When will damaged my Ferik Chloride?

[Willen]

-When will be damaged my Ferik Chloride? I bought an half kg of Ferik which was like black sand but now it is starting to melt down like oil. I think i should have to pack it to safe from air. When will this be damaged? - Few gram, I made liquid ferik mixing with water and used for few pcb. Now it's not clear liquid like before. When will this liquid be damaged?

 

[jpanhalt]

The "black sand" was probably anhydrous ferric chloride. Ferric chloride has another crystalline form that contains 6 molecules of water per molecule of ferric chloride. It is called the hexahydrate and is yellowish tan in color. Both versions can absorb water from the atmosphere. What you have is probably a mixture of anhydrous ferric chloride with various amounts of hydrates.

The good news is that ferric chloride is quite stable, so the material you have will work fine for etching PCB's. You do not need to protect it from air. The downside is that you don't know the exact formula weight of what you have. The solution to that is to make a saturated solution. That is, add water and let it mix for a long time until no more dissolves. That saturated solution is about 42% (as I recall) and can be used for etching as is, or you may want to dilute it a little to get faster etching.

Once you have your etching solution, just keep it in a closed container, and it will last essentially forever.

John

 

[picbits]

My ferric chloride is around 6 years old, has etched many many PCBs and is still going.

I had a rush job on a couple of weeks ago and needed to etch 40 eurocard PCBs so I "broke out" another fresh 5 litres into my spare tank - it's only when you use the fresh stuff that you realise how old and contaminated 6 year old stuff can become ....

I have a 25kg sack of sodium persulphate to mess about with as well when I get the time.

 

[jpanhalt]

When I said ferric chloride would last "forever," I meant if unused. I believe that was the context of Willen's question, as he seemed worried about the stability of the ferric chloride crystals he had purchased.

When ferric chloride is used to etch PCB's, it does become exhausted as the oxidized copper and ferrous salts deplete the active agent and may precipitate as mud.

The etching solution can be replenished by adding HCl and bubbling air through it to reoxidize the iron salts to ferric (III) chloride and copper salts to cupric (II) chloride. Cupric chloride itself is a good etchant, so the bath remains active. Reoxidation by air works fine, if you are not in a hurry; ozone or chlorine gas can also be used for quicker results. I would not recommend using sodium hypochlorite (ordinary chlorine bleach, NaOCl), as that adds sodium to the mixture, and you risk releasing chlorine gas as it is added to the acidic solution. Sodium hypochlorite has been used, however, to reoxidize the etching bath. Just be sure the acidity is kept high by addition of HCl.

There are many descriptions of both types of etching baths and how to use them. There are ways described in the various methods to determine how much HCl needs to be added.

John

 

[picbits]

My Ferric Chloride actually came with a use by date of just under a year from when I purchased it (ready mixed - not crystalline). I very much doubt it's going to expire anytime in the next 5+ years.

Don't ever try and mix it in large quantity with gypsum plaster to solidify it for disposal though or you'll get what I had - a foam ferric chloride monster making it's way across the garden !

 

[kubeek]

LOL, imagine doing that inside
As for the use by date, I guess that is just the manufacturer making sure you don´t come with complaints.

 

[crutschow]

LOL, imagine doing that inside
As for the use by date, I guess that is just the manufacturer making sure you don´t come with complaints.

Or increasing sales by implying that you need to buy more ferric chloride.

 

[panic mode]

under a year...?

I used same bottle of ferric chloride for several years. Etching was eventually getting slower and slower of course but it was still getting job done. To speed up etching, I would warm it up a bit, leave board float (one side submerged only or for occasional rush job, i would even steer it a bit. The thing I like about it is that it is stable and easy to use. Seeing submerged board is not easy but it takes no effort to pull it out, take a look and throw it back into the etchant. The ugly thing was if there was a spill (yes, I was a bit clumsy at first and didn't take long to implement certain rules). This would ruing clothing and stain skin. Fortunately there is no burn or rash but skin did turn black and the stains remained visible for about a week. If you ever tried peeling fresh walnuts or playing with permanent marker, you will know the feeling. It didn't take long to realize that using gloves and being near water tap was a good idea. Being able to quickly rinse anything that was in contact with it dramatically reduced or eliminated the problem. I don't think i lost single drop in a very very long time.

 

[Willen]

Mistake removed.

 

[Willen]

After etching few PCBs, I kept the ferric liquid into the bottle. I can see 2 layer of liquid, there are clean liquid at the top side and thick copper lotion at the button. Can I get back my clean and fine ferric like before by just simply removing this lotion of copper?

 

[jpanhalt]

The clear layer at top will continue to work for etching. The bottom layer, I suspect, is the same solution as the top layer, but contains suspended particles ("mud"). The mud is a mixture of iron and copper oxides and chlorides. If you take a little bit of the mud, add some HCl and bubble air through it, it will probably redissolve and give you a greenish-brown solution containing copper(II)chloride (cupric chloride) and ferric chloride.

In other words, if you start with a ferric chloride etching solution and use it only to etch copper, it will last forever, if you replenish the chloride using HCl and keep it oxidized. Eventually, it will become mostly cupric chloride, which is a deep emerald green color. Cupric chloride is a good etchant in its own right. The amount of acid you need to add can be determined by titration -- something like 1 molar free acid should work -- or just by experience. Too much acid will cause more undercutting during etching. If it etches too slowly, adding more acid will speed it up.

If you have 100 mL of solution + mud, I would add 10 to 20 mL of concentrated HCl, then bubble air through it overnight and see what happens.*

The solution becomes more viscous with the mud. Your choice is between adding HCl and reoxidizing the bath versus just filtering off the mud. A little mud doesn't hurt the etching, but if the solution is too viscous, it will slow down the process, make getting fine lines more difficult, and make observation more difficult.

John

*Concentrated HCl, 38%, is about 12 molar. 10 mL diluted to 110 mL total volume = 1.1 molar in the final solution.