FreeLists / si-list / [SI-LIST] Re: Decoupling capacitors for BGA

["Mark Alexander" <mark.alexander@xxxxxxxxxx>]

Craig,

Are you sure it's 9 mil drill and not 9 mil finished? =20

It could be that you've got a 12-13 mil drill for 9 mil finished; that's =
closer to 10:1 aspect ratio.

-mark

=20

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] =
On Behalf Of craig mathew
Sent: Friday, May 12, 2006 10:08 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Decoupling capacitors for BGA

Hi Avanindra,
  =20
  I have a similar question. We are using 0201 decaps at the bottom of =
our BGA device for decoupling. We are using 9 mil drill size for via.=20
  =20
  Unfortunately we are up against two odds, our PCB is close to 125mil =
thick and we have small via drill, This increases the via inductance. Is =
there a way I can calculate to what frequency will my decap work =
effectively?
  =20
  I may be really dumb here but more I think more it seems logical to =
place decaps around the periphery of the device than at the bottom.
  =20
  Thanks
  Craig M
  =20
  =20
  ----text deleted-----
  =20
  Subbu,
if your board is not thick, you may want to consider using 0201 caps
directly underneeth the BGA aray, especially if GND and VDD are located
directly diagonally across from each other.
If you connect caps via individual traces to the pins, you will get alot =
of
resistivity.
Which can be a plus if your goal is to dampen high-frequency noise. =
However,
if you make traces very thin and long, you may slow your response time =
too.
So calculate your resisitivity per square to figure out what is the =
optimal
cap connection for you.

Dagmara



        =09
---------------------------------
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