Complete Guide of Mouse Bites in PCB

Introduction

In the world of PCB manufacturing, precision, cost-effectiveness, and efficiency are essential. One often overlooked yet crucial feature in panelized PCB fabrication is the use of mouse bites. Mouse bites are tiny perforated holes along the edges of a PCB that allow individual boards to be easily broken off from a larger panel after assembly.  

Mouse bites are particularly useful in scenarios like surface mount technology (SMT) assembly, hand-assembled prototypes, and low-volume production runs. Their implementation can streamline the depanelization process, reduce tooling costs, and offer greater flexibility for irregular board shapes.   

In this complete guide, we will explore what mouse bites are, how they compare to other separation methods, and when and why to use them in your next PCB project. 

What is Mouse Bites in PCB

The mouse bites, also called perforated breakaway tabs, are the sharp edges, that are left over after stamp hole depanelization when the PCBs are manufactured in a panel using break-routing/break-off tabs. Mouse Bites are a line of tiny holes in a PCB board just like the holes around postage stamps, permitting small PCBs to be used in an array. These rows of holes earned the nickname "mouse bites" because the indentations left behind after they break resemble the bite marks of a mouse that nibbled on the board. Mouse bite perforation is standard for FR4 panels. Drilling these holes leaves rough edges of extra remaining material sticking out the side, while a V-groove PCB with a V-scored edge is smooth. 

In PCB manufacturing, especially for PCB designs, mouse bites are a common technique used when multiple small boards are grouped into a larger panel for easier assembly and processing. This method allows for easy separation after the assembly stage, which is crucial for efficiency, especially in high-mix low-volume production.

Why mouse bites are used

Mouse bites serve several purposes in custom PCB fabrication:

• Ease of Separation: They allow individual boards to be snapped out of a larger panel without complex tools.
• Better Grip: When a board must be mounted or inserted into a tight slot, mouse bites help create a textured edge for gripping.
• Cost-Effective for Hand Separation: Particularly for small runs or prototypes, this method reduces labor and tool requirements.
• Design Flexibility: They're ideal for oddly shaped or non-rectangular boards, especially those where V-scoring isn't feasible.

While standard on FR4 PCBs, mouse bites are also compatible with other substrates like aluminum PCB boards, though special care must be taken during the depanelization of metal-core materials due to their added thickness and rigidity.

The design of mouse bites

If you penalize individual PCBs within the panel, you only need to rat-bite the PCB edge. If you penalize a set of PCBs, you need to rat-bite both edges of the tab. For routed boards, we always see the rat bites at both sides (on the rial side and the board side). Routing a board and adding rat bites is more expensive than a simple v-score. Non-rectangular outlines are routed and usually supported with mouse bites or small tabs.  

One important aspect is to have a clean edge after the breakaway tab is removed. Slight inset of perforation is preferred because it provides an edge which requires little to no additional labor to clean up.

The spacing between breakaway tabs can range from 60 mm to 90 mm, but I recommend 77 mm from center to center as shown in Figure 3. Try not to exceed 100 mm between tabs and try to evenly space them apart.

How Mouse Bites Work in Panelization

Mouse bites are used during the panelization process to create an array of PCBs that can be processed together during assembly. Here’s how it works:

1.  Multiple PCBs are arranged into a single panel, connected by narrow breakaway tabs.
2.  These tabs contain lines of drilled mouse bite holes.
3.  After assembly and soldering, the individual boards can be snapped out by hand or using tools like pliers. 

The drilled holes weaken the connection enough to allow for easy separation, yet maintain panel strength during the manufacturing process.

 Slight inset of perforation is preferred because it provides an edge which requires little to no additional labor to clean up.

? Learn more in our detailed guide:Mouse Bites Panelization for SMT Assembly

Here are PCBs with mouse bites before depanelization:

Mouse bites vs. V-Scoring

It’s worth noting the difference between mouse bites and V-scored PCBs. V-scoring involves cutting V-shaped grooves into the panel, which creates a smooth edge after breaking. Mouse bites, in contrast, leave behind a jagged, unfinished edge unless post-processing is performed.

Mouse bites, in contrast, use a series of small perforated holes—often arranged in a line—leaving behind a jagged, unfinished edge unless additional post-processing such as sanding is applied. While not as clean as V cut PCB edges, mouse bites are more suitable for curved edges or irregular board outlines.

That said, for applications where smooth edges are not critical, mouse bites provide a faster and more flexible depanelization option. They are particularly advantageous when laser direct imaging is used for creating highly detailed and compact circuit designs, where board shapes might be irregular or compact spacing is needed.

Suggested Reading: V-Scoring vs. Stamp Hole Depaneling: Choosing the Right Method for Your PCB

Cost-Saving Benefits of Mouse Bites

One of the primary reasons manufacturers prefer mouse bites is their cost-effectiveness. Here are the ways mouse bites can help reduce overall manufacturing expenses:

1. No special cutting equipment required: Unlike V-scoring or routing, mouse bites can be created using standard CNC drilling machines.
2. Lower labor costs: Boards can be manually snapped apart without advanced machinery. 
3. Reduced panel waste: Enables more flexible array design, optimizing panel utilization. 
4. Ideal for low-volume runs: Great for prototyping and small-batch productions where tooling costs must be minimized.

? See how mouse bites impact your bottom line:Cost-Effective PCB Manufacturing: How Mouse Bites Can Save You Money

When to Use Mouse Bites in Hand-Assembled PCBs

For low-volume, hand-assembled PCBs—such as in prototyping, research labs, or startups—mouse bites offer a reliable and low-cost solution.

• No need for depaneling equipment
• Easy to break by hand with pliers
• Can be combined with fiducials for alignment

This method is especially useful in early development stages where speed, cost, and accessibility are key.

? Discover real-world applications:Mouse Bites are a life saver in hand assembled PCBs

Strength and Reliability Considerations

A common concern with mouse bites is the structural integrity of the PCB edge after depanelization. Because the break tabs are physically snapped, they often leave behind:

• Rough edges (which may need sanding)
• Potential microcracks if not handled properly
• Slightly weaker corner strength compared to routed or scored boards

However, with proper design considerations—such as increasing the tab width, using fewer mouse bites per tab, and post-break sanding—these issues can be mitigated.

 ? Learn about durability:The Impact of Mouse Bites on PCB Strength and Reliability

ALLPCB: Your Partner in Precision Mouse Bites PCB Manufacturing 

Mouse bites offer a practical and economical approach to PCB panelization and depaneling. Whether you're creating early-stage prototypes, managing hand-assembled boards, or optimizing for cost-efficiency, this method provides a flexible solution that balances quality and ease of use.

At ALLPCB, we specialize in high-precision, custom PCB fabrication—including expertly designed mouse bite layouts for seamless panelization and clean depaneling. Whether you need rigid-flex PCBs, durable aluminum PCB boards, or advanced HDI solutions using laser direct imaging (LDI), our team ensures your boards are manufactured with unmatched accuracy and consistency. 

From quick-turn prototypes to complex multi-layer arrays with breakaway tabs, ALLPCB helps you reduce lead times, control custom PCB cost, and maintain the highest manufacturing standards. Let us be your trusted partner in building smarter, cleaner, and more efficient PCBs—designed with mouse bites that work.