Hi Werner,
I highly respect your opinion, but would have to disagree (at least to
some extent :-)).
From the materials science point of view (and I'm a scientist, as you
mentioned once :-)), it's relatively easy to define ductile and brittle
materials. All one would have to do is to define the deformation at the
failure point. Obviously, both types of solders (Pb-free and Pb-Sn) will
fall within the category of ductile materials.
You obviously know that there are a few publications showing that
neither Pb-Sn, nor Pb-free solders exhibit brittle-to-ductile transition
under "regular" conditions (to be exact, though, it might exist for
Pb-free at extremely low temperature under extremely high loading rate).
As far as the failure mode is concerned (brittle or ductile), then it
could be caused by either high stress or high (critical) deformation
accumulated by the material prior to failure. The actual failure mode
will depend on a number of variables, including the loading rate.
Regards,
Vladimir
AMD
-----Original Message-----
From: Leadfree [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier
Sent: Friday, January 19, 2007 2:35 PM
To: [log in to unmask]
Subject: Re: [LF] SAC+, SACN and Low-Ag SAC Solder Ball Alloy
Hi Vladimir,
You are both right and wrong.
First, 'brittle' [as well as ductile] is no a technically defined term
but a
descriptive comparative term; thus something can only be more or less
brittle
than something else.
Second, these LF-solders have a higher tensile strength and a somewhat
higher
modulus [at the same temperatures and strain rates, of course], as
compared
to SnPb; this results in higher stress levels on the interfaces under
the same
loading conditions and thus interface failure woulkd occur earlier for
Lf-solder joints, whether the interfaces are more brittle or not.
Werner
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