how much ammonium persulfate per liter? (for etching)

[powerplayj]

I work in a Biotech lab and have access to granular 98% Ammonium Persulfate.  Does anyone have an approximate recipe amount optimal for etching?  I also have ferric chroride but would like to try AP first.

[Rick]

I am using MG chemicals persulfate and the instructions from the bottle
state: 250 grams of persulfate to one litre of water. Not sure if my persulfate
is the same concentration as yours, but I would guess most commercially
available products should be pretty close. I mix mine up in a litre size juice
bottle (plastic cap) and cap it for the next etch. You dont need much for a small 2" x 4" board. Maybe 3/4" deep in a 5" x 5" tupperware container. Heat up the solution first for speedy etching. I use an old microwave dedicated to this purpose and zap the solution for 30 secs, then just float the board copper side down for probably 7 mins depending on the board size. Even with this small amount of etchant, I can do 2 boards, the second taking a bit longer,
maybe 10 - 12 mins. Just keep the solution hot, zap it in the micro again, or
warm it with an overhead lightbulb, or whatever you come up with.
(( for those not familiar with the metric system - 1 litre is just a pinch more
than 4 cups (.95L = 4 cups), and 250 grams is just a pinch less than 9 ounces (8.9 oz)) Close enough, though you may want to be as precise as possible.
...Rick

[powerplayj]

Cool!  Yeah, 1L should get me through quite a few boards.

Thanks,

Jason

[Paul Perry (Frostwave)]

You need hot water to dissolve it easily. The 98% stuff is the same as you get from electronics suppliers.

[powerplayj]

250g per liter worked great!  Whoever gave the tip about drilling the the PCB at the site of the standoffs and inserting toothpicks during etching, gets my praises.  The boards etched much faster when they were not lying flat on the bottom.

I have a few incomplete traces which are either due to not cleaning the board well enough or not laying enough toner.  I'll try printing to the office copier vs. the laser printer next time to see if I can layer down more toner on the PNP Blue.

The sharpie helped but didn't help as much as I had hoped.

[formerMember1]

hey, i wonder if instead of using a light bulb to heat the etching solution, i could stick the etching solution into my toaster oven that i use to bake boxes. It should probably stay heated for long enough to etch the board. Anybody know if there is a danger to trying this method.  

thank you  :wink:

yeah, that is a good idea about sticking toothpicks in the standoff holes prior to etching, I'll have to try that when i etch my boards.

cool  

[KORGULL]

The sharpie helped but didn't help as much as I had hoped.

AP can dissolve the sharpie ink. I use a paint pen - it holds up well against the etchant, but unfortunately, I haven't found one that allows you to draw with as much precision as a Sharpie. They are kinda drippy and hard to control the paint flow. It's been getting the job done though.

formerMember1, I boil a large pot of water on the stove and then dump it into a plastic basin - put the etchant and board in a small tupperware type container or thick plastic zip-lock bag and submerge it in the tub of hot water. Boards etch very fast.
If you heat etchant in a toaster oven using a plastic container it might melt - if you use a metal one the etchant might eat holes in it.
You also might end up creating more fumes than you need to.

[formerMember1]

yeah you are right that makes sense, i'll do the tupperware way, tonepad has great picture essay about that.

thanks man

[brad]

I may be mistaken, but isn't Ammonium Persulfate used as a main ingredient in solid rocket booster fuel or something?  I thought it was pretty volatile stuff.

[Fret Wire]

I may be mistaken, but isn't Ammonium Persulfate used as a main ingredient in solid rocket booster fuel or something? I thought it was pretty volatile stuff.

From the first hit on a search:

Ammonium Persulfate
Ammonium persulfate crystals are used as an alternative to the traditional ferric chloride to produce a cleaner copper etchant solution. Ammonium persulfate is a white, crystalline, odourless salt. It is used as initiator for the polymerisation of monomers and as a strong oxidizing agent in many application. It has the particular advantage of being almost non-hygroscopic, of having a particularly good storage stability as a result of its extremely high purity and of being easy and safe to handle.

Since it's an industry standard method of etching pcb's (heated, no less), I'd have to say it's not very volatile, or it wouldn't be recommended, liability being what it is these days. It might be part of a chemical process used to make propellents. Or maybe synthisized with other chemicals, but not as sold for etching.

[Paul Perry (Frostwave)]

that's ammonium perCHLORARTE not sulphate in rocket fule AFAIK.
I like pyrotechnics as much as the next guy (if the next guy is Guy Fawkes ) but, trust me, tht persulphate isn't going to blow anything up.
Here's a safety sheet http://www.jtbaker.com/msds/englishhtml/a6096.htm
but, I think the bit about explosives is a bit 'optimistic' from a mad bombers point of view.

[Rick]

I believe the toothpick suspension trick came from Mark Hammer (correct me
if i'm wrong). I have not tried this yet, but it it sounds interesting.
So far I've simply just plopped the boards on the etchant and floated them
there for the duration. Even with a little gentle agitation (board floats and bumps into the sides of container) the board hasn't sunk yet. However, at times I've seen an air bubble under the board and of course no etching happens there. I just pick up the board, reposition and hopefully no more bubbles. I'm wondering though with the toothpick trick is the bubble thing eliminated? (maybe due to easy agitation without sinking boards). And how deep is the board in the solution for best results? I'm guessing though that the toothpick method would be superior for shaking the bubbles out. ...Rick

[formerMember1]

yeah i am gonna try the toothpick way.  It probably was mark hammer, he always gave me great tips.

[powerplayj]

Mine didn't float in Ammonium Persulfate but I didn't put more than a few cm of etchant in also.  I probably used 50-100ml of etchant for 4 boards (2 at once).