I etch about half a dozen printed circuit boards each year at home, using an aqueous ferric chloride AKA iron(III) chloride etchant solution. As I want to minimize the costs and hassle of buying new and disposing of old etchant, I would like to know what steps can I take for maximizing the amount of boards I can etch with a given amount of etchant. I have no background in chemistry, so any suggestions are appreciated.
-
I prepare a certain amount of etchant solution at a time, use it until it fails to dissolve copper effectively, and finally transfer it to a waste tank awaiting disposal. Does the batch size affect the amount of circuit boards I can etch with a given amount of ferric chloride?
-
Is etchant sensitive to light or fluctuating temperatures while in storage?
-
Is etchant oxygenation beneficial or detrimental? Many vendors of the chemical and several PCB fabrication tutorials clearly state that FeCl3 etchant stores indefinitely if kept in an airtight container. On the other hand commercial PCB etching devices purposefully stir the etchant by blowing air bubbles trough it, oxygenating the solution in the process, seemingly without adverse effects.
Best Answer
If you store Ferric Chloride in a sealed glass jar, it stays viable for years - I have some that I prepared 10 years ago and it still works fine. Just keep the jar out of direct sunlight and somewhere not too warm - mine is stored in the garage out of the way - it's not temperature controlled and that doesn't seem to matter.
You can also prolong the etchant by the way you use it. Typically you would just dip the board in a pool of the etchant, but this is not so good as it will reduce the effectiveness of the etchant as it fills with cupric chloride (remnant from etching).
The way I read somewhere (and subsequently use) is to put a small amount on a sponge (like the sort you use for washing up, though not one that you ever plan to use for washing up ever again!). Then, making sure you are wearing gloves, simply wipe the sponge across the board that you are etching. You will notice the sponge starts going green. You can keep adding small amounts more onto the sponge as it gets used up.
This actually results in a nice quick etch, and it means pretty much all of the etchant on the sponge is used up. It also means you don't pollute your jar of ferric chloride with copper meaning it stays at full strength.
Ferric Chloride isn't nice stuff in terms of disposal (well in terms of anything but etching speed really), so the alternative would be to go the safer route of using Hydrochloric Acid + Hydrogen Peroxide. This stuff is easier to dispose of as far as I know.