PCB mouse bites are perforated breakaway tabs that hold boards in a routed panel and allow controlled separation after assembly. Their performance depends on hole geometry, tab placement, board thickness, clearance, and depaneling method.
They are especially useful for irregular board outlines or locations that need selective panel support. See WellerPCB’s PCB manufacturing process guide for the related fabrication and panelization steps.
What Mouse Bites Actually Do in a PCB Panel
Routing removes most of the laminate around each PCB but leaves small bridges. Closely spaced holes weaken those bridges so the board can be broken or cut free after assembly. The remaining laminate, not the holes, carries the load before depaneling.
Too much material raises breakaway force and bending; too little can let boards move or detach. Tab width, router path, board-edge clearance, and panel support therefore have to be considered together.
Do Not Treat One Mouse-Bite Dimension as an Industry Standard
Published examples differ because suppliers use different tooling and process rules. Use them for scale only; production dimensions should come from the selected fabricator.
| Source / Context | Published Example | Engineering Takeaway |
|---|---|---|
| Altium | Routing area typically 1.5–2 mm; hole-wall spacing smaller than hole diameter | Routing and edge clearance are coupled with the hole pattern |
| Sierra Circuits | 0.5 mm hole diameter; 0.76 mm typical spacing; 3- or 5-hole patterns | Hole count and spacing depend on available tab geometry |
| JLCPCB | Recommended 0.5–0.8 mm hole diameter with supplier-defined spacing | Production windows vary by fabricator |
Geometry check:
Mouse-Bite Geometry
d
Hole diameter
p
Center-to-center pitch
w
Laminate between holes
w = p − d ·
Pitch is not the same as edge-to-edge spacing.
Place Breakaway Tabs Where the Panel Needs Support
Place tabs to keep the panel rigid through fabrication, handling, SMT assembly, inspection, and testing. Their number and location depend on PCB size, weight distribution, connectors, and panel geometry.
Distribute support along the board
Long boards, heavy connectors, or asymmetric assemblies may need more support than small PCBs. Extra tabs are not automatically safer because every break point can transfer stress into the board. Routed tabs are useful on irregular outlines because support can be placed selectively.
Account for board thickness
Do not copy one tab pattern across different board thicknesses. With the same plan-view geometry, a thicker board can require greater separation force. Review the actual stackup, thickness, and depaneling method.
Protect sensitive features
Breakaway Stress Risk
Keep brittle components, critical copper, vias, and constrained features away from the mouse-bite fracture zone. Sierra Circuits recommends at least 3 mm between its mouse-bite holes and traces or surface-mount components; treat this as supplier guidance, not a universal minimum.
Also review nearby edge constraints using WellerPCB’s SMT PCB layout guidelines .
Plan the Finished Edge Before Choosing the Break Line
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Mouse-bite tabs leave localized laminate remnants after separation. Hidden edges may tolerate them, while enclosure interfaces, connector edges, cosmetic surfaces, or precision mounting features may require trimming, sanding, secondary routing, or another depaneling method.
Keep the perforation close to the intended edge
Altium recommends placing holes tangent to the PCB edge, while Sierra also describes positioning perforations close to the outline. Moving the pattern inward can reduce protruding remnants, but it consumes usable board-edge clearance for copper and components.
Mechanical decision: define the acceptable final edge before panel release. Manual breakout, cutting, routing, and automated depaneling do not produce the same edge condition or stress history.
Need a panelization or DFM review before fabrication?
Send the board outline, assembly method, component placement, board thickness, panel preference, and finished-edge requirements. WellerPCB can review routing, breakaway features, tooling constraints, and manufacturability before release.
Mouse Bites vs V-Score
Choose by board geometry, support needs, finished-edge requirements, and acceptable depaneling stress.
| Decision factor | Mouse-bite / tab routing | V-score |
|---|---|---|
| Board outline | Irregular or curved perimeters | Straight shared edges |
| Support placement | Selective tab locations | Support follows the score line |
| Finished edge | Local remnants may need cleanup | Continuous scored separation edge |
| Panel processing | Router slots required around tabs | No routing slots along the score line |
| Stress pattern | Concentrated around tabs | Distributed along the scored edge |
Choose the depaneling method before final component placement is frozen.
Use a Five-Step DFM Sequence
Five-Step DFM Sequence
1
Lock Depaneling
2
Set Support
3
Protect Areas
4
Apply Fab Rules
5
Verify
- Lock depaneling: choose manual, cut, routed, or automated separation.
- Set panel support: place rails and tabs for the required rigidity.
- Protect sensitive areas: verify component and copper clearance around each breakaway point.
- Apply fab rules: use the selected manufacturer’s hole, pitch, routing, gap, and tab-width definitions.
- Verify the result: inspect representative depaneled boards against defined acceptance criteria.
Show Routing and Breakaway Intent in the Fabrication Data
The panel drawing should distinguish the finished PCB outline from the router path and retained tabs. Indicate the routing-tool diameter and path. If the fabricator owns panelization, provide the single-board data plus assembly and mechanical constraints, then approve the proposed production panel.
Identify rails, fiducials, handling margins, and orientation where relevant. WellerPCB’s PCB assembly process provides the wider assembly context.
Define Depaneling Acceptance Before Production
Set measurable limits for residual nub height, laminate damage, copper exposure, cracked brittle components, solder-joint damage, and mechanical fit. If depaneling stress is significant, compare representative boards before and after separation using the normal electrical or functional test.
Mouse-Bite PCB Release Checklist
- Choose tab routing, V-score, or another depaneling method before final layout.
- Verify panel rigidity through assembly, handling, inspection, and test.
- Confirm hole diameter, pitch definition, hole count, tab width, routing gap, and router capability with the fabricator.
- Check component, copper, via, mounting-feature, and overhang clearance around breakaway regions.
- Review outer- and inner-layer copper near perforations.
- Define the acceptable residual nub and any required edge cleanup.
- Show the finished outline, route path, and retained tabs clearly in the fabrication data.
Frequently Asked Questions
What size should PCB mouse-bite holes be?
There is no universal diameter; use the selected fabricator’s validated panelization rules.
How many holes should a mouse-bite tab have?
The count depends on tab width, board support, hole geometry, and supplier rules. Three-hole and five-hole patterns are common examples.
Should mouse-bite holes be plated?
They are mechanical perforations, not electrical interconnects. Confirm drill treatment with the fabricator.
Why do mouse bites leave rough PCB edges?
The laminate between perforations fractures during depaneling, leaving localized remnants.
When is V-score better than mouse bites?
V-score is usually the simpler choice for straight shared edges; mouse-bite tabs offer more flexibility for irregular outlines or selective support.
