Introduction: Clean-Cut FR4 Perfboard (Protoboard/Prototype PCB)
(tl;dr: aviation snips & carborundum stone under water)
As we roll into the third decade of the 21st century, very high quality custom printed circuit boards can be ordered in very small quantities for very low cost ... if you don't mind waiting or live in the right neighborhood. But more often I just want to cobble something together now.
A currently common form of "perfboard" for electronics tinkering is double-sided, through-hole plated, HASL finished 1.6mm FR-4 glass fiber reinforced epoxy PCB. The material is durable and hard to burn. The solder pads are easy to solder and hard to lift off the board. It's available in lots of project-friendly sizes.
It's also a bit unfriendly for cutting to a specific size with a clean finish. Unfriendly as in difficult and hazardous. Or expensive for a tool that few hobbyists will buy.
This 'ible describes a simple, cheap, quick and hazard-reduced way to cut and cleanly finish pieces of FR4 perfboard. The real steps in the middle are easy, plus all these words before and after.
Step 1: Um, Hazards?
Glass is mostly harmless. But fraying or grinding glass fibers makes dust that's at least irritating and can be bad. So I'd rather not breath or disperse the dust. And avoiding a dusty mess helps keep the job simple.
Lead is a bioacccumulating poison. Don't eat it. Avoid dispersing it randomly into the environment. Etc.
Let's assume the solder finish contains lead. In a quick look I didn't find any sellers advertising these boards as RoHS or "lead free". The boards that I have leave lead-colored marks where scrubbed on white paper.
Shedding little bits of lead and grinding lead into dust on your fingers today could go very badly later.
So for this 'ible:
- use reasonable care with cutting and dressing freshly cut edges
- grind under water
- wash your hands (I'm probably supposed to say "wear gloves")
- edit: this from the CDC looks like it should go here:
Washing your skin with standard soap and water is not enough to completely remove lead dust. Search “lead wipes” in any browser for a list of NIOSH-licensed, commercially available products that are proven to decontaminate your skin.
Remember this is just some unqualified rando's drivel that you found on Teh Interwebz. Believing any of it is on you.
Step 2: Set Up
Find a work surface that is
- easy to wipe up (hard, non-porous, non-absorbing)
- where you don't handle food.
Set your grinding stone in a tray/tub/container and fill with enough water to cover the stone.
Step 3: Cut
The snips easily cut along a line of holes.
The edges will be a little rough with frayed glass and fragments of metal plate ready to crumble off. A quick scrub on the stone will knock off the bits that were going to fall off otherwise. Wipe the snip blades and wipe up debris with a something like a damp paper towel. Keep remainder pieces in a bag or container because they still have lots of rough cut plating bits that will crumble off with any significant handling.
For the piece that you will finish and use, continue to clean up the edges more thoroughly...
Step 4: Grind Edges Flat
Holding the stone under water, grind away the remaining plated half-holes.
Grind with force to cut faster, you're not likely to break the board.
Step 5: Chamfer
Chamfer away the small slivers of solder pad that remain vulnerable to peeling away from the faces of the piece.
Step 6: Cleanup
The water will be milky with the dust that you're not breathing and the stone will hold some bits of plate.
Scrub the plate fragments out of the stone, in the water, with an old toothbrush. Rinse off the stone and put it aside to dry.
Let the water in the tub stand undisturbed for a while.
After the metal particles have settled, carefully pour off the waste water leaving the ground metal in the bottom of the tub. Wipe up the damp metal dust with a bit of paper towel. Dispose of the leaded paper and any PCB pieces that you won't keep in a locally appropriate way that won't get dispersed.
Wash out the tub and don't use it for food.
Wash your hands. (edit: the CDC says use NIOSH-licensed "lead wipes")
Step 7: Make Your Thing
Your thing will be your own thing. Unless you're making one of these.
Step 8: On Tools
Apart from writing this 'ible, I use a diamond hone similar to example up in the Supplies list (this one.which appears to be discontinued). That works great but didn't really fit the spirit of this 'ible. To write this, I tried a carborundum stone for the example photographed. It worked well enough. Considering low cost and wide availability, that makes more sense for this go-buy-that-to-do-this context. I wonder how well this US$10 HF diamond hone set would do.
You may already have a coarse sharpening stone. If so, it may be loaded with oil. I don't know how well or poorly that would work out -- for the PCB, for the stone or for cleanup. Maybe a new stone, never oiled, would work better than an oiled stone.
Step 9: On Saving All the Bits
I keep all the little remainder pieces. The photo shows my current stash, which is getting thin -- evidence that the last few perfboard widgets have used up scrap rather than making more.
The tiny chips may look silly, but the collected examples in the Introduction include a few made with tiny pieces like that. At least one of the less-tiny examples fit exactly on one of the remainder pieces already in hand.
At some point I thought maybe I was a little crazy to keep such fragments. When I wanted to wire a stereo jack for the three-terminal widget in the photo and found a scrap exactly the right size, I stopped worrying about that. (obviously I didn't bother with cleaning up the edges of that piece)
Step 10: ...and Some More Notes
...or quit reading and go do something.
... still reading?
Score & break is another way to cut a PCB without any special tools. If:
- each break goes all the way across the material breaking it into two pieces -- no inside corners
- there is enough material to hold or clamp on both sides of the break - hard to break off small/short pieces
1.6mm FR4 requires assertive scoring and breaking.
With these perf boards I've been able to score and get clean breaks along the solid material between rows, preserving all the plated through holes on both sides of the break instead of wasting a row. Apart from some compelling reason why you absolutely can not throw away a row of holes, it's not anywhere near worth the bother.
You may have noticed some sub-0.1" parts in the first photo. SOIC, SOT23 & other SMT tricks were out of scope for this 'ible but may spawn another 'ible another day.
old tools image:
Stanton, Gary Ward. Former sheep shearer Tom Furlong, Havre, Montana. 1979. https://www.loc.gov/resource/afc1981005.afc1981005_gs14/?sp=4