Panel Tab Routing: 6 Rules for Clean Depaneling

Panel tab routing is the practice of leaving small bridges of laminate between a board and its panel frame, separating them later with a router. The tabs hold the board through printing, placement, reflow and test, and they are cut at the end of the line. Panel tab routing decisions are made at the layout stage, and they decide how clean the separated edge is and how much stress the board sees at separation.

This guide gives six rules for panel tab routing, from tab width to edge inspection, and explains where V-score is the better choice. The rules apply to both routed and V-scored designs, since many panels use both.

What Panel Tab Routing Has to Achieve

The tabs have to hold the board rigid enough for printing and placement, survive the thermal excursion of reflow without warping, and then release cleanly. Rigidity and clean release pull in opposite directions, and the tab width is the parameter that balances them. A tab that is too narrow flexes during printing, which shifts the deposits.

The second requirement is that the separation happens without damaging the board. A router bit leaves a smooth edge if it cuts rather than tears, and a V-score leaves a controlled groove if the board is separated along it. Panel tab routing gives more freedom of outline, while V-score gives a faster separation along a straight line.

Rule 1: Set Tab Width From the Load

Tab width is the distance across the bridge measured parallel to the board edge. A typical starting point is 3 mm for a small board and up to 5 mm for a heavy one, with the figure increasing with the mass of the assembly and the number of tabs reduced accordingly. Fewer, wider tabs are usually stiffer than many narrow ones.

The tab width should also leave room for the routed cut on both sides. Where the tab is narrow and the router bit is wide, the cut consumes most of the bridge and leaves a weak section that may break before the end of the line. The layout should show the finished edge and the cut path so that the remaining material is visible.

Rule 2: Keep Tabs Clear of Components

A tab has to be placed where the separation will not disturb a component. The stress from cutting or breaking a tab travels into the laminate, and a component within a few millimetres of the tab can be cracked or lifted. The keep-out applies to both sides of the board, because the router cut is a through cut.

The tab should also avoid high-value areas such as a fine-pitch device or a ball grid array, where a small amount of flexure is enough to crack a joint. Where the layout forces a tab close to a component, the separation method should be reconsidered in favour of a lower-stress process such as a fine router bit or a laser cut.

Rule 3: Choose the Tool for the Edge

The router bit determines the edge quality and the stress. A two-flute carbide bit removes material cleanly at the right chip load, while a worn or improperly fed bit smears the resin and leaves a burr. The bit diameter also sets the minimum internal radius that the outline can have.

V-score is a different process: a pair of circular blades cuts a groove on both faces, leaving a controlled web that is broken later. It produces a clean edge with low stress but it only works along a straight line, and the groove depth has to be controlled because it reduces the section that carries the board through the line. Our depaneling methods comparison sets out where each process is appropriate.

Rule 4: Support the Panel at the Cut

The panel has to be supported on both sides of the cut during depaneling, and close to it. A panel that is unsupported flexes as the bit passes, which produces a ragged edge and transfers stress into nearby joints. The fixture should support the board, not the frame, where the board is the part that matters.

Support also matters during the earlier processes. A panel with too few tabs will sag in the middle under its own weight and under the force of the squeegee, which changes the print and the placement. Where a large panel needs more tabs than the outline allows, a centre rail can be added and cut away at separation. Our notes on warpage describe how the panel behaves under load.

Rule 5: Control Burrs and Exposed Fibres

A burr on a routed edge is resin that has been pushed rather than cut, and it forms when the bit is dull, the feed is wrong or the panel moves. Burrs matter because they break off later as particles and because they interfere with the fit of the board. Exposed glass fibres are the same failure seen after the resin has been removed.

Both are controlled by the cutting parameters and by the bit condition. The feed per tooth has to be high enough for the bit to cut rather than rub, and the bit has to be replaced before the edge degrades. The edge is checked under magnification against the edge quality criteria for the product.

Rule 6: Inspect the Separated Edge

Inspection covers the edge profile, the presence of burrs or delamination, and the position of the edge relative to the datum. The edge position matters where the outline is a functional dimension, and it should be measured on a sample from each lot. The profile should be free of steps and of resin smear.

The inspection should also look at the board, not only the edge. Cracks from separation appear as a change in the laminate near the tab, and a joint near a tab can crack without any visible mark on the edge itself. Comparing the area around each tab against a reference board is a quick check that catches stress damage.

Panel Tab Routing Versus V-score

V-score suits a rectangular board with straight edges and a high volume, because separation is fast and the edge is clean. Panel tab routing suits an irregular outline, a board with internal cut-outs, or a product where the edge must carry a connector. Many panels combine the two, scoring the straight sides and routing the corners.

The choice also affects the edge left behind. A V-scored edge has a bevel that reduces the usable height of the edge, which matters for a card that slides into a guide. A routed edge is square and full height, which suits a connector or an edge that has to seal. Our depaneling notes and the guidance published by IPC both describe the dimensional consequences.

FAQ

How many tabs does a panel need? Enough that the board does not sag or shift during printing and placement, which usually means four to six for a board of typical size and more for a heavy one. The count should be checked by supporting the panel as it will be supported in production.

Can tab width be reduced to make separation easier? Only to the point where the panel still behaves as a rigid panel. Below that point the print and placement suffer, and the saving at separation is smaller than the loss earlier in the line.

Is a router bit or a scoring wheel better for a connector edge? A router, because the scored bevel reduces the edge height and can interfere with the connector. Where a scored edge is used, the connector position should be moved away from the score line.