How to make PCB etch solution using anhydrous ferric chloride powder

[Boncuk]

it is supposed to be perfect for plants...

... also for trees. The more copper it contains the faster the tree will die.

 

[mvs sarma]

Possibly, you may perceive more selectivity of the dilute etchant for the unmasked areas. In reality, that probably is not the case. It is just that over etching occurs more rapidly with a faster solution. Subjectively, my best etchings have been done with a relatively rapid etch rather than a slow one.

If one were to use a mask that was slightly soluble in the etchant, say those who use ink jet printers and bake the image before etching, the length of time exposed to the aqueous etchant, not the concentration of ferric chloride or persulfate, may be more important for controlling selectivity. John

Thanks John, I will have few boards etched, as you suggested.

 

[jpanhalt]

It would however be useful to know how it works as I have HCL and H2O2 in the garage most of the time. That makes me wonder how a mixture of NaHSO4 and Na2S2O8 would work as I have both of them as dry powders.

Mike.

The etching process is oxidation of copper to cupric mostly. The HCl and sulfuric acid + peroxide are supposed to be quite rapid. Some have reported just a few minutes. Of course, your ammonium persulfate is pretty fast and is on the order of speed what I like.

I am not sure what exactly the active ion is with sulfuric acid; however, I don't think the mixture of sodium bisulfate (NaHSO4) with the peroxide you have (Na2S2O8) would offer any advantage over the peroxide alone. The peroxide with a little sulfuric acid might be good to try. John

 

[pitronix]

I'm using HCL and H2O2 for etching PCB-s and it is way faster than any above mentioned proccess. Persulfat is a nasty chemical way more dangerouse than FeCl3 especialy storing dry chemical in biger ammount! I studied chemistry so I think I know what I'm talking about. Using HCl and H2O2 is fastest way but problem is fact you should use 30% H2O2 which is a very nasty. It can and WILL ignite things made of organic material when come in contact but not instantly but after drying for some time. So if you are not very good at handling hazardous chemicals stick whit FeCl3 !!! And whwn I say good I mean 2+ years of practice in uni organic chemistry lab, seriouse one!

 

[jpanhalt]

Since we are talking about relative risks, here are some MSDS data summarized from the JT Baker Chemical Company. Obviously, anthing that will etch copper has got to have some risks to it. I have included the label categories of risk severity. Notice the similarities. The etchants using hydrogen peroxide and HCl or sulfuric acid can be made using use 3% peroxide; althouh, many of the recipes use 30% .

Hope this helps keep the risks in perspective. John

SEQUENCE: Health; Flammability; Reactivity; Contact
(Source:JTBaker Chemical Company MSDS)

Hydrogen peroxide 30% ---- 3,0,3,4
Hydrogen peroxide 3% ----- 2,0,1,2
Sodium persulfate ----------- 2,0,3,3
Ammonium persulfate -------2,0,3,3
Ferric chloride ---------------3,0,2,3

Hydrochloric acid 33-40% ---3,0,2,4
Sulfuric acid 52-100% --------4,0,2,4

FULL LABEL INFORMATION

AMMONIUM PERSULFATE

Health Rating: 2 - Moderate (Life)
Flammability Rating: 0 - None
Reactivity Rating: 3 - Severe (Oxidizer)
Contact Rating: 3 - Severe (Life)

SODIUM PERSULFATE

Health Rating: 2 - Moderate
Flammability Rating: 0 - None
Reactivity Rating: 3 - Severe (Oxidizer)
Contact Rating: 3 - Severe (Corrosive)

HYDROGEN PEROXIDE 30%

Health Rating: 3 - Severe (Life)
Flammability Rating: 0 - None
Reactivity Rating: 3 - Severe (Oxidizer)
Contact Rating: 4 - Extreme (Corrosive)

HYDROGEN PEROXIDE 3%

Health Rating: 2 - Moderate
Flammability Rating: 0 - None
Reactivity Rating: 1 - Slight
Contact Rating: 2 - Moderate

FERRIC CHLORIDE

Health Rating: 3 - Severe (Life)
Flammability Rating: 0 - None
Reactivity Rating: 2 - Moderate
Contact Rating: 3 - Severe (Corrosive)

 

[stickpin]

Hmm I'll use bigger letters.
NEVER add water to dry Ferric Chloride

Why is that?
ive done it before, as long as you put all the correct amount of water in at once(?)
Is it because you are creating a very strong solution (but only until all the rest of the water is poured in) and could heat up quite alot

 

[mvs sarma]

"At once" doesn't ever happen in real time. There is a scope for the water fallen would heat-up and eventually splash. Perhaps, it is always better to scrupulously follow the advises given by chemical pundits, instead of learning by experience.

 

[Oznog]

Note that the commercial etchants such as the link by Pommie and this one (https://www.jtbaker.com/msds/englishhtml/f1080.htm) have ferric chloride at a concentration of about 40% by weight. That means, 40 g of ferric chloride (anhydrous) in 100 g of solution. That is considerably more concentrated than a couple of teaspoons (assuming a density of 4, that would be about 40 g) in 250 mL or about 14% w/w. I am sure the more dilute solution will work. I am just pointing out that it is considerably less concentrated than commercial etchant and may work more slowly.

Actually to be a bit clearer that would be 40% by weight would be 40g of ferric per 60g of water for 100g of solution. Almost as much powder as water! IIRC doesn't etchant also contain a *small* amount of HCL? Or is HCL created when adding ferric chloride to H2O? I forget.
I wanted to save on etchant by making my own at one point- found that the mass of ferric chloride was enough to bring the price of materials up to something close to what etchant costs in the store anyways.

Actually there have been some guys swearing by putting on a thick glove, sopping a kitchen sponge in ferric chloride etchant, and lightly rubbing the board while letting the excess run into the tray, sop it up again. Supposed to etch the board REALLY fast.

If you do the traditional etching tray, inverted runs MUCH faster and cleaner. What works is get some little skinny neodymium disk magnets, put a pair on each corner, on opposite sides of the board, the magnetic attraction should hold them in place. Or some kind of plastic edge clip. We want to keep the inverted board off the bottom but don't want it spaced so high that it requires filling the tray with a lot of extra etchant just to reach the board.

 

[jpanhalt]

IIRC doesn't etchant also contain a *small* amount of HCL? Or is HCL created when adding ferric chloride to H2O? I forget.

There is an equilibrium between ferric chloride and water that produces a small amount of HCl . You can view it as follows:

1) Ionization of FeCl3 in solution gives Fe ions and Cl ions;

2) Water ionizes to H ions and OH ions; and

3) The four ionic species are in equilibrium, combining and re-ionizing continuously. In that process, some H combine with some Cl to give a small amount of HCl.

Although most HCl is ionized in solution, HCl itself is a gas and can be lost from the mixture, so you do get acidic fumes. I find this kind of reaction with certain salts of ammonia intringuing. Solid ammonium carbonate, chloride, etc. (any salt where the acid is volatile) will simply evaporate by releasing ammonia and the acid gas. The carbonate gives off CO2 as the acid. John

Edit: If you want to add a little HCl, it probably doesn't hurt. As I understand it, the added chloride helps. That's why I include a pinch of table salt in my recipe.

 

[pitronix]

Altough I like to support people doing different kinde of experiments I would again suggest to keep on experimenting with temparature, concentration and etc. of FeCl3 in water solution and keep away from experimenting acids and H2O2 combos! I have a friend who ended up in hospital after adding to much H2O2 30 % to HCl 12%. poisenous fumes are realy nasty! I did a lot of etching and galvanization with nasty chemicals and it sometimes ends up bad no mater how carefull you do. I used to work with HF for glass etching, conc. acids for metals including HNO3 and H2SO4 etc. this are not things to be done home alone DIY folowing some tutorial. I gave a guy sodium hydrate cause he asked for it, luckly I asked him what he wanted to do with it. It turned out that he got some tutorial on net thet was supposed to use solution oh NaOH but instead some idiot wrote sodium hydrate. This koul have ben fatal mistake!!!

 

[jpanhalt]

I gave a guy sodium hydrate cause he asked for it, luckly I asked him what he wanted to do with it. It turned out that he got some tutorial on net thet was supposed to use solution oh NaOH but instead some idiot wrote sodium hydrate. This koul have ben fatal mistake!!!

It may just be a translation issue, but do you mean sodium hydride (NaH) instead of sodium hydrate? "Hydrate" implies the presence of an oxygen, thus google searches turn up NaOH as the empirical formula for sodium hydrate. John

John