V-Score vs Tab Routing: Choosing a Depaneling Method

Depaneling looks like the last step in fabrication, but the method chosen at the panel stage sets the mechanical stress that every component near the board edge will see, and it decides how much of the panel is available for product. V-score and tab routing cover almost all production, and they are not interchangeable on a given design. This article compares what each leaves behind, the stress each applies, and the measurements that keep the separated edge inside specification.

How V-Score Is Cut and What It Leaves

A V-score is formed by two circular blades, usually ground to an included angle of 30 or 60 degrees, pressed into the panel from both sides so that they remove material without cutting through. The web that remains at the centre is typically one third of the board thickness, and it is that web which fractures when the panel is separated.

Depth control decides whether the score works at all. A web that is too thick will not break cleanly and tears the laminate when force is applied, while a web that is too thin releases the panel in the machine and can crack the board during plating or handling. A tolerance of plus or minus 0.1 mm on the score depth is a practical requirement, verified on a sample from the same stack-up. The drawings involved are listed in our fabrication notes.

Tab Routing, Perforations and Mouse Bites

Tab routing leaves the board attached by small bridges of laminate, usually three to five millimetres wide and spaced no more than about 50 mm apart along each edge. Each tab is separated afterwards by hand, by a cutter or in a fixture, and the resulting surface is a cut laminate edge rather than a fractured one.

Perforated tabs, formed by a row of small drilled holes, localise the break and leave a cleaner edge, but the holes reduce the strength of the tab. Holes of 0.5 mm on 1.0 mm centres give a predictable break line, and the material left beside the tab has to be counted when the drawing specifies the space available for the board outline.

The break line belongs on the fabrication drawing as a dimensioned feature, not as a note. When the tab width and position are drawn, the assembly house can check the keep-outs before the panel is released.

Matching the Method to the Board

V-score suits rectangular boards with a straight uninterrupted edge, thickness above about 1.0 mm, and no components within a few millimetres of the break line. It is fast, it needs no additional routing time, and it leaves a panel rigid enough to travel the assembly line without a carrier.

Routing suits curved outlines, internal cut-outs, thickness below 1.0 mm, and edge connectors that must not be scored. It also suits panels where the break line would fall beside a row of fine pitch components. The trade is cycle time and dust, both of which have to be engineered rather than accepted, and both of which interact with how the production floor is arranged around the machine.

Stress from Manual Breaking

Breaking a scored panel by hand bends both the separated board and the panel, and the strain reaches roughly four or five millimetres from the score. A capacitor or a BGA inside that band is loaded in exactly the orientation that produces a crack, and the damage usually passes electrical test at the moment it is caused.

A tool that applies a rolling or shearing action instead of a bending one reduces the strain considerably, and the tool should be confirmed against a strain measurement rather than a visual result. Where a hand break is unavoidable, a keep-out of five millimetres from the score line, applied to both placement and copper, keeps the highest value parts out of the affected band, which is the same reasoning used in our guide to board flatness.

Router Bits and Cutting Parameters

Depaneling routers run carbide bits of two to three millimetres diameter, usually at 30 000 to 40 000 rpm with a feed between 25 and 40 millimetres per second. The cut is taken in two or three passes, with the final pass only a fraction of the bit diameter deep, so that the laminate is not lifted as the tool exits.

Bit wear is the variable that governs edge quality in production. A worn bit raises the cutting temperature, melts the resin and leaves glass fibres standing proud of the surface, so the bit should be replaced on a count of linear metres cut rather than when an operator notices the finish.

Panel Rails, Fiducials and Utilisation

Both methods need a rail that the printer and the conveyor can grip. Five millimetres is the usual minimum, and the rail carries the fiducials and the tooling holes, normally 3.0 mm in diameter, that locate the panel in the printer and the placement machine.

Utilisation follows from how much material the break line consumes. A scored line removes almost nothing, while a routed outline removes the bit diameter plus clearance on both sides, and on a small board the difference is worth several percent of the panel. That difference belongs in the quotation comparison, because the two methods do not produce the same number of boards per panel. Material behaviour behind this is covered in our notes on laminate properties.

Rails are also the part of the panel that carries tooling holes, and a rail that is too narrow to hold them forces the panel to be located from the board outline, which usually costs placement accuracy.

Edge Quality and Burr Acceptance

The acceptance figure for a routed edge is normally a burr height below 0.1 mm, no fibre protrusion that can be felt, and solder mask intact to within 0.2 mm of the outline. A scored edge is judged by the web remnant, which should be a controlled fracture rather than a tear with delamination visible in section.

Both conditions are checked on a sample rather than on every board, but the sample has to come from the production machine with the production tooling. An edge produced by a bench router with a new bit looks different from one produced by a machine whose bit has already cut several hundred metres of panel.

Dust, Cleanliness and Ionic Contamination

Routing produces a fine dust of resin and glass that settles on the board. It is electrically insulating but hygroscopic, so dust retained in flux residue around the joints can show up later as a leakage failure under humid conditions.

Where routing is performed on assembled panels, the cut area is normally cleaned by vacuum extraction at the bit followed by a wash. The verification is an ionic contamination measurement against a limit of about 1.56 micrograms of sodium chloride equivalent per square centimetre, taken from the board surface rather than from the extraction duct, using the methods described in our guide to cleanliness measurement.

What the Drawing Has to Say

The panel drawing should state the separation method, the rail width, the tab width and spacing where routing applies, the score depth where scoring applies, and the keep-out from every break line. Left unsaid, the choice is made by the fabricator on the basis of cost and habit, and the assembly house receives a panel whose edge treatment it never specified.

The assembly drawing then carries the matching information: the maximum handling stress at the break line, the components excluded from the keep-out band, and the method by which the panel will actually be separated on the line. When both drawings agree, depaneling stops being a source of latent damage and becomes a process with a measurable output.

FAQ

Is a scored edge acceptable on a controlled impedance board? Yes, provided the score lies outside the trace area and the residual web does not cut into the reference plane, so the copper has to be kept clear of the score line and the clearance shown on the drawing.

How wide should a breakaway tab be? Three to five millimetres is typical. Narrower tabs break unpredictably, and wider ones need more force, which raises the stress on whatever sits nearby.

Can thin boards be scored? Below about 1.0 mm the web becomes too fragile to survive assembly handling, so routing with a carrier or a pallet is the practical alternative.