On Sun, 28 Oct 2012 05:38:53 -0000, you wrote:
>Thanks.
>
>When you say 'bubble air through it' you mean like w/ a fish tank air pump w/ those 1 way valves?
Yes, exactly that. You want a plastic air stone, not a porous stone,
because the acid attacks that stone. Not sure about this plastic, but
there are kinds of plastic (nylon, for instance) that are not as acid
resistant as you'd like. Avoid stainless steel, too.
>Do I know how much air I need based off the color and if so, what color am I looking for? In the past I had some weak acid and it turned teal blue but this stuff is staying bright lime green.
A decent air pump should be fine. More air is better than not. It
does several things, one is oxygenate the etchant, the other is keep
it moving so fresh etchant hits the boards.
The bright lime green sounds a bit odd, because most of my stuff is
blue/green, not lime. The ratio I used was 4x peroxide (the 30 vol or
3% stuff) to 1x muriatic acid (38%, IIRC). The opaque olive green is
when it needs more HCL, I think. Adding peroxide to the dark green
stuff turned it blue, as I remember.
>
>Also, yes, I did heat it up. I was using a small 'tupperware' dish in a larger one that was filled w/ water ~120-140F.
120 is fine, but perhaps a little warm. 140 is too hot. I'd go 100
to 120, warm to the touch, but not burning.
I also use a fish tank heater, sealed. You have to get ones that you
can misadjust to over temperature, they have dials on top that you can
keep on turning.
>
>When you say a bit slower, I assume you mean than the first batch and not my slow 45min marathon etch?
I get about 20 minute etches at the end of a batch, where the etchant
is oxygenated a lot, and the etchant is hot. The first batch can take
almost that 45 minutes, so if that is too long for people, then I need
to tweak the process a little. I'm looking at building a new etchant
tank anyway, but the distribution of the bubbles is fairly important,
and makes a substantial difference in the etching speed.
Harvey
>
>Bob
>
>--- In Homebrew_PCBs@yahoogroups.com, Harvey White <madyn@...> wrote:
>>
>> On Sun, 28 Oct 2012 05:21:57 -0000, you wrote:
>>
>> >I have been using H2O2 from the pharmacy / Muriatic Acid combo, 2:1 - works well and is easy to get, but it doesn't work after the initial use. It seems every etch, I need to make a new batch. The etchant turns into a bright lime green color on the first etch and it does what I need to pretty quick and it seems like there is decent activity - bubbles which only happens on the first time use, after that maybe bubbles when I first put in the pcb/Cu but they go away very quickly.
>> >
>> >After use, I will put the solution in a clear, sealed glass container and even if I use it the next day, after I start, 45min later my etch is still not done, so I dispose of it and make a new batch at which time I am done in 15mins.
>> >
>> >What am I doing wrong or where is the mixture out of balance? Again, I just did an etch this evening and had to make a new batch, which is now a bright lime green color.
>>
>> The etchant uses the oxygen from the peroxide to enable the etching.
>> To continue to etch with that solution, you need to bubble air through
>> it. It will also help to heat the solution to 100 degrees F or so.
>>
>> The solution will gradually turn a darker green. If it turns olive
>> (IIRC), then the chemistry is out of balance. The peroxide provides
>> oxygen only for the first day or so, at which point the etchant turns
>> into a CuCl etchant, which works very well, is a trifle slower, but
>> never wears out. I think that there's a good review of this chemistry
>> in the group archives, which explanation is better than mine.
>>
>> You'll find that if you add some relatively concentrated peroxide to
>> the etchant, it will start to work the way you expect, but the word is
>> concentrated. Not really needed.
>>
>> Some people take the peroxide etchant mix and deliberately add copper
>> to it, producing the CuCl etchant to start with.
>>
>> You will eventually have to add either Muriatic acid to the mix to
>> replace the chloride ion, again, IIRC.
>>
>> Harvey
>>
>> >
>> >Thanks in advance,
>> >Bob
>>
>