pcb etchant

[andrew2022]

what do you think is the best chemical to use for pcb etching?

 

[Johnson777717]

HYDROFLORIC ACID!!!! :shock:

No just kidding. That stuff is extremely nasty and requires a bunch of control measures and PPE (Personal Protective Equipment).

I use Ferric Chloride and I like it because it is cheap, widely available at a lot of electronics stores, and is somewhat docile to the home electronics buff. I haven't had any problems associated with the Ferric Chloride. It etches nicely at a warm temperature and produces some good resulting PCB's. It is also reusable to a point. I haven't reached a point where my old ferric chloride wont etch, so I don't know what the life-span is.

 

[andrew2022]

i use ferric chloride aswell. was just wondering if anyone used something which lasts longer/etches faster etc

 

[Johnson777717]

Alright, I did a little bit of research at MG Chemicals, who produces the three common copper etching solutions.
Website here:
**broken link removed**

Some simple facts about the etching solutions:
1. Ferric Chloride
A. Stated as providing a more consistent etch than Ammonium Persulfate
B. Stated as etching twice as fast than Ammonium Persulfate
C. Roughly 10-20 minute etching time.
D. Will not remove most etch resist inks.

2. Ammonium Persulfate
A. Translucent liquid allows the user to see the progress of the etching process.
B. Roughly 30 minute etching time.
C. No flash point stated on MSDS, so it is not directly flammable.
D. May remove some etch resist inks. Must use a compatible etch resist pen.

3. Sodium Persulphate
A. Flash point at 180 deg F. FLAMMABLE!
B. The solution is shock sensitive
C. Solution decomposes when heated.
D. Cleaner solution, allows increased visibility during etching.
E. Will not remove most etch resist ink.
F. Must be stored in a ventilated container due to gasseous nature.

So it looks like Ferric Chloride is the most common, most stable, Most docile and consistent etchant solution.

 

[kentken]

I use Sodium Persulphate and have good luck. I use a toner transfer method, and tuch up with a sharpe, but the etch will sometime eat though the marker. put hot water in a ziplock bag and mix in chemical, and swish.
Very clean chemical.

Have fun

 

[spyghost]

hcl + h2o2 + h2o

 

[pike]

i used ammonium persulphate, it's quite clean, but once you heat it with water it starts to decompose...kind of expensive seeing i have little money to spend.

Ferric Chloride is quite good as you can use over and over if you run electricity through the used etchant. (electrolysis) the copper simply builds up over the terminals and the etchant regains it's corrosive form again.

 

[Johnson777717]

Ferric Chloride is quite good as you can use over and over if you run electricity through the used etchant. (electrolysis) the copper simply builds up over the terminals and the etchant regains it's corrosive form again.

I haven't ever performed the electrolysis on Ferric Chloride. What kind of voltage and amperage do you use to perform this? Any special procedures?

Thsi process would be extremely helpful, considering most regulations wont allow you to dispose the Ferric Chloride down the sewer due to the copper content. The regulations that I have read instruct to remove the copper, add baking soda in order to even out the PH level to around 7, and then flush into the sewer.

Thanks for the great idea!

 

[andrew2022]

Ferric Chloride is quite good as you can use over and over if you run electricity through the used etchant. (electrolysis) the copper simply builds up over the terminals and the etchant regains it's corrosive form again.

I haven't ever performed the electrolysis on Ferric Chloride. What kind of voltage and amperage do you use to perform this? Any special procedures?

Thsi process would be extremely helpful, considering most regulations wont allow you to dispose the Ferric Chloride down the sewer due to the copper content. The regulations that I have read instruct to remove the copper, add baking soda in order to even out the PH level to around 7, and then flush into the sewer.

Thanks for the great idea!

but then if it was corrosive again you wudnt need 2 get rid of it down the sewer

 

[Johnson777717]

but then if it was corrosive again you wudnt need 2 get rid of it down the sewer

Good point.

 

[pike]

no i mean that you can use it over and over again, and keep on etching boards with the same etchant!

Seeing that copper has an atomic positive charge, the copper will build up on the negative terminal.(like charges repel, different charges atract.)
I dont know what voltages are needed but, the amount of current doesn't really matter if you have all the time in the world. I'm guessing any where like 12v and over.

honestly though, i have never tried it myself, but theoretically it seems correct. (well to me)

 

[Oznog]

Yeah, but isn't the anode going to corrode? I seem to recall I used ferric chloride to electrically etch (on purpose) even a stainless steel spoon once.

Now you can definitely use the board itself as an anode, and get really fast etch times. As the traces form, they'll become isolated from the anode connection and stop this effect in places one by one. Moreover, the point where you'd electrically connect the power supply is very difficult to protect from corrosion unless it's totally out of the solution.

 

[pike]

I know that it is corrosive even in its weak used up form, but platinum doesn't react with it. The reaction of corrosion occurs because the FeCl exchanges elcetrons with the steel to form a chemical bond. (rust)

But if we place a charge on the terminals, the FeCl will be repelled but the copper will be attracted to the terminals. Then you have FeCl just sitting in the tank. As soon as you switch off the power, the FeCl starts eating the copper coating on the terminal.

Switching the power back on would reverse this reaction.

 

[babui2008]

Eternally-replenishable Novel Etching Solution (based on persulfate-type etchant)

I have got a way to recycle and reuse persulfate-type copper etchant infinitely. Its an electochemical setup that will cost you a lot when you set it up for the first time. But it does not require any kind of maintainence. You dont have to add any chemicals later. You can reuse the same solution forever.

THEORY : First, I will discuss the theoritical principles involved.

sodium/ammonium persulfate (Na2S2O8 / (NH3)2S2O8) etches copper in the following way :-

Na2S2O8(aq) + Cu(s) ----> Na2SO4(aq) + CuSO4(aq)

The electrochemical mechanism reverses this in the following way :-

CuSO4 ---> (Cu)2+ + (SO4)2-

At cathode (-ve electrode) :

(Cu)2+ + 2e ---> Cu (copper gets deposited on the electrode itself, thus removing copper ions from the solution)

At anode (+ve electrode) :

2 (SO4)2- ---> (S2O8)2- + 2e

Thus the persulfate ions ,ie. the primary oxidiser, is regenerated from the sulfate ions.

REQUIREMENTS : You will need the following components to set up your etching apparatus.

1) a platinum electrode (1 pcs) for the anode : This will be the most expensive component in the whole apparatus. Also note, there are two varieties of Pt electrodes. A) The platinized platium electrode , which is black or grey in colour because it is coated with Platinum Black (an allotrope of platinum), and, B) The shiny platinum electrode, without the coating, which has a shiny silver-like appearance. You are supposed to use the shiny-type Pt electrode. The black one won't work.
2) a copper electrode for the cathode : you may use a length of a copper wire (after striping off the insulation) or a spare bit of copperclad pcb. Make sure this electrode has a large surface area.
3) a glass/plastic container to hold the solution and act as your etching tray
4) sodium persulfate (Na2S2O8) : Alternatively, sodium sulfate (Na2SO4) may be used to begin with and sodium persulfate can be generated from that by electrolysis.
5) a little bit of conc. sulfuric acid (H2SO4) to lower the pH a bit : an acidified solution helps to speed up the etchant-regeneration process.
6) water : ordinary tap water would do but distilled water is better.
7) Power Supply - a mechanism to supply a lot of current (about 5-10 Amps) at controlled voltages to the electrodes : A simple 9-volt battery with a potentiometer might do. But a 9-volt battery can't supply sufficient amount of current. So the regeneration process may be too slow to be acceptable. A better way is to draw the power from the house-electric supply. Use a 12-volt DC wall transformer/adapter to get a 12V DC source of current. Then prepare a custom voltage-regulation circuit that uses the 12V DC output and can provide 5-10 Amps at a voltage that you can control precisely.
(Note : the required output voltages are typically between 0.5V to 4.5V DC with a control precision of atleast 0.1V)
8) You can also add an agitator mechanism (aquarium pump) and a heater mechanism (immersion heater / aquarium thermostat) to the apparatus to speed up the etching process.

SETUP THE APPARATUS :-

Prepare a sodium persulfate solution at a concentration of 230 gram/litre. If you are starting with sodium sulfate instead of sodium persulfate, mix at a concentration of 460 gram/litre. Add to it about 10 ml of conc. sulfuric acid per litre of the solution. Your etching solution is ready.

Now pour your etching solution in your etching tray and drop the electrodes in it. (the copper electrode is supposed to be the cathode (-ve) and the platinum electrode is to be anode(+ve). Make sure you connect them correctly.)

Now, if you mixed your solution with sodium persulfate, you are ready to go. But if you used sodium sulfate, you need to run a current through the solution so that sodium persulfate can be generated within the solution. Calibrate the voltage of the regulator and let the current run for some time (about one hour). (The voltage calibration process is being given below, as a part of the etching process.)

THE ETCHING PROCESS :-

Drop the pcb, which is to be etched, in the solution and start a current in the circuit.

Then you need to adjust the potentiometer or the v-reg to supply the correct voltage.
The goal would be to set the voltage as large as possible but just short of when a vigourous bubbling starts at the platinum anode.

(Note, if you are are using an aquarium air-pump to agitate the solution, you must turn it off during this voltage calibration process. Otherwise you wont be able to distinguish the bubbling at the anode. After calibration, you can turn on the pump and leave the apparatus to etch your pcb.)

Ideally, You must begin with a voltage as low as possible and increase the voltage until you can see a lot of bubbling at the anode. Once you find the threshold point, you must set the voltage to slightly less that.

POST-PROCESSING OF ETCHANT SOLUTION :-

After etching is completed, remove the pcb from the solution and let the current run for some more time. This will allow all copper ions dissolved in the solution to get deposited on the cathode and clean-up the solution. (It is easy to detect presence of copper ions in the solution. Copper ions impart a blue colour to the solution. So wait till the blue colour fades away)

After this process completes, you must remove both the electrodes from the solution before you remove power from the electrodes. If you remove power from the electrodes while they are in the solution, the cathode which is made of copper, turns into an ordinary copper rod, and the etchant immediately starts eating away copper from the electrode. So if you leave the cathode in the solution without power supply, the etchant will essentially get used up and you will need to regenerate it again before you can use it.
Note that, although the solution doesn't react with the platinum electrode, but if left in it for a long time, it can corrode the suface. And you don't want the most expensive part of your etching apparatus destroyed.

Best of Luck with your new etching system
------------------------------------------- ---------------------

 

[mvs sarma]

Wah Nice Babui2008,

Nice set up and such nice explanation to those interested for a similar setup.
Thanks

 

[twasnow]

I use either of the persulfates heated to about 40 Degrees Celsius with a fish tank heater cranked past the mechanical stop (but still working).

(I use one with enough wattage to heat the amount of water you are using to 40 degrees in under an hour... the approximate length of time it will take you to get the pcb ready from either plotting or using a photo-resist method (my personal favorite)

the tank I use is a modified fish tank with aquarium silicone absolutely no leaks and it has been used for over 2 years.

the modified tank has a divider 2 inches of tank for the persulfate and 8 inch bath of developer. (the tank is 10x10x12 total)

in the bottom of the etcher I have a regular fish tank "bubbler" which really speeds up the etching process. (make sure you get one with no metal.)

and of course you need a lid ( made two separate lids for two materials) and added plastic roach clips to suspend the board (there are also grooves at the bottom for a pcb to sit in.)

the best part about persulfate is that when it evapourates and crystalizes it is pretty benign, and easy to dispose of... same with the liquid.

3 main advantages to using a persulfate over ferric chloride:

1.) it comes in crystal form.. very easy to store and handle
2.) you can see through it while etching and simply based on colour you know when it needs to be changed.
3.) disposal is very easy once spent and is at room temperature it pretty much doesn't corrode anymore at all.

added bonus: it doesn't KILL clothes like ferric chloride does.

boards take about 15 min to etch for me.


I won't go near ferric chloride anymore I tried it once and it cost me an extra 70 bucks in clothes and about 10 boxes of baking soda

 

[Centretek]

for Ferric Chloride, use steel wool for the anode @ around 3-6 V.
The steel wool reacts with the chlorine ions and reconstitutes as FeCl as the copper is removed by the cathode.

 

[shokjok]

Ferric chloride is like auto coolant. You cannot re-electrolyze it repeatedly without affecting its quality or appearance. Eventually it will resemble Gatorade and will need to be disposed of safely and properly. If it were possible to re-use it this way, it would be more expensive to manufacture and distribute, and MG Chemicals would be short-lived.

 

[jpanhalt]

Ferric chloride is like auto coolant. You cannot re-electrolyze it repeatedly without affecting its quality or appearance. Eventually it will resemble Gatorade and will need to be disposed of safely and properly. If it were possible to re-use it this way, it would be more expensive to manufacture and distribute, and MG Chemicals would be short-lived.

Perhaps you would care to give a little more detail of the chemistry involved in your assertions so we can have a more rational discussion.

By auto coolant, do you mean radiator fluid (ethylene glycol) or air conditioner? Either can be recycled repeatedly. Ethylene glycol is easily recoverable and reused on an industrial scale. Check Wikipedia.

Ferric chloride also can and is recycled. The iron never goes away. The problem is to get rid of the copper, and ways for doing that are described in this thread.

Ferric chloride is an industrial chemical, is produced in tank car quantities, and has many uses. I doubt MG Chemical actually makes what it sells.

John

 

[babui2008]

Ferric chloride (FeCl3) cannot be reproduced by electrolysis.

The ferric ion in ferric chloride acts as the oxidising agent while etching:

2 Fe(3+) + Cu ---> 2 Fe(2+) + Cu(2+)
[Note how Fe(3+) gets reduced to Fe(2+) while Cu is oxidised to Cu(2+)]

To regenerate the corrosive etching properties of used etchant, Fe(2+) need to be oxidised to Fe(3+). We cannot oxidise Fe(2+) electrolytically, because, Fe(2+) will have to donate one electron at the anode to be oxidised to Fe(3+). However, the anode being positively charged will repel Fe(2+) ions and thus prevent the reaction.

Hence, FeCl3 cannot be regenerated by electrolysis.