Homebrew PCBs

--- In Homebrew_PCBs@yahoogroups.com, "Stefan Trethan" 
<stefan_trethan@g...> wrote:
> Thanks for posting your results.
> I didn't know ferric chloride can be used in conjunction with tin, 
i  
> thought only sulphuric/peroxy etchants can be used for that....
> 
> 
> your method is surely a possibility, if direct EDM of copper 
doesn't work.
> However, it also is a large effort in comparision, and I'm not sure 
there  
> aren't easier ways to apply resist for  etching.
> 
> ST
> 

Stefan,

Following my last post, I did some more experimentation with the 
simple power supply, a single sided pcb and tap water dielectric. I 
produced single shot sparks and examined the craters in the copper 
layer under a microscope. Some had shiny bottoms and some had dull 
bottoms. Shining a strong thin light beam onto the rear of the pcb, 
it became obvious that the dark bottomed holes had in fact been 
blasted to the laminate, ie a clear hole in the copper. I also 
received Bob Langlois's book, and read all the posts I could find 
from Carl et al regarding his PCB-EDM. I now understand his approach, 
and the Garden of EDM PWM power supply, and the more I think about it 
the more I like this approach. The essence of success seems to be in 
the controllable power supply. Seeing the small holes convinced me. 

I am therefore going to dump the tin resist approach and concentrate 
on a machine similar to Carl's philosophy.

First is to build the Garden od EDM power supply and do some tests on 
hole size and quality with varying parameters.

If anyone has any suggestions on how to replace the IGBTs with 
MOSFETs in that design, I would appreciate any comments.

Roger