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Re: ADC125, signal dist module, 2eSST tests



Hall D Electronics:

Hi Fernando,
	It would be great to get a thermal simulation... I will prepare a P-CAD 
file with the principal heat-generating components for the main & 
mezzanine boards. Do you intend to model details such as thermal trasfer 
through vias, or only the component and board and some idealized 
connection between them? Do you need component height attributes in the 
file?
	The ADC's _are_ indeed in a QFN package.
	I understand what you're saying about turbulent flow being important, 
but still I think that if the hot region is obstructed by too much stuff 
(such as heatsinks or turbolators of some sort) it may just divert the 
flow and yield worse results than a more "open" design. Does your 
thermal simulation software solve the fluid dynamics problem, or just 
the board thermal conduction problem with some ad-hoc assumptions about 
transfer into the air?
	Thanks,

	Gerard

p.s. The layer stack info is all in the P-CAD file. Or maybe that 
doesn't come through in the P-CAD2002 format, I don't remember - I can 
send it separately then, let me know.



Fernando J. Barbosa wrote:
> Hi Gerard,
> 
> The VME spacing of 8 mm between modules is very wide by today's
> standards, given the low profiles of the SMT components. Good heat
> transfer, via forced convection, is accomplished by turbulent flow
> around the components and so most of the air in the ~8 mm gap doesn't
> contribute much to the cooling of the components. That is, the cross
> section of the air flow responsible for cooling is small and a small
> percentage of the total flow. Therefore, the use of mezzanine boards is
> a very good approach to increasing  packaging density while maintaining
> proper cooling of the components. Packages such as QFN provide great
> heat transfer efficiency to the board but are not available on your ADCs
> but increasing the mass connected to the chips will also help.
> 
> In any case, I can perform the thermal simulations for your layout once
> you have settled on the placement. All I need is the PCAD PCB file,
> power dissipation per component and type and layer metal content
> (#layers, percentage of metal, thickness, etc.) Just let me know when
> you have all these information.
> 
> Regards,
> Fernando