Just for discussion here....
I gotta ask about using "oil" (or whatever) with etchant. Let's
say that it DOES prevent undercut...what would be the chemical
process going on if it prevents undercut and yet does
a good job of removing the unwanted /unprotected copper?
Maybe the "oil"-etchant just works faster so that it doesn't
have TIME to do any significant undercutting?
Charlie
On 24 Sep 2013 17:36:35 -0700 <
andrewm1973@...> writes:
Rotary one for an area 1/4 of an A4 sheet of paper should be able to be
cobbled together for much less than $100. If you want to go for
something more like a full sheet of A4 paper then pump is a better
option. Here in Aus the right pumps are $150..$200
I coat my own brass with dry film photo resist. Look at Adam Seychells
PDF on how to do this. It is same ball park price to do it with photo as
it is to use Pulsar paper PLUS the TRF film. It's just a bit dearer to
set up equipment at the start. The quality and repeatability is miles
ahead. You never ever get pinholes / pitting with photoresist.
Inkjet printers onto ink-jet transperancies purchased from screen
printing places work great. Much better than laser in my experience
unless you have a small car sized/price laser printer.
The dry film resist has fairly good contrast, but a good photo tool never
goes astray. Small home office lasers (Like my HP4xxx) don't do good
solid blacks on large areas. Toner enhancement spray helps a bit but
(some) inkjets just work better for this and are much cheaper.
I have no knowledge of oil to prevent undercut. It sounds interesting
though as I often etch 0.7mm brass.
---In
Homebrew_PCBs@yahoogroups.com, <
homebrew_pcbs@yahoogroups.com>
wrote:
Thanks very much for the Info! A rotary type would also be cheaper to
realize, so If I get to build one then I will probably go for a rotary
tube one.
Toner transfer is easy to do and cheap, so far I am satisfied with my
results I dont have a very high faliure rate.
Photoresist would be another thing to have a look at. PCBs you can get
precoated but brass copper and german silver sheet does not come
precoated. But there are some Photoresist films out there like pureetch ,
z-acryl, Image-on and the like. These would surely be easier to apply
than coating with laquer. I will have to do some research on these.
AFAIK real photo negatives work best as a mask for exposing, I have read
in passing ,but with no real focus on this kind of topic, that there
could be some problems with laser printed masks not dense enough, but
surely this could also be solved.
While reading on some older patents on etching machines I stumbled on
something only briefly mentioned, apparently they used a small amount of
oil in the etchant (how much and what kind etc was not specified(just :
"as known to those familiar with the craft" etc etc.) to lessen the
undercut. The oil would cling more firmly to the walls of th etched
grooves slowing the etching there while being washed away on the bottom
of the grooves by the action of the spray. Ever heard of this?
--- In
Homebrew_PCBs@yahoogroups.com, <
homebrew_pcbs@yahoogroups.com>
wrote:
Spray etchers (using diaphram pumps) I have seen have droplets not mist.
The point of the droplets is to have some weight behind the impact to
move the insoluble precipitate. I would imagine an atomized mist be very
ineffective with FeCl3.
If you look on ebay at the ceramic nozzles for sale for spray etchers,
they are definitly not atomizing nozzles. They are a fan pattern
The banding I had with the spray etcher was only in early builds before I
found the solution to stop it.
As far as etching the bottom of the plate more. With the spray-tube
etcher you can actually etch the top of the plate more depending on motor
speed. At lower speeds the bottom etches more. At higher speeds the top
etches more. Find the "Sweet spot" for your tube and it is pretty even.
Better than most nozzle/pump spray etchers I have seen that don't hold
the target horizontal.
If you want to build a pump/nozzle spray etcher that does a better job
than the rotary tube types you are GOING to have to move the nozzles or
the target. As stated above the proper nozzles are a fan pattern. Large
professional ones move the target through the machine. Smaller ones
(Adam Seychell) move the nozzles back and forth.
WRT the toner not holding up in electro etch. Have you thought about
dropping toner transfer and moving to photo-resist. It's a lot more
convenient if you are producing the same design over and over again. It
also does MUCH better results on long etches (thick brass)
--- In
Homebrew_PCBs@yahoogroups.com, <
homebrew_pcbs@yahoogroups.com>
wrote:
"over here" is germany...sry. There are some commercial suppliers for
acid resistant pumps but they are not cheap, quite the opposite.
By spray I mean finely atomized with nozzles, the "etchinator" does make
some "spray" of sorts but the droplets are much larger than the spray
with nozzles and pump. Both methods work, but all the professional
Etching is done with the spray nozzle type.
I have heard some good and some bad from the rotary tube type, there is
not overly much to find in terms of user feedback but one of the problems
reported was banding in some areas while etching and that the lower parts
are always slightly overetched due to the etchant running off downwards
when the plates are vertical.
This would also be a concern with the nozzle type, some means of
constantly moving either nozzles or the workpiece would be needed to etch
a larger plate (A5-a4 size) in an even way.
So far a etching machine of either type is still in the back of my head
but I was not willing to go thruh the trouble of building one.
I would rather try and make the electroetch work since it seems to
produce less undercut than traditional method is cheaper in the long run
and it would be much easier to use a setup with two electrodes(Kathode)
and the workpiece(anode) in the middle to make some double sided etching.
I am not sucessful because my toner does not hold up in copper sulfate
electolyte, it gets gradually eaten away before the etch is finished. If
I can find a toner that will work its by far the easier method.
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