Plastic for Storing Ferric Chloride

[pupil]

Hi,
I hand drew and etched my first pcb today. I'm very happy with how it turned out and look forward to the next project.

I'm left with a question about storing the used ferric chloride though. I understand that glass and plastics should work fine for this. The liquid ferric chloride I bought comes in a #2 polyethelene plastic bottle so surely that is a good plastic to use. Well, I went looking around my kitchen for some #2 jar, but didn't have any that made sense. I ended up storing the used etchant in a peanut butter jar, a #1 "polyethylene terephthalate" plastic. It's been about 12 hours and everything seems fine....

Does anyone know if polyethylene terephthalate is safe to store in? Do most people just use any plastic and not worry about what kind?

[mremic01]

I wouldn't worry about it that much. The worst thing that can happen is that it makes the plastic brittle and prone to cracking. It won't just dissolve it. I've been using a flimsy plastic tray for over a year now (a cheese danish came in it). It's less flexible than it used to be and the sides have some cracks in them, but near the top edge so nothing's going to spill. A peanut butter jar should get the job done, and if you're really worried about the long term, it should definitely last long enough until you can find some glass jars. Think of it as an excuse to buy some chips and salsa.

[merlinb]

PET is fine, I've stored FeCl in soda bottles for years.

[antonis]

I'm not a wise ass but the formula is "FeCl3" (IUPACK: Iron trichloride)

There isn't any formula like FeCl..
(the stable compound with the less Cl atoms is FeCl2 - Ferrous Cloride..)

P.S.
@merlinb, I'm just trolling..

[Mark Hammer]

When storing "used" etchant, it is helpful to store it in as tall and slender a container as you can.  The reason is that the molecules that have bound with the copper are heavier, and sink to the bottom.  The lighter "unused" molecules of etchant remain near the top.  When it's time to etch another board, you can decant the etchant into your etching tray, and have stuff that is nearly brand spanking new.

[antonis]

When storing "used" etchant, it is helpful to store it in as tall and slender a container as you can.  The reason is that the molecules that have bound with the copper are heavier, and sink to the bottom.  The lighter "unused" molecules of etchant remain near the top. 

I've not tried it but it should be a good idea for the whole procces of etching (i.e. in a plastic bag with lips sealed/zipped) holding it verticaly so the PCB be allways in contact with "pure" etchant...

[Mark Hammer]

Personally, I just float the board, copper side down, on top of the etchant bath, and warm up the back (component side) of the board with a heat gun or hair dryer or lamp.  The used etchant sinks to the bottom of the bath, and the board stays in contact with the fresher stuff.

[antonis]

Any specific reason for heating the board..??
(does it help the chemical reaction or just "circulate" the bath..??)

[rring]

The best way to etch is to soak a sponge in etchant and gently rub back and forth. The etching process goes much faster - uses less etchant. You can etch one side of a board in about 3 to 5 minutes. Much less pitting and under cutting also.

Check out this picture : this is a ferric chloride etch of an aluminum enclosure. Both pieces were etched in the same bath at the same time - with duplicate resists. The back plate was just soaked in the solution and agitated occasionally. The top of the enclosure was etched in less than half the time using  a sponge dipped in the same bath.

Also for etching aluminum - you can use spent ferric chloride...the copper chloride etches just as well if not better so save your waste and use it to etch enclosures.

[Seljer]

Any specific reason for heating the board..??
(does it help the chemical reaction or just "circulate" the bath..??)

Heat generally makes any chemical reaction progress faster.

I put a aquarium air pump at the bottle of my etching tank (a tall tupperware thing) to add some extra agitation, and in theory, the bubbles also replenish oxygen in the etchant extending it's usability.

[Mark Hammer]

Any specific reason for heating the board..??
(does it help the chemical reaction or just "circulate" the bath..??)

Both.  And for those of us who live too many degrees away from the equator, it helps the etchant to work just as well in the autumn as it does in the summer!  

Professional etchant baths are generally heated.  If a person does one-offs, like I do, with large intervals between, you tend to have an etchant bath that is much less than "professional".  In reality, only the etchant near the copper really needs to be warm.  Heating the entire bath merely ensures that the copper will not be in contact with any etchant that isn't.  But I've found that heating the board itself transfers heat to the nearby etchant, and accomplishes what needs to be accomplished.  I used to use a gooseneck lamp whose bulb I could situate an inch or so above the board, but don't have it anymore, so I use a heat gun instead.  Either is fine, although one wants to be careful of melting whatever plastic container you're using by application of too much heat.

[antonis]

Heat generally makes any chemical reaction progress faster.

I thought that it was true only for endothermic reactions..
(for those which absorb energy in the form of heat..)

Propably the reaction between Ferric Cloride and Copper is of this kind - although I've been told that it's not wise to exceed the temperature above 43C (110F) because of the risk of excessive fuming...

[pupil]

Awesome replies! Thanks people.

[PRR]

>>Heat generally makes any chemical reaction progress faster.
> I thought that it was true only for endothermic reactions..

True for nearly all chemistry, except in some special cases.

Watch paint dry. Dries faster on hot days.

Oftentimes, when you want to dissolve something, you are told to warm it up.

Cold iron rusts slow. Hot iron rusts right before your eyes.

Silicon chips rot when water/air gets under the oxide. They make them to last a decade or more. But how can you test for a decade when the sales department wants to sell them NOW! ?

The usual way is to test for a month at very high temperature, then assume that every 10 degrees C cooler will last twice as long. So test at 150 deg C, rate for 100 deg C max, after a month you can be pretty-sure the real parts will serve for 32 months (and 1,000 months or 80+ years at more typical 50 deg C max).

A historically useful generalization supported by Arrhenius' equation is that, for many common chemical reactions at room temperature, the reaction rate doubles for every 10 degree Celsius increase in temperature.

As that article says, this is not an Absolute Rule. But it is true more often than not.

[Arcane Analog]

As opposed to storing the spent portions still in the etchant I prefer to screen the "used" particles out.

I simply place a coffee filter in a funnel and pour the used etchant into the filter which screens the spent portions. You can use the "same" etchant a number of times.