Hi Werner,
 
I agree with your comment and your method completely.
 
I would consider reviewing Young's modulus and a variable for degradation in the STII due to thermal excursions for inclusion in your STII value.
 
What if we were to take a sample of a PWB, make our measurements, calculate the STII to use as our control? Then expose similar samples to 3, and 6 thermal excursions (260°C)  to simulate assembly and assembly/rework. I bet the STII would change based on those thermal excursions. The degree of STII change would be a reflection of material robustness through assembly and rework.
 
Best regards,
 
Paul

________________________________

From: [log in to unmask] [mailto:[log in to unmask]] 
Sent: Tuesday, September 02, 2008 11:11 AM
To: Paul Reid; [log in to unmask]
Subject: Re: [TN] TMA result


Hi Leo & Paul,
With Pb-free, you need to consider Td, Tg and CTE for reliability in combination---that is why I developed the STII (Soldering Temperature Imact Index)-parameter.
Also, you also need to consider that you get different CTE's in the x and -direction (about 2 ppm/C), not to say anthing about the diagonal.



Werner



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