Liam/Tom/Mike
Thanks all for your suggestions. It sounds as if there are several
routes I could go from here.
Liam - your suggestion of a different type of etchant sounds like an
obvious one to try. I see you're UK based - can you direct me to a
UK supplier of this etchant and I'll give it a go. In fact my
process is an industrial one (www.vantage.co.uk) - I have tried to
stick with just one supplier to have half a chance of making it work!
Tom - It is electro-tin (I tried immersion tin before, and quickly
realized the limitations!) The surface is matt by design - does
that sound like white tin? In fact, since my post, I have managed
to get a persistent coating, but it has required a ∗ridiculous∗
thickness of tin - a step of some 100 microns, and of course with an
appalling surface topology. It should definitely require less than
this!
I didn't know you could plate solder - I'd always seen solder as a
substance to be applied molten (therefore melting the resist). It's
definitely an avenue to look into if I remain unsuccessful with the
tin.
My catalyst is indeed Palladium based. Your suggestion of missing
out the e/less copper is alluring - the fewer baths the better. How
does this work?
Thanks again all. Max.
--- In
Homebrew_PCBs@yahoogroups.com, "Mike Putnam" <circuit@g...>
wrote:
> I have to differ with you, Tom. I used Tin Plate (Electrolysis) in
my shop
> for many years and not Gold. Gold plating was too expensive. I
etched with
> Ferric Chloride with no problems ever. Perhaps the trick is in how
fast you
> are able to etch the panel.
> -Mike
>
> ----- Original Message -----
> From: "twb8899" <twb8899@y...>
> To: <Homebrew_PCBs@yahoogroups.com>
> Sent: Saturday, April 26, 2003 11:40 AM
> Subject: [Homebrew_PCBs] Re: Oh no, blank fibreglass again!
>
>
> > 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.
> >
> >
> >
> > Be sure to visit the group home and check for new Bookmarks and
files:
> > http://groups.yahoo.com/group/Homebrew_PCBs
> >
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> >
> >
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> >