My chemistry is for Tin/Lead (it' all about the organics, which I called
brightener thinking of Bright tin which my kit was originally purchased as)
This is Solderon BHT-90 series I could buy the separated Tin con, Pb
con,Anti foam , and carrier but they offered me a small pre mix to try it
out. (RohmHaas directly) I'll be buying the components in the future. My
solution is yellow.
The surface of the plated tin does turns black in the etch, but a quick rub
with a scotchbright cleans it up nicely
I only plate flash copper, No acid copper - not anymore anyhow.
It works perfectly
Flash copper. small particle density, thus giving the kind of thru plating
you could only get with high powered pulsed acid copper. I haven't noticed
any increase in anode usage. as the organics keep the suspended copper in
check. The plate actually comes from what's suspended. The anode dissolves
as needed in to the solution. I have to keep a pump going to keep the
copper suspended as ph fluctuates, as it's very near the point of copper
sulfate precipitation. I use whatever is in the ink that Think and tinker
sell, I thought it was silver based, but it's black like carbon. ... which
makes me wonder why it costs what it does.
I think the biggest diff noticeable for acid vs. flash - would be the
hardness of the finish. But this is of little consequence to a pcb.
Acid is faster. and easier to maintain. (cheaper too) but I like the flash
much better for this application.
I asked another group about this some time ago, and the only result I got
was a recommendation for Electroless!
My copper solution is green.
I would probably keep the acid, If I wasn't plating tin.
(whenever I use the term tin assume I mean SnPb)
Yes everything I'm using is "store bought" not diy. I have about 20
different testing solutions (Broh. Blue, Pan ind, EDTA Tet sodium, mercuric
nitrate!! ,silver nitrate,nitric acid, etc... and related lab equipment to
fully test all components of all solutions.) I'm really trying to keep a
Very very low effluent.
∗Most pcb thru history have been SnPb, I assume Nasa was assuming this as
well, pure Tin is pure Tin, and will do as pure tin does, no matter where it
is. I suspect the whiskers would be more of a problem on high density
layouts. I just err on the side of caution, as my product is a life support
device ... for reef aquariums : )
I still have my pure bright tin setup, actually expecting another on here
soon, but I'm using it for other stuff, (emi shield on plastic housing)
JT
----- Original Message -----
From: "Adam Seychell" <adam_seychell@...>
To: <Homebrew_PCBs@yahoogroups.com>
Sent: Thursday, April 01, 2004 7:19 PM
Subject: Re: [Homebrew_PCBs] plated tin as the etch resist
> Jeremy,
>
> Thanks for the info,
> I assume your plating solutions (including flash plate) were
> purchased as proprietary products. so I understand why you
> wouldn't know exactly what's in the mix. As for tin plating , you
> mentioned sulfuric acid, which would mean the tin is stannous
> sulfate { also called tin(II) sulfate or SnSO4} . Is the solution
> a milky white/yellow or pale brown color ? This is normal
> color(s) for this plating bath.
>
> As for copper, I suspect you must be running a conventional acid
> copper bath to build up the copper to significant thickness. I
> understand the flash plate is primarily to get converge of copper
> inside the holes, after that, the copper is plated at high speed
> in acid copper. If you try plate too much from the
> alkaline/copper sulfate/sodium hypophosphite bath then you will
> consume too much copper and make bath maintenance difficult. I
> use carbon based method to prepare holes for electroplating in
> acid copper bath. I'm still experimenting with this.
> A good overview on method of making holes conductive is at;
> http://www.epa.gov/dfe/pubs/pwb/ctsa/ch2/ch2-1.pdf
>
>
> If your anodes are 10% lead then all I suspect this will do is
> create a excessive black film over the anodes as they are
> consumed. The reason is lead sulfate formed during dissolution of
> the anode is completely insoluble and therefore will not plate on
> the PCB. In order to plate tin/lead you need the a different type
> of chemistry. For details on tin/lead plating see:
> http://www.pfonline.com/articles/pfd0023.html
>
> I must admit I haven't tested for solderability on one of my very
> old tin plated PCBs. The oldest one is about 2 years.
> What I was saying about tin whiskers is if there has been real
> life problems with plated tin finish PCBs ? The NASA article on
> whiskers demonstrates whiskers problems on IC legs and
> connectors, but nothing on PCB's. I'm wondering if the solder
> reflow process eliminates the whisker problem since the tin is
> mixed with some lead from the solder. Very few PCBs are
> fabricated with pure tin as a final finish, but I'm curious if
> this the reason is because of the whisker problem.
>
> Adam
>
>
>
> Jeremy Taylor wrote:
> > My tin setup is Sulfuric based, Tin stuff and Brightener
> > The Tin is pattern plated at 100 milliamps per sq in (.0001 per 10 mins)
I
> > shoot for 0003~0004 "
> > My tin Tank is 3 Gallons
> >
> > The Flash copper is alkaline, mostly copper sulfate with hyposodium base
and
> > organics.
> > The copper is panel plated, with 1 amp per 10 Sq In (.00025 per 15 mins)
,
> > I shoot for a 0.0005" coverage
> > My copper tank is 3 Gallons
> >
> > The electroless Nickel is a bit complicated on keeping exact track of
how
> > much you have used. I know that it has Nickel in it,
> > But other than that Its Part A, Part B, Part C and Water. It must be
HOT
> > 195 Deg F.
> > Plates very evenly 0.00025" per 15 min. I shoot for .0003".
> > The Nickel tank is 1/2 a gallon.
> > My plating-dev-strip-etch, "system" is 32" wide X 8 feet long
> >
> >
> >>I have never heard of problems of
> >>electroplated tin creating whiskers. Do you have any knowledge of
> >>tin whiskers being a concern in PCB production.
> >>here is an interesting articles on tin whiskers.
> >>
> >
> >
http://nepp.nasa.gov/whisker/reference/tech_papers/brusse2002-slides-tin-whiskers-attributes-mitigation-CARTS-europe.pdf<
> >
> > I'm a little confuse by your statement. as the link you posted is
absolutely
> > a great resource on tin "whiskers" and even they end by recommending
> > avoiding PURE tin. ... and that is what I've done with a 10% Lead
content.
> >
> > I'm not going to argue the merits of intermetalic alloy formation, lots
of
> > factual info already out there. 1 month is not very long, ,,, 3 Year is
a
> > good testing point.
>
>
>
>
>
> Be sure to visit the group home and check for new Bookmarks and files:
> http://groups.yahoo.com/group/Homebrew_PCBs
> Yahoo! Groups Links
>
>
>
>
>