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lhlbluesky_lhl

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how to estimate pad and pcb capacitance?
Sep 09^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.

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purplewolf Senior Member Offline Posts: 103	Re: how to estimate pad and pcb capacitance? Reply #1 - Sep 10^th, 2010, 2:14am i use .4 pico
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Lex Senior Member Offline Posts: 201 Eindhoven, Holland	Re: how to estimate pad and pcb capacitance? Reply #2 - 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.
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pancho_hideboo

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Re: how to estimate pad and pcb capacitance?
Reply #3 - 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.

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ywguo Community Fellow Offline Posts: 943 Shanghai, PRC	Re: how to estimate pad and pcb capacitance? Reply #4 - 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?
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Lex

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Re: how to estimate pad and pcb capacitance?
Reply #5 - 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..

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pancho_hideboo Senior Fellow Offline Posts: 1424 Real Homeless	Re: how to estimate pad and pcb capacitance? Reply #6 - 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 ".".
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