PCB drilling - drill bit material selection

Question

I am planning to buy a bench drill (something like that one) to make small hole, 0.5-1.0 mm.

I recently used a Bosh drill and 1mm steel drill bit to make a hole on a FP4 fiberglass board, but the drill bit broke on the second hole drilling process.

Now, I will buy 0.6 mm drill bit but I am not sure what material it needs to be. Could anyone who knows these equipment tell me what material the drill bit should be made of, so that I can use the same drill bit for long? and what do you think about "Tungsten Carbide"?

Answer 1

Whatever size drill press you use, from a small Dremel press mount to a floor-standing shop drill press, you want to make sure that the chuck does not wobble. I originally used a cheap benchtop drill press, but the chuck wobbles about 1/64" (.4 mm), which is inadequate for most PCB drilling.

You should look for carbide bits instead of high speed steel (HSS). Tungsten carbide is great for PCB, but they are brittle. They won't become dull as quickly when drilling FR4 PCB material. Having a good press that doesn't wobble helps a lot in avoiding broken bits.

For holes < 1mm, sometimes even the Dremel can be too unsteady, and break bits. You might want to look for a "jewelers drill press" which is designed for small precision work.

One example is the Microlux mini drill press that Micro Mark sells, though you can find similar ones for sale on eBay.

Answer 2

I have exactly same PROXXON bench drill at home. Most of the times I drill with 0.65mm HAM 380 (cost about 5 EUR). It feels like it can stay sharp forever. In my experience it was like new with over 500 holes. I have broke few drill bits as well, but it was just my fault. Also I have found that it's quite uncomfortable to use collet set, so you may want to consider buying Proxxon Drill Chuck (28122) as well.

Answer 3

Whatever the material, make sure you use a drill press to make the holes. Without a drill press, the slightest bump will break the drill. That is probably what happened in your case. That is specially true for carbide drill bits, that are really brittle.

As a hobbist, I use a Dremel Workstation 220 (drill press adapter for Dremels) with 0.6, 0.8 and 1.0mm high speed steel (HSS) for drilling holes on phenolic boards and I'm yet to break a drill while drilling boards (have drilled several thousand of holes).

I have, however, broke one HSS drill bit in my fingernail when I touched it while trying to clean the board. That was a vivid lesson not to submit drill bits to any lateral forces while the drill is on. Also a lesson to take more care while operating power tools.

HSS are only good for phenolic boards, though. They aren't good for fiberglass boards at all. They loose the cutting edge after a handful of holes. Use carbide drill bits for fiberglass boards.