Hi Yuan,
What i am saying is that if Cu trace (not PTFE or BT) has higher stress, it
means that the Cu trace has higher strain.
In your query on stress and strain, the CTE of PTFE and BT have to be given
for an answer. Also, what type of stress and strain? where in the structure?
where is the Cu trace that has crack?
rgds
TL
-----Original Message-----
From: LI YUAN [mailto:[log in to unmask]]
Sent: Saturday, March 10, 2001 8:40 AM
To: Zhang Tong Long
Cc: 'TechNet E-Mail Forum.'
Subject: RE: [TN] Substrate trace crack
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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