Mail Archives: geda-user/2017/06/18/18:39:21
Not meaning to start an etchant war in the geda list, heating the
etchant, (perhaps by setting the etchant container in a plastic
container of 150 F hot tap water,) speeds up the etching. Every 10C
increase in etchant temperature reduces the etching time by half.
A 10cm X 7 cm, 50% interconnect can be etched in about 5 minutes
with HCL/H2O2 etchant.
10X10 mil lines are a good baseline, since QFP packages require them.
Its more complicated since how long a 10X10 mil, (in both directions
on the PCB-they produce different as-made lines in each direction,)
can be made is the issue. In the web page, I used two lines coiled up,
(20 feet each,) on a 10X7 cm PCB, with no shorts or opens allowed as
the certification. This required a 5X5 mil to be available over short
runs, (several inches,) as minimum for the lithography.
Note that it is different for positive and negative resist. In one,
the lines go away, the other, the interstitial space goes away, as the
limit of the lithography is reached. (On the web page, the 5 mil lines
came out 6 mils, mostly due to artwork artifacts produced by a US $100
laser printer, using inexpensive cellulose vellum as the media.)
What prompted the web page is that 3M is going out of the transparency
business, (an artifact of the digital revolution-I used 3M religiously
for many years,) and finding/certifying an alternative media required
requalification of the entire process.
As far as expense goes, its about US 4 cents, (plus the cost of the
PCB,) in expendables, for a 10 cm X 7 cm PCB. The fast method
processing time is 12 minutes and 19 seconds, (record time,) to the
drill press.
With that said, perhaps it would be appropriate to get back to geda(1)
stuff.
FWIW ...
John
BTW, I have no affiliation with any click through products on the
page. The technique is used by trade schools in third world
countries, and availability at distant places was a
requirement. That's also why the entire system runs on 12 V, (as in
solar charged lead acid batteries.) Also, why costs had to be
minimized.
John Griessen (john AT ecosensory DOT com) [via geda-user AT delorie DOT com] writes:
> On 06/18/2017 10:37 AM, karl AT aspodata DOT se wrote:
> > I usually use natriumperoxidisulfate for etching, would there be any
> > advantage to use H2O2/HCl instead ?
>
> The advantage I like for middle of the road 10 mils line and space, (not attempting 6 or 4 mils),
> is that the CuCl2 etchant is easily neutralized so it is not an environment problem.
> When you add NaOH to make it neutral, the copper precipitates out as oxide dust
> that is heavy, so easy to separate out of the bottom of a pan. The water is slightly salty
> with NaCl after neutralizing, but OK to pour on the ground without killing plants.
>
> I've not found any recycler that buys copper oxide dust, but we have a household disposal
> service by the city that will accept things as long as they are not industrial output.
>
>
> It can be turned back to copper by heating in a retort with charcoal and no oxygen...
> but I gave that kind of gas fired foundry work up in '02. Maybe later with a microwave
> absorbing crucible in a 7X microwave, as in the "microwave steel" method...
--
John Conover, conover AT rahul DOT net, http://www.johncon.com/
- Raw text -