pcb etchant

[jpanhalt]

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.

Electrostatic repulsion plays a very small part in the rate of reaction. Contact with the electrode is effectively diffusion controlled. There are numerous sources to support that. However, more simply, if electrostatic repulsion was the controlling factor, how can you explain the production of any valence of >1 cation at the anode, including iron(II)?

Hence, FeCl3 cannot be regenerated by electrolysis.

See: Electrolysis - Wikipedia, the free encyclopedia

Oxidation of ions or neutral molecules can take place at the anode, and the reduction of ions or neutral molecules at the cathode. For example, it is possible to oxidize ferrous ions to ferric ions at the anode:

John

 

[3v0]

It is clear that you are more then a bit biased in favor of Ferric Chloride.

Ferric chloride is nasty stuff to be around, even the fumes are corrosive. It corrodes or stains everything it touches including your lungs.

I like sodium persulphate because it does not have the problems associated with Ferric Chloride.

I have stock in the crystal form that is about 2 years old and it still works.

**broken link removed**   Ferric Chloride               Sodium Persulfate
Health Hazard:       3                              2*     
Fire Hazard:         0                              0       
Physical Hazard:     0                              1

Explanation of the HMIS® Ratings
HMIS® III - HEALTH HAZARD RATINGS
* Chronic Hazard Chronic (long-term) health effects may result from repeated overexposure
0 Minimal Hazard No significant risk to health
1 Slight Hazard Irritation or minor reversible injury possible
2 Moderate Hazard Temporary or minor injury may occur
3 Serious Hazard Major injury likely unless prompt action is taken and medical treatment is given
4 Severe Hazard Life-threatening, major or permanent damage may result from single or repeated
overexposures
* *

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.

 

[jpanhalt]

It is clear that you are more then a bit biased in favor of Ferric Chloride.

Bias has nothing to do with it. I was addressing the hocus-pocus chemistry claims.

As for the subject of etching, I have tried both perchlorate and ammonium persulfate etchants. I prefer ferric chloride. What little HCl is evolved is a gas; whereas, any sulfuric acid splashed from the persulfate sticks around. It is non-volatile.

Also, the photoresist I use (Injectorall) is attacked somewhat by the "per-etchants;" whereas, it is extremely resistant to ferric chloride. However, my main reason for using ferric chloride is simply that its solution can be used and stored easily. So, I can do one board and 6 months later do another board with the same solution and no additional reagents.

John

 

[mvs sarma]

Bias has nothing to do with it. I was addressing the hocus-pocus chemistry claims.

As for the subject of etching, I have tried both perchlorate and ammonium persulfate etchants. I prefer ferric chloride. What little HCl is evolved is a gas; whereas, any sulfuric acid splashed from the persulfate sticks around. It is non-volatile.

Also, the photoresist I use (Injectorall) is attacked somewhat by the "per-etchants;" whereas, it is extremely resistant to ferric chloride. However, my main reason for using ferric chloride is simply that its solution can be used and stored easily. So, I can do one board and 6 months later do another board with the same solution and no additional reagents.

John

At times I was able to use Ferric chloride with long gaps, but it warranted addition of little powder.

 

[jpanhalt]

Hi Sarma,

Ferric chloride is one of the most stable etchants there is. Some HCl may be lost with time, and a little HCl, not ferric chloride, is probably all that needs to be added. Of course, adding ferric chloride will work too.

I am right now experimenting with what is called the Edinburgh Etch, which involves simply the addition about 6 to 7 g of citric acid per 80 mL of ferric chloride etchant and diluting to a total of 100 mL with water. The solution is less viscous, and the citric acid acts to keep sludge from forming. The absence of sludge increases both etch rate and resolution. I don't have any results yet to report, but since it is an old recipe, I suspect others may already have tried it or be interested in trying it.

John