Ferric chloride, or more specifically the solution that is commonly used, is a combination of FeCl2 (ferrous chloride) and FeCl3 (ferric chloride). FeCl2 is pretty stable and would much rather stay in its cozy formation, because you know what they say about threes and parties. However, this is not true when there is an excess of chloride in the immediate vicinity. Chlorine will readily combine with just about anything (which is why it is so corrosive) and will assume a less than stable combination with the ferric chloride, making FeCl3. FeCl3 is now in a situation where its formation is stable enough to keep that hobo chloride around, but it really does not want it. This makes it very useful, especially when the product created through the reaction is soluble. Hint: copper chloride is somewhat soluble.
Here’s an overly simplified breakdown of the reaction:
*Note: this etching project was fairly small, with pieces 4 by 4 cm long, so if your project is larger feel free to use as much FeCl as you need. Just consider that any FeCl you use will create a “dirty” mix, which may hamper further etching with the same solution.*
So then, back to the current project:you need that copper eroded ASAP. To do that, first start with enough hot water to reach the 50 ml line of the secondary container. The hot water will be used to heat up the ferric chloride. Now grab 50 ml of ferric chloride and dump it into the 300ml beaker, then set the beaker inside the container with the hot water. Now the hard part: just leave it. Let it simmer for a minute or two, with occasional stirring. This part is tricky to explain, and there does not seem to be a clear consensus on what in the high hell the temperature should be. Sources do however agree that above 30 degrees Celsius will work. That’s not to say that a cold solution will not work, just that it’s going to be a lot slower than a hot solution.Just be careful, a boiling solution won’t work much faster than one that is at a more moderate temperature.
that said, you can just dump the PC board directly into the ferric chloride. There will be no vigorous reaction; instead it will opt to black out. If it remains still for a while, a layer of black silt (copper chloride) will cover the board, which can easily be removed via agitation. Simply move the liquid around (vigor anywhere else is encouraged, but for the moment keep calm) by gently tilting the container back and forth to provide fresh etchant to the area.Ferric chloride is very, very brown, so it is possible to make out when something is going wrong, but not so much when you are done. To tell if the board is done,either you will have to be remove it from the etchant or you will have to take your best guess, champ. To overcome this particular problem, people will often use sponges to rub etchant over the surface. The combined chemical and mechanical action makes the etching process a good deal faster. This would have been the method I would have gone with except for the fact that my gloves disintegrated the moment they came into contact with the etchant (*FUN*).