Immersion tins will wisker, regardless of the tin morphology, as the
thickness exceeds 15 microinches. Wiskers are less of a concern with IT
then with electrolytic tin because the thickness is far less and boards tend
to be assembled rather quickly. Because of these two facts the PCB industry
is less concerned with wiskers then the airspace industry was in the past.
Once IT is alloyed with lead during assembley via the use of 63/37 solder
paste wiskers are no longer a concern.
I was a coauthor of an article publish at Lead-Free a couple of years ago.
The article is titled "Rapid Deposition. High Build, non-Electrolytic Tin
for Use in the PWB Industry". We looked at several venders of IT and all
produced wiskers to some degree. The work is well documented with SEM
photos of some wiskers.
The only difference between electroplated tin and IT is that the electrons
used to reduce the tin come for the oxidation of copper and not an external
DC power source. Of course this makes it ideal for coating the small
surface mount areas without electrical continuity attainable after strip and
etch.
Best Regards,
Rob Durante
text message paging: http://www.nextel.com/
message ID: 7148225829
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Marsico, James
Sent: Wednesday, February 07, 2001 10:29 AM
To: [log in to unmask]
Subject: Re: [TN] More about white tin (another question)
What about the concern of tin whisker growth? I believe that, for some
reason, it isn't an issue with the "white" tin process. Is there published
data verifying this? For aerospace or space applications? What's the
difference between white tin and regular tin plating? What makes this so
special?
Jim Marsico
Senior Engineer
Production Engineering
AIL/Electronics Systems Group
An EDO Company
[log in to unmask] <mailto:[log in to unmask]>
-----Original Message-----
From: Michael Khusid [SMTP:[log in to unmask]]
Sent: Wednesday, February 07, 2001 11:36 AM
To: [log in to unmask]
Subject: [TN] More about white tin
Hello everyone,
I used white tin finish on our medium-sized board which has several
high
count BGAs. The boards looked nice and the finish was very flat.
However,
our assembler reported problems soldering to it, like voids in BGAs
and
similar issues (no shorts or opens though). They also recommended
HASL as a
preferred finish. This does not sound right to me since HASL will
not be as
flat as white tin.
I am thinking that they may have used wrong solder paste and/or did
not use
enough of it. If I am on a right track, what solder paste is
preferred for
white tin? Are there more gotchas for the white tin process? Would
other
finishes like HASL or OSP be better for the board?
Thanks,
Mike Khusid
> -----Original Message-----
> From: DJ Robison [mailto:[log in to unmask]]
> Sent: Tuesday, February 06, 2001 3:08 PM
> To: [log in to unmask]
> Subject: Re: [TN] White tin
>
>
> I've used Omikrom quite a bit. I prefer it to bright acid. It
> has better
> coverage and is an easier process. The only negative so far
> is that it may
> react to some Flux's by staining.
>
> DJ Robison
> Process Engineering Technician
> TTM Technologies, Inc.
> Redmond Division
> 17550 NE 67th Court
> Redmond, WA. 98052
> (425) 883-7575 ext. 229
> [log in to unmask]
>
>
>
> -----Original Message-----
> From: crbuerke [SMTP:[log in to unmask]]
> Sent: Tuesday, February 06, 2001 11:43 AM
> To: [log in to unmask]
> Subject: [TN] White tin
>
> Would like to hear about any experiences anyone has
> with respect to the Omikron white tin immersion
> process used on boards.
>
> Chuck Buerke
> Photonics Systems
> Toledo, Ohio
>
> __________________________________________________
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