Hi Derek,
I ran some more searches to find a less-outdated link.
Here's some notes:
http://portal.groupkos.com/index.php?title=Tin_WhiskersPhysics Today -- May 18, 2009
"Using Laue diffraction measurements made at the Advanced Photon Source at Argonne National Laboratory in Illinois, the researchers noted that at the CuSn interface, Cu6Sn5 develops along the tin grain boundaries and is most pronounced directly beneath a whisker's root. That observation, coupled with residual strain measurements, led the team to propose the following mechanism: Deep penetration of Cu6Sn5 into the 3-μm-thick tin layer induces in-plane compressive strains near the CuSn interface and in-plane tensile strains nearer the surface. Out-of-plane and in-plane strain gradientsnot the strains themselvesthen provide the driving force that leads to whisker growth by transporting Sn atoms to the whisker nucleation site as a strain-relief mechanism. (M. Sobiech et al., Appl. Phys. Lett., in press.)"
It sounds like the whisker grows like a wart, with atoms adding from the metal surface that are migrating due to the asymmetric strain of an alloy blending to a non-alloy. Metal-creep over an alloy-bubble at the surface.
AZdon
--- In Homebrew_PCBs@yahoogroups.com, Derek <derek@...> wrote:
>
> Unfortunately we need to follow the regulations to create the products.
> I read the article yesterday and was quite impressed - they still do not
> know the cause of the whisker growth. What was interesting is that the
> growth has been known since the 1940's. The chart of using various
> solders based on the situation is a good reference. And the point that
> lead, in general, is non-soluble; so where vapors could be generated or
> wiped off and into one's mouth, etc, lead is restricted - paint and
> gasoline are examples. But withing packaged semiconductors and on coated
> PC boards, tough to get the "lead out". :-)
>
> Derek Koonce
> DDK Interactive Consulting Services
>
>
>
> On 11/18/2011 1:10 AM, Russell Shaw wrote:
> >
> > The stupidy of European government knows no bounds.
> >
> > Understanding and mitigating tin whiskers
> >
> > <http://www.eetimes.com/design/military-aerospace-design/4230652/Understanding-and-mitigating-tin-whiskers?pageNumber=0&Ecosystem=communications-design
> > <http://www.eetimes.com/design/military-aerospace-design/4230652/Understanding-and-mitigating-tin-whiskers?pageNumber=0&Ecosystem=communications-design>>
> >
> >
>