How to manually "sand down" a PCB to make it look like EMX module

I have a PCB that looks exactly like the footprint of the EMX module:

This means I have metallized drill holes at the border of the PCB. Now, the PCB manufacturer requires me to pay some extra $ in order to create that board because of that. Therefore I decided to enlarge the dimensions of the PCB, just as much so the pads fit on the PCB and the drill holes are no longer at the border.

You might feel the question comming:
When I receive the PCB’s, I want to manually ‘sand down’ the border until halfway the drilled holes. The question is if I will damage the metallization by doing that? Does anyone have any experience with this?


You could fill all the holes with solder, then sand the edges very carefully. It’s still a risk.

I would love to see a time-laps video if that :slight_smile:

I would try it on a spare or scrap PCB first, but only if saving that extra money worth the risk of ruining the board.

@ WouterH - Find somebody with a high power Laser to slice the edges off for you. As Gus says post a video on youtube i’m sure you will get many hits, Or look big and pay the money, lol…

I have some spar boards here from the same manufacturer I can test on. Well now it’s 55EUR for 2 pieces, if I wanted drilled holes on the border, they asked 102 EUR for 2 pieces. Sorry but I’m not willing to pay that :slight_smile: It’s still a prototype.

@ Davef: soldering the pads first is a good idea

@ WouterH,

It will help, but if you sand as far as half way, it will not help! Good Luck! I think Ive seen it before when QA wanted to know how good the soldering was, but those boards had components fitted.

@ WouterH - What kind of sander are you going to use? If you have a belt sander that also has the vertical sanding disc. I would use the vertical sanding disc as I have sanded the little nubs off after you break a board out of a panel before.

Ouch! Almoust 100% more! Time to change the manufacturer.

Direction of the sander move will be important. Perpendicular to the holes to minimize possibility of lifting the pads.

@ Architect - Good point.

When I did this it was on the downward motion of the disc.

I was thinking of using this dremel:

With this grinder:

@ WouterH - Are you going to do this free hand or are you going use a dremel table?

Along those lines, could someone use a CNC mill to do it? Any sort of automated process would be much better than doing it by hand for accuracy.

@ WouterH

I think you are taking a large risk to save a few ducats.

You are going to have to cut four sides of the board to a high degree
of accuracy. If you ruin one cutout, by destroying the edge plating, you
have ruined the board.

You will spend hours preparing for the cuts, with maybe a
a 50% chance you will succeed.

The payout is not worth the risk in my opinion. :slight_smile:

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I’d be totally expecting the plated hole to rip off as soon as you look at it wrongly, let alone wave a dremel near it. That however may not be a problem, as long as you don’t damage the laminate, as you should be able to re-tin it with solder. Good luck, and yes I think like everyone else we would like to see video evidence. :slight_smile:

Yes a CNC mill would work, as I am pretty sure this is how our board house makes the EMX and G120 boards

I would imagine they do it before soldering and laminating though - guess I was wondering if the cutting action of the mill would damage/crack the laminate or solder. Similarly, I wonder if the high-power laser would melt either layer?

If you have access to a bandsaw with a fine blade and a fence, that would be my first stop. I think it would be less likely to break off the studs than a circular cutter like the Dremel. Also, if you are planning to do many of these then be prepared that the Dremel cutter wheels have a very short life and are not usually cheap to replace. If you go that route then you would get one of the router table attachments also and use a fence to keep the cut straight.

Thanks for all the answers. I still will give it a try, as this is a prototype and only a two layer board, so if it screw things up, I still can ‘fix’ it.

Reading all the answers here, I will order the final board already finished.

Ok, so I did a test on an other prototype (from the same manufacturer) and it seems like I was worried about nothing. It was a 10 second operation and all the metallizations are still measuring through and they look intact. Also see my sophesticated setup :wink: