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Old 8th March 2007, 07:54 PM   #1
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Question Help: ferrous chloride/water ratio

I just purchased 1lb. of anhydrous ferrous chloride. I need someone to check my numbers so I don't end up botching the whole mixing process.

The etching solution ratshack sells is about 40% FeCL by weight and 1-3% HCI.

So 1lb. = 454 grams and 1 liter of water weighs 1kg. That would mean I need just a tad bit more than 1 liter of water correct?

That doesn't seem like a lot of solution to me. I didn't do the math before hand and was hoping 1lb would make a little bit more than 1 liter. For what I paid for the anhydrous powder I could have just bought 4 16oz. bottles of pre-mixed. Oh well, live and learn.
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Old 8th March 2007, 08:19 PM   #2
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454 / 0.4 = 1135 g water
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Old 8th March 2007, 08:54 PM   #3
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A good liter of ferrous chloride solution lasts a while. The trick is not to dump it, but fill it in a plastic bottle and store it safe and cool (and check it for pressure buildup from time to time).

Before you reuse it, wait until any copper mud from etched boards has settled on the ground of the bottle (usually takes a day or two). Then gently pour the solution back into your etching container without spilling the copper mud with it.

The solution will exhaust only after a considerable number of boards (and re-uses). The liquid can be neutralized with anything basic (i.e. caustic soda from photoresist laquer developing) and disposed off, just don't spill it around, it will stain your kitchen basin or drain forever.

The copper mud is hazardous waste and has to be handled and disposed appropriately.

Cheers.
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Old 8th March 2007, 09:53 PM   #4
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Thanks guys,

I just finished making the mix...... and a mess. I'm definitely buying pre-mixed next time. I threw about half a cup of "The Works" toilette bowl cleaner in the mix. It's the only way for me to get HCI without going out of my way. It contains 20% HCI by volume.

Time to see if this stuff will etch.
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Old 8th March 2007, 10:03 PM   #5
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Why have you added bleach? I never added anything when I bough the pellets.
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Old 8th March 2007, 11:52 PM   #6
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Not bleach.

HCI = hydrochloric acid
NaClO = Sodium hypochlorite (bleach)

The stuff from radioshack has HCI so I just copied their formula. I think it has something to do with the FeCL dissolving better and something about copper precipitates. I dunno. My mix turned out good though, I just etched a board in about 5 minutes.
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Old 9th March 2007, 12:33 AM   #7
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You do not need hydrochloric acid to etch boards. In this case, the ferrous chloride is sufficient.
The stuff you get from Radio Shack, as near as I can tell, is nearly spent solution from production shops. It has just enough umph remaining to do a couple of small boards.
Back when I used Radio Shack solution to etch boards, they did not list hydrochloric acid. If they're adding it now, it's likely because they're using even more depleted solution than in the past and they're trying to beef it up.
If you're mixing a straight, fresh solution of ferrous chloride, I think you'll find that it's vastly more powerful than the Radio Shack solution.
Throwing "The Works" into a solution just because it's on hand is asking for trouble. You might as well throw gunpowder in while you're at it. This is one of those "if you don't know what you're doing, don't do it" sorts of things. You could easily set up a reaction that would evolve chlorine gas.
Is your Will up to date?

Grey
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Old 9th March 2007, 01:43 AM   #8
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I appreaciate your concern Grey, but all is OK in Anonyville. No chlorine gas clouds here.

I found the article that explained the use of HCI when using anhydrous FeCL.

Quote:
You should always use the hexahydrate type of ferric chloride, which is light yellow, and comes as powder or granules, which should be dissolved in warm water until no more will dissolve. Adding a teaspoon of table salt helps to make the etchant clearer for easier inspection.
Anhydrous ferric chloride is sometimes encountered, which is a dark green-brown crystalline powder. Avoid this stuff if at all possible Use extreme caution, as it creates a lot of heat when dissolved - always add the powder very slowly to water, do not add water to the powder, and use gloves and safety glasses You may find that solution made from anhydrous FeCl doesn't etch at all, if so, you need to add a small amount of hydrochloric acid and leave it for a day or two.
Quote was taken from here http://www.electricstuff.co.uk/pcbs.html.
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Old 9th March 2007, 08:25 AM   #9
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Oh my,

I used to be like you. Really.

I also wanted do improve upon things I hadn't even started. Wanted to make everything perfectly optimal right from the start.

I'm okay, I'm over it when it comes to board etching!

No, really, there are so many things while printing, etching, drilling, stuffing, soldering and testing boards, which might go 'suboptimal' when you do it for the first couple of times, that you shouldn't worry too much about the very first step. Just use the ferric chloride you buy like the manufacturer advises. It will work. It might work better and more professional in other ways, but not really using ferric chloride, so why bother.

Cheers.
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Old 9th March 2007, 01:39 PM   #10
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I wasn't really trying to improve anything; I just wanted it to work. I purchased anhydrous FeCL instead of hexahydrate. I read in more than one place that the anhydrous form was not preferred, so I was a bit worried and just followed someone else's advice about adding the HCI. I guess I could have tested the mix before I added the HCI, but I didn't see a reason at the time to not add it.

Everything turned out OK, maybe with a bit of luck. I realize I probably should have thought a little more before I acted. Maybe next time.

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