RE: [SI-LIST] : Layout of Bypass Cap

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From: Michael Nudelman (mnudelman@tellium.com)
Date: Fri Mar 16 2001 - 10:49:14 PST


Kai:
 
It is better to connect a pin to a cap by a short trace and then the cap to
a plane by a via.
In case you connect just the cap to the plane and the pin to the plane you
incur double via inductance between the IC and the cap.
However the latter in the most cases is still OK, especially when the IC is
such, that to connect by a short fat trace the pin to the cap is impossible;
then the double via inductance may be less than the trace inductance.
 
In any case your goal is to minimize the inductance between the cap and the
IC,

-----Original Message-----
From: Kai Siang [mailto:bigmac@singnet.com.sg]
Sent: Friday, March 16, 2001 01:17
To: si-list@silab.eng.sun.com
Subject: [SI-LIST] : Layout of Bypass Cap

Hi,
 
A question on bypass caps. How do I place bypass caps ? Do i connect a fat
short trace from the pad of surface mount cap to the supply pin of the IC
and then punch a via to the power plane near this pin ? Or can i place the
cap physically near the supply pin and just punch a via into the power plane
? Which approach is better ?
 
 
Thanks
Kai Siang
 

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