Archive of the former Yahoo!Groups mailing list: Homebrew PCBs

Hi everyone.

A newbie to this group, I am (perhaps over-ambitiously) attempting
to set up a micro through-hole plating line at home. It's a lot
more involved than I ever thought it would be, but I now have most
of it working fine. ...Except what should be the easy bit - the
final stage - the etching!


To give a brief description of what I do...

STAGE 1: Starting with plain, copper-clad board, I do the drilling.
STAGE 2: Apply photopolymer laminate, then expose & develop. (This
is positive photopolymer, so the copper which will ultimately become
tracks is exposed to the air on developing the pattern)
STAGE 3: Go through a 6-stage process to electroless-plate the
entire thing (including the holes & edges). The copper cover it puts
on is pretty thin, but uniform at 1-2 microns.
STAGE 4: Electroplate the copper - this gives reasonable thickness
to the copper applied in stage 3 - I aim for 25 microns.
STAGE 5: Electroplate with tin to 10 microns. This
(theoretically!) protects the copper from etchant.
STAGE 6: Remove remaining resist. Then etch. This should leave
the tin-plated areas untouched, everything else should be zapped.


But alas no! Stage 6 fails, because both tin ∗and∗ copper are
etched, leaving me with a fine, blank piece of fibreglass! It
matters not whether I use Ferric Chloride or Sulphuric/Peroxide
etchant - they both destroy what has been so lovingly created!! So
I reckon there must be something awry with my tin plating.

It's a total impasse, and nothing I do, from increasing/decreasing
current to re-formulating the tin plating bath according to
manufacturer's instructions seems to change things.

Does anyone else use a similar process, or have any clue about what
might be the problem here?

Max.