Drill Bits

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A great number of holes with small diameters of about 1 mm or less must be drilled in printed circuit boards (PCBs) used by electronic equipment with through-hole components. Most PCBs are made of highly abrasive fiberglass, which quickly wears steel bits, especially given the hundreds or thousands of holes on most circuit boards. To solve this problem, solid tungsten carbide twist bits, which drill quickly through the board while providing a moderately long life, are almost always used. Carbide PCB bits are estimated to outlast high speed steel bits by a factor of ten or more. Other options sometimes used are diamond or diamond-coated bits.

In industry, virtually all drilling is done by automated machines, and the bits are often automatically replaced by the equipment as they wear, as even solid carbide bits do not last long in constant use. PCB bits, of narrow diameter, typically mount in a collet rather than a chuck, and come with standard-size shanks, often with pre-installed stops to set them at an exact depth every time when being automatically chucked by the equipment.

Very high rotational speeds—30,000 ...
... to 100,000 RPM or even higher—are used; this translates to a reasonably fast linear speed of the cutting tip in these very small diameters. The high speed, small diameter, and the brittleness of the material, make the bits very subject to breaking, particularly if the angle of the bit to the workpiece changes at all, or the bit contacts any object. Drilling by hand is not practicable, and many general-purpose drilling machines designed for larger bits rotate too slowly and wobble too much to use carbide bits effectively.

Resharpened and easily available PCB drills have historically been used in many prototyping and home PCB labs, using a high-speed rotary tool for small-diameter bits (such as a Moto-Tool by Dremel) in a stiff drill-press jig. If used for other materials these tiny bits must be evaluated for equivalent cutting speed vs material resistance to the cut (hardness), as the bit's rake angle and expected feed per revolution are optimised for high-speed automated use on fiberglass PCB substrate.