Homebrew PCBs

Max,

We always used solder plating as a resist and it worked fine. After 
etching either reflow the solder or strip it off and apply one of the 
newer "white tin" coatings if you want tin plating. Are you using 
immersion tin or really electroplating it? Immersion tin is worthless 
as a metallic resist but some electroplated tins will work if they 
are plated heavy enough. By switching to solder plating you will 
eliminate the problem. The same plating bath can probably be used.

Ferric chloride will not work unless gold is being used as the etch 
resist. Sulfuric/peroxide will work as an etchant for solder plated 
boards. After stripping the photoresist dip the panel in a 10% 
peroxide dip and then etch. This keeps the black crud from forming on 
the solder plated surface for a better reflow finish. After etching 
dip the panels in a 10% hydrochloric acid dip for about five minutes 
to brighten the solder plating for reflow. Skip the peroxide and 
hydrochloric dips if the solder is being stripped after etching. They 
are only required for solder reflow quality.

Bake the boards for at least 30 minutes at 300 degrees F after 
etching and before reflowing. This is for outgassing any trapped 
moisture and will keep the plated through holes from blowing out when 
soldering.

BTW, are you using the newer activated palladium cataylyst and 
skipping the electroless copper stage?  Good luck on your new system!

Tom


--- In Homebrew_PCBs@yahoogroups.com, "Max Davies" <max.davies@b...> 
wrote:
> 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.