PCB developer

Discussion in 'General Electronics Chat' started by lesio, Dec 3, 2008.

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  1. lesio

    Thread Starter New Member

    Dec 3, 2008
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    Hi

    Does anybody knows where in Canada to buy silicate based pcb developer
    I have hard time to find any source for that

    Thanks

    lesio
     
  2. nomurphy

    AAC Fanatic!

    Aug 8, 2005
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    The obvious one -- how about over the internet?
     
  3. lesio

    Thread Starter New Member

    Dec 3, 2008
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    This is not obvious at all.
    I am not going to order from GB and only they have something
    I am looking in Canada and if do not have any clue about this market do not reply stupid answers

    Lesio
     
  4. jpanhalt

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    Is the formula for your silicate-based developer proprietary?

    If not, what is the formula, maybe we can help you find and/or make it.

    John
     
  5. jpanhalt

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    Sodium silicate (water glass) is very commonly available in the US, so I did check ebay, and most of the sellers there seem willing to ship to Canada for a very small premium. None were GB. Presumably, you can still by NaOH (lye) or KOH in Canada. I prefer KOH.

    John
     
  6. lesio

    Thread Starter New Member

    Dec 3, 2008
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    I can get 25 Kg. bag of Sodium Metasilicate Pentahydrate very cheap.
    Do I need anything else as a developer or just to add a water and go.
    I am not good at chemistry at all
     
  7. SgtWookie

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    Jul 17, 2007
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    Chemical Name or Synonym: DISODIUM TRIOXOSILICATE, PENTAHYDRATE ; CRYSTAMET
    Molecular Formula: Na2SiO3.nH2O n=5
    aka SODIUM METASILICATE

    http://www.technick.net/public/code/cp_dpage.php?aiocp_dp=guide_pcb#2.1.2.5.2
    The following came from under "Developer" about 3/4 of the way down the page:
     
  8. lesio

    Thread Starter New Member

    Dec 3, 2008
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    Thank you
    But this is not liquid. It is 25kg of sort of crystals
    I assume I have to add water and it should be ready, shouldn't it?
     
  9. SgtWookie

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    All I know is what I read on that page.

    I suggest that you carefully measure and mix up a small batch. Then test to see how strong it is using the info in the paragraphs I posted. Once you find the right crystal-to-water ratio, write it down somewhere.
     
  10. jpanhalt

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    Jan 18, 2008
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    How much sodium silicate pentahydrate should be used?

    That is not a question that can be answered easily and referenced based on a short search of the web.

    JTBaker Chemical Company sells a product described as 40% sodium metasilicate in water. JTBaker does not say whether that is wt/wt percent or wt/vol percent. Other data in the MSDS inclines me to think it means wt/wt %. PQ Corporation gives much more detail (http://www.pqcorp.com/productlines/sodiumsilicatespecs.asp) and offers several formulations based on different empiric ratios of SiO2 to NaO.

    For the sake of etching, I am assuming that 40% wt/wt will work fine. The main purpose of the silicate is to provide a buffer with a high pH, and because of the buffering capacity, the final pH will not be nearly as sensitive to concentration as a developer made with simply NaOH or KOH would be.

    A 40% wt/wt solution should contain 40 g of sodium silicate and 60 g of water per 100 g of solution. Sodium metasilicate pentahydrate (Na2SiO3 . 5H20) has a formula weight of 212/g per mole, which means it is only 57.5% sodium silicate by weight. In other words, 40 g of sodium silicate requires 69.6 g of the pentahydrate. A 40% solution of sodium silicate would therefore be made by mixing 69.6 g of the pentahydrate with 30.4 g of water and waiting for the solid to completely dissolve. That might take a very long time, which is why commercially available sodium silicate is so often sold as the solution.

    Once you have the 40% solution, I found this one recipe for how much to use (http://www.electricstuff.co.uk/pcbs.html#Sources) :


    Comment:

    The pH of the solution just described should be about 13.5. In my experience various brands of positive-sensitized PCB require different strengths of developer. Some developers are simply sodium carbonate, which can be considered like sodium silicate in which the silicon atom has been replaced by carbon. The pH of carbonate developers is probably lower (i.e., less aggressive) than the silicate based ones. I was unable to develop Injectorall boards using sodium carbonate solution alone. However, I have used a 0.5 M solution of KOH for many years without problems. To a very rough approximation, a 0.5 M KOH solution should have a pH of about 13.5 as well, or a bit less. Note: The Moorshead recipe has approximately 10 moles of NaOH per liter which is then diluted 1:5 to 1:9. Therefore the final concentration of NaOH is about 1 to 2 molar. Because of the buffering capacity of the silicate, however, the solution should not be as aggressive as a neat solution of sodium hydroxide in water at the same concentration.

    If I were to experiment with the Moorshead recipe, I would probably stick to a 1:9 dilution of the stock concentrate, or maybe even a 1:10 dilution. I would also start with about half as much NaOH (i.e., 200 g/L) to see how it works.

    To the OP: If you do any experiments, I would be anxious to hear of your results. Please include the brand of sensitized board you are using.

    John
     
  11. lesio

    Thread Starter New Member

    Dec 3, 2008
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    Thank you for detailed info, but I am confused
    I have:

    Description:
    Product name: Sodium Metasilicate pentahydrate;Formula: Na2SiO3.5H2O;Molecular Weight: 212.14
    Product name: Sodium Metasilicate pentahydrate
    Synonyms: DISODIUM TRIOXOSILICATE, PENTAHYDRATE ; CRYSTAMET
    Formula: Na2SiO3.5H2O
    Molecular Weight: 212.14
    Properties: Sodium metasilicate pentahydrate is a kind of white granules, non- toxic, tasteless and environment-safe. It is very soluble in water, insoluble in alcohol or acids. Aqueous solution of sodium metasilicate pentahydrate reacts alkaline. It has the capabilities of removing scale, emulsifying, dispersing, wetting, penetrating, and also has the capability of buffering PH value.
    EINECS No.: 2299129


    Why do I need NAOH?

    Outside Canada/USA they sell developer in crystals DP50 (50g bag) and I think it is sodium Metasilicate pentahydrate

    Am I wrong and completely confused?


    Les
     
  12. jpanhalt

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    Jan 18, 2008
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    1) 212 should be viewed as a formula weight for the hydrate, not molecular weight for Na2SiO3. The reference I cited (PQ) goes into that aspect.

    2) The article by Moorshead did not reference why NaOH was needed. I suspect it was needed to get the pH high enough to remove resist. The silicate still acts as a buffer, but the more NaOH that is added, the less the buffering capacity is. It seemed like a lot in the original version, which is why I suggested reducing it.

    3) "Solubility in water" refers to the amount that can dissolve, not the rate of dissolution. It is quite common to have compounds that are extremely soluble, yet very slow to dissolve. Sugar is another example. I have no first hand experience dissolving sodium silicate, but various sources refer to it a dissolving slowly.
    Now that you have the crystals, try dissolving 70 g in 30 mL of water and report back after it dissolves or next week, whichever occurs first.

    John

    Edit: By the way, the different hydrates probably dissolve at different rates. So, it really would be interestig to hear how rapidly the pentahydrate dissolves.
     
    Last edited: Dec 10, 2008
  13. lesio

    Thread Starter New Member

    Dec 3, 2008
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    John
    Can you please translate it:
    92.655% by weight water 5.130% by weight Na 2 SiO 3 .5H 2 O 1.250% by weight NaHPO 4 .2H 2 O 0.850% by weight Na 3 PO 4 .12 H 2 O 0.110% by weight NaOH 0.005% by weight (50 ppm) of an ethoxylated nonylphenol having a mean degree of ethoxylation of 9

    to simply english and tell how does it relate to crystals I have

    Many thanks

    Les
     
  14. jpanhalt

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    If the crystals you have were sold to you as pure sodium metasilicate pentahydrate, the formulation you give is not that.

    Roughly translated, that formulation is 5% by weight (5 g per 100 g of solution) of sodium metasilicate pentahydrate, 1% disodium hydrogen phosphate (the empirical formula should be Na2HPO4, not NaHPO4 as written), and 1% trisodium phosphate. Both of the phosphate salts are as hydrates. Trisodium phosphate (TSP) is a stong base somewhat like sodium metasilicate. It looks like a little sodium hydroxide was added to adjust (raise) the pH.

    The formulation suggests that the powders (as hydrates) were dissolved in the amounts shown to give the final solution. It would be unusual and incorrect to suggest that those salts retain stoichiometric hydration in solution.

    The ethoxylated nonylphenol is a wetting agent.

    Your solution is mostly water according to the formula, and I suspect it is ready to use for something, such as removing resist, cleaning, or any of the hundreds of other uses for solutions of sodium metasilicate. Like TSP, sodium metasilicate makes a great cleaning compound that is not limited by concerns over phosphate pollution.

    The fact that it is 5%, rather than 50% suggests to me a higher stock solution that has been diluted.

    How it relates: You have one of the components of that mixture.
    John
     
    Last edited: Dec 10, 2008
  15. lesio

    Thread Starter New Member

    Dec 3, 2008
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    Hi
    I have done some experiments

    1. dissolved 70g os sodium silicate in 30g of water in few minutes with help of warm water.

    After that I prepared 1:9 dilution and tried to use as a developer.
    And nothing

    I will try different ratio

    Any comments?

    Lesio
     
  16. jpanhalt

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    I don't think the main problem is the ratio of sodium silicate to water. Buffers do show concentration dependence, but such changes are proably not enough to affect its action in this case.

    You need to run a "control" of sorts. I have been using 0.5 M KOH for years; 0.5 M NaOH should work the same. To make 0.5 M KOH, dissolve 8.4 g of KOH in 300 mL of water. To make 0.5 M NaOH, dissolve 6.0 g in 300 mL water. It doesn't matter which one you make. Each should work well enough as a control. Alternatively, do you have any developer from the manufacturer you can use as the control? Test your exposed board with the control developer. If nothing happens, there is probably a problem in your exposure time or intensity.

    If the control works, but the silicate solution doesn't, then that explains why the Moorshead formula included NaOH. However, note that Moorshead adds 400 g of NaOH to a liter of silicate solution, which makes it roughly 10 Molar in NaOH before dilution, and somewhat over 1.0 M after a 1:9 dilution. That is why I suggested cutting the amount of NaOH in half for a starter, which would get you closer to the 0.5 M solution I am accustomed to using.

    John
     
  17. lesio

    Thread Starter New Member

    Dec 3, 2008
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    Positive developer from MG Chemicals works with the board I did.
    BTW I have used pcb from MG Chemicals as well.
    Their developer is just solution of NAOH and it is easy to over develop if a board is too long in the soulution.
    I used 1:10 ratio for developing.
    I wonder if I can use their soultion and mix with mine (silicate based)
    Should I still use 200 ml of MG and 1000g of mine?

    Please advise

    Lesio
     
  18. jpanhalt

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    From the information you have on the MG developer, it is a little hard to know what ratio you should mix with the silicate solution.

    But, here's a shot. You say you use the MG at a 1:9 dilution. If 0.5 M is the target concentration for just NaOH, the stock solution should be about 4.5 molar (i.e., 180 g of NaOH per liter). That is about half what Moorshead recommends as solid NaOH per liter of silicate mixture and is my guess for a starting point.

    Here is what I would try: Mix equal portions of your silicate and MG developer. Then dilute 1:5 or to be precise, 1:4.5.

    The math: Equal proportions of each gives a single solution that is 1/2 strength in each component. A 1:5 (or 1:4.5) dilution of that gives a final solution that is the same as a 1:10 or 1:9 dilution of your original silicate solution and is approximately 0.5 or 0.45 M NaOH, based on the above assumption for what MG's developer is.

    If that works, then you can begin your quest for NaOH or KOH and roll your own. If it doesn't work, try a 1:2.5 dilution to try and get a handle on the necessary NaOH concentration. If that works, then just follow Moorshead's recipe.

    Please keep us updated.

    John
     
  19. lesio

    Thread Starter New Member

    Dec 3, 2008
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    Than you
    I will experiment more and let you know

    FYI this is solution from MG Chemicals:
    Chemical Name
    Percentage by weight

    De-ionized water
    90 - 96

    sodium hydroxide
    4 - 10

    Like I mention for developer I need to dilute 1:10
    Developing time is about 2 minutes

    Lesio
     
  20. jpanhalt

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    10% by weight NaOH is 2.5 M. 4% by weight is only 1 M. The silicate probably slows the action of the NaOH a little, so the guestimate above at a 1:5 dilution might be pretty close. It's going to take some experimentation. You could take the solution made with equal parts of silicate stock and MG developer and make a 1:2.5 dilution, dilute that 1:2 to get a 1:5 dilution; dilute again 1:2 to get a 1:10 dilution and see what happens. Start with the highest dilution first and dip successively in the more concentrated solutions. BTW, a 1:2 dilution means 1 part is mixed to a total volume of 2, not 1 part is mixed with 2 parts of diluent.

    John
     
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