Submillimeter PCB holes

Today I drilled holes. Lots of tiny, stoopid little holes. The boards I have recently etched needed drilling, so I decided that today, after a hard day rebuilding my new home, it was time drill. Muscle aches everywhere and dead tired, but what the hey; Let's rock and roll. The first holes would be the vias, because if there is one thing that could go wrong during drilling, it is the vias, because they are so small. No use spending time first drilling all the 'easy' big holes, only to screw up on one of the small holes later on. So it was said, so it was done. I can hardly believe it, but I actually drilled all 3 boards I had laying around and did not screw up a single hole, even though I am quite tired. And also, by drilling holes I could confirm that all the boards have their top and bottom very nicely aligned, which is good news. It means that the toner transfer system I use is effective. Hurray for toner transfer method! Here is the result. All the holes are nicely in the middle of the vias. On both sides.

PCB top

PCB bottom

I find the experience of drilling holes this size not very amusing. It requires a very steady hand, a steady drill press, proper lighting and lots and lots of concentration. And all the time during drilling I have this fear that the next drill might spell disaster and I'll have to redo the whole thing. The holes you see in the pictures are 0.6 mm in diameter and the via's copper shape is 1.1 mm in diameter (it's actually an octagon). This board is to be my first go at a home built ARM board. Quite a demanding board layout for a first try at home etching and drilling. It took me lots of time to actually get this far. Maybe more on that later.

One of the hardest parts of drilling is getting the drill aligned with the hole. Aiming a 0.6 mm drill spinning at 15000 RPM at vias of 1.1 mm is not easy. One of the mistakes you can make is to hit the via off-center. If it is only slightly off, that is less than (1.1 - 0.6) / 2 = 0.25mm, then there is no real problem. If the offset is bigger, chances are you will have problems because you can't solder the via. Or maybe you've hit another via, pad or trace, in which case the board is damaged. Mistakes like this can be fixed by soldering wires to repair the damage, if you want to. But sometimes the mistake is not fixable, in which case you have to etch and drill a new board.

Today I discovered a way to make it easier to aim the drill. Normally a new drill is metallic in colour and the really small drills are therefore pretty hard to see because the metallic colour does not contrast very well with the board which you are drilling. I have found that if you first drill a couple of random holes in a piece of scrap PCB, the white powder from the drilling process sticks slightly to the drill, making it much better visible when drilling. What also helps a lot is to not remove the toner from the board before you drill. The black toner creates a nice contrasting background for the whitish drill. Shiny copper, on the other hand, is a nightmare to drill, because it shimmers, making it hard to focus on it. This is what my setup looks like:

Drill setup

And a close up, to get an idea what drilling small holes is about. Notice the diameter of the drill. It is sooooo tiiiinyyyy. 

Drill setup closeup

Another thing I have found out is that you can prevent the really small drills from breaking by drilling only as deep as necessary. So when you pull the lever of the drill press to puncture the board, try to feel the resistance. As the drill exists on the other side of the board, the resistance will suddenly drop. That is the exact time to stop pulling the lever and to retract the drill. If you drill too deep, the drills usually snap off in the blink off an eye. This is because they are really brittle and inserting them deep into any material limits their flexibility even further. Even the slightest vibration in the drill press will cause 'snapage' of the drill.  (Do you like the word 'snapage'? I just made it up.) My first attempts at drilling today lead to a nice collection of snapped drills:

 Broken drills

Fingers are also a favorite place for drills to snap. This was a 1.0mm drill that got stuck about 1.0cm into my finger before snapage occurred. The only thing I regret is not taking a picture before pulling the piece of drill out.

 Ouch

~J