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Politics : Formerly About Advanced Micro Devices
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To: Scumbria who wrote (50951)2/25/1999 12:47:00 PM
From: kash johal  Read Replies (1) of 1572099
 
Scumbria,

Re: L2 cache / heat problem

Well I think that we can rule heat out:

HEAT: It cannot be heat related. The Cache does not take that much power. And if it was causing them a problem they would have to LOWER the VCC and only be able to ship 400's.

I think it must be Yield related.
Clearly as they raise VCC they get a whole bunch more parts to pass the speed bin tests. My assumption on only the 400/450's was that they were going to ship the balance of speed bin failures as cheap laptop chips.

We know that at 2.2V the CXT core yields around 50% of parts at 400Mhz and above at the most. Raising the VCC by 10% can easily raise that substantially (maybe as high as 70-80%). Basically it is a gaussian distribution and it is a pretty narrow spread with these newer processess.

Yousef and Paul are absolutely correct that too high a VCC can damage the gate oxides and cause reliability problems. All semi companys are paranoid about such problems-so they guardband this quite agressively.

I suspect that they came out with 2.2 to ensure absolutely no reliability problems with the 0.25 micron parts. Then as they have life-tested higher voltage parts thru high temp tests they may well have concluded that another 10% was no problem. In which case they can start using the more aggressive VCC. I am sure you know that Paul/Yousef are are doing some scare mongering on this issue. If AMD is shipping it they will have life tested with still quite some margin on the reliability issue.

Regards,

Kash
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