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March 2001

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Date:
Fri, 9 Mar 2001 17:39:45 -0700
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My colleague is adament that PTFE should have larger strain even thought
has less stress, because PTFE's Young's modulus is only 3 GPa compared to
BT of 14.5. I really don't know if his point is true or not. My initial
reaction is PTFE has less strain, but I canot convince my self let alone
him.

Just assume a very simple case, a 2-layer structure: one is die and BT;
the other die on top of PTFE. Assuming 2 materials perfect adhesion.
Cooling down from 100 to 0, assuming stress free @ 100C. Which will have
higher stress? which will have higher strain? Can anyone offer some help?

Thanks,

Yuan Li


On Fri, 9 Mar 2001, Zhang Tong Long wrote:

> For Cu higher stress basically mean higher strain because it can be
> considered as linear elastic material in the temperature range of -65C to
> 300C.
>
> But be cautious about the results from simulation, which can be misleading
> sometimes.
>
> rgds/TL
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]]On Behalf Of LI YUAN
> Sent: Friday, March 09, 2001 5:57 AM
> To: [log in to unmask]
> Subject: [TN] Substrate trace crack
>
>
> We were debating  PTFE vs BT. Our simulations show that PTFE has less
> stress. However, one of my colleagues argued that cu trace failures are
> strain dominant failures, hence less stress does not mean better substrate
> reliability. I don't know whether he is wrong or right. Please advise.
>
> Thanks a lot,
>
> Yuan Li
>
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