Author Topic: Etching PCB - dealing with anhydrous ferric chloride  (Read 1709 times)

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Offline shaheansar

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Etching PCB - dealing with anhydrous ferric chloride
« on: October 23, 2020, 08:35:53 am »


I'm looking into PCB etching,which requires ferric chloride (There are other etchants, but they're pretty hard to come by where I live and too expensive if I can find them).

The issue is that where I live, only anhydrous ferric chloride is sold (Which is stupid. They don't even label it properly as anhydrous - got exposed to HCl fumes for 2-3 hours, thankfully the doctor found nothing abnormal with me and I got sent off with some anti allergy meds).

I'd like to know what equipment I'll need to deal with this stuff safely. I always use nitrile gloves with these, but in particular what kind of respiratory protection will I need? I plan on just having 4 PC fans blow these fumes outside the window. If I must, I will invest in respiratory protection (It's very expensive where I live, the NIOSH approved ones at least). I'm assuming a 3M 6002 will be enough. Please keep in mind I will be using this stuff at home. If you have any suggestions regarding alternatives, do mention them. If I can find it, I'd rather use that than this.
If this isn't the proper place to ask these questions, please direct me to a place more suitable for these questions.
 

Offline mikeselectricstuff

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Re: Etching PCB - dealing with anhydrous ferric chloride
« Reply #1 on: October 23, 2020, 08:42:06 am »
Anhydrous FeCl (dark green/brown) is no good for etching. The Hexahydrate form (yellow) is normally used.
I have a vague recollection that adding Hydrochloric acid to the solution made from anhydrous makes it work as an etchant.
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Online Siwastaja

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Re: Etching PCB - dealing with anhydrous ferric chloride
« Reply #2 on: October 23, 2020, 08:44:19 am »
IMHO, invest some time into building a proper fume hood. Doesn't need to look fancy, just a closet where you suck air out, and have a sliding door made of transparent plastic or glass. Keep the door as far down as possible, with just enough gap to operate things with your hands. This way, no further personal protection needed.

This is assuming you don't generate huge amount of nasty gases and blow them directly at your neighbor's open window.
 

Offline shaheansar

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Re: Etching PCB - dealing with anhydrous ferric chloride
« Reply #3 on: October 23, 2020, 08:45:50 am »


This guy is from the same country as me and from what I can tell, it's just anhydrous ferric chloride 
I myself have also successfully etched a PCB with  it (Was quite slow at 10 mins though)
 

Offline shaheansar

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Re: Etching PCB - dealing with anhydrous ferric chloride
« Reply #4 on: October 23, 2020, 08:47:21 am »
Is that kind of a rudimentary fume hood good enough? This stuff does release nasty HCl fumes after all. Will the plastic even be stable with those fumes floating around?
 

Online Siwastaja

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Re: Etching PCB - dealing with anhydrous ferric chloride
« Reply #5 on: October 23, 2020, 08:54:34 am »
HCl isn't a super poison. Get the level down enough and it's fine. You have a strong concentration of it (some 2% IIRC) in your stomach! Having too much airborne causes eye/skin/lung irritation and rusts metal objects in your room. This rusting is also why I'd recommend getting rid of the fumes (using fume hood) instead of just protecting your eyes and airways.

I'd trust a fume hood over a potentially leaky gas mask with potentially insufficient or worn-out filters any day; if you go the personal protection way, it's going to be expensive, and you need to get new filters all the time.

What comes to the fume hood, obviously it's up to you to do it properly. It has to be mostly airtight with no large gaps, then have strong enough exhaust fan(s). I think it is fairly easy to get rid of 99% of the fumes so that 1% leaks to the room.

AFAIK acrylic won't last forever, nor will polycarbonate, if you use those as a window material. But I bet they will still last for years given just occasional fumes.
« Last Edit: October 23, 2020, 08:58:12 am by Siwastaja »
 

Offline shaheansar

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Re: Etching PCB - dealing with anhydrous ferric chloride
« Reply #6 on: October 23, 2020, 09:10:47 am »
HCl isn't a super poison. Get the level down enough and it's fine. You have a strong concentration of it (some 2% IIRC) in your stomach! Having too much airborne causes eye/skin/lung irritation and rusts metal objects in your room. This rusting is also why I'd recommend getting rid of the fumes (using fume hood) instead of just protecting your eyes and airways.

I'd trust a fume hood over a potentially leaky gas mask with potentially insufficient or worn-out filters any day; if you go the personal protection way, it's going to be expensive, and you need to get new filters all the time.

What comes to the fume hood, obviously it's up to you to do it properly. It has to be mostly airtight with no large gaps, then have strong enough exhaust fan(s). I think it is fairly easy to get rid of 99% of the fumes so that 1% leaks to the room.

AFAIK acrylic won't last forever, nor will polycarbonate, if you use those as a window material. But I bet they will still last for years given just occasional fumes.

How would I go about making airtight sliding doors? If it was static good ole silicone will do the job (Assuming it's stable under HCl fumes), but how would sliding ones work?
 

Offline mikeselectricstuff

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Re: Etching PCB - dealing with anhydrous ferric chloride
« Reply #7 on: October 23, 2020, 10:52:16 am »
According to this, if you leave anhydrous out for long enough it turns into hexahydrate

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Offline T3sl4co1l

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Re: Etching PCB - dealing with anhydrous ferric chloride
« Reply #8 on: October 23, 2020, 12:27:34 pm »
Yes, it's deliquescent so it will make a solution by itself.  Pouring water on it releases quite a bit of heat, and HCl fumes as you noted.  Do it slowly and do it outside.  The release of HCl means some rust will be left in suspension.  Add more HCl (or muriatic acid or whatever it's sold as) to dissolve it.

You also need to top it up with HCl from time to time, as dissolving Cu (and oxidizing everything back fresh, with exposure to air or preferably a bubbler) will precipitate more rust.

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Online Siwastaja

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Re: Etching PCB - dealing with anhydrous ferric chloride
« Reply #9 on: October 23, 2020, 02:46:44 pm »
How would I go about making airtight sliding doors? If it was static good ole silicone will do the job (Assuming it's stable under HCl fumes), but how would sliding ones work?

Obviously a standard fume hood isn't airtight, it doesn't need to be. The idea is you can bring stuff in and out, operate things with your hands, and so on, necessitating a significantly large opening on the bottom. The idea is that the exhaust fans pull air from the hood, so air only goes in from the openings; the inside of the hood have lower air pressure than the room. This idea can be extended: if there are some holes elsewhere, they also suck air from your room, not the other way around.

In simplified theory, this is. Real fluid dynamics is complex, and in practice if you have a hole to an area with lower air pressure in it, air mostly goes one way, but along the edges, eddy currents and whatnot mix some of the air so a minuscule percentage of air flows to the opposite direction.

Or, if the total area of the openings is just way too large, then there is no pressure difference anymore.

Hence, if you have real dangerously poisonous gases, don't try to build a simple DIY fume hood.

But for PCB etchants causing some fairly low amount of HCl droplets and gas, that's fine. It's possible even just standard kitchen hood would be almost good enough. Add some walls to it, open the front wall from the bottom for access, and likely some 99% of the air will flow from your room, to the hood, then outside the duct. Pay attention where you push the air, preferably not to your neighbor's open window, or such way that it immediately gets sucked back to your house.

You can test it opening some smelly thing in the hood, smoking a cigarette if you like or ask someone who does that shit to themselves do that for a demonstration.

Obviously, as with all Internet advice, the responsibility is yours.
« Last Edit: October 23, 2020, 02:52:02 pm by Siwastaja »
 

Offline Cerebus

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Re: Etching PCB - dealing with anhydrous ferric chloride
« Reply #10 on: October 23, 2020, 03:20:52 pm »
... Pouring water on it releases quite a bit of heat, and HCl fumes as you noted.  ...

So don't! Add it slowly to water rather then the other way around. That way there's all the bulk of the water to take up the heat. This is exactly the same situation that the rule "Add acid to water, not water to acid" was invented for.

I haven't used Fe (III) Cl3 for years but when I used to it was always the anhydrous form that turned up and I never had a problem with making a solution, or with HCl evolving, because I always added the Ferric Chloride to the water, just like my mum* taught me to.


*Mum was an Analytical Chemist, but most people ought to have had this drummed into them by their secondary school chemistry teachers. I just got this particular bit of schooling a bit younger than most people do.
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Offline HB9EVI

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Re: Etching PCB - dealing with anhydrous ferric chloride
« Reply #11 on: October 23, 2020, 05:42:21 pm »
never got anhydrous FeCl3, always hexahydrate, but even this is hygroscopic; so just let it stand on a wet place like a cellar or garage; it'll soak itself the necessary water out of the air so that it can be easily solved in water without who knows what kind of exothermic reaction.
 

Offline jpanhalt

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Re: Etching PCB - dealing with anhydrous ferric chloride
« Reply #12 on: October 23, 2020, 06:10:21 pm »
"Ferrous chloride" would be FeCl2 or Fe(II)chloride (synonyms).  I suspect the bottle is likely mislabeled.  If not, a solution with additional HCl to provide the additional chloride will convert to Fe(III) chloride in air.

I suspect you really need Fe(III) as the etching reaction involves oxidation of the copper.
 

Offline shaheansar

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Re: Etching PCB - dealing with anhydrous ferric chloride
« Reply #13 on: October 23, 2020, 06:21:23 pm »
... Pouring water on it releases quite a bit of heat, and HCl fumes as you noted.  ...

So don't! Add it slowly to water rather then the other way around. That way there's all the bulk of the water to take up the heat. This is exactly the same situation that the rule "Add acid to water, not water to acid" was invented for.

I haven't used Fe (III) Cl3 for years but when I used to it was always the anhydrous form that turned up and I never had a problem with making a solution, or with HCl evolving, because I always added the Ferric Chloride to the water, just like my mum* taught me to.


*Mum was an Analytical Chemist, but most people ought to have had this drummed into them by their secondary school chemistry teachers. I just got this particular bit of schooling a bit younger than most people do.

I always added the powder to the water, in teaspoon quantities, and let each one mix well before adding more (That school education sure did save me). It still released enough HCl fumes that I still have some pain in my chest 2 days later, under meds. I'm not sure how safe it is.
 

Offline Benta

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Re: Etching PCB - dealing with anhydrous ferric chloride
« Reply #14 on: October 23, 2020, 06:51:40 pm »
In the early years, I used ferric(III)chloride for PCB etching, I never do that anymore.

It's incredibly messy and the remains need to be treated as chemical waste. Lose a drop of the brown goo somewhere, and you'll never remove it again. Also it gasses out (both in solid and dissolved form) and will corrode everything in the vicinity.

I use two methods depending on accurace and urgency.

1: For precise and controlled etching, Na2S2O8 aka "disodium peroxodisulphate" aka "sodium persulfate" is perfect. It's a white powder to be dissolved water, 230 g to 1 l of water. The solution can be stored and reused.
It does need some extra effort, though: the solution should be heated to 50 C, and aeration of the etching bath (aquarium pump) for homogene results is recommended.
Downside: as you have problems getting ferric chloride, sourcing this might be impossible in your location.

2: Brute force etching with stuff you can probably get without problems:
~30% hydrogen peroxide, ~30% hydrochloric acid and tap water.
0.25 l H2O2, 0.25 l water and 0.5 l HCl. Always add the acid last!!!
ONLY DO THIS OUTSIDE AND WEAR PROTECTION GLASSES AND PROTECTIVE CLOTHING!!!
The etching is hard to control and will take around 20 seconds. As the process is exotherm, the etching bath will get warmer and warmer, so if you're doing serial etching of several PCBs, the last one could take only 5 seconds.
Expect underetching of the tracks, as pulling out the finished PCB and washing it in water takes a little time. Meaning this process it not suitable for fine geometries. Track width should be 0.25 mm or more.
The solution can be diluted with water after etching and is then pretty harmless. Depending on your local laws, it might even be allowed to flush it in the toilet.

« Last Edit: October 23, 2020, 07:11:53 pm by Benta »
 

Offline mag_therm

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Re: Etching PCB - dealing with anhydrous ferric chloride
« Reply #15 on: October 23, 2020, 07:51:10 pm »
I use MG Chemicals Positive Developer and Ferric Chloride, both in 475 ml containers which last  a long time here .
They give a Ferric Chloride disposal procedure on website FAQ.
 

Offline shaheansar

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Re: Etching PCB - dealing with anhydrous ferric chloride
« Reply #16 on: October 23, 2020, 08:01:27 pm »
In the early years, I used ferric(III)chloride for PCB etching, I never do that anymore.

It's incredibly messy and the remains need to be treated as chemical waste. Lose a drop of the brown goo somewhere, and you'll never remove it again. Also it gasses out (both in solid and dissolved form) and will corrode everything in the vicinity.

I use two methods depending on accurace and urgency.

1: For precise and controlled etching, Na2S2O8 aka "disodium peroxodisulphate" aka "sodium persulfate" is perfect. It's a white powder to be dissolved water, 230 g to 1 l of water. The solution can be stored and reused.
It does need some extra effort, though: the solution should be heated to 50 C, and aeration of the etching bath (aquarium pump) for homogene results is recommended.
Downside: as you have problems getting ferric chloride, sourcing this might be impossible in your location.

2: Brute force etching with stuff you can probably get without problems:
~30% hydrogen peroxide, ~30% hydrochloric acid and tap water.
0.25 l H2O2, 0.25 l water and 0.5 l HCl. Always add the acid last!!!
ONLY DO THIS OUTSIDE AND WEAR PROTECTION GLASSES AND PROTECTIVE CLOTHING!!!
The etching is hard to control and will take around 20 seconds. As the process is exotherm, the etching bath will get warmer and warmer, so if you're doing serial etching of several PCBs, the last one could take only 5 seconds.
Expect underetching of the tracks, as pulling out the finished PCB and washing it in water takes a little time. Meaning this process it not suitable for fine geometries. Track width should be 0.25 mm or more.
The solution can be diluted with water after etching and is then pretty harmless. Depending on your local laws, it might even be allowed to flush it in the toilet.

I'm unable to get my hands on any sodium persulphate, as you guessed. I'll have to contact actual chemical suppliers, but they are very industry oriented and the quantities sold are very much unreasonable as a single person IMHO. I am able to source some ammonium persulphate though (It's kinda expensive, but safety first). How dangerous would these chemicals be? The reason I want to get away from FeCl3 is that this chemical is only sold in it anhydrous form and it released HCl fumes when mixed with water, so going the second route you suggested is not ideal even if it's easy to source. The other issues I can deal with. If sodium/ammonium persulphate don't vaporize into something that'll eventually eat through my lungs, it'd be nice. If there are other safety precautions I should take when dealing with them, do mention them.
 

Offline jpanhalt

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Re: Etching PCB - dealing with anhydrous ferric chloride
« Reply #17 on: October 23, 2020, 09:21:09 pm »
In the US, 41% ferric chloride is used by the barrel in sewage treatment plants as a flocculator.  Sure, if your area has a law against it, you don't want to do it, but disobeying such laws will not bring Armageddon to your county. 
 

Offline mikeselectricstuff

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Re: Etching PCB - dealing with anhydrous ferric chloride
« Reply #18 on: October 23, 2020, 09:37:33 pm »
In the US, 41% ferric chloride is used by the barrel in sewage treatment plants as a flocculator.  Sure, if your area has a law against it, you don't want to do it, but disobeying such laws will not bring Armageddon to your county.
ISTR reading that  the issue with disposing of used FeCl3 is not the FeCl3 itself, but the dissolved copper after being used for etching
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Offline sleemanj

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Re: Etching PCB - dealing with anhydrous ferric chloride
« Reply #19 on: October 23, 2020, 09:39:50 pm »

2: Brute force etching with stuff you can probably get without problems:
The etching is hard to control and will take around 20 seconds. As the process is exotherm, the etching bath will get warmer and

Use less concentrated components and you will have etching as slow as you like.


 
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Offline Benta

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Re: Etching PCB - dealing with anhydrous ferric chloride
« Reply #20 on: October 23, 2020, 09:44:37 pm »
I've only worked with sodium persulphate and have had no problems with gases or odors.
Ammonium persulphate could be an option, but I've no experience with this.

 

Offline Benta

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Re: Etching PCB - dealing with anhydrous ferric chloride
« Reply #21 on: October 23, 2020, 09:47:06 pm »

2: Brute force etching with stuff you can probably get without problems:
The etching is hard to control and will take around 20 seconds. As the process is exotherm, the etching bath will get warmer and

Use less concentrated components and you will have etching as slow as you like.
 

Did you try?
Please come back with your results.
 

Offline Cerebus

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Re: Etching PCB - dealing with anhydrous ferric chloride
« Reply #22 on: October 23, 2020, 09:56:22 pm »
In the US, 41% ferric chloride is used by the barrel in sewage treatment plants as a flocculator.  Sure, if your area has a law against it, you don't want to do it, but disobeying such laws will not bring Armageddon to your county.

There's a world of difference between controlled dosing of raw water in a water treatment plant with pure ferric chloride (with, no doubt, subsequent testing to make sure that unacceptable residual levels are absent), and dumping used, contaminated, ferric chloride etchant in an uncontrolled manner into waste water and hoping that it doesn't cause trouble. Dumping chemical waste may not necessarily cause "Armageddon" but it would still show a callous disregard for what that pollution might do to other people downstream of you and to the environment.
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Offline shaheansar

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Re: Etching PCB - dealing with anhydrous ferric chloride
« Reply #23 on: October 23, 2020, 10:30:02 pm »
I've only worked with sodium persulphate and have had no problems with gases or odors.
Ammonium persulphate could be an option, but I've no experience with this.

That's quite nice. Is it usable indoors? I might actually look into industrial chemical suppliers and pay the ridiculous amount for 25Kg if it's that safe compared to what I currently have on hand. I live in an apartment with my family so I'm quite concerned about the odors and fumes as they may negatively affect their health. I've only been able to find Sodium Persulphate in powdered form (25Kg of that stuff, unfortunately. Not going to be cheap to say the least), are there any concerns regarding adding it to water - exothermic reaction or release of fumes for example? Will I have to invest in any sort of respiratory protection?
 

Offline jpanhalt

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Re: Etching PCB - dealing with anhydrous ferric chloride
« Reply #24 on: October 23, 2020, 10:37:41 pm »
In the US, 41% ferric chloride is used by the barrel in sewage treatment plants as a flocculator.  Sure, if your area has a law against it, you don't want to do it, but disobeying such laws will not bring Armageddon to your county.

There's a world of difference between controlled dosing of raw water in a water treatment plant with pure ferric chloride (with, no doubt, subsequent testing to make sure that unacceptable residual levels are absent), and dumping used, contaminated, ferric chloride etchant in an uncontrolled manner into waste water and hoping that it doesn't cause trouble. Dumping chemical waste may not necessarily cause "Armageddon" but it would still show a callous disregard for what that pollution might do to other people downstream of you and to the environment.

You have been well indoctrinated.  FeCl3 is used very commonly as a home treatment to clear roots from drains.  I am not talking about treating drinking water.  I am talking about treating raw sewage.
 


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