Homebrew PCBs

Stefan Trethan wrote:

>Larger bubbles are supposedly required to get good scrubbing action at the  
>surface of the PCB.
>  
>

  I'd guess larger bubbles gives greater displacement, so higher 
velocity for the etchant as it comes back in as the bubble passes..

>With your large air pump i suppose big bubbles are good, if you can create  
>them in enough places so no streaks are visible.
>I reckon a moving air source would make things much easier to get even,  
>maybe a tube with a spiral pattern of many holes, that is rotated slowly  
>by the air in some way would be possible.
>
>ST
>  
>
  That could be extremely workable.  Think of a hose going down an arm, 
and then out an inch or two under the board.  A pendulum going back and 
forth under the board.  Linearize the swing and you would get almost 
guaranteed even etching, and it should be much easier to make and use 
than trying to get any long tube with holes along it to work evenly.  
Flood of bubbles and then a short time of contact to etch, I bet it 
wouldn't even be that much slower than a tank full of bubbles.

  Really, could come off both sides and make 3 short wands horizontally 
for bubbles from the arm.  More bubbles for faster etch, still 
reasonable enough to get them even, and the motion is really the key for 
evening things out..

  Heck, might work well with just 3 of the 1" or 2" stones sticking out 
from the arm.  While they suck for stationary use, with the motion they 
might work well and not have to make holes in tubing etc.

Alan