Don't you need capacitance to model thermal transient response, as opposed
to steady state.
Scott McMorrow
Consultant - R&D
Teraspeed Consulting - A Division of Samtec
16 Stormy Brook Rd
Falmouth, ME 04105
(401) 284-1827 Business
http://www.teraspeed.com
On Fri, Aug 28, 2015 at 11:21 AM, Shimko, Steve (ES) <s.shimko@xxxxxxx>
wrote:
I have not seen a capacitor symbol used in the thermal models, but that
does not mean that there are not capacitive like effects that occur,
especially during thermal transients (such as when first turning on).
Steve
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Jason Young
Sent: Friday, August 28, 2015 11:11 AM
To: Charles.Grasso@xxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: EXT :[SI-LIST] Re: Not SI - Thermals!!
Hi,
I'm not an expert, and will bow before those with better advice, however I
have a little recent experience. A PCB is made of copper, k=400W/mK(ish)
and loft insulation(glass fibre/epoxy) k=0.3W/mK(ish). Heat will not jump
across breaks in planes. Dissipating heat laterally on an inner layer is
good, but it's still sandwiched in layers of a thermally poor conductor.
Dissipating on an outer layer is better. I can't emphasise how important
thermal vias are. "Ten 0.25mm thermal vias are as effective at conducting
heat through the board as 1 sq inch of FR4 with no vias" based on a lot of
assumptions but it gives you a sense of their importance. Consider copper
filled vias if you have real problems. Of course getting the heat from the
package to the board is one problem, getting it out of the lovely small ID
is another problem.
TI have a nice application note. See page 4.12 (96):
http://www.ti.com/lit/ml/slup224/slup224.pdf
If they are using capacitors as models, I can only assume they are
modelling thermal mass and not looking at system in equilibrium.
Best regards,
Jason
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Grasso, Charles
Sent: 28 August 2015 15:39
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Not SI - Thermals!!
Hello all,
Please forgive the sharp right turn I am taking!
I am getting into the thermal modeling at the PCB level and the system
level. Naturally my first port of call is a search engine -I ended up
looking like Marty McFly after using the power amp at the Docs house! The
information is overwhelming. So - two questions, one detailed and a general
one.
1 (detailed) why are thermal heat paths represented both visually and
schematically as resistors but then other papers use capacitance as the
electrical analogy?
2. General: I am a tyro (totally and completely) at this. Would you nice
folks point me to an "Idiots Guide to Thermal Effects in Electronics
Systems" kind of book - I' d even take a Cliff Note version! - or other
useful starting point?
Thanks again!
Best Regards
Charles Grasso
Compliance Engineer
Echostar Communications
(w) 303-706-5467
(c) 303-204-2974
(t) 3032042974@xxxxxxxxx
(e) charles.grasso@xxxxxxxxxxxx
(e2) chasgrasso@xxxxxxxxx
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