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Ammonium persulphate etching vessels

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ragnar

Tue Jan 19 2010, 01:22PM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

Hi all,

For my PCB work until recently, I've had the most reliable setup of boiling ammonium persulphate in a Corning Vision glass pan on a gas stove. Hot etchant, clean, crisp traces on the copper.

Unfortunately, I didn't bring my pan with me to Europe. The manufacture of these flame-compatible saucepans ceased decades ago, and they're hard to find on eBay or expensive to ship from the USA.

Does anyone have experience with PTFE-coated pans or pure aluminium? Can the oxide layer resist the etchant? What about 'ordinary' Pyrex baking dishes; will they promptly explode on exposure to flame?

Thanks

IntraWinding

Tue Jan 19 2010, 04:59PM

Registered Member #2261 Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581

I think for you it's just a case of knowing the magic Brit word 'Saucepan'.

I searched eBay for:

(glass,corning,Pyrex) saucepan* -(lid*,advert*)

and got 8 hits, some at very reasonable prices I think

I've used these for chemistry myself. One with a lid is useful.
Don't boil up caustic alkali if you want the pan to remain transparent!

Bored Chemist

Tue Jan 19 2010, 06:48PM

Registered Member #193 Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022

Most etchants will chew up aluminium in a very surprising way. I wouldn't want to rely on a bit of PTFE to stop them.

LutzH

Tue Jan 19 2010, 07:12PM

Registered Member #1721 Joined: Sat Sept 27 2008, 08:44PM
Location:
Posts: 136

Hello:

Although the following is based on knowlege from the "Grapevine" it does seem to be supported in real life:

Corning a while back developed some types of "super pyrex" very high silica glasses. The purpose was to develope types of glass which could withstand sudden extreme temperature changes like quartz, but which could still be fabricated, and worked, via conventional glass fabrication means. Vicor is an example of such a glass for scientific application.

The Corning Visions cookware is a common example, although some folks claim it is nothing but Pyrex? This material does seem to be slightly more resistant to extreme temperature changes than pyrex in my personal opinion based on my cooking experience, but I am no expert here.

My advice would be to try to use Pyrex, if you cannot find the other glass. Pyrex with some type of heat spreader should be fine. This is done in the lab by using a wire mesh/asbestos screen between the bunsen burner, and the flask.

Today of course we do not want asbestos anymore, but we have replacement materials. I have used Pyrex baking pans directly on electric stove elements with no problems. I do however ramp up the heat in a gradual manner. So if you have gas, you might try a SS wire mesh screen, with the flame turned down a little, or some other heat spreading device, like a ceramic plate.

The key to not breaking any heat resistant glass, is doing things gently, and in a gradual manner. I would stay away from PTFE coated Al, there are always micro-pores in the coating. S.Steel would be a better option then, you could try a small amount of SS to see if it holds up.

I have not used Ammonium Persulfate, so I just do not know much about it. Does it work better than Ferric Chloride for PCB etching? I am curious also, because there are cheap consumer products here like concrete cleaner for example, which are Ammonium Persulfate based. I may give these a shot in the future then.

ragnar

Tue Jan 19 2010, 07:33PM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

Thanks Intrawinding for the suggestion of eBay UK and the clever search string, Bored Chemist for keeping me on the straight and narrow, and LutzH for the insight.

Ammonium persulphate was the first etchant ever available to me and I had good results. I've done only a few boards with ferric chloride and while I couldn't compare undercut or trace fidelity, the cleanup leaves a lot to be desired!

Hence "if it ain't broke, don't fix it" - the glass really did perform well with the etchant. That 7" one will at least get me going! I've nabbed it for GBP6.50. Easy!

IntraWinding

Wed Jan 20 2010, 02:28AM

Registered Member #2261 Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581

What a bargain! The wonder of eBay

I thought it was a glass ceramic, but it's hard Googling the transparent amber stuff rather than the earlier white translucent stuff.

You can certainly stick a pan of cold water straight on a full flame gas ring without a second thought - no need for any special care there, but boiling over is a problem as the thick 'glass' holds a lot of heat and keeps things boiling well after you take it off the heat.

In fact anything thermal you can do with a metal pan seems ok, but obviously it's better to err on the side of caution. My last one survived all sorts of thermal abuse I'd never try on normal lab borosilicate, then it broke when I caught the pouring lip on something solid.

Steve Conner

Wed Jan 20 2010, 10:02AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Wishing you a happy new saucepan, BP!

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