In a message dated 04/06/2000 7:56:36 AM Central Daylight Time,
[log in to unmask] writes:

<< Solder Wizards & Wizettes:

 What are the differences between creep and grain boundary sliding in solders?

 Thank you.
 Dave Fish >>

Hi Dave!

I just learned something because of your question...that was because I didn't
know what the difference was either. So I went on a search. Go to:

http://chipscalereview.com/chipscalen2/9809/m.abtewb1.htm

There's a pretty extensive article about the physical properties of all
solders while under the title of; "Lead Free Solders for Surface Mount
Technology Applications"

Here's a copy and paste from the article when talking about "Creep and Grain
Boundry Sliding":

Time-Dependent Monotonic Deformation

This type of deformation is commonly referred to as "creep," a measure of the
time required for a material to fail when it is under a constant load at a
constant temperature. Creep involves deformation mechanisms, such as grain
boundary sliding, vacancy diffusion, etc., which require a thermally-driven
diffusion process. Therefore, creep deformation becomes critical only when
the temperature exceeds half the absolute melting temperature of the
material. For most soldering alloys, room temperature is well above half
their absolute melting temperature. Consequently, for solders in SMT, creep
is considered the most important deformation mechanism.

Another thing I learned was that by alloying zirconium with SnAg and SnAgCu
solders (again lead free) there have been some studies done that have shown
would prevent grain boundry sliding during steady-state creep. But the
article said that there should be more extensive tests done. That's at:

http://www.ivf.se/elektronik/Ep/Publications/LeadfreeSoSanAbstr.htm

If you go to:

http://semiconductor.supersites.net/chipscalen2/9811/technicald1.htm

There's an article there titled: "CSP Reliability Studies Performed with
Combined FEA and microDAC Measurements" which gets into some good discussion
about creep and CSP failure analysis...

-Steve Gregory-

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