[SI-LIST] Re: Balancing Copper and dielectric losses?
- From: steve weir <weirsi@xxxxxxxxxx>
- To: jeff.loyer@xxxxxxxxx, <leonard.dieguez@xxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Wed, 06 Jul 2005 14:14:30 -0700
Jeff, if you have a short interconnect and low-loss dielectric, a skinny
trace over thin dielectric affords more skin loss and will be less likely
to resonate than will a wide trace over thick dielectric. The trick of
course is picking the right dielectric thickness to balance desired and
undesired loss when both long and short interconnects have to run on the
same etch layer(s).
Regards,
Steve.
At 12:49 PM 7/6/2005 -0700, Loyer, Jeff wrote:
>Leonard,
>In this posting, it's implied that there's some benefit to balancing the
>dielectric and copper losses. Is this merely a boo-boo, or is there
>some phenomena I haven't heard of?
>
>I'm also surprised to hear the "wonders for group delay" comment. Can
>you clarify what you mean by that?
>
>Jeff Loyer
>
>
>-----Original Message-----
>From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
>On Behalf Of Leonard Dieguez
>Sent: Wednesday, July 06, 2005 11:34 AM
>To: steve weir; leonard.dieguez; rsefton@xxxxxxxxxxxxx;
>Charles.Grasso@xxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
>Subject: [SI-LIST] Re: Q on Trace Width and Jitter for Diff Pairs
>
>Steve,
>
>I agree with you that you need the "right amount". For a given material
>and bit rate there is always the right trace width if you want to
>balance the dielectric loss to the copper loss.=3D20
>
>So for short interconnect I feel the problem would be creating a
>resonator or sharp filter. Impedance matching really becomes harder
>problem. I will normally use a 3D EM simulator like Ansoft HFSS to
>simulate each structure then do a end to end simulation. In this case I
>would try to excite the two points that we are worried about resonating.
>One problem with FR4 is that it is not well behaved and it does wonders
>for group delay. It is also hard to simulate if you want to take that
>into account. By the time you get PCBs back the "Mixture" may not be
>exactly what you thought it was.
>
>Leonard. =3D20
>
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