Mouse Bite Tabs: A Complete Depaneling Guide
A mouse bite is the row of small perforations that joins a panel to its frame or to a neighbouring board and lets the assembly be snapped apart after soldering. The break is quick and needs no machine, which is why the process survives on high-volume boards. It is also the roughest depaneling method in common use, and the cost appears as stress at the break line and burrs on the edge.
This guide covers how mouse bite tabs are sized and perforated, how tab routing is planned around them, the depaneling stress they impose, and the edge quality limits that decide whether the method is acceptable for a given board. It applies to single-sided and multilayer panels with and without plated edges.
What a Mouse Bite Is and Where It Fits
Five to seven small holes across a tab leave a web of material thin enough to snap by hand. The method needs no router time, no fixture and almost no floor space, so it is the cheapest depaneling option per board once the panel is designed for it. It also produces the most debris and the largest local strain.
Mouse bite fits boards where the break line is not critical: a solid copper area away from components, no plated edge, no controlled impedance trace crossing the tab. Where any of those conditions exists, tab routing with a router bit or a laser is usually the better choice.
How Mouse Bite Tabs Are Sized
Tab width is set by the weight of the board and the number of tabs around the perimeter. A small board can hang on three or four tabs a few millimetres wide, while a heavy assembly needs more material or more tabs. The tab must be strong enough to survive reflow and handling without breaking early.
The working figure for most laminated boards is a tab of 2.5 to 3.5 mm with a perforation pattern that leaves about 0.8 to 1.2 mm of material between holes. Thinner material, or a brittle high-frequency laminate, needs a narrower web because the break force rises sharply as the web thickens.
Perforation Pattern and Hole Pitch
The holes should be placed on the break line and evenly spaced, with the outer holes set in from the tab edges so the corner is not left with a sharp spur. Pitch is usually 0.5 to 0.9 mm, and the hole diameter is chosen so the finished web is a consistent width across the tab.
Hole placement is a fabrication issue as much as a design one. A drill that wanders or a panel that shifts during drilling leaves an uneven web, and the break then starts from the thinnest point and tears across the tab. A first-article check should measure the web at several tabs rather than one.
Tab Routing and the Depaneling Sequence
Tab routing removes the material between boards and leaves the tabs as the only connection. The router bit has to clear the tab ends without nicking them, and the sequence should leave the panel supported until the last cut. Cutting all the way around before the tabs are released lets the panel flex under its own weight.
The order matters at the end of the run as well. Snapping should be done after all soldering and cleaning, because the break leaves loose particles that can lodge under components and cause shorts. Where the break has to happen earlier, the panel should be cleaned again before the next process step.
Depaneling Stress at the Break Line
Snapping bends the tab and the board around it, and the strain reaches well beyond the break line. A component placed within about 5 mm of a tab sees part of that strain, and a ceramic capacitor or a glass-bodied diode can crack without any external mark. Depaneling stress is therefore a layout constraint, not only a process one.
The stress is reduced by keeping the break line away from components, by using more and narrower tabs rather than fewer wide ones, and by supporting the board during the snap. A simple support block under the panel removes much of the bending and is the cheapest available improvement.
Edge Quality After Breaking
A broken edge has burrs and a rough fibre texture that a routed edge does not, and the burrs can be sharp enough to cut gloves and to bridge to adjacent metal. Edge quality limits should therefore be written for the product rather than assumed, with a maximum burr height and a rule about loose material.
Where the edge is visible or functional, the panel should be designed for routing instead. Where mouse bite is retained, the edge should be deburred on a jig and inspected under magnification at the start of the run. Our notes on edge quality describe the acceptance checks.
Tooling, Fixtures and Operator Technique
The break is usually made with a small hand tool or a fixture that holds the board and pushes the tab. A fixture gives a repeatable bend direction and a repeatable speed, which matter because a fast snap strains the joint more than a slow one. Hand breaking without support is the least repeatable option.
Operator technique still decides the result. The board should be held flat, the bend applied along the tab line rather than at an angle to it, and the waste material caught rather than dropped on the bench. Our guide to depaneling methods compares the fixture options.
Inspection and Limits
Inspection after snapping covers three points: burr height at the edge, cracks in components near the break line, and loose debris on the board. The third is the most common cause of field failures from this process, because a fragment of fibre or solder mask can sit unnoticed under a component.
Cracks are the harder check and need magnification or a bend test on a sample. Where crack detection matters, the panel should be moved to a routed process, and the yield loss from cracked parts should be compared against the cost of the router. Panel level yield figures for both options are discussed in our notes on panel array yield, and the general requirements for separable boards are covered by IPC.
Verification and Records
A record that identifies the operator, the date and the settings is worth more than a record that identifies only the result. A measurement taken at the wrong point of the process describes the wrong thing, however carefully it is made.
FAQ
Is mouse bite acceptable for a board with plated edges? No. The break tears the plating and leaves exposed copper and a ragged edge, so a plated edge requires routing or laser depaneling instead.
How far should components be kept from a mouse bite tab? At least 5 mm where ceramics and glass-bodied parts are involved, and more where the board is thick or the tab is wide. The distance should be verified with a strain measurement on the first article.
Can mouse bite holes be used for a controlled impedance board? Only where no reference plane or signal trace crosses the tab. The perforations change the local geometry, so a trace through the area will not meet its impedance target.
