Genny,

I don't think there will be any easy answers to your
questions.  There is a standard available for tin
whisker testing, but like other people who have posted
in response to your query, my understanding is that
tin whiskers are still not completely understood. The
standard will test for those conditions that seem to
be around when tin whiskers form, but it's not a
guarantee that you won't get tin whiskers in the
field.

Regarding your question about what you should test for
if your component manufacturers say their products
have been through tin whisker testing, the situation
there is also complicated. There have been a number of
tin whisker website links posted on this forum in the
last year or so.  If I remember right from some of
those links, there are procedures that component
vendors can follow, such as annealing or an extra tin
dip on the leads, that seem to retard the growth of
tin whiskers.  But when the part gets run through an
IR reflow or wave solder process, the details of that
process (especially how long or short the cooling
phase is) can undo some of the effects of the
annealing.

Admittedly, it's been a while since I've read about
tin whiskers.  If we now have a better idea of what
causes them and how to avoid them, that is great news
to me.

-Camille Good
Portland, Oregon


--- Genny Gibbard <[log in to unmask]> wrote:

> The components we've been sourcing all say that
> they've been thru tin
> whisker testing.
> Is there any value or reason to doing additional
> testing at the finished
> assembly level that uses those components, as well?
>
> Are lots of companies doing this?
>
> Just for information purposes, I investigated the
> cost of tin whisker
> testing on one assembly, and I was told we should
> test three samples,
> the test would take 18wks +, and cost $14-17K.
>
> They recommended we test components or coupons,
> instead.  Since the
> components have already been tested by the
> manufacturers, the only
> reason I can see for doing that is if we didn't
> trust the manufacturer,
> or wanted independent validation.
>
> Are there conditions on an assembly, though, that
> might not exist at the
> component level that make it important to retest?
>
> This is a huge investment.  Just trying to figure
> out whether it is
> worth it.
>
> Genny
>
>
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