Homebrew PCBs

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


On Wed, 24 Aug 2005 00:05:31 +0200, ralucas4277 <ralucas4277@...>  
wrote:

> Hi All,
> This is a continuation of the discussion on the forum CNC_PCB-Design
> with Stefan on EDM & Etch Resist.
> Stefan suggested tin as an etch resist, and I followed this up. Here
> are my tests to date.
> Built a simple EDM power supply, 2 x 30V trafos with 70 Volt 6800uf
> reservoir cap, and dubious 2 x 1uF discharge caps for ablation. Used
> Don Lancaster's trick of light bulbs as ballast resistors, but only
> had 2 x 100 watt (240V), (yes I'm in the UK).
> Obtained strong spark, but slow spark repetition rate.
> Coated a section of copper clad pcb with tin/lead solder using
> soldering iron. Etched a line through the tin/lead solder by spark
> erosion by hand. Electrode was 1mm copper wire (all this came out of
> my junk box). Dielectric was diesel fuel (works well but smells).
> Continued ablating the tin/lead until the copper showed. Copper is
> readily visible through the tin. Etched in Ferric Chloride solution.
> Result is complete etching of the EDM exposed copper.
> This demonstrates to me that isolation milling by EDM is possible,
> and that pcb production by this method is a real possibility.
> Spark eroding by hand was difficult, I could generate a repetitive
> spark for about 2-3 seconds, but when moving the electrode the spark
> ceased either due to over current (short circuit) or under current
> (open circuit).
> Next trial is to mount an electrode control on the cnc and try for an
> isolation mill on a pcb. I need to adjust the RC time constant for
> high spark rate for this application, since the objective of this
> excercise is to ablate the tin relatively quickly, and then etch the
> copper.
> Will keep you posted.
> Roger