Are circuit boards toxic when exposed to heat?

[caphair]

I want to make a blade to clean underfill off of some mobile phone ics that's safer than metal (sometimes metal cuts through the solder mask or rips pads off)

I have junk circuit boards laying around and I was experimenting with some. Managed to shape a knife tip attached to an x-acto blade handle that worked surprisingly well.

However it does leave an odor when using which got me wondering about the materials used. Is there a health risk? If so does anyone have any suggestions on materials I could use that would work just as well without causing damage?

[stj]

Re: Are circuit boards toxic when exposed to heat?

i dont think the fiberglass mat burns, but the epoxy may not be all that good.
but your using it to remove epoxy anyway.

why not use a ceramic?

[caphair]

Re: Are circuit boards toxic when exposed to heat?

i dont think the fiberglass mat burns, but the epoxy may not be all that good.
but your using it to remove epoxy anyway.

why not use a ceramic?

Are all circuit boards made of fiberglass and epoxy? This one burns a little and chars.

Ceramic is a great idea, but would it be sharper than metal and damage ics if too much pressure is applied?

[stj]

Re: Are circuit boards toxic when exposed to heat?

ceramic, like metal is only as sharp as you choose.

most pcb's are fiberglass (FR4)
but there is also paxoline - cheap brown crap that is often used for single-sided products
i dont know what paxoline is made from.

[Harvey]

Re: Are circuit boards toxic when exposed to heat?

i dont know what paxoline is made from.

Its epoxy bonded paper.

[caphair]

Re: Are circuit boards toxic when exposed to heat?

The one I used must be paxoline as it burns like paper. Is the epoxy used toxic?

How could you tell if a circuit board is paxoline or fiberglass?

[stj]

Re: Are circuit boards toxic when exposed to heat?

paxoline cracks,
fiberglass - if you snap it you will see the fibers

[eccerr0r]

Re: Are circuit boards toxic when exposed to heat?

It's purely the epoxy and the fire resistance compounds mixed in the epoxy that's toxic, but the idea that the epoxy and fire resistance compound will self extinguish when brought to flame. The paper in FR2 will burn like any other paper.

If you remove/scrape off the soldermask on the board portion, FR4 fiberglass is greenish/translucent due to the fiberglass (though the multilayer soldermask will disguise it). Sometimes if you scrape off an edge you can see the fibers, and if you run your fingernail across the edge, it will snag and rip your fingernail as glass is harder than keratin. FR4 is very stiff.

FR2 phenolic paperboard/paxoline is opaque and layered. It will flex and crack when bent, and when it cracks and breaks, you'll see it split how mica splits as it's similar in composition. Typically FR2 is whitish/brownish when the soldermask is removed.

If you have some prototyping board that has a whole grid of holes drilled in it, chances are it's FR2 to keep things cheap. It will be brown colored. This is not to say that there's no FR4 prototype board - FR4 prototype board is much more expensive, and typically it will be greenish translucent, again if it doesn't have green soldermask on it.

[caphair]

Re: Are circuit boards toxic when exposed to heat?

It's purely the epoxy and the fire resistance compounds mixed in the epoxy that's toxic, but the idea that the epoxy and fire resistance compound will self extinguish when brought to flame. The paper in FR2 will burn like any other paper.

If you remove/scrape off the soldermask on the board portion, FR4 fiberglass is greenish/translucent due to the fiberglass (though the multilayer soldermask will disguise it). Sometimes if you scrape off an edge you can see the fibers, and if you run your fingernail across the edge, it will snag and rip your fingernail as glass is harder than keratin. FR4 is very stiff.

FR2 phenolic paperboard/paxoline is opaque and layered. It will flex and crack when bent, and when it cracks and breaks, you'll see it split how mica splits as it's similar in composition. Typically FR2 is whitish/brownish when the soldermask is removed.

If you have some prototyping board that has a whole grid of holes drilled in it, chances are it's FR2 to keep things cheap. It will be brown colored. This is not to say that there's no FR4 prototype board - FR4 prototype board is much more expensive, and typically it will be greenish translucent, again if it doesn't have green soldermask on it.

Great info thanks. So it seems the one I shaped into a knife was FR2. Is there any toxic risk the way I'm using it? Hot air used is around 250-300c. The charring must be the paperboard being burnt but what about the epoxy and fire resistance compound be air born as well?

[eccerr0r]

Re: Are circuit boards toxic when exposed to heat?

Well FR2 was not meant to be heated at all. I'm surprised it lasts at all, this stuff is weak.

If I frequently have to heat the thing so that it charcoalizes frequently, I'd probably refrain from doing so, but if you infrequently do it, it's probably okay.

[caphair]

Re: Are circuit boards toxic when exposed to heat?

Well FR2 was not meant to be heated at all. I'm surprised it lasts at all, this stuff is weak.

If I frequently have to heat the thing so that it charcoalizes frequently, I'd probably refrain from doing so, but if you infrequently do it, it's probably okay.

Thanks again. Any health risk using FR4 in this fashion? At this point I'm more curious for reference. I may opt for a ceramic alternative

[eccerr0r]

Re: Are circuit boards toxic when exposed to heat?

They both basically use the same kinds of things, if you're heating them up to charcoalization point, you're releasing the flame resistance molecules and this is the nasty stuff.

FR4 is kind of dicey because if you sharpen it to a point (it'll be hard because of the glass fibers) you'll still get fibers pointing out of the bulk... may or may not be fine, but definitely a scraper...