Homebrew PCBs

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. 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. 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 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

I haven't yet found a solution for the pump.

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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