Ammonium Persulphate - a couple basic questions

[KORGULL]

Hi, I'm going to try etching some boards for the first time this weekend using Ammonium Persulphate:

1) I've read about using baking soda to nuetralize Ferric Chloride before disposal - so it is not as bad for the environment. Can I do the same with Ammonium Persulphate?

2) How critical is the mix ratio? Should I actually weigh the crystals and use a measuring cup for the water? Or just estimate and add more water/crystals as I go, until it seems to be working?
The package says to mix 250 grams per 1 litre of water.
I plan to mix enough to etch something like three 2"x3" boards and one or two 3"x6" boards, then dispose of the mixture. The package says once it is mixed it must be stored in a vented container to allow gas to escape. I'd rather not have a bunch of this stuff sitting around my house venting toxic gas.

If anyone can answer these questions and/or tell me anything else about your experiences using/storing/disposing this stuff I'd really appeciate it.
Thanks.

[scottosan]

Hi, I'm going to try etching some boards for the first time this weekend using Ammonium Persulphate:

1) I've read about using baking soda to nuetralize Ferric Chloride before disposal - so it is not as bad for the environment. Can I do the same with Ammonium Persulphate?

2) How critical is the mix ratio? Should I actually weigh the crystals and use a measuring cup for the water? Or just estimate and add more water/crystals as I go, until it seems to be working?
The package says to mix 250 grams per 1 litre of water.
I plan to mix enough to etch something like three 2"x3" boards and one or two 3"x6" boards, then dispose of the mixture. The package says once it is mixed it must be stored in a vented container to allow gas to escape. I'd rather not have a bunch of this stuff sitting around my house venting toxic gas.

If anyone can answer these questions and/or tell me anything else about your experiences using/storing/disposing this stuff I'd really appeciate it.
Thanks.

Also be aware that etch resistant markers are not compatible with Ammonium Persulphate

[KORGULL]

scottosan wrote:

Also be aware that etch resistant markers are not compatible with Ammonium Persulphate

I did not know that.
What can I use to touch-up any spots that don't transfer well after ironing on the pattern? Nail polish? White out pen? Speedball painter pen?

I am aware that I will need to heat this solution for proper etching to occur.
I plan to put the board/solution in a heavy-duty freezer bag with a zipper lock and submerge it in a tub of hot water and agitate it by hand.

[sean k]

I use this stuff all the time and use aluminium dishes on the stove.In a dish big enough to hold the PCB I put enough just boiled water to cover the PCB and add a few heaped teaspoons of the AP.If its not enough  and is taking awhile I put some more of the AP in.Usually takes about five minutes.I hold the dish above the hot plate,on its lowest setting,and just swirl it from side to side.I use regular permanent black markers and usually do two coats on the actual tracks.I then just chuck it down the sink with more water.Maybe the last thing I do is wrong but its what it says on the canister it comes in so who am I to argue.

[brett]

Hi.
Yeah, I use AP.
2 plastic containers - large one for a "bath" of hot water, and a smaller one for a mix of AP and hot water.  After a few minutes if it's not quite doing the job I refresh the bath with freshly boiled water.  If bubbles appear on the pcb I lift it clear of the solution, so that all of the pcb has contact with the solution.

I also dispose down the sink with lots of water.  AP is environmentally fairly safe.  The dissolved copper is not so good, but the amount you're disposing is very small.

cheers

[puretube]

OUCH !!!  :roll:

[ESPguitar]

How hot is the water?

about 50 degrees??

Thanks,

RB

[KORGULL]

Thanks for the replies.
I'd rather not pour it down the drain if there is a better way.....anyone?

I'm not finding much on this by searching the internet. Most data sheets say something like: Dispose of in accordance with local regulations.
Some documents say absolutely do not pour AP down drain, while others seem to imply that you should. :?
Aside from the environmental concerns; I also worry about the pipes in my 100 year old house.

[Paul Perry (Frostwave)]

There are two points to disposing of spent persulphate.
1. unused persulphate corroding things
2. copper ions (toxic to plants & some bacteria, eg in septic tanks).
Here's the word from the experts: add excess scrap aluminum and some common salt as catalyst.
http://www.kepro.com/fmc4.htm

I suggest doing it outside, doing it in a large container (in case it started to froth over). Using lumps of aluminium would make the reaction a lot slower, but that might not be a problem at home.
You can tell when the reaction is finished.. the blue copper ions are gone, and there isn't anything happening anymore.

Note I havn't actually done this myself, but I've done a lot of things 'very similar' to this when younger :wink:

[KORGULL]

Thanks for that link. It is the most informative web-page I've seen about  this yet.
PaulPerry wrote:

Note I havn't actually done this myself, but I've done a lot of things 'very similar' to this when younger

I'm pretty sure I remember reading a thread or two where you said you  use this stuff - how do you dispose of it? Down the drain with lots of water? I guess that's what most people do?

[sir_modulus]

Ahh welcome to the land of Nish!  

First off, I'd follow the mixing rules, as they give you a nice formula that doesn't waste the etchant crystals as just floating crystals (meaning the soloution is fully saturated, and there are still crystals left), and gives you a nice saturated soloution.

Next, how to use it! What I do, is use a small vitamin bottle, or one of those Nalgene bottles. I place the etchent in the container, and put it in a larger aluminum or steel pot filled with boiling water. I let the etchent sit for a while, and put the PCB in. I like the Nalgene bottles, as you can see the progress, and they're spill proof, so you can even pick it up and gently rock it to improve the etching speed.

When you're done with the etchent, I'd recomment putting small bits in a toilet, and flushing it down the drain little by little.

I would actually recomment Sodium Persulfate over Ammonium Persulfate, because the sodium one works with sharpies.

Warnings:
1) Ammonium Persulfate releases a lot of fumes, and they are not good. Do this in a decently to a well ventilated area, or if your stove has a fan/fumehood, turn it on.

2) This stuff IS toxic. Be careful with where you put it, and make sure it's not near any food etc..

3) This stuff does freeze, so people like us, up here in Canada...if you leave it in the garage...it will freeze solid  :oops:

4) Plastic, plastic, and more plastic! I read someone up there telling you to put the etchant in contact with an aluminum container (to hold it).....BAD! This is an etchant! Not only will it eat through metal, it also will lose it's ability to etch if you make it etch it's containers etc..


Cheers,

Nish

P.S.
Sodium Persulfate

P.P.S. Yes, I know Ferric Chloride is a bit messy...but I just got the etching kit from M.G. Chemicals and I now use it all the time. I just find Ammonium Persulfate etc... are just a hassle to use.

[KORGULL]

Thanks, I think I might just return the un-opened bottle of AP and get some ferric chloride instead. Aside from the staining, it does seem easier to deal with.

[Paul Perry (Frostwave)]

I personally prefer the persulphate.
1. it doesn't stain.
2. much less poisonious in its fresh state
3. Ferric chloride is MUCH worse to spill on yourself.
4. you can actually see the board while it is etching (don't underestimate this advantage!)

The only downside, is that it needs to be warm.
I find that a prepared persulphate solution keeps for at least a couple of months.

[sir_modulus]

Paul is right too:

Don't get me wrong here, I have a barrel of ammonium persulfate also, it's just that I don't like it as much as the ferric chloride. It's just a matter of personal preference, and is mainly based on the fact that, if I'm careful, then I can use Ferric Chloride inside the house, but I can't do that with ammonium persulfate (fumes).

Cheers,

Nish

[Paul Perry (Frostwave)]

I can use Ferric Chloride inside the house, but I can't do that with ammonium persulfate (fumes).Nish

That's strange, I never noticed any fumes from the persulphate, at least not from the solution. Finely divided persulphate powder isn't a good thing to breathe (industrial exposure eventually can lead to asthma, like many things can).

WHOOPS :oops: just checked while typing this & it looks like persulphate even in solution isn't all that good for you after all:
http://thorax.bmjjournals.com/cgi/content/abstract/41/1/42

Really, it's all a good argument for stripboard

[KORGULL]

Paul Perry wrote:

Really, it's all a good argument for stripboard

I originally planned to only ever use perf-board and avoid dealing with any chemicals, but some of the projects I want to do now (delay,chorus,theremin) would be easier to do with a PCB - so I thought I'd try my hand at a few.
I searched through the archives here (again) and am as undecided/confused about which etchant to use as ever.  :?   I probably worry too much.

I just bought a couple pieces of stripboard from Aron so I guess I'll see what I can do with it. I figure It's possible to build just about any stompbox circuit even on perf - with a good layout and some (many?) jumpers.