[SI-LIST] Re: Return path and C/S Impedance
- From: Alan Hilton-Nickel <AHilton@xxxxxxxxxx>
- To: "'si-list@xxxxxxxxxxxxx'" <si-list@xxxxxxxxxxxxx>
- Date: Mon, 4 Aug 2003 12:32:09 -0700
Sudheer,
What is the source of the heat you are trying to dissipate? If it is from
one of the chips on the board, I would expect an extra pair of power and
ground planes to do the job nicely. If you have a heat sink on the part that
you are connecting to the thermal planes, but isolating those planes from
the ground system, you are likely making an EMI antenna.
Depending on what your answers to the above question is, you may want to
consider this stackup:
TOP
GND
PWR
SIGv
SIGh
GND
PWR
BOT
And connect your heat sink directly to the ground planes with multiple
connection points as close as possible to the chip to minimize
inductance/loop area.
Alan Hilton-Nickel
NVIDIA Corp.,
Santa Clara
> -----Original Message-----
> From: Sudheer B S [mailto:sudheer@xxxxxxxxxxxx]
> Sent: Monday, August 04, 2003 9:57 AM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Return path and C/S Impedance
>
>
> Hi All
>
> I have one quection about return paths for the signals on
> few routed
> layers
>
>
> The layer stackup is designed for Controlled impedance of 50 Ohms
> (1.6mm thickness)
>
>
> Present stackup Proposed Stackup
>
> TOP TOP
> GND GND
> SIGv SIGv
> SIGh Thermal1
> PWR Thermal2
> BOT SIGh
> PWR
> BOT
> ( Distance between SIGv and SIGh remains same in the proposed layer
> stackup )
>
> As per the thermal analysis inputs Two thermal layers has to
> be added to
> dessipate the heat ( meant only for Thermal via's)
>
> If I introduce the two layers between SIGv and SIGh ( Thermal
> layers not connected Electrically to maintain
> the same C/S Impedance of the routed signals in SIGv and SIGh
> ) , does this have any adverse effects on the signals
> return path and
> Impedance routed in SIGv and SIGh ?
> where these Thermal layers can be connected to ? , the
> chasis ? if
> so then it will be connected electrically
> Is this a better idea to preserve the C/S Impedance of few
> signals ?
>
> Any inputs to imrpove this configuration will be of
> great help
> to me :-)
>
> Regards
>
> SUDHEER
>
>
>
>
>
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