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Dangers of H2O2/HCI etchant

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Conundrum

Mon Mar 15 2010, 12:53PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

Hi all.

Was a little concerned to find that many people using this etchant are unaware of the serious danger of cleaning the board with acetone (aka nail polish remover) pre or post etching.

the danger arises especially if the etchant and rinse solution is reused multiple times as the byproducts build up in the form of organic peroxides (read- KABOOM!) which then become more unstable when the board is dried (ie air dried or with a hairdryer etc)
No fun cleaning up after glass in the eyes.

unless you know exactly what you are doing and use a non acetone (i.e. water) based rinse then clean off the board using the safer uv expose/develop method, you run the risk of serious personal injury or worse.

best to avoid this and pay the extra $$$ for persulphate and recycle responsibly when used.

look up organic peroxides on wikipedia.. (link not included for obvious reasons)

Please note. this can also happen under certain conditions with benzoyl peroxide (aka hardener for styrene) such as when it reacts with spilled solvents in a badly organised chemicals cupboard.

-A
#include "justbecauseitischeapdoesnotmeanitissafe.h"

Bored Chemist

Mon Mar 15 2010, 07:25PM

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

Persulphate is also capable off making organic peroxides (though it's not as good at it).
The potential for making chlorine always bothered me about the HCl/ H2O2 mix.
In any event all of these peroxy things decompose and give off oxygen which can burst bottles.
Storing used etchants is asking for trouble.

Conundrum

Wed Mar 17 2010, 07:32AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

uh oh. this is a little concerning.

should i dispose of my used etchant even if it has been regenerated using the platinum + copper rod trick?

thanks for the heads up. -A

Bored Chemist

Wed Mar 17 2010, 08:00PM

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

No, all the peroxide will be "dead" by now.

Dr. H.

Wed Mar 17 2010, 09:37PM

Registered Member #931 Joined: Mon Jul 30 2007, 05:25PM
Location: Bulgaria
Posts: 486

Good day guys

Conundrum wrote ...

best to avoid this and pay the extra $$$ for persulphate and recycle responsibly when used.

actually I've found a big chemistry store here that sells the sodium persulfate soooo cheap that it is cheaper to use it rather than the H2O2/HCI. To speak in number - about 2$ for a pound of sodium persulfate, wich makes about a gallon of solution. I personally think it is much better than the H2O2/HCI mainly for safety reasons.

You shoud look for the sulphates in chemistry stores rather than electrnocis store (they asked almost 6 times more in a big electrical store for a pound - and that is the cheapest I coud find).

Cheers

ZeroHour

Sun Feb 10 2013, 10:18AM

Registered Member #9665 Joined: Thu Jan 17 2013, 10:49AM
Location: The Netherlands
Posts: 7

Hi,

Would it be safer if the etchant isn't reused many times, but instead let's say something like 10 times?
I'm wondering how big this danger is, because it would be a bummer if this means using this etchant is too dangerous to use.

Wouldn't the amount of organic peroxides produced be too small to cause any kind of danger?

Thanks for your time.

Edit: I don't know a lot about chemistry, so please forgive me if my questions are stupid

Conundrum

Sun Feb 10 2013, 11:33AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

Not a stupid question at all.
Generally, reusing etchants is a bad idea because the copper tends to etch "patchy" resulting in a mess.
The copper chloride (CuCl) one is a bit safer and can be regenerated using electrolysis to salvage the copper.
I did wonder about making multitrack boards this way, by overpainting the tracks+photoresist with silver or carbon then plating more copper on top.
A simple additional etching step once the stack is complete should yield a flat PCB with about 20 layers of tracks and nice predictable dielectric between them.

-A

ZeroHour

Mon Feb 11 2013, 02:33PM

Registered Member #9665 Joined: Thu Jan 17 2013, 10:49AM
Location: The Netherlands
Posts: 7

Thanks!
I'm not planning to make PCB's with more than 2 layers yet, but this is some useful information.
Going to check if I can make or get myself an electrolysis rig.

Shrad

Mon Feb 11 2013, 03:06PM

Registered Member #3215 Joined: Sun Sept 19 2010, 08:42PM
Location:
Posts: 780

don't you guys rince your boars before dissolving leftover resin?

if so, what's the point of making peroxydes if there is no other substance on the board than resin?

Bored Chemist

Thu Feb 14 2013, 07:56PM

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

Shrad wrote ...

don't you guys rince your boars before dissolving leftover resin?

if so, what's the point of making peroxydes if there is no other substance on the board than resin?

What are you talking about?

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