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Registered Member #63
Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425
A problem that often annoys me with ammonium persulphate solution, is that if I'm going to boil water in a kettle and do an etch, I have to use an exact amount of ammonium persulphate (hopefully enough), and discard the rest. Often, the solution doesn't stay hot enough for a clean and fast etch, even if the board and utensils are preheated.
I'm about to purchase some glass cookware for use with ammonium persulphate, and hoping to get some insight from others first.
I'm considering the idea of gently heating the solution on a gas stove to keep it hot enough. Are the fumes something a typical stove-hood-extractor-thing would handle alright?
Is there any reason why I shouldn't store my solution in the glassware for extended periods of time? Will vapours be problem at a low temperature?
Registered Member #193
Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022
There are two problems with storing ammonium persulphate solution, both related to it's instability. First, because it's not stable it won't be much use the next time you come to etch something. Second, and more important, it gives off oxygen as a gas when it decomposes, this will cause a pressure build up and burst the bottle. Not something you want to happen. Ammonium persulphate shouldn't fume much in use, a cooker hood would work fine, I'm not sure it would even be needed. Rather than using a stove to heep it warm I would look at things like the heaters sold for aquaria, home brewing or plant propagation. You don't need to get the stuff all that hot. Also, while glassware designed for cooking shouldn't crack when heated like that, a flame is a bit unsubtle. Put the glass dish over a metal pan with water in it and heat that, the steam will heat the etch bath evenly.
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
I like the method of making it up in 100ml batches, and only using what you need. Think about it, I pay about $20/kg for the powder, so that is about $.50/etch...
As to keeping it hot, I just set it out in the sun The concrete outside is about 150F, just about right for a nice etch. Once it cools off I am planning to just dunk some resistance wire in the solution (I am going to use a rubber glove with the wire and some water in it to keep it from contaminating the etch) to keep it warm.
I am currently working on a board with an excessive amount of 8mil traces (with 8 mil spacing...), and the 150F etch with a toner resist worked pretty well. In fact had I managed to get the toner transfer to work better the board wouldn't have needed any rework
Registered Member #76
Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458
mh, another question comes up when i read how difficult it seems t be to etch with ammoniumpersulfate. Is it really that fast? what is the advantage?
Dont know. I buy my etch tools at a german company. the chemicals are inexpensive and i never had problems. why not use Iron³chloride or Sodiumpersulfate?
I use 500gramms of iron³chlorid with 1liter of water. with this i can etch around 50 100x160mm single sided pcbs until the bath is saturated. 500gramms cost me about 4$ (2,65€ or so) thats 0,08$ per pcb.. you must not even heat it up or so, and you can leave it open in a safe area so that kids and animals cant come close to it. you can leave it open for months. it wont evaporate or so. its a bit dirty but the best solution for a fast and inexpensive etch...
Registered Member #63
Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425
I use ammonium persulphate for a number of reasons:
A) you can see straight through it, B) you don't mind too much if you get a drop on your hands or your clothes, C) you can store it as a dry powder and make up as necessary,
and also the fact that I have the most experience with it.
Are there any Australians who have found a photopaper that works really well here for a toner transfer method?
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Optimizing an ammonium persulphate etch
The concrete outside is about 150F, just about right for a nice etch. Once it cools off I am planning to just dunk some resistance wire in the solution (I am going to use a rubber glove with the wire and some water in it to keep it from contaminating the etch) to keep it warm.
