[SI-LIST] Re: BGA vias outside the package
- From: Scott McMorrow <scott@xxxxxxxxxxxxx>
- Date: Wed, 28 Jan 2009 13:43:30 -0500
Ryan
Use a 2D field solver to compute the impedance of the trace you'll use
to connect the outer layer planes to the balls. If microstrip, prop
delay is approximately 150 ps/in. Once you know your trace impedance
you can compute the incremental inductance.
Z = sqrt(L/C)
tpd = sqrt(LC)
solving for Inductance
L = Z x tpd
For 50 ohm microstrip that would be 7.5 nH of inductance per linear inch
of trace.
For 40 ohm microstrip = 6 nH/inch
For 30 ohm microstrip = 4.nH/inch
For 20 ohm microstrip = 3 nH/inch
You can use this, along with available publicly published analytical
formulas for planes and vias to compute the total inductance in the
power delivery system up to your ball pads, to determine you power
system impedance vs. frequency.
regards,
Scott
Scott McMorrow
Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
(401) 284-1827 Business
(401) 284-1840 Fax
http://www.teraspeed.com
Teraspeed® is the registered service mark of
Teraspeed Consulting Group LLC
Ryan Sequeira wrote:
> Would like to understand the effects of supplying power and ground to the
> BGA by connecting
> vias to the VCC/GND plains and traces outside the BGA package.
>
> Pros: Allows for larger vias outside the package.
> Cons: Compromised noise performance through trace length added to VCC/GND
> trace length.
>
> Is there something else that needs to be taken care of....
>
> The BGA device is a CPLD, IO=3.3V, Core=1.8V, Fmax = 180MHz, VCCO(3.3V) - 11
> pins, VCC(1.8V) - 4 pins, GND - 15 pins
> The device is a 132csBGA, 0.5mm pitch, 0.3mm pad. So cannot afford to drop
> the vias within the BGA area. Microvias would be too expensive...
>
> Ryan
>
>
>
>
> ______________________________________________________________________________
>
> DISCLAIMER
>
> The information contained in this e-mail message and/or attachments to it may
> contain confidential or privileged information. If you are not the intended
> recipient, any dissemination, use, review, distribution, printing or copying
> of the information contained in this e-mail message and/or attachments to it
> are strictly prohibited. If you have received this communication in error,
> please notify us by reply e-mail or directly to netsupport@xxxxxxxxxx or
> telephone and immediately and permanently delete the message and any
> attachments. Thank you.
>
>
> ______________________________________________________________________________
>
> This email has been scrubbed for your protection by SecureMX.
> For more information visit http://securemx.in
> ______________________________________________________________________________
>
> ------------------------------------------------------------------
> To unsubscribe from si-list:
> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>
> or to administer your membership from a web page, go to:
> //www.freelists.org/webpage/si-list
>
> For help:
> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>
>
> List technical documents are available at:
> http://www.si-list.net
>
> List archives are viewable at:
> //www.freelists.org/archives/si-list
> or at our remote archives:
> http://groups.yahoo.com/group/si-list/messages
> Old (prior to June 6, 2001) list archives are viewable at:
> http://www.qsl.net/wb6tpu
>
>
>
>
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List technical documents are available at:
http://www.si-list.net
List archives are viewable at:
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
