Ferric Chloride For PCB Etching 100 gms Pack.....

[Jammy]

Friends I have Copper Clad PCB - Paper Phenolic 6*4 Inches....
so, with the 100 gms Ferric Chloride Pack how much PCB's can be made...


Hoping for reply soon...
Jammy

 

[tom_pay]

This is actually a very complicated question. If you knew exactly the area exposed to the chemical, which depends on your PCB layout. And a few other things you could work it out, but this would quite difficult.

I have found that Ferric Chloride actually lasts a long time. I have had a pot of about 100mL for almost three years and did a fair few boards of varying sizes. So it defiantly lasts. Only, when it gets older it takes a longer time.

Sorry I cannot be any more specific.

Tom

 

[jpanhalt]

I don't think the question can be answered, because there is simply not enough information given. First, let's consider an over-simplified view of the chemical reactions involved in etching. Ferric chloride (Fe(III)Cl3) oxidizes copper to CuCl (initially) and that creates the etching one observes. Thus:

FeCl3 + Cu ----> FeCl2 +CuCl

That equation would imply that one mole of FeCl3 would etch 1 mole of copper. We don't know whether the 100g of ferric chloride Jammy has is the anhydrous form (FW 162) or the hexahydrate form (FW 270). Let's assume it is the anhydrous form. So, 100 g = 0.62 mole. 0.62 mole of copper (AW 63.5) is 39.2 g. For 1 oz copper sheet, that would be roughly the amount of copper on 1.3 sg. ft. (1,200 cm^2). As mentioned, that would be removing all of the copper, but then, you wouldn't have a PCB left. If you remove only 10% of the copper, then your area would be 10 times bigger, which is quite large for a hobbyist.

Now for the problems:
1) Much of the CuCl formed is further oxidized by FeCl3 to CuCl2. That would reduce the amount that could be etched in half, if the reaction went to completion and formed only CuCl2.
2) Under acidic conditions, both ferric chloride and copper chlorides can form oxides. Those oxides can be created by exposure to oxygen in the atmosphere. That effect of air will increase the amount of copper that can be etched, particularly, if there is excess acid present (see #3).
3) Finally, if one simply adds HCl to the used etchant and bubbles air through it, you can convert the ferric chloride etchant to cupric chloride etchant after you etch enough copper. Cupric chloride etchants can last forever, so long as you keep adding HCl and allow re-oxidation by room air.
4) As mentioned, the ferric chloride etchant will work more slowly as the active chemicals are consumed. It will also develop muddiness or sludge.

John