Router Bit Selection for Depaneling

Routing separates boards from a panel with a rotating bit that follows the outline. It is the most flexible depaneling method, since it can follow any shape and it leaves an edge with no taper, and its quality and its cost both depend on the bit. Selecting the bit means balancing the diameter that the outline needs against the life that the abrasive laminate allows.

The Bit and Its Geometry

A router bit has a shank, a cutting edge and a geometry that determines how the material is removed. A two flute bit is common for laminate, because the flutes clear the chips and the heat.

The diameter sets the minimum radius that the outline can follow and the width of the cut. A smaller bit follows a tighter corner and removes less material, at the cost of a weaker tool and a lower feed rate.

The cutting edge can be straight or helical. A helical edge shears the material, which produces a cleaner edge and less delamination, at a higher cost. The choice depends on the edge requirement of the product.

Coating and Material

A carbide bit is the standard. The laminate is abrasive because of the glass, so a plain tool steel bit wears quickly and produces a rough edge long before it fails.

A diamond coating extends the life considerably for a high volume operation, and it is justified where the tool change stops the machine. The coating does not improve the edge quality, it only postpones the wear.

The bit should be inspected for wear on a schedule rather than when the edge quality falls. A worn bit produces a rougher cut, more dust and more heat, and the change is gradual enough that it is easily missed.

Feed Rate and Spindle Speed

The feed rate is the speed at which the bit moves through the material, and the spindle speed is the rotational speed. The two together set the chip load, which is the thickness of material removed by each cutting edge per revolution.

A low chip load rubs the material instead of cutting it, which generates heat and burns the resin. A high chip load overloads the bit and produces a rough edge with delamination. The correct value is a compromise that depends on the bit and on the laminate.

The speed should be set from the laminate rather than from the machine’s maximum. A hard, highly filled material needs a slower feed and the bit heats faster, so the parameters have to be re established when the material changes.

Edge Quality

The edge of a routed board should be smooth with no visible delamination and no burr of copper. A delamination appears as a white line where the resin has separated from the glass, and it is a sign that the cut is too aggressive or the bit is worn.

The copper burr is more important on a board that will be inserted into a connector, because the burr can prevent the board from seating or can damage the contact. The burr should be checked on the finished edge rather than on the panel.

The cut quality is influenced by the support as well as by the bit. A panel that is not fully supported during the cut will deflect, and the deflection produces a rough edge on the side that was pulled into the bit.

Stress on the Board

Routing applies a much smaller bending moment than scoring, because the bit removes the material rather than breaking it. The force is mostly in the plane of the panel, which is what makes the method suitable for a board with a component close to the edge.

The heat is the other stress. The bit generates heat that is carried away by the chips and by the air, and a dull bit or a low feed rate can raise the local temperature enough to soften the resin and smear the edge.

The panel should be supported close to the cut and the components should be clear of the tool path. A component that is lifted by the air blast or struck by the bit is a defect that is entirely avoidable.

Chip Removal and Dust

The cutting produces a dust of glass and resin that is abrasive and a health hazard. The extraction has to be effective at the cut, not only at the enclosure, and a partially blocked nozzle leaves the chips in the cut where they are recut.

The chips in the cut increase the heat and the tool wear. The extraction should be checked at the start of every shift, and the filter should be replaced on a schedule rather than when the airflow falls visibly.

The dust is also a contamination risk for the assembly. A board that is routed before assembly should be cleaned, because the dust that remains on the surface interferes with the paste and the solder.

Cost and Tool Life

The cost of routing is driven by the machine time and the tool life. A small bit that follows a complex outline takes longer and wears faster, so the outline should be designed with the routing in mind.

The number of boards per bit depends on the bit, the material and the parameters. The figure should be measured rather than taken from a catalogue, because the laminate and the parameters affect it more than the bit alone.

The tool change should be planned rather than reactive. A planned change at a defined number of boards costs less than an unplanned one, and it keeps the edge quality within the specification for the whole run.

When Routing Is the Right Choice

Routing is chosen for a shaped outline, for a board with a critical edge, for a panel with a component close to the separation line and for a mixed array with different board sizes.

It is not the fastest method. A panel of identical rectangular boards can be scored or punched faster, and the choice should be made from the outline, the volume and the edge requirement together.

The design should provide the data that routing needs: a defined outline with a radius that the bit can follow, a tooling hole for the machine datum and a keep out for the tool path around any tall component.

Practical Rules

Match the bit diameter to the smallest radius in the outline, set the feed and speed from the laminate and change the bit on a measured schedule. Support the panel near the cut and extract the dust at the point of cutting.

Record the parameters and the tool life with the build records and the depaneling methods, and review the panelization design and the v cut scoring guide when the separation method is chosen.

FAQ

Why does the chip load matter? It is the thickness of material each cutting edge removes. Too low rubs and burns, too high overloads the bit and delaminates the edge.

How often should a router bit be changed? On a measured schedule based on the number of boards, not when the edge quality visibly falls. A planned change is cheaper than a reactive one.

Why does routing stress a board less than scoring? It removes the material with a bit rather than breaking a web. The force is mostly in the plane of the panel, so a component near the edge sees much less bending.