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Design >> Analog Design >> Dies Per Wafer Formula
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Message started by qiushidaren on Mar 1^st, 2007, 12:49am

Title: Dies Per Wafer Formula
Post by qiushidaren on Mar 1^st, 2007, 12:49am

Hi all,

In Rabaey’s book <<Digital Integrated Circuits-A Design Perspective>>, he gives us a formula for evaluating the dies per warfer, which is dies per wafer = π*(waferdiameter/2)^2]/die area – (π*waferdiameter)/sqrt(2*die area), I wanna know where is the second term (π*waferdiameter)/sqrt(2*die area) derived from? Thank you in advance.

Regards,
Terry

Title: Re: Dies Per Wafer Formula
Post by ACWWong on Mar 1^st, 2007, 2:04am

i guess it must be the circumference of the wafer (probably doesn't account for the slot though...) where you cannot fit in a full die.

Title: Re: Dies Per Wafer Formula
Post by ACWWong on Mar 1^st, 2007, 2:06am

oh, and its derived by dividing the circumference by the die diagonal, to give you the number of "uncomplete" die.

Title: Re: Dies Per Wafer Formula
Post by Andrew Beckett on Mar 1^st, 2007, 4:57am

That's a fairly reasonable first order approximation. Of course, most of the time the actual die placement on the mask (and the corresponding stepper information for when the reticles are stepped) will be optimised to maximise the number of dies. That equation obviously doesn't take into account the wafer flat, or the ring around the edge which can't be used (in some cases), nor if you have test dies on the wafer, and of course the die size needs to include the scribe - you don't necessarily know how big the scribe is up front because it will depend on how many test structures need to be put in the scribe, but normally it is kept to be as small as possible to maximise the utilised area of the wafer.

Regards,

Andrew.