How to determine Power/Ground Pad number in Chip?

[clifftsai]

Hi:

How can I use more accurate analysis or steps to
determine the number of VDD/VSS (Power/Ground)
I should have in CHIP to supply enough current
and power for CHIP core and I/O pad.

There are two kind of Power Pad generally.
(1) VDD/VSS for core.
(2) VDD/VSS for I/O.
How to decide the number of them.

thanks!

 

[moorhuhn]

I wrote quite large list of recommendations, but this f... server logged me
out and everything was lost. So again briefly:
There are recommendadion for your I/O library provided by vendor,
use also spice to simulate SSO and package inductancy effects.
I took always more pwr pads than came out from these calculations
Core: You need power estimation, IR drop analysis on your rails and state
the limit to be able to rely on your timing analysis.

 

[lassyy]

Number of Power pad is mainly decided by max. DC and AC current. for analog circuit, DC current is important, and for digital circuit AC is important.One pair of VDD/VSS pads(60umx60um), The max. current is about 60mA. General, at least 20% margin will be given.

 

[tinybull]

another question

how to determine the power-ring and guard-ring width in the chip ? I have heard there is a formula , does someone know how to calculate ?