PCB Breakaway Tab Design for Depanelling
What a Tab Has to Do
A breakaway tab is the small bridge of material left between a board and its neighbour or the panel rail when the rest of the outline has been routed away. It holds the board in place through assembly so that the panel can be handled, printed, placed and reflowed as a single unit, and then it is cut or broken so the finished board can be separated. A tab therefore has two jobs that pull in opposite directions: it must be strong enough to survive the assembly line and weak enough to be removed without damaging the board. Most depanelling damage originates from a tab design that solved only one of those requirements.
Tab Geometry
The tab width is the primary variable. A narrow tab is easy to break but flexible, which means the board can move relative to the panel during assembly and the placement accuracy suffers; a wide tab is rigid but needs more force or a cutter to remove, and the force is transferred into the board. Typical widths run from two to five millimetres, with wider tabs used on heavier panels and on boards whose components prevent a break close to the edge. The tab length, which is the depth of the bridge between the board edge and the panel or the neighbouring board, sets how much material has to be removed and how much access a cutter has. Long shallow tabs are harder to cut cleanly than short deep ones. The number of tabs follows from the board size and the mass: at least two per board, usually four, and more on a large or heavy assembly.
Placement Rules
Tabs belong on the edges of the board where there are no traces, no vias and no components, because the separation process creates a local stress concentration. A common rule is to keep all copper at least half a millimetre, and preferably a millimetre, inside the tab area, and to keep components much further away: a ceramic capacitor or a BGA near a tab is a candidate for a crack during separation, particularly if the board is broken by hand. Tabs should be placed away from connector positions and from any edge that will be beveled or that forms part of a mating interface, because the leftover stub of a broken tab is a mechanical and cosmetic defect there. Where the panel has to be handled by an edge, the tabs near that edge are the ones that carry the load, so they should be the widest.
Routed Tabs and Perforated Tabs
A plain routed tab is a solid bridge that is cut with a router or a cutter after assembly. The advantage is strength and predictable separation; the disadvantage is the extra operation and the burr left at the cut. A perforated tab, often called a stamp hole, is a row of small drilled holes across the bridge that weakens it so it can be snapped by hand or with a light fixture. It is cheaper to separate and is widely used on small modules, but it leaves a rougher edge with a row of half holes, and the perforation weakens the panel, which limits how much weight the tab can carry during assembly. Some designs use a routed tab with a partial perforation to get both a defined break line and enough strength.
How Separation Stress Reaches the Board
When a tab is broken by bending, the board and the panel rotate about the tab and the stress passes through the board edge into the nearest copper and the nearest component. The stress is highest when the board is thick, when the tab is wide and when the break is done by hand. The remedies are all mechanical: reduce the tab width, use a fixture that supports both sides of the break line, cut rather than break for thick boards, and keep components and heavy copper away from the tab. Where a design cannot move the components, the panel should be separated with a cutting tool rather than by hand, and that requirement should be stated in the assembly documentation rather than left to the operator.
Designing the Panel Around the Tabs
The tab layout should be decided with the panel layout, because the two constrain each other. Tabs on the shared edge between two boards allow both to be separated in one break, which is efficient, but the break line then lies between two sets of components and must be kept clear on both sides. Tabs on the panel rail are easier to design but leave a stub on the board edge that has to be cleaned. Where the panel contains a mix of board sizes, the tabs of the smaller boards usually need to be wider because the panel handling load is carried unevenly. Finally, the test coupon and the tooling holes should not be supported only by the tabs of the boards that will be separated first, or the coupon will fall away before the panel has finished its route through the process.
FAQ
How wide should a breakaway tab be? Typically two to five millimetres, wider for heavy panels or where separation cannot happen close to the edge, and narrower where hand breaking must be easy.
How many tabs does a board need? At least two and usually four for a small board, with more added as the board size or the assembly mass increases.
What is a perforated tab? A tab with a row of small drilled holes across it, which weakens the bridge so it can be snapped, at the cost of a rougher edge and a weaker panel.
How close can components be to a tab? Keep them well away. A millimetre of copper clearance is a minimum, and brittle components should be further, because separation concentrates stress at the tab.
Should tabs be broken by hand? Only for thin boards with a clear area. Thick boards and assemblies with heavy components should be separated with a supported fixture or a cutter.
Conclusion
A tab is a structural element, and it should be sized for the load the panel carries and placed where the separation stress cannot reach the circuit. Keep the copper and the components clear, decide whether the tab will be cut or snapped, support the break if the board is thick, and plan the tab layout together with the panel rather than after it. The panel and separation capabilities available are part of PCB capabilities, the panel and clearance planning belongs in PCB design and layout, and the routing that produces the tabs is described in PCB manufacturing. A prototype PCB assembly run on the real panel shows whether the separation damages anything in 2026.
