Tab Routing Control for PCB Depaneling: 6 Rules
Tab routing is a depaneling method in which the board is held in its panel by small bridges of laminate, and a router removes the material around the board while leaving those bridges until the last operation. The tabs are then cut, and the board is released with a defined edge.
The method is chosen where the board outline is complex, where a smooth edge is required, or where the panel has to carry the board through assembly before separation. Each of those advantages comes with a set of control points that decide whether the separated board is flat and free of burrs.
<img src="https://www.gopcba.com/wp-content/uploads/2026/09/147.png" alt="Router bit cutting tabs on a PCB panel during depaneling” />
What Tab Routing Does
The router follows the board outline at a small depth offset, leaving a narrow tab at intervals along the edge. The tab holds the board in place and carries it through the assembly line, and it is cut last so that the board remains supported for as long as possible.
The amount of material left in the tab is a design decision. Too little and the board moves during assembly, which disturbs printing and placement. Too much and the separation operation has to apply force that stresses the board.
Because routing removes material rather than shearing it, the method produces less stress than a punch or a guillotine, which is why it is used on boards carrying brittle components or fine traces near the edge.
Router Bit Geometry and Wear
Router bits are made with a defined flute geometry, and the geometry is chosen for the laminate and for the cut. A bit with too few flutes removes material quickly but leaves a rough edge, while a bit with many flutes cuts more slowly and produces a smoother wall.
Wear is the main variable in service. A dull bit rubs instead of cutting, and the rubbing generates heat that softens the resin, smears the edge and produces a burr on the copper. The chip load record that governs drilling applies in the same way to routing.
Bit life is therefore counted in metres of cut rather than in hours, and the count is tracked per material and per bit type. A change of laminate changes the wear rate, and a bit that was suitable for one panel may be unsuitable for the next.
Feed Rate, Spindle Speed and Heat
Feed rate and spindle speed together set the chip load, and the chip load decides how much heat the cut generates and where that heat goes. A high feed with a low spindle speed produces a large chip, a rough edge and a hot bit.
Heat is the enemy of edge quality. Above a certain temperature the resin softens and smears, and the smear is then dragged along the edge and appears as a rough, whitish band. The affected area is also more prone to absorbing moisture and to plating defects if the edge is later plated.
The stack height matters as well. Cutting two panels at once increases the load on the bit and changes the way the chip is evacuated, so the feed rate for a stack is not simply the single-panel rate.
Tab Width and Board Support
Tab width is set from the mechanical requirement during assembly and from the separation method. A narrow tab releases easily but allows the board to flex, while a wide tab holds the board firmly and needs more force to separate.
Where the tab is cut, the tool leaves a small step or a nub, and the size of that nub is part of the specification. A nub that is too large interferes with the enclosure or with a connector, while one that is too small may allow the tab to break during assembly.
Support under the board during routing is also part of the control. A board that is unsupported at the edge deflects under the cutting force, and the deflection appears as a taper on the edge and as stress on nearby components.
Burrs, Dust and ESD
Routing produces dust, and the dust is both a contamination risk and a static risk. The dust is drawn away by extraction at the cutter and is not allowed to settle on the panel, because laminate dust is abrasive and can be carried into the assembly area.
Burrs form on the copper at the edge when the bit is dull or when the cut is too hot. A burr that is left in place can lift during handling and can also create a short to an adjacent structure where the board is fitted into a metal housing.
Static control is part of the same operation. The cutter and the extraction generate charge, so the fixture is grounded and the boards are handled with normal ESD precautions. The panelization choices that determine how much material surrounds the board are described separately.
Inspection, Records and Change Control
The separated board is inspected for edge quality, nub size, burrs and delamination at the edge. Delamination is checked because a hot cut can lift the layers apart, and that defect is not visible from the surface.
Records should include the bit type, the cut length on the bit, the feed and speed, the stack height and the inspection result. Those values explain most of the variation between two runs of the same panel.
Where the board must fit a housing, the edge condition has an effect on flatness as well. The coplanarity notes describe how that requirement is verified, and the general acceptance criteria for a finished board are set out in the board quality notes. The wider set of checks around the panel is listed in the fabrication notes.
Panel Design and Handling Around the Tabs
The panel layout decides how well tab routing works. Tabs placed along the long edges support the board during printing and placement, while tabs at the corners leave the middle free to flex.
Tab position also decides where the separation stress lands. A tab next to a fragile component transfers the cutting force into that area, so the layout should keep tabs away from parts that cannot take it and away from fine traces.
Handling after depaneling is where a good panel becomes a damaged board. Boards stacked with the tab nubs facing each other can chip the edge, and a board dropped onto its corner after separation can crack a ceramic part that survived the routing.
Where the board will be fitted into a housing, the tab nub has to be small enough not to interfere with the fit, and the plan for removing it is agreed between the board designer and the assembly process rather than left to the operator.
FAQ
When is tab routing better than a v-score? When the board outline is not a straight line, when the components are sensitive to bending, or when the edge has to be smooth. A v-score is faster and cheaper for a rectangular board that can tolerate the stress.
Why does the edge go white after routing? That is resin smear caused by heat. Reducing the feed rate or replacing a dull bit usually removes it, and the smear should not be plated over because it fails adhesion.
How is the correct tab width chosen? From the load the board sees during assembly and from the force the separation tool applies. The width is verified on the first article rather than calculated once and forgotten.
