[SI-LIST] Re: Question regarding thermal layers
- From: Dennis Tomlinson <det_werks@xxxxxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Sun, 10 Aug 2003 16:28:02 -0700 (PDT)
> > The thermal layers are DC isolated from circuit ground.
> Why?
This is an existing system.
>> Why not connect them to ground (or power) and let them do useful electrical
>> work too?
The thermal layers connect to the chassis - both thermally, and electrically. If
I use the stackup I'm proposing, I'll optimize thermal conductivity, but
microstrip
signals will tend to use these layers as a return. The thermals should be
tightly coupled to
GROUND at the higher frequencies, but at lower freqs I suspect I'll need
several
stragegically placed capacitors to help complete the loop.
If I bury the thermal layers deep within the stackup, say dead center, and
surround
them with GROUND/POWER layers, I can keep return currents off of them.
Thermal performance, however, will go to hell in a handbasket. I can partially
fix this
with thermal vias placed underneath most critical parts, but I give up
cherished routing
channels. These disadvantages will undoubtedly cost me two or four additional
layers. I'm already a bit over the height limit, so....
Any thoughts?
Dennis
Hal Murray <hmurray@xxxxxxxxxxxxxxx> wrote:> The thermal layers are DC isolated
from circuit ground.
Why?
Why not connect them to ground (or power) and let them do useful electrical
work too?
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