You can route big slots (for example for isolation) but usually narrow
*plated* slots for component leads are made with drilled slots. The routing is normally done after through-hole plating, so routing so that the edges would be plated would require an additional operation. Not good.Drilled slots (G85) are made with a bunch of overlapping drilling operations so it's like a slightly higher hole density. Usually no noticable additional cost unless hole density is really high. No additional tools either, just a bit of time on a huge multi-spindle machine. (and since the holes are close spaced the X-Y moves between holes are very fast).
Here is Excellon's description:
******************************************************************** Slot G85G85 Cuts a slot by drilling a series of closely spaced holes between two points. The start of the hole is programmed with an X and Y coordinate, followed by the command, followed by the ending X and Y coordinate. The tool is specified with a T command prior to the G85 command. The tool size MUST be specified prior to using this command. The size may be provided by the Operator through the console, in the part program body, or the part program (M48) header. The slot is as wide as the drill bit used. The slot is created by drilling a series of evenly spaced adjacent holes from one end of the slot to the other. This leaves protrusions around the edge of the hole. Then another set of spaced holes is drilled between the previous set. This continues until a smooth sided slot has been produced. The holes are spaced close enough that these protrusions are less than 0.0005".
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