the nearest components.
Sometimes, stress damage to components or circuitry from breaking the tabs may not be discovered until later or may result in intermittent problems that are difficult to debug. For this reason, locating breakout tabs away from these sensitive areas is critical to the success of the circuit board. However, manufacturers must ensure enough tabs (and proper placement) to support during manufacturing, or the board may flex too much for reliable assembly. Here is where the knowledge and experience of a local PCB contract manufacturer are essential.
Your PCB Contract Manufacturer Has the Experience in Panels You Need
There are many variables to work with when setting up a printed circuit board manufacturing panel; fortunately, your PCB CM has ample experience doing this. The CM will confirm whether V-grooves or PCB mouse bites best suit your design based on different design criteria and the board’s specific needs. They also understand your business needs and will tailor the panel’s creation according to your expected production volumes and the board’s requirements.
At VSE, we’re a team of engineers committed to building electronics for our customers. That dedication includes creating design panels for our customer’s PCBs as part of our manufacturing workflow. Our engineering and manufacturing teams have years of experience working with different panel requirements. You can rest easy knowing that we will create a perfect panel for your application.
