Etchant Solution Test Trick

[vanessa]

I found a way to test old etchant solution. You may already do this but if not...

This is for people (like me) that hold on to use etchant solution. I have jars marked, 'clean', 'dirty', 'bad'.

I take a small amount of the old etchant solution and drop it into a small cup (I use an old tuna can). You can rate how well it will perform by dropping a little bit of baking soda into the solution.
I have found that new etchant solution bubbles over like those crazy volcano science projects back in grade school. It goes down from there. When the etchant solution is dead you'll get little or no bubbles. You can rate your bad solution before you use it saving you wasted time.

I'm sure there is a better way of doing it, maybe even a scientific approach. But hey I'm just DIY ya know.

[H.Manback]

I'm not a chemist, but isn't this potentially unsafe? What you are doing I understand is kind of determining if the solution is acid enough to make the reaction with the baking soda strong enough to make the cup overflow. What happens when you have a very strong acid

This doesn't mean you're wrong with this or anything, I just don't like the idea of people trying that with a other kind of etchant and getting hurt or anything. What etchant do you use anyway? Ferric chloride, hydrochloric acid?

[Mark Hammer]

Actually, it's quite sensible....assuming there is that great a risk of losing track of which etchant bath is which!!

The foam from a couple of drops of ferric chloride will not result is significant volume, overflow, or danger when the baking soda is added, and the baking soda will effectively deactivate the etchant.  All she is doing is what one would normally do to deactivate etchant for disposal purposes...but in a tiny enough amount that it can be used as a test procedure.

[H.Manback]

Oh ok, that sounds sensible

Now you mention it, I do recall that you can neutralize the acid with baking soda. I haven't gotten into the pcb etching thing yet, but it's the next thing on my to-do list.

[RLBJR65]

Thanks thats a great idea! Using small amounts of each should be safe enough. Sure beats ruining a good board!

Richard

[Ge_Whiz]

That's as good a scientific method as any I can think of. 

[vanessa]

All she is doing is what one would normally do to deactivate etchant for disposal purposes...but in a tiny enough amount that it can be used as a test procedure.

Yes Mark that's how I got the idea. It hit me the last time I etched a PCB. It took sooooooooo long to etch the darn thing. I knew that the etchant solution had to have been bad. When it finally was finished (like an hour later) I went to dispose the remaining solution (see below) that was left on the walls of my etchant tray. I poured some water in the tray and then added a little baking soda to deactivate what's left. Usually it foams up. This time not much happened. So I did a test with new etchant and really old bad stuff just to see if I could tell. And yes it's a good indication of how much strength you have left with your solution. By the way it's best to put a little water in the test cup with the solution as even bad solution will foam up a bit. So I guess the water dilutes it enough to get a good reading on it.

(I do not throw etchant solution down the sink, I put the majority of the leftover solution into a container marked 'bad' and when I get around to it I take it to the junk yard. They have a disposal system setup for oil and other wastes)

[Rick]

Vanessa, It's a good trick with the baking soda tests! I see you probably have some lab experience. n'est pas? I will have to play with this also, with your method and perhaps PH test strips if they work in this solution?!, because I use mainly ammonium persulphate for etching, and I am going to have to learn the strengh of my etchant after many uses to prevent way too long etching episodes on occasion. I know from experience that I can get 3-4 good etches from a small batch for maybe 3 small boards in my given setup, so I've been a bit lazy on the test front. You're suggestion is a great idea for sure !!!

Aron,
We had a "wizard of the week"  award at work some time ago. Maybe it would be fun to start one here for good ideas such as Vanessa's. And the prize??? ...a trip to Hawaii (or realistically maybe a 3pdt switch)

later ...Rick 

[Connoisseur of Distortion]

first time etching, i thought this stuff would come in handy. being brilliant, i decide that pouring the etchant into a large container of baking soda would sufficiently neutralize the poison. Now, i am talking about roughly 3 cups of FeCl3 into a tupperware container with baking soda in excess.

looked like some grisly bubble bath.

[Paul Perry (Frostwave)]

Rick, you probably know this, but I suspect the 'baking soda trick' won't work with persulphate. Very different chemistry. If you have the time, I suggst a tiny scrap of PCB as a test.

[hank reynolds 3rd]

I've used the Baking soda trick since I scorched a corner of the garden while I was at uni,a few years ago....nothing EVER grew there again,even the soil changed colour !!!
Since then I've always used it, as I always have 'worst case scenario' visions of a dog getting poisoned and stuff....

Sam

[Paul Perry (Frostwave)]

I scorched a corner of the garden while I was at uni,a few years ago....nothing EVER grew there again,even the soil changed colour !!!

Yeah, even a very small concentration of copper in solution will stop root action. People flush copper sulphate down storm water drains to kill invading roots. (Not saying this is great ecological practice, but it's actually sold for this purpose).

[Big Red]

yeah, I was looking at some powered ferric chloride for sale and one of the recommendations for its use was to clean out plumbing! on all the tutorials I have read reccomend NOT pouring it down the sink, but taking it to a junkyard or such

[Paul Perry (Frostwave)]

yeah, I was looking at some powered ferric chloride for sale and one of the recommendations for its use was to clean out plumbing!

I'm pretty cavalier with chemicals, but I certainly wouldn't try to clean anything with ferric chloride! for a start, it stains 'stainless' steel, but more importantly, goes thru brass like a rocket In fact, I can't think of ANYTHING that might block pluming & be helped by ferric chloride.

[hank reynolds 3rd]

Wouldn't it eat into the piping, or at least tarnish/pollute or corrode it a bit???