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When do we use Irms value from process manual?

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ms_90

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Whatever scenarios i have faced, i always used Idc value to determine the width of metal.
So, why Fab has provided the Irms value in the process manual?
when do we need it?



thanks in advance..
 

Quite easy, if you want to consider the metal trace width with ac-signals.
 

You should have a different electrmogration rule for AC (zero
average), which Irms would index rather than Idc. Irms of course
works fine for DC signals against a DC rule, too. You just have
to make sure your basis matches your application.

Irms may also pertain to resistor power-density rules, similarly.
 

johnjoe said:
Quite easy, if you want to consider the metal trace width with ac-signals.
Click to expand...

i will give you an example
say for particular technology node you will find two current values ie Idc and Irms
so now Idc=0.2mA/um and Irms=0.8mA/um (i am specifying these values as an example)
Now for same metal width Irms is more than Idc. so, if there will be a AC signal n you are using Idc values to calculate metal width then you will get more wider metal and it will be good to avoid EM.

So in my experience i always used Idc for calculating metal width even though AC current is flowing through the net.

Now can someone please tell me when that Irms current is needed?
 

Sometimes you're limited in space and don't have the opportunity to take the larger width. Or in RF-applications, where an increased metal width has worse properties compared to narrow trace width. E.g. consider an on-chip transformer, you don't want to use wider width than necessary because of trace parasitics. And it becomes even more important with increasing frequency.In the case of dc-current or low frequency application, I agree with you, let's say for supply routing and if you have the space!
 
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    ms_90

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thanks a lot johnjoe..
 

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