Hi Adam
>Thanks for the pointers to the rotary pipe etching machine.
>I would agree this machine looks mechanically simpler and
>cheaper than a oscillating spray nozzle type etched. I did
>have a suspicion that this may not give a totally uniform
>etch. From what the experts say about spray etching (or any
>cleaning) is the impact velocity of the liquid is what does
>the real work.
Acording to Bungard the etching process of THEIR machines is total
uniform - as oposed to the (el cheapo) machine I unfortunately first
bought. I must admitt though that I don't have first hand experience
with their machines. As soon as time permits - that's currently a bit
a problem :) - I will take a closer look at this. I may end up buying
one of those Bungard machines but we will see.
> Currently I have a bubble etched and it does
>not produce reliable etching. Despite many different
>arrangements of the air sparger I have tested, I found only
>a limited etch uniformity can be achieved.
I totaly agree on this one. IMHO serious (fine artwork) kind of PCB's
can't be etched with those. I had one myself but it's sitting on the
shelf now.
>The second
>problem is etch undercut of the tin plating resist. The
>boards I'm making use the pattern plating process, where tin
>metal is plated on the tracks to act as a etch resist in a
>ammonical type etching solution. The tin overhangs the track
>a small amount and then breaks off creating slivers of tin
>and potential short circuits. I scrub the boards with a
>stiff nylon brush to remove the tin slivers.
>
>Going by what a couple of professionals have said and also
>from someone who built their own hobby spray etching
>machine, is that spray etching is the only way to get
>uniform etching and minimize etch undercut.
I agree here too, but I think that the rotary principle is suffiently
good to do this. Again, I can't proofe this at the very moment.
>I had some thought on the spray etcher design. I was going
>use some 20 mm PVC pipe and 4 pipe elbows to make up a
>rectangle frame which fits internal to the tank. A flexible
>rubber hose connects the pump outlet to the PVC pipe at some
>point where etchant is pumped in. Four spray nozzles are
>also fitted to the rectangular pipe frame such that they
>spray inwards to the center of the tank. The PCB will then
>hang vertically in the center of the tank and the PVC
>rectangular frame will sit horizontally and oscillate up and
>down spanning the PCB height. The mechanism to drive the
>oscillating rectangular frame will consist of eight pulleys,
>one at each inside corner of the tank. A cord will run
>passed the pulleys so when they rotate there are vertical
>cords moving at all four corners at the tank walls. The
>rectangular frame is attached to the vertical cords so it
>moves up and down as the pulleys rotate.
>A DC motor mounted outside on the tank lid will drive the
>inside pulleys via a belt. Two small holes in the lid will
>be needed to pass a drive belt.
>
>These nozzles are about AU$10 each
>http://www.bete.com/metric/products/pages/spn.htm
This sounds like a good concept (and thanks for the pointer to the
nozzles). Please keep us up to date on your progress. Etching is
really the only step left here that does not work too well at the
moment. (I'm actualy currently "hand etching" by moving the PCB within
the Fe3Cl bath by hand up and down for 20 minutes and that's really
tedious. The "advantage" of this method is that I can control where
and how fast it etches within some reasonable degree with different
kind of moving the board but again - it's a pain...)
>I haven't yet found a solution for the pump.
Yes, I figure this is getting difficult. Have you ever considered
building the pump also? I was thinking about having a PVC tube formed
as a circle and then some kind of rotor equiped with little wheles at
the ends to minimize friction that squeezes the tube thereby moving
the liquid inside the tube. I remember that there are pumps that
operate this way used by RC plane modelists. I have no clue though if
it's feasable to build one of those that is delivering the pressure
needed.
Markus
>Adam
>
>
>
>Markus Zingg wrote:
>> I agree with Stefan that building a rotary kind of spray etcher is
>> most likely a lot easier. I do have one that I boght a while ago. I
>> first was happy, but over time it turned out that it does not create
>> reliable reproduceable results. That's however not due to it's
>> principle of operation but more because of some bad ideas on behalf of
>> the manufacturer.
>>
>> I created a little homepage for you showing pictures of the
>> (depreciated) etcher I have and most importantly a little video of the
>> MUCH better Bungard spray etchers which should give you some good
>> ideas on how to build your own.
>>
>> www.myhome.ch/mzingg/pcbstuff
>>
>> Markus
>>
>>
>>>Anyone here every built a spray etcher ?
>>>I'm looking at building a spray etcher on the cheap, but I cannot
>>>find a suitable pump. Pressure requirements are fairly high for
>>>sprays nozzles to work effectively. The pump must be capable of
>>>at least 10 meter head (1 bar), but all low cost fountain pumps
>>>are rated no more than 4 meters head. Getting hold of a pump is
>>>the killer. Example, the Iwaki MD-70RZ has 16 meter head but
>>>sells for AU$500. The etchant I'm using won't effect stainless steel.
>>>
>>>
>>>
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>>
>>
>>
>>
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>
>
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