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February 2001

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Subject:
From:
Robert Lazzara <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Mon, 12 Feb 2001 09:20:01 EST
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In a message dated 2/12/01 8:07:09 AM, [log in to unmask] writes:

JAMES: If immersion tin does whisker, wouldn't exposed traces (not solder
pads) be

a concern even after assembly?
ROBERT: In my experiences tin "whiskering" of nonporous immersion white tin
(IWT) ceases to be a theoretical possibility after assembly, as the greater
mass of the solder alloy provided at assembly displaces the IWT. You can't
find the IWT after proper assembly -- including pad edges -- as the matte
nature of the IWT promotes whole-pad wetting (unlike OSP).

JAMES: Is whisker growth a function of the environment or just time?
ROBERT: In the case of IWT (versus electroplated tin), "whiskering" exists
only as a theoretical possibility. Search the TechNet archives (and anywhere
else); I assure you that you'll find not a single complaint about nonporous
immersion white tin whiskering, irrespective of time or environment.

JAMES: Could the tin in the immersion tin process be alloyed (with a small
percent of something else) to prevent whisker growth?
ROBERT: Whether you assemble with tin/lead, tin/silver, tin/bismuth or tin
kryptonite, the IWT is alloyed by a large percentage of something else upon
assembly. You've got a greater likelihood that the tin from your assembly
solder will "whisker", but I'll leave that aspect to the abundant solder
experts.

- Robert Lazzara

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