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Design >> Analog Design >> Calculation of minimum number of via: mean, rms or peak current to consider ?
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Message started by IvoryDesigner on Dec 4^th, 2012, 3:19pm

Title: Calculation of minimum number of via: mean, rms or peak current to consider ?
Post by IvoryDesigner on Dec 4^th, 2012, 3:19pm

Hi,

I using a cmos 180nm technology. I have a digital buffer that have 20 mA peak, 0,6 mA average ans 3.8 mA rms.

So I have a general question about which current to use to check the minimum number of via, as the documentation of the design kit give only Jmax (maximum DC current density).

I know the saver way it to consider the maximum, but for density intergration I can't afford it unless it is a must!

Thank you to enlighten me about that point and to share your experience about routing constraint to deal with high AC current.

Regards,

KC

Title: Re: Calculation of minimum number of via: mean, rms or peak current to consider ?
Post by XY-oriented on Dec 5^th, 2012, 4:55am

one tech I use a lot specify the max current/via for rms values and add that the peak current should not exceed 10 times the rms level.

in your case, since the peak is too high compared to the average (DC ?) I would design for 20mA/10 =2mA

Title: Re: Calculation of minimum number of via: mean, rms or peak current to consider ?
Post by tzg6sa on Dec 5^th, 2012, 6:21am

Except some extreme cases only the DC current matters, since the effect of AC currents on electromigration is some order of magnitude weaker.
Search for "AC current electromigration" if you want more detail.

Title: Re: Calculation of minimum number of via: mean, rms or peak current to consider ?
Post by IvoryDesigner on Dec 5^th, 2012, 2:10pm

Hi,

Thank you both for your helpful answers. I will look for "AC current electromigration" for more details.

Best regards !

KC

Title: Re: Calculation of minimum number of via: mean, rms or peak current to consider ?
Post by IvoryDesigner on Dec 5^th, 2012, 3:23pm

Hi here is a good link I found that explain which current to consider depending of the current type (bidirectional or unidirectional):
http://www.masamb.com/EM-IITD.pdf

KC