Hi Jean-Paul,
I am glad we are on the same wavelength, perhaps with a difference in
emphasis.
In a message dated 08/11/2003 16:25:29, [log in to unmask] writes:
>It depends on what you call valid or invalid results.  For
model/acceleration factor
>development, I look for datasets for which the failures were confirmed as
>solder joint fatigue failures, with cracks propagating in the solder itself.
I fully agree. when I say "valid" I mean in terms of being able to make
pronouncements regarding the reliability of LF-solder joints relative to
Sn/Pb-solder joints in product.

>I don't know what the dominant creep mechanism is since I have not seen more
>than what is shown on the NPL web site.  However, I have seen similar trends
>at stress levels of about 20-30 MPa, which is why I think it's a concern
>(because those stress levels may be reached in some accelerated tests).
>At lower stress (with most data being in the range 10-20 MPa), SAC is more
>creep-resistant than SnPb by as much as several orders of magnitude.  I think
>the consensus on that one is well established.
>On the other hand, there is very little creep data at low stresses (<
>5-10MPa), which is the area of most interest for many service conditions.
We are in agreement. I am more concerned with product reliability, and thus
the low stress region.

>I am optimistic that the gaps will be filled over time and hopefully it won't
>take as long as it took for SnPb (although there is still work in progress
there).
I sure wish I could share your optimism.

Regards,
Werner

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