[tinwhiskers] Re: Bourns announces hot dipping of tin - comments?
- From: John Barnes <jrbarnes@xxxxxxxxx>
- To: tinwhiskers@xxxxxxxxxxxxx
- Date: Fri, 13 Feb 2009 12:03:04 -0500
Denny,
From what I have collected (14,300+ documents on lead-free electronics
as of Wednesday, February 11, 2008), hot dipping has a considerably
lower risk of growing tin whiskers than matte tin electroplating, which
in turn has a lower risk than bright tin electroplating.
The two main factors are:
1. The sizes of the grains in the hot-dipped coating are much larger
than for the electroplated coatings. So there are many fewer grain
boundaries (especially between 3 or more grains), which are the
preferred starting points for tin whiskers.
2. The high temperature and high thermal conductivity of the solder
bath causes intermetallics to grow very quickly at the
substrate-solder interface, and be instantly annealed. This reduces
the compressive stress from the continuing growth of Cu6Sn5, which
is a major driving force for tin whisker growth.
The main problem with hot dipping is that it cannot be used for many
integrated circuits and other tight-pitch components, because of the
high risk of solder bridges.
My 950+ page (3.5MB) bibliography on lead-free electronics, the RoHS and
WEEE Directives and the like, is freely available at
http://www.dbicorporation.com/rohsbib.htm
John Barnes KS4GL, PE, NCE, NCT, ESDC Eng, ESDC Tech, PSE, SM IEEE
dBi Corporation
Lexington, KY 40511-2105
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