I'm thinking the chemistry involved with electrolytic tin is going to result
in whiskers/growth and I would suggest it not be used for a final finish. If
you are like many shops you use the tin/lead as an etch resist in process,
which is fine, but for final finish immersion tin would be better.
Check out Florida Cirtech's website, they have a nice study you can download
and print regarding the differences between the two type baths (electrolytic
and their Omikron).
(and again, this is not an endorsement for any specific chemistry, the site
mentioned offers greater volumes of literature is all, and I like my
literature)
I would think storage would not be an issue with plated tin or tin-lead
provided they were sealed properly, but with the plated tin, some humidity,
some contamination, and mild current...these are all good conditions to
cause growth.
And I'm thinking tin will indeed flow, it just takes a higher temperature...
Franklin
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Fineline Circuits, Inc
Sent: Friday, October 14, 2005 9:20 AM
To: [log in to unmask]
Subject: [TN] Electrolytic Tin Plating
Hi Technetters:
Now that Leadfree is here or close to, we would like to change the
electrolytic tinlead plating tank to electrolytic tin tank.
I would like to know if the other fab houses have done this and if so which
vendors tin chemistry has a wider window of operation. Are they seeing any
tin whiskers/sliver problems etc..especially if the boards are stored for
few months.
Also it is my understanding that you can mask over this plated tin since it
does not flow. In this case you can totally avoid stripping the tin and tin
levelling.
We currently do offer other finishes including electroless tin , immersion
nickel/gold, silver....
If there are other consideration in making this change I would appreciate
your input.
Franklin, like you I would like to see more fab houses participating but I
would like to remain with technet.
Thanks
Sona Sitapara
Fineline Circuits Inc.
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