PCB Mouse Bites and V-Grooves are two different design/fabrication techniques in PCB manufacturing. You may have seen circuit boards with little notches on the side or seen others that are flat. Today we will discuss what these two are and which may be the right use for your project. Printed circuit boards (PCBs) are normally printed from large panels of materials which are standard sizes for the manufacturing and printing process. Before bare boards are shipped out and populated, the fabrication shop will usually depanelize the boards into individual units. Depanelization is a process where the larger manufactured panel is snapped into individual boards and any leftover material is removed. It is worth noting that pick and place equipment can also run panelized boards for efficiency but this planning must be done ahead of time and should be communicated to your fabrication shop.
The panelized layout of printed circuit boards, or its array, is usually done by your supplier. They know what size materials they stock and how many of your boards can be created with each size. This allows them to mitigate wasted materials and keep your costs down. This is also why many shops have a MOQ for boards.
PCBs are typically made from performant composite materials in order to stop thermomechanical warping, insulate where needed, and enable channels either integrated into the layers or on the exterior to conduct as required by the engineer’s design. The reinforcement material used is typically a glass fiber that helps dimensional accuracies over a range of usage temperatures with epoxy or phenolic-based matrix to aid this necessary attribute.
PCB assemblies are typically mounted on standoffs or bosses and will need to resist fatigue and cracks forming during the mounting and use of the circuit board. This makes PCB design a challenge for long-lasting products with even the best manufacturers failing at times to ensure that their designs meet the specification of the final application.
In addition to thermal-mechanical challenges, the board also needs to resist moisture ingress and layer delamination through hydrolysis. This is a problem for PCBs especially in instances where exposed surfaces of reinforcement material are present. A clean surface is preferred to limit this ingress along interface cracks between the glass fiber and matrix material.
PCB mouse bites resemble the holes of a postage stamp and are drilled into a PCB. This can allow boards to snap under pressure with some cards using a cutting process to reduce the perforation size needed. After snapping the board there will be a rough surface left which resembles a mouse’s bite. This can be used to create better grip during mounting. The holes used for the breakout tabs may vary, but in most cases, manufacturers will use five holes in a breakout tab with the following dimensions:
Hole size: 0.020 inch (0.5mm) diameter
Spacing: 0.030 inches (0.76mm) apart from each other
When designing the placement of the breakout tabs around the board, there are a few things to keep in mind:
- Avoid placing these tabs close to sensitive components or traces since the stress of depanelization may damage them
- Have enough tabs that the board can be handled properly both by a person and equipment.
- Don’t put too many tabs, this will just slow down the manufacturing process and increase wear on parts.
- Locate tabs where they have at least 0.125 inches of clearance to the nearest components.
Alternatively, a v-groove can be cut into the board on one or both sides allowing the snap edge to be smooth and perfect for mounts that first require a slide fit into a groove.
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