Homebrew PCBs

Stefan Trethan wrote:

> On Thu, 13 May 2004 07:24:08 -0700, Mark <mfraser@...> wrote:
> 
> 
>>Gun Blueing from your local hardware store.
>>Very slightly dampen a corner of a cloth with it, rub briskly.
>>You'll get a black sooty deposit if you put too much on / leave
>>it wet etc.; start with a less dampened corner of the cloth.
>>Keep rubbing....
>>
>>Same deal as prep for etching / plating - clean.  Kitchen cleanser
>>like ajax etc.  Wash well.
>>
>>Rubber gloves - it leaves a nasty odor that's hard to wash off.
>>Nothing terrible in the MSDS.
>>
>>CHeaper than most of the brass-blackening compounds in the few
>>hobby shops that sell them.  Faster, too.
>>/mark
>>
>>
> 
> 
> Never seen anywhere around, thought about it too...
> 
> I am on to something, left it immersed in strong NaOH solution mixed with 
> sulphur overnight.
> It got black, very black, but the copper was etched :-( . Might work just 
> fine if
> i only leave it for a short time.
> 

I though sulfur was insoluble and therefore wouldn't have an 
effect, but I'm no expert. I've seen copper site in some 50g/L 
NaOH photoresists stripper solution overnight and came back next 
morning to find a copper(II) oxide film ,i.e black.

The oxide will dissolve away in any acid.

Commercially they use sodium hypochlorite ("pool chlorine") mixed 
with NaOH to make black oxide film on PCB s prior to lamination 
of inner layers. Apparently the epoxy sticks a whole lot better 
to Cu oxide than to the metal. I've never tried it but I think 
the NaClO acts to massively speed up the oxidation rather than 
relying on dissolved atmospheric oxygen. Worth a try....

Adam