Tip for Feric Users

[tranceracer]

While etching a board the other day, (5W LM2002 and LM386 mini amps) I noticed a lot of crap floating around in my used feric solution.  These particles would settle on my board and result in spots of unetched Cu so I'd have to swirl the etchant constantly to keep the particles in suspension.  Well as they say necessity is the muthah of re-invention ( ) so i decided to build a simple "filter".  All it is is a plastic butter sized container with a bunch of holes drilled in it and a coffee filter.

I filtered the feric chloride thru this little filter into another container and presto, clean feric chloride!   

So if your feric starts to have a lot of suspended junk floating around just filter it and use a little heat to milk all the life out of your feric solution.

just thought I'd share... 

[R.G.]

Good tip.

Whenever I use FeCl, I use small plastic clips to suspend the PCB above the bottom of the container, and put it in UPSIDE DOWN, that is, copper towards the bottom. Then the heavy dark particles fall away from the copper to the bottom and don't occlude the copper etching.

But removing the precipitate is even better.

[cpnyc23]

Nice tips guys - perhaps on my next round I will combine them!

-chris

[Franky]

When using Na Persulfate, those particles disapear after a while, when you put the etchant back into its bottle, and let it deactivate, it will continue to corrodate these little copper particles. Then it turns blue (oxyded copper Cu++ ions if my chemistry is good) and when it's gone dark/medium blue, you've got to change it..

About ferric, I don't know if it continues to be active with those particles when it's cold.

[R.G.]

There is some scheme for running sulphuric acid/peroxide baths indefinitely, as they precipitate out waste copper as copper sulphate crystals and can be replenished with sulphuric acid. No change in strength as I remember, because the etching and precipitation happen in equilibrium at good etching strength.

All you gotta do is keep around a five gallon bottle of 30% sulphuric acid and keep it properly replenished as well as not broken, lost, drunk by toddlers, etc.