PCB alterations post-production. Or, how do I not stab myself while scraping off the copper?

Question

I made a PCB that I am happy with (it works!). This is for a power circuit, and I have realized (way too late) that I want a switch on the board as well. I bought a switch from a hardware store that seems to be ok for the purpose.

I have the location of the thick VCC trace where I want the switch identified, and I think I can drill two slots using a small drill. The only problem that remains is the copper trace between the two slots. I want to remove that copper to make sure it cannot turn on without the switch being on.

I have 2oz copper traces. The trace I will need to remove is about 7 mm in width and probably 1 cm in length.

The only two ways I can think of getting rid of this trace region are:

1. Try to scrape it off with an exacto knife. I have only ever taken solder mask off with a knife, so I don't know how well this will work on copper...
2. Try to overheat that region of the PCB and hope the copper peels off. I've done this accidentally a few times. Well, the transistor burned and took the traces with it).

Is there a better/safer way? I could probably just not put the switch on the board, but put it on a separate prototype board by itself and wire that to the power board.

Answer 1

Assuming your PCB is low-voltage, then just a wide-ish cut from a scalpel will do. Personally, I've had success with a technique akin to a lumberjack cutting a tree with an axe. Put one cut in as deep as possible, then shave off bits from either side, making a "V"-shaped "canyon" until you're satisfied that the cut is big enough. If your circuit is high-voltage, then make two cuts with a decent separation distance, then use the scalpel to cut underneath the trace and lift it off the board.

If possible, hold the board tightly in a vice whilst you're doing this, to allow you to have only one hand (the one holding the scalpel) near the blade.

Answer 2

Don't try to scrape it off. Instead, use an Xacto knife or something similar, and make cuts at each end of the area to be removed. Make sure you get all the way through. That is, all the way through the copper, not the substrate. Also, cut through the resist at the edges of the area.

Now take the point of the knife and start poking under one of the corners. You'll find that the copper peels away from the board without heat. When you have a large enough corner pulled up, grab it with your needle-nose pliers and simply peel the piece off.

Answer 3

The one time I had to cut a thick power trace, I used a Dremel with a round bit. It was enough to get into the copper, but leave the FR4 beneath it with only a little bit of surface scuffing.

Answer 4

Well I'd just score two ends of it with the exacto knife to make a little section. Then if you want you can heat that up a little and just peal it off with the knife or a pic. Do you really need to remove the trace or will cutting it suffice?

Answer 5

The easy way to remove larger portions of thick, wide trace is to scrape the solder-mask from the copper, cut through the copper trace at each end of the section that you want to remove, then flood the trace in between those cuts with a soldering iron and lots of solder.

You will need to keep the solder molten for anywhere from 10 to 30 seconds, sliding the soldering iron tip from one end of the trace section to the other.

The adhesive holding the copper to the PCB substrate will fail at some point and the trace section simply peels off after it has cooled.

Been there, done that, works well.

Answer 6

Hold a sharp knife like a pen and scrape