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Design >> Analog Design >> how to estimate pad and pcb capacitance?
https://designers-guide.org/forum/YaBB.pl?num=1284040859

Message started by lhlbluesky_lhl on Sep 9^th, 2010, 7:00am

Title: how to estimate pad and pcb capacitance?
Post by lhlbluesky_lhl on Sep 9^th, 2010, 7:00am

for 0.18 um technology (tower), in general, what is the capacitance of an analog pad? can it be in the order of pF? 1pF, 2pF, 3pF, or any other value?

besides, for a 20mm-long wire in pcb board, in general, what is its equivalent resistance and capacitance? can it be 50 ohm and 1pF? or any other value?

please help me, and explain to me more about this, i really need your help, thanks all, thanks.

Title: Re: how to estimate pad and pcb capacitance?
Post by purplewolf on Sep 10^th, 2010, 2:14am

i use .4 pico

Title: Re: how to estimate pad and pcb capacitance?
Post by Alexandar on Sep 10^th, 2010, 2:41am

Depends on the size of the bondpad? You can find in the design rule document the cap/um2, and calculate it. I think the value purplewolf gave is reasonable.

Title: Re: how to estimate pad and pcb capacitance?
Post by pancho_hideboo on Sep 10^th, 2010, 8:31am

Lex wrote on Sep 10^th, 2010, 2:41am:

I think the value purplewolf gave is reasonable.

No, it is too large.

Capacitance of bonding pad is far less than 0.3pF~0.5pF in process which have more than five metals.

But if you have fairly large ESD elements attached to bonding pad, total input capacitance could be 1~2pF order.

In addition to these, selection of package is very important factor.

Title: Re: how to estimate pad and pcb capacitance?
Post by ywguo on Sep 10^th, 2010, 8:49am

If you have the schematic of your I/O cell or CDL, who do not simulate and get an more accurate value?

Title: Re: how to estimate pad and pcb capacitance?
Post by Alexandar on Sep 13^th, 2010, 12:07am

pancho_hideboo wrote on Sep 10^th, 2010, 8:31am:

Lex wrote on Sep 10^th, 2010, 2:41am:

I think the value purplewolf gave is reasonable.

No, it is too large.

Capacitance of bonding pad is far less than 0.3pF~0.5pF in process which have more than five metals.

Is it? For a 100x100 um pad, by calculation I get 0.4pF. But that is under the consideration that all metals are present under the pad (as is obligated by the design rule manual). So please illucidate why this number is too high..

Title: Re: how to estimate pad and pcb capacitance?
Post by pancho_hideboo on Sep 13^th, 2010, 3:56am

Lex wrote on Sep 13^th, 2010, 12:07am:

So please illucidate why this number is too high..

purplewolf wrote on Sep 10^th, 2010, 2:14am:

i use .4 pico

Sorry I was missing ".".