PCB Panelization Mouse Bites: Design Rules, Dimensions, and When to Use Them

Written by the PrototypeGuru Editorial Team. Researched against technical guidance from Altium, JLCPCB, AllPCB and BestPCBs. Last updated for PrototypeGuru readers.

If you’ve ever snapped a small PCB off a larger panel and felt that satisfying little crack as the tabs let go, you’ve used mouse bites. They’re one of the most common panelization methods in PCB manufacturing, and also one of the most frequently misunderstood, because the exact numbers that make them work well aren’t codified in a single standard the way a lot of other PCB design rules are.

PCB panelization mouse bites are a set of small perforated holes drilled along the boundary between adjacent boards in a panel, leaving thin material bridges that hold the boards together through assembly and let them be snapped apart afterward by hand or with minimal force. They’re popular because they’re simple, cheap, and don’t require any specialized depaneling equipment, but getting the hole size, spacing, and placement wrong can leave you with boards that break unpredictably, damage components near the edge, or leave stubs that need manual filing.

This guide walks through what mouse bites actually are, the dimensions different manufacturers actually recommend, how they compare to v scoring, where to place them on your panel, and the mistakes that cause the most problems during assembly and depaneling.

What Are Mouse Bites in PCB Panelization?

A panel, in PCB manufacturing terms, is a larger sheet holding multiple copies of the same board, or sometimes several different boards, arranged together so they can move through the fabrication and assembly line as one unit instead of hundreds of tiny individual pieces. Panelizing boards this way dramatically speeds up pick and place assembly, reflow soldering, and inspection, since the equipment handles one panel instead of many small boards.

Mouse bites are one of the two dominant methods for holding those individual boards together on the panel, then separating them again once assembly is finished. According to Altium, mouse bites are cutout regions and holes placed between the boards in a panel, which leave behind small material tabs connecting the boards. The name comes from the look of the resulting edge after separation, a row of small semicircular notches that resembles something had been nibbling at the board’s edge, not unlike a mouse bite.

The alternative approach, v scoring, cuts a narrow V shaped groove partway through the board material instead of drilling holes, and the two methods solve the same panelization problem in fairly different ways. Which one makes sense for a given board depends heavily on its shape, how it will be separated, and what the final edge needs to look like, all of which this guide covers in more detail below.

PCB Panelization Mouse Bites: Typical Hole Diameter and Spacing

This is where things get genuinely inconsistent across the industry, and it’s worth being upfront about that rather than presenting one false precise number as if it’s universal.

Board thickness and material also factor into this more than most layout guides mention. A thicker rigid FR4 board can tolerate slightly larger hole diameters and wider spacing without weakening the connection too much, while a thin or flexible board needs tighter, more conservative tab geometry to avoid the connection snapping unpredictably before assembly is even finished. If your design uses an unusually thin substrate or a flex section anywhere near the panel edge, it’s worth flagging that specifically when you send your panelization request, rather than assuming your fabricator’s default mouse bite numbers were chosen with that material in mind.

Mouse Bites vs V Scoring: Which Should You Choose?

The choice between mouse bites and v scoring usually comes down to board shape and what happens to the edge after separation.

According to Altium, v scoring works well when boards will be separated using a rolling blade or by hand along the scored groove, and it can even subdivide larger boards into smaller units when needed. It produces a straight, continuous cut line, which makes it a natural fit for rectangular boards with simple outlines. BestPCBs’ comparison reinforces this: v scoring suits straight, continuous separation lines and is space efficient since adjacent boards can share a single score line, but it demands a straight outline and tends to introduce some flex across longer board edges during handling, which means components need to be kept clear of both the score line and the surrounding flex zone.

Mouse bites, by contrast, handle irregular, curved, or complex board outlines far better than v scoring can, since the holes can be placed at specific points around almost any shape rather than requiring a continuous straight line. AllPCB specifically recommends mouse bites for irregularly shaped or nonrectangular PCBs, economical small to medium production runs, and prototyping, where the flexibility in board shape matters more than achieving a perfectly clean edge.

The tradeoff is edge quality. V scoring leaves a clean, straight edge with minimal post processing. Mouse bites leave small nub remnants where each hole was drilled, and depending on how carefully the holes were placed, that can mean a visibly serrated edge that may need light sanding or filing if appearance matters. For a board where the edge sits inside an enclosure and is never seen, this tradeoff rarely matters. For a board with an exposed or cosmetic edge, it’s worth weighing more carefully.

BestPCBs makes one point worth repeating directly: the separation method should be chosen before the array geometry is frozen. Panel rail width, spacing between boards, and component clearances all change depending on which method you pick, so deciding late in the layout process tends to force rework rather than a simple swap.

How Many Mouse Bites Does Your Board Need?

The number and placement of mouse bite sets depends mostly on board size, and the guidance here is more consistent across sources than the hole dimensions are. JLCPCB recommends a minimum of two symmetrically placed mouse bite sets for boards under 30mm in width, which keeps the board balanced and prevents it from twisting or flexing unevenly during handling. For longer boards, they recommend adding an additional set roughly every 50mm to 60mm along the edge, distributing the holding points evenly so no single tab bears a disproportionate share of the mechanical load during panel handling or reflow.

This distribution matters more than it might seem. A board held by just one or two tabs concentrated in one area tends to flex around that pivot point during handling, which can stress solder joints on components located near the opposite edge. Spreading tabs evenly around the board’s perimeter, or at minimum symmetrically on opposing sides, keeps that mechanical load distributed and reduces the chance of invisible stress damage that only shows up as an intermittent failure much later. For boards using low power circuit designs where the layout tends to be compact and space constrained, fitting enough mouse bite sets without crowding components close to the panel edge can require some careful layout planning early on, since there’s often less margin to work with than on a larger board. Panel weight is another factor worth considering on larger runs. A panel loaded with dozens of small boards, each with its own set of SMT components, adds up to meaningful total weight moving through pick and place and reflow equipment, and mouse bite tabs are carrying that weight at every connection point until the panel is depaneled. Underestimating how much total panel weight a given tab count and spacing can reliably support is a less common mistake than getting the per board dimensions wrong, but it does show up on larger panels or unusually dense boards, and it’s a reasonable question to raise with your fabricator if your panel is significantly larger or heavier than a typical small prototype run.

Where to Place Mouse Bites on Your Panel

Placement is where most of the practical design mistakes happen, and it’s worth treating as seriously as the dimensions themselves.

Altium’s guidance is specific: place the holes tangent to the PCB edge, use a reasonably large hole diameter relative to the tab width, and keep the spacing between holes smaller than the hole diameter itself to leave adequate strength in the connecting material. They also recommend allowing 1.5mm to 2mm of routing area around the mouse bite holes themselves, and specifying the exact routing tool diameter and path in your fabrication drawings rather than assuming the fabricator will infer it.

JLCPCB adds a clear warning worth repeating directly: avoid placing mouse bites in areas with vias, traces, mounting holes, or protruding components. A mouse bite drilled through or near a trace can sever a copper path you didn’t intend to cut, and one placed too close to a mounting hole or connector can weaken the board edge exactly where mechanical stress from a connector or screw will later concentrate. Use the larger blank regions of your board outline for mouse bite placement wherever your layout allows it.

This is also where component derating considerations overlap with panelization decisions more than people expect. Components placed very close to a mouse bite edge experience more mechanical stress during both panel handling and the final break than components in the board’s interior, and a component already operating near the edge of its rated tolerances is a worse candidate for that position than one with more margin. If you’re already working through component derating guidelines for a design, it’s worth factoring panel edge proximity into that same pass rather than treating it as a separate, later concern.

Mouse Bites and SMT Assembly: What to Watch For

Mouse bites interact with the assembly process in ways that are easy to overlook until something goes wrong on the line.

During reflow and pick and place, the panel moves through equipment as a single rigid unit, and the mouse bite tabs are what’s actually holding that rigidity together at the board boundaries. If a tab is too thin or spaced too tightly relative to what the panel’s weight and handling actually demand, boards can shift slightly or even separate prematurely mid process, which throws off placement accuracy for every component near that edge. This is more likely to matter on boards with a mix of SMT and through hole components, since through hole parts typically go through a separate soldering step and add extra handling cycles where a marginal tab has another chance to fail.

The flip side matters too. Tabs that are too strong relative to what manual depaneling can handle mean more force is required to snap boards apart after assembly, and that extra force gets transmitted through the board and into nearby solder joints and components, not just into the tab itself. This is exactly the tradeoff AllPCB’s guidance points at when it notes that smaller holes give a stronger connection at the cost of needing more separation force. Matching your tab strength to your actual depaneling method, by hand, with a specialized depaneling tool, or with a router, rather than defaulting to whatever number looks safest on paper, avoids both failure modes.

Common Mouse Bite Design Mistakes

A handful of mistakes account for most of the mouse bite related problems that show up after boards come back from fabrication.

How to Specify Mouse Bites for Your Fabricator

Since there’s no universal standard governing mouse bite dimensions, clear communication with your fabricator is what actually prevents problems, more than any specific number you choose on your own.

At minimum, your fabrication drawing or notes should specify the hole diameter you’re requesting, the spacing between holes within each mouse bite set, the number of holes per set, and the exact locations of each mouse bite set around the panel outline. Altium’s guidance specifically recommends including the routing tool diameter and path in your fabrication drawings, since the router bit used to cut the mouse bite slots has its own minimum clearance requirements that affect how tightly you can space features near the panel edge.

Most fabricators, including the major prototype and small batch houses, will review your panelization request and flag anything outside their standard process capability before manufacturing begins, but that review only works well if your design files clearly show what you’re asking for rather than leaving it to be inferred from a generic template. When in doubt, a quick message to your fabricator’s engineering support before submitting a design for panelization saves far more time than discovering a mismatch after boards are already in production.

Depaneling Mouse Bites: Breaking the Panel Apart

The actual separation step is simpler than the design work leading up to it, but it still benefits from some care.

Boards held together by mouse bites are typically snapped apart by hand, applying steady, even pressure perpendicular to the tab rather than a sharp twisting motion, which reduces the chance of stress damage to nearby components. For larger production runs, a dedicated depaneling tool, essentially a small rotary cutter or specialized pliers designed for this exact purpose, applies more controlled and consistent force than manual snapping and is worth the investment once volume justifies it.

After separation, inspect the broken edge for any remaining nub material or sharp points, particularly if the board’s edge will be visible or handled by an end user. Light sanding or filing at this stage is common practice and takes only a few seconds per board once you’ve done it a handful of times. Skipping this step on a board where the edge actually matters is one of the more common reasons mouse bites get a reputation for looking unfinished compared to v scoring, even though the underlying panelization decision itself was perfectly reasonable.

It’s also worth planning who actually does the depaneling and when. On a small prototype run, it’s common for the same person handling assembly to also snap boards apart by hand immediately afterward, which keeps feedback tight if something isn’t separating cleanly. On a larger production run handled by a contract assembler, depaneling is often a separate step entirely, sometimes handled by different equipment or a different team than the one that ran reflow. Making sure whoever does that final separation step knows your intended technique, by hand versus a dedicated tool, and has been told about any particularly fragile components near the panel edge, avoids a surprising number of late stage defects that have nothing to do with the original board design and everything to do with a handoff gap.

Frequently Asked Questions

Mouse bites remain one of the simplest, most accessible panelization methods available, and for irregular shapes, small production runs, and prototyping, they’re often the right default choice. The dimensions that make them work well aren’t governed by one universal standard the way some other PCB design rules are, which means the real skill in using PCB panelization mouse bites well isn’t memorizing one perfect number, it’s understanding the tradeoffs between hole size, spacing, placement, and your actual depaneling method, then confirming the specifics with your fabricator before committing a design to production.

Note: This article covers general design guidance based on published fabricator documentation and is not a substitute for your specific manufacturer’s design rules. Always confirm exact panelization specifications with your fabricator before finalizing a board for production.Get