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NatriumHydroxide as developer ~ NaOH to water ratio?

Discussion in 'General Electronics Chat' started by johankj, Feb 9, 2007.

  1. johankj

    johankj New Member

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    Hi all.

    I'm thinking of using NaOH as a developer for my presensitized PCBs. The PCBs are coated with type FR-4 positive resist. (Don't know what FR-4 means)

    What I've got is pure crystallized NaOH, but to which ratio do I dissolve it to?

    From the wholesales website (ELFA), the developer they sell (Expensive!) is said to contain NaOH, but doesn't mention if it contains anything else. Their water to developer ratio is 20g to 2ltr water. That's 1:100 grams NaOH to mil-liters water.

    Any suggestions, or experience with NaOH? What would be a good water temperature? And the water to developer ratio?

    I think I've seen acetone being mentioned as a developer too. Has anyone done this? I've also read about people putting all sorts of fancy chemicals into the developer, are they really necessary and what do they do?

    Sorry for always posting such long-winded questions :p The NaOH:H2O ratio is what I really want to know, the rest i curiosity. :D
     
  2. justDIY

    justDIY Active Member

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    NaOH, otherwise known as Sodium Hydroxide or Caustic Soda. I'd start with a small amount in water and see what happens. Add more crystals to water if it needs to be stronger. I don't think it takes much - the crytsalized packets of naoh that I use as developer are pretty small compared to the liter of water I put them into.

    The manuf. states the water temperature should be room temp, so what, 20-22C?

    When you're experimenting, remember to add crystals to water, not water to crystals.
     
  3. Sceadwian

    Sceadwian Banned

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    The reason being caustic soda reacts with water creating heat. One of the guys that works at the metal finishing shop I do routinly added causitc soda to a cleaning bath while it was cold, till one day he wasn't paying attention and did it while the tank was still hot. The extra heat generated was enough to cause the entire 100 gallon tank to start boiling.
     
  4. dave

    Dave New Member

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  5. johankj

    johankj New Member

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    You see, that's what had me confused for a while. I though Sodium Hydroxide was something else, since the chemical formulae is NaOH. Here in Norway, Na is pronounced Natrium, and not Sodium ?? A little short-circuit in my brain, that's all :D
     
  6. johankj

    johankj New Member

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    Yeah, I don't know how much experimenting I get to do, as I'm also using a brand new UV-exposure unit. Too many variables for that.

    I'm thinking of doing this:

    • I'll make three baths of NaOH, of a 10 gr to 1 ltr, 11 gr, and 12 gr, solutions.
    • Or maybe I'll make up a 10 gr to 1 ltr solution, and then a 20 to 1 ltr solution which I can dilute the developer with should it be too weak.
    • I'll probably just be lazy and do just a 5 gr to a half liter water.

    Do you reckon the ratio's ok?
     
  7. justDIY

    justDIY Active Member

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    having a weak solution will work, the developing time will just be lengthened. Having too strong a solution however will strip all the resist, not just the exposed parts. so start with 5 or 10 grams and put in your pcb. agitate it continuously (I use a foam paint brush). If you don't see anything in 2-3 min, add another 5g of crystals. When my developer is "fresh", it starts working the instant I drop in the pcb ... it looks like the resist starts "smoking" in the water.
     
  8. johankj

    johankj New Member

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    I used a NaOH bath, and it worked beautifully.

    I mixed 5 grams NaOH crystals in 1/2 liter water.

    It dipped the PCB into the solution, and it started smoking immediately. I panicked :eek: and yanked it out of there, rinsing it furiously under running water. I'll use a weaker solution next time.

    I could see the schematics now, where there before was non (My PCBs have no visible/transparent resist). :) Oooooh, very exiting.

    I went ahead with the etching, and after a looooong time, the copper started to fade. :D

    Overall I'm very pleased with the results. The image I've attached is a test-strip i did (30mm x 100mm), with varying UV exposure times (1 min. intervalls). Maybe I should post my UV-box experiment, now that I know it works so well...
     
  9. johankj

    johankj New Member

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    Wops, forgot the images....


    skann2.jpg
    This is after I cleaned it up with acetone...

    skann0001.jpg
    ...And after the drilling. I think i used a 0.8mm drill bit. Need to get a smaller one I think...

    BTW, the UV-exposure unit uses LEDs, and not fluorescent tubes...
     

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