[SI-LIST] Re: Determination RLC value of a pin
- From: "Tom Dagostino" <tom@xxxxxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Wed, 12 Dec 2012 10:17:11 -0800
Siddharth
The pin starts at the point of contact between the board's solder pad and
the IC and continues all the way to but not including the metal on the
silicon die. So the pin model in IBIS describes the electrical path from
board to silicon. As Lynne points out each pin can have a different path,
where Zo, length, coupling, etc. can be different from other pins in the
same package.
Tom Dagostino
Teraspeed Labs
9999 SW Wilshire St.
Suite 102
Portland, OR 97225
USA
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tom@xxxxxxxxxxxxx
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-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Lynne C. Green
Sent: Tuesday, December 11, 2012 8:55 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Determination RLC value of a pin
Hello, Siddharth,
Not sure I understand your question. Here are some possible answers.
Hopefully one of them will help you in your IBIS debugging.
- The length between the I/O pad (on chip) and the PCB attach can vary for
each pin (history: this was a serious issue for large DIPs). As a rule of
thumb, signals in the center of a package have a shorter length
(smaller R and L) than signals in the corners. Bond wire length can
also vary for each pin.
- For flip-chip technology with no package, where the "bump" is the entire
interconnect, equal RLC values might make sense.
- The RLC values might represent a different package than the one you are
using.
Regards,
Lynne
"IBIS training when you need it, where you need it."
Dr. Lynne Green
Green Streak Programs
http://www.greenstreakprograms.com
425-788-0412
lgreen22@xxxxxxxxxxxxxx
On 12/11/2012 8:22 PM, Siddharth Rajagopalan wrote:
> Dear experts,
> I came across some IBIS files for DDR memory where
> there are several RLC values for the pins of the same group. For
> example, Different pins of DQ group have different RLC values. I was
> of the understanding that the geometry of a pin (in this case, a bump
> under the
> IC) determines the RLC value of that particular pin. Don't these pins
> have the same bump geometry. why do we have different values?? Kindly
> help me correct my understanding.
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