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How to make PCB etch solution using anhydrous ferric chloride powder

Discussion in 'General Electronics Chat' started by pkshima, Jan 28, 2008.

  1. pkshima

    pkshima Member

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    I thought this would be very easy to find on the internet but got disappointed.

    I have already bought 500g 'anhydrous ferric chloride powder'. Do i just add it to water or what ?

    secondly, when I am done with the solution, how should I dispose it off ?

    Thanks in advance
     
  2. blueroomelectronics

    blueroomelectronics Well-Known Member

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    http://homepage.eircom.net/~ei9gq/pcb.html
     
  3. pkshima

    pkshima Member

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    Thanks for replying Bill.

    I had seen that page but it doesnt have the instructions I need. I already have anhydrous ferric chloride powder. I want to know how make a solution out of it. I think I just need to add it to water but no idea in how much water.

    also how do i dispose the solution later.
     
  4. dave

    Dave New Member

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  5. blueroomelectronics

    blueroomelectronics Well-Known Member

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    Hmm I'll use bigger letters.
    NEVER add water to dry Ferric Chloride
     
  6. pkshima

    pkshima Member

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    Read again Bill, I said .... "Add it to water" not "Add water to it". Or do you mean not to do mix water to it in any way ?
     
  7. blueroomelectronics

    blueroomelectronics Well-Known Member

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    It's supposed to have instructions printed on it. If not contact whoever you bought it from for the instructions. Your right you add it to water, I never use the stuff as it's just a mess. Contact your cities hazardous materials department and ask them what to do with the waste.
     
    Last edited: Jan 28, 2008
  8. picbits

    picbits Well-Known Member

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    And when you are disposing of it don't try mixing it with normal plaster (the stuff you put up on walls).

    I thought I'd try and solidify a couple of litres of it using single coat plaster.

    Having evacuated the rabbit from his hutch watching the large mass of foam heading towards his hutch, I proceeded to find every bucket and pot available to try and stem the flow from the bucket I'd mixed them together in.

    It took me 2 days to clean up after that episode :p
     
  9. mvs sarma

    mvs sarma Well-Known Member

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    You try to mix only that much as you need . don't ever make solution of entire 500gr into solution..

    to my experience, you hardly need one to two teaspoons(NEVER STEEL ONES-- ONLY USE PLASTIC)of ferric chloride for 250mlod water,is sufficient to etch two boards of 4*3 " size. you can always use plastic jugs if the dept is sufficient or gp for shallow plastic trays.

    when you are done with it-- you need not be in hurry to dispose, unless you don't have any more boards in the near future. As such it can be transferred into a plastic container and closed off with an additional plastic sheet between the cap and the bottle.
    Also the entire thing can be sealed in a plastic cover and stored --especially AWAY FROM CHILDREN AND SERVANT MAIDS- AS THEY WOULD NOT KNOW THE CONTENT AND ITS SERIOUSNESS.
     
  10. Pommie

    Pommie Well-Known Member Most Helpful Member

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    You can dispose of used ferric chloride by mixing it with sodium carbonate (or bicarbonate) and you will get a sludge of copper carbonate powder and a solution of sodium chloride (salt). You can pour the solution down the drain and throw the sludge in the garbage.

    Personally, since finding Ammonium Persulphate I would never use Ferric Chloride again. AP is so much cleaner.

    Mike.
    Edit just found this.
     
    Last edited: Jan 29, 2008
  11. picbits

    picbits Well-Known Member

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    I've got a sack of Sodium Persulphate which I'll start using one my FeCl has got too weak to be of any use.
     
  12. Gayan Soyza

    Gayan Soyza Active Member

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    Hi pkshima how did you transfer your drawing to the PCB.What method did you use?
     
  13. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    Note that the commercial etchants such as the link by Pommie and this one (http://www.jtbaker.com/msds/englishhtml/f1080.htm) have ferric chloride at a concentration of about 40% by weight. That means, 40 g of ferric chloride (anhydrous) in 100 g of solution. That is considerably more concentrated than a couple of teaspoons (assuming a density of 4, that would be about 40 g) in 250 mL or about 14% w/w. I am sure the more dilute solution will work. I am just pointing out that it is considerably less concentrated than commercial etchant and may work more slowly.

    As it turns out, the commercial etchant is just a little more dilute than a saturated solution. If you buy ferric chloride as the hydrate (hexa), it will probably come in big chunks or very coarse amorphous granules. You can just add the calculated amount of water (an amount of water equal to 0.5 times the weight of ferric chloride hexahydrate will give 40% w/w) and let it sit for a few days. Gentle warming helps. Concentrated solutions are stable for a very long time.

    For use, one can use the solution as is or add a little water, if you want something a little less viscous. Some sources suggest adding a little table salt (NaCl) too, which is supposed to increase the etching speed.

    The difference in this procedure is starting with the hydrated salt instead of the anhydrous salt. The hydrate is usually less expensive, but most important, it does not produce the heat that the anhydrous salt does upon addition of water.

    In many areas, disposal of small amounts of etchant down the drain is allowed. The hazard is not so much from the ferric chloride, but from the dissolved copper (mostly cupric).
    Adding carbonate (as suggested) alkalinizes the solution and causes both iron and copper salts to precipitate. Sodium hydroxide (lye) could also be used as the hydroxides of both metals are insoluble. John
     
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  14. pkshima

    pkshima Member

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    Thanks a lot for all the info everyone !
    Gayan, I havent transfered the image to the board yet but I think I will just print it out on a glossy paper (art paper) and iron it onto the board.
     
  15. mvs sarma

    mvs sarma Well-Known Member

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    I feel, yes slowly it will work, but at least it won't over-etch into the carbon coated areas, and perhaps it could be fastened by slightly increasing the temperature of the solution.
     
  16. Boncuk

    Boncuk New Member

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    Pommie, it is much cleaner at the first glance. You forgot to mention that you only have satisfying results if you heat it to 55deg/C. Getting to 56deg/C you have a big problem if you leave your etchant cuvette filled with the stuff. It crystalizes while cooling and gets harder than concrete. You can soften it again using natrium persulfate, but this causes tremendeous heat in the cuvette and you have to watch the temperature closely so the cuvette won't burst.

    Even using the prescribed max. temperature the temperature distribution is not equal all over the cuvette. Using an aquarium heater the problem arises already right there.

    As for the disposal, I filled the used up solution in a big plastic bucket and put it aside to have the water evaporate in the air. When it was dry I used take it to the hazardous goods garbage disposal. (Charge is on weight!)

    The only advantage I see is the fact that Ammonium Persulfate is rather clear, you can observe the process of etching and apply corrections if etching is not equal on the board.

    Anyway, I returned to the "brown water". Results are fairly good at room temperature (Thailand: 35deg/C +). Since there is no such thing as a hazardous garbage authority nobody cares where you dispose it off. I prefer "Khlongs" (flood control system for the rainy season). There are thousands of them all over the country and may be the poison reduces the birth rate of mosquitos. :)

    Hans
     
  17. whiz115

    whiz115 Member

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    it is supposed to be perfect for plants... :rolleyes:
     
  18. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    Possibly, you may perceive more selectivity of the dilute etchant for the unmasked areas. In reality, that probably is not the case. It is just that over etching occurs more rapidly with a faster solution. Subjectively, my best etchings have been done with a relatively rapid etch rather than a slow one.

    If one were to use a mask that was slightly soluble in the etchant, say those who use ink jet printers and bake the image before etching, the length of time exposed to the aqueous etchant, not the concentration of ferric chloride or persulfate, may be more important for controlling selectivity. John
     
  19. Pommie

    Pommie Well-Known Member Most Helpful Member

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    I just put a couple of teaspoons of Ammonium Persulphate in a Chinese takeaway container and add some boiling water from the kettle. Float the board on top and 5 minutes later its etched. As for disposal, I just throw it in the pool. The copper is a good algaecide and 200mL in 85,000L isn't going to matter anyway.

    Mike.
     
  20. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    Have you ever tried the HCl or H2SO4 plus hydrogen peroxide etchants? When my current stock of ferric chloride is gone, I was thinking of going in that direction, as the starting materials are still readily available in the US. John
     
  21. Pommie

    Pommie Well-Known Member Most Helpful Member

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    I haven't because I do so few boards these days, maybe 1 or 2 per year. It would however be useful to know how it works as I have HCL and H2O2 in the garage most of the time. That makes me wonder how a mixture of NaHSO4 and Na2S2O8 would work as I have both of them as dry powders.

    Mike.
     

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