PCB Router Bits: Depaneling Tool Selection and Cut Quality
A PCB router bit is a small carbide end mill, usually between 0.8 mm and 2.4 mm in diameter, that cuts the outline of a circuit out of its panel. It looks like an ordinary cutter and behaves like a precision tool: the edge geometry, the number of flutes, the coating and the feed parameters together decide whether the panel separates cleanly or arrives with burrs, delamination and dust everywhere.
What the Tool Has to Do
Depaneling is not the same as cutting metal. The workpiece is a laminate filled with woven glass, and the cutting edge has to shear fibres rather than deform them. A sharp, hard edge with a controlled rake angle removes material cleanly, while a dull or badly ground cutter rubs, generates heat and tears the resin.
The cutter also has to evacuate its own chips. Glass filled epoxy produces an abrasive dust that packs into the cut if it is not cleared, and packed dust raises the temperature, wears the tool and leaves a rough edge. Chip evacuation is therefore one of the two or three variables that matter most, alongside spindle speed and feed rate.
Cutter Geometry
Most depaneling tools are two flute end mills made from sub-micron carbide. The flute count balances chip clearance against edge strength: more flutes give a smoother cut at high feed, fewer flutes give more room for the chips to escape. A 1.6 mm or 2.0 mm cutter with two flutes is the common default for general panel routing.
Coating choice follows the material. A hard coating such as titanium aluminium nitride extends life on abrasive laminates, while an uncoated polished tool cuts slightly cooler where heat is the limiting factor. The helix angle sets the direction of the cutting force, which matters on thin panels and on boards with components close to the outline.
Up Cut and Down Cut Behaviour
An up cut tool lifts chips out of the kerf. Evacuation is good and the cutting force pulls the panel toward the tool, which is helpful on a well supported board. The trade off is a slightly rougher top edge, because the fibres are pushed upward as they are cut.
A down cut tool pushes material downward, which leaves a cleaner top surface and holds the board against the table. The chips, however, have to travel downward through the kerf, and evacuation suffers unless the support underneath is designed for it. Many shops use up cut tools for general routing and switch to down cut where the top surface quality is critical, such as around a connector or a visible edge. The way the kerf interacts with nearby features is part of the wider question of slot and edge routing rules.
Spindle Speed, Feed and Chipload
Spindle speed for depaneling normally falls between 20,000 and 60,000 rpm, and the feed rate between roughly 10 and 30 mm per second. What matters most is the chipload, the thickness of material removed by each cutting edge, which follows from the feed rate, the spindle speed and the number of flutes.
A chipload that is too small means the edge rubs instead of cutting, which burns the resin and wears the tool quickly. Too large and the edge can chip, especially on small diameter cutters. Once the process is stable, the parameters should be recorded per product, because changing a cutter diameter or the board thickness without adjusting the feed moves the process outside its window.
Tool Life and Wear Monitoring
Carbide wears progressively when cutting glass reinforced laminate. The first sign is a change in cut quality rather than a broken tool: the edge roughens, more burr appears and the spindle load creeps upward for the same feed. Monitoring either the load or the edge quality lets the cutter be replaced before the panels start to fail inspection.
Typical life for a small router bit is measured in tens of metres of cut, and it falls sharply as the board gets thicker or the glass content rises. Resharpening is possible on larger tools but rarely worthwhile on the smallest diameters, where the geometry is hard to reproduce and the price is low. Tool life is stated in the notes on manufacturable design guidelines as a process parameter, and it should be tracked per product rather than per machine.
Burrs, Delamination and Edge Quality
A burr is copper pushed out of the cut rather than sheared. It appears when the tool is dull, the support is inadequate or the feed is too high. Burrs matter because they can bridge two nets that were supposed to be separate, and because they create loose material that travels through the rest of the process.
Delamination shows as a white or lifted edge where the resin has separated from the glass. It usually comes from heat, which in turn comes from poor evacuation or a worn edge. Supporting the panel with a backing board, taping the underside and taking a finishing pass at reduced feed all improve the result on difficult materials.
Designing the Panel for Routing
Leave enough room around each circuit for the cutter. A rout channel of 2 mm with components kept about 1 mm clear of the outline is a reasonable starting point, and a panel that leaves less forces the shop to slow down and inspect more. The number and position of the tabs that hold each circuit before final separation also matter: too few and the board flexes, too many and the separation step becomes difficult. Tab geometry and panel layout are part of board outline and mounting design, and they should be agreed with the assembly house rather than decided in isolation.
Selecting a Cutter for a Specific Job
Start with the outline geometry. A panel with tight internal radii forces a small cutter, because the radius of the cut cannot be smaller than the tool. If the design needs a 0.5 mm internal corner, the shop has to use a tool of that size, which means lower feed rates, shorter tool life and more passes around the outline.
Board thickness comes next. Thin panels can be cut in a single pass with a small tool, while thick multilayer boards need either a larger cutter or several depth passes, and a single deep pass invites deflection and a tapered edge. The support under the panel has to match the strategy: a backing board for a single pass, and a well clamped stack for multiple passes.
Finally, consider the quantity. For a few panels, tool life is not the deciding factor and the shop will use what is already loaded. For a long production run, a coated tool with a carefully chosen geometry costs more per piece but reduces the number of tool changes and the risk of a shift in cut quality partway through the order. Recording the parameters and the tool used for each product turns that experience into a repeatable process rather than a matter of operator memory.
FAQ
How long does a router bit last? Life is measured in metres of cut and depends on the laminate, the board thickness and the parameters. A small cutter on a thick glass filled panel may last only a few dozen metres before the edge quality falls away.
Up cut or down cut for a top surface finish? Down cut tools leave the cleaner top edge but evacuate chips poorly. Where the visible edge matters, use down cut and design extra support underneath to compensate.
Can routing replace V scoring? Yes for most shapes, and it allows curved outlines and internal cut outs. V scoring is faster and cheaper on straight lines, but it stresses the laminate and leaves a rougher edge.
