[SI-LIST] Re: Question regarding thermal layers

Dennis,

This is the second time in about a week that someone has suggested using
"thermal" layers in addition to 'ground" layers. I responded to the last one
suggesting they use the thermal layers as ground, but maybe I'm missing
something. What is is it that makes you feel that a sheet of copper that you
are using to conduct heat cannot also do the job of conducting current?

Alan Hilton-Nickel
NVIDIA Corp,
Santa Clara, CA

> -----Original Message-----
> From: Dennis Tomlinson [mailto:det_werks@xxxxxxxxxxxxx] 
> Sent: Sunday, August 10, 2003 4:27 AM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Question regarding thermal layers
> 
> 
> I am designing a conductin cooled module which will employ 
> thermal layers in the stackup and underfill on selected 
> devices. The thermal layers are DC isolated from circuit 
> ground. I am proposing the following stackup:
> 
> 1. Signal + Comps
> 
> 2. Thermal
> 
> 3. Ground
> 
> 4. Signal
> 
> 5. Signal
> 
> 6. Ground
> 
> 7. Signal + Area Fills (1.8V, +5V)
> 
> 8. Signal + Area Fills (-5V, 2.5V)
> 
> 9. Power (3.3V)
> 
> 10. Signal
> 
> 11. Signal
> 
> 12 Ground
> 
> 13. Thermal
> 
> 14 Signal + Comps
> 
> My question is in regard to using the thermal layers as 
> signal returns. The dielectric between thermal and ground 
> layers is 5 mil core. I am contemplating the use of some 
> strategically placed bypass caps between thermal and ground 
> layers, as well as between thermal and 3.3V layers. Anyone 
> care to critique or comment on this plan? Would it make sense 
> to swap layers 9 (3.3V) and 12 (Ground)? Thanks in advance,
> 
> Dennis Tomlinson
> 
>  
> 
> 
> 
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