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What are Mouse BITES in PCB

Mouse bites circuit board
Mouse bites in printed circuit boards are sections of the manufacturing panel that helps in assembling and fabricating circuit boards. Some individuals utilize the “mouse bite” term to describe and explain the over-etching of copper. However, what we mean here is different.

PCB manufacturers lay out circuit boards in a panel making use of CAM – Computer Aided Manufacturing systems. This panel ensures that the assembler and fabricator is given additional board material for any handling during all processes involved in manufacturing, which is very critical for the smaller boards.

Normally, panels have a uniform size, and you can lay out multiple instances of your printed circuit board design within the panel’s outline. The panel will not just make board manufacturing easier. It also allows the processing or multiple boards in panels for a similar cost as one board.

Once the fabrication, as well as assembly processes of these circuit boards, has been completed, then you must separate them from their panels. The process of separating them is known as depanelization. You can achieve the depanelization process either by breaking out the boards along the “V-grooves” or pre-scored lines, or cut them out.

The boards you have to break out have to be routed already around its outlines. This will help in bringing a separation between them and the panel, which are held by just small material tabs. The removal of the “breakout tabs” takes place, thereby making the board free from the manufacturing panel.

These tabs also feature small holes, which ensure the easy breaking of the PCB, and reduce the stress of the boards. With each of the tabs broken along the holes’ lines, the material remaining will have the appearance of a “mouse bite” until you have smoothed it out.

Mouse Bite PCB: Locations, Dimensions and Sizes
The holes utilized for breakout tabs may vary. However, majority of manufacturers utilize five holes in breakout tabs having these dimensions.

The hole size is usually 0.5 mm or 0.020 inch in diameter. Concerning the spacing, they are 0.76 mm or 0.030 inches apart.

The spacings and sizes of the mouse bite PCB holes appear random. This reduces the cleanup needed after the breaking out of the board from the panel. Though, it takes less effort for a smaller hole to smoothen out, it will also need more holes to be drilled and leave out much bulk material.

However, if there are too big holes, the board will end up having mouse bites that are larger and will need smoothening out. The hole placement within this breakout tab is important as well. The goal here is drilling them nearer to the PCB edge. This helps in reducing the tab material leftover that needs to be removed.

Constraints to consider during placement of breakaway Tab PCBs
There are some constraints to consider while performing the breakout tabs’ placement around the outline of the board.

Don’t make use of many tabs in order to save wear, effort, and time on its router bits.
Have enough tabs that can support the PCB board fully in its panel throughout the operations of PCB assembly.
Tabs having a minimum clearance of 0.125 inches should be located to the closest components.
Don’t place the tabs close to circuitry or sensitive components areas. This could cause the board to experience more breakout stresses.
At times, stress damages coming to the circuitry or components due to the tabs breaking may not be seen till later. It may also cause intermittent issues that won’t be debugged easily. This is why the location of breakout tabs, a distance away from any sensitive area, is very important to the circuit board’s success.

Also, if you don’t use enough tabs, and you don’t place them strategically to support your board during the manufacturing process, your board may end up flexing too much. This will prevent a reliable assembly. Now, this is the point where the experience and knowledge of your PCB manufacturer comes in.