Mixing Ferric Chloride Hexahydrate Granules

[johnnybegoode]

I bought 500 grams Ferric Chloride Hexahydrate Granules in a package

The only
Instructions:
"Pour the granules into a suitable container and add 0.75 litres of hot tap water.
Mix until all the granules have dissolved.
Make up 1 litre working solution"

My question:
1. Do I throw all the 500 grams granules into the mix?
2. Is there any expiry date? And how many times can it be reused?

Thanks

[Seljer]

Yep, you'd throw them all in there. Though 1L of etchant is a lot, you could probably halve everything for a smaller batch.

No idea about expiry date, eventually, if you leave the mixed etchant alone the water eventually evaprates and you end up back with the crystals. It can be reused quiet a lot, I think I got at least 10 regular sized PCBs out of one batch of etchant, you realise when theres not much more power left in it when it ends up etching really really slowly (if at all).

[George Giblet]

There's no rules but I generally use 200g/litre (final volume).   You trade etch time for concentration.  Agitating the solution is far more economical here.

I'm not aware of any expirely date, I've used 5yr old solutions and they work fine.  You can buy premade solution (it's an expensive way to buy it), for the hell of it look at what periods they are quoting.

As far as re-use goes if it's taking too long tp etch, or the solution looks ugly then chuck it.  The amount of solution you start with relative to the board size is a big factor.  I tend to use bare minimum of solution and chuck it earlier.