Max,
For solder plating just use solder bars as the anodes. I'm not sure
what plating chemistry in used in your process. We used LeaRonal
products for years but they merged with another firm. I don't know if
their products are available any more.
The solder plating chemistry was called Solderon NF. Solder plating
will always plate tin and lead which must be "reflowed" after
etching. After etching the plated traces have a dull gray color. Coat
the panel with flux and dip it in soldering oil at about 450 degrees
F for around ten seconds to reflow. The tin and lead will melt into
the solder alloy and bond to the copper trace. Remove the panel from
the hot oil and quench in warm water.
On the subject of etching, Mike is correct about using tin for a
resist if it's thick enough. Like he said, it's all in the timing.
We always used sulfuric peroxide etchant for solder plated boards and
ferric chloride for print and etch. The peroxide etchant was used in
a heated PVC tank and the ferric chloride was used in a Chemcut 315
spray etcher. We never had much success with tin resist in the spray
etcher. It seemed to blow right through the tin but copper etched in
about 1 minute in this machine.
I have even etched with no resist at all. This is not hard to do if
you are pattern plating on 1/8 ounce copper laminate. We used this
type of copper laminate for extremely fine line circuitry. The plated
copper pattern is much thicker than the laminate copper. In the spray
etcher this thin background copper would etch in about 10 to 15
seconds with minimal attack to the thicker circuit pattern.
I now have a very small shop and only use ferric chloride in a small
spray etcher. On plated through boards I just "tent" the holes by
exposing the dry film right over the plated holes. This keeps out the
etchant while removing the background copper. This method does
require the artwork to have solid pads with no center dot.
After etching I solder mask and then solder coat the board if
required. Most of my products use single sided boards so I just
solder them and don't worry much about solder masking and solder
coating.
The newer activated palladium catalyst method leaves a conductive
film through the holes. This deposit is conductive enough to allow
direct copper plating without using electroless copper. Electroless
copper is the largest source of pollution in a pwb shop not to
mention it's high cost of operation. There are no "plate out"
problems when using the activated palladium process and there is
little to no odor as well. This process is offered by several
companies and the one I use was made by Solution Technology.
Tom
--- In
Homebrew_PCBs@yahoogroups.com, "Max Davies" <max.davies@b...>
wrote:
> 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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> > >
> > >