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Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
I want to get pure sodium hydroxide for developing my pcb. Is food-grade pure? Any suggestions where I can get some cheaply? I've seen it on Amazon. In the past I've seen it in some stores.
I'm talking about developing and stripping, not etching.
You where asking about sodium hydroxide(HaOH) , it's usually sold as drain cleaner, while small blobs, but, for negative etch masks it's bad, it's used for stripping not developing.
Sodium carbonate (No2CO3) is used for developing, and it can be made from backign soda( sodium bicarbonate, NaHCO3).
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062
Hi, you really are better off with silicate as it is much more forgiving and has a multi year shelf life. Sodium carbonate can be made from bicarbonate by heating, also you can kludge together a basic silicate using water glass (Na2SiO3) and sodium carbonate.
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062
Leave that with me, I am out at the moment but will try and check to get exact amounts. It needs a lot of experimentation as despite silicates being kinder than NaOH it can still overdevelop if you get it wrong enough.
EDIT. from "Mikeselectricstuff.com"
"Thanks to Robin Moorshead for the following procedure to make silicate developer solution: Take 200cc of "water glass", add 800cc of distilled water and stir. To this add 400g of sodium hydroxide (caustic soda). Important safety precautions: The sodium hydroxide solid must NEVER be handled, use disposable gloves. When the sodium hydroxide dissolves in water it produces a great deal of heat so it must be added a little at a time and each portion allowed to dissolve before more is added. If the solution becomes very hot leave it to cool before adding more sodium hydroxide. The solution is VERY caustic and it is particularly damaging to the eyes, use eye protection when making and handling it. It also ruins clothing. Water glass is also known as "sodium silicate solution" and "egg preserver", It used in fire proofing fabrics, for waterproofing walls and making "chemical gardens". Caustic soda is used for clearing drains and available from any chemist. The solution cannot be made by dissolving solid sodium silicate. This solution will be the same strength as the concentrate, and so will need diluting - about 1 part concentrate to 4 to 8 parts water, depending on the photoresist used and temperature.!"
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Buying NaOH
