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Thermalright sp-97 question (for Asus A7V8X-X)

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September 5, 2004 2:41:23 AM

Archived from groups: alt.comp.periphs.mainboard.asus (More info?)

Hello,

I recently got a Thermalright SP-97. I noticed it is very heavy (585g
without the fan).

Before I install it, I was wondering if this is too heavy?

It comes with a backplate to go behind the mobo to help with weight
dissipation. But it just seems so heavy... I'm looking for some
reassurance that my mobo (Asus A7V8X-X) won't crack 6 months later
from weight of this heatsink.
September 5, 2004 9:10:40 AM

Archived from groups: alt.comp.periphs.mainboard.asus (More info?)

In article <6c38b64b.0409042141.5c2cc0e2@posting.google.com>,
genericaudioperson@hotmail.com (xy) wrote:

> Hello,
>
> I recently got a Thermalright SP-97. I noticed it is very heavy (585g
> without the fan).
>
> Before I install it, I was wondering if this is too heavy?
>
> It comes with a backplate to go behind the mobo to help with weight
> dissipation. But it just seems so heavy... I'm looking for some
> reassurance that my mobo (Asus A7V8X-X) won't crack 6 months later
> from weight of this heatsink.

Raw data for the Athlon can be found in the Barton datasheet:

http://www.amd.com/us-en/assets/content_type/white_pape...

Table 20. Mechanical Loading
Location Dynamic (MAX) Static (MAX) Units Note
Die Surface 100 30 lbf 1
Die Edge 10 10 lbf 2

Die edge is if the heatsink is accidently inclined by 2 degrees.
Static force is the force of the spring loaded screws that hold the
heatsink down. The mass of the heatsink is a bit more than a pound,
and the max static force allowed is thirty pounds of force. The
dynamic force is that force applied to the processor die, when the
computer chassis receives a shock.

Force is applied to the heatsink for a number of reasons. There is
a bare minimum needed to just keep the heatsink in place. Additional
force is needed to meet the minimum force needed to make the thermal
interface material work. Note that, the boxed processor solutions have
an amount of force applied to make thermal tape or phase change material
work, and grease needs much less force than that.

As for the rest of my research, I chose Intel's web site, as the
AMD search engine is a PITA.

Page 16 of this document, mentions shock and how the dynamic force
is related to heatsink mass:

ftp://download.intel.com/design/Pentium4/guides/3005640...

"The heatsink mass can also add additional dynamic compressive load
to the package during a mechanical shock event. Amplification factors
due to the impact force during shock must be taken into account in
dynamic load calculations. The total combination of dynamic and static
compressive load should not then exceed the processor datasheet
compressive dynamic load specification during a vertical shock. For
example, with a 0.454 kg [1 lb mass] heatsink, an acceleration of 50G
during an 11 ms shock with an amplification factor of 2 results in
approximately a 445 N [100 lbf] dynamic load on the processor package.
If a 445 N [100 lbf] static load is also applied on the heatsink for
thermal performance of the thermal interface material and/or for
mechanical reasons, the processor package sees 890 N [200 lbf]. The
calculation for the thermal solution of interest should be compared
to the processor datasheet specification."

Roughly translated, this means your heavier than allowed heatsink
should be treated more gently than its less heavy counterpart. I expect
the silicon die of the processor will get damaged, before the printed
circuit board will. Fiberglass is very strong, and flexure of the PCB
is more likely to bust solder joints under the BGA chips, than damage
the FR-4 itself. The 11 ms shock sounds like a standard value that
comes from a shaker table used for engineering testing.

If the heatsink comes with a backing plate, that helps reduce bend near
the socket solder joints. Ideally, the mass of the heatsink should be
tied into the motherboard tray (but those really aren't that strong
anyway - mine isn't).

This document is a slide set that discusses some of the issues.
Treat this as general reading material.

ftp://download.intel.com/design/Pentium4/guides/2907280...

When Thermalright designed the heatsink, they should be aware of
the 30lbF limit on fastening the heatsink to the motherboard. The
100lbF limit you can help, by treating the computer with more
respect. If moving the computer (and this is good advice no matter
how your computer is constructed) consider how violent the transport
company is - if going UPS remove the disk drive, all plug-in circuit
cards, the power supply (due to its mass, it could tear the
screws out of the case, the heatsink (if it has any amount of copper
in it - due to mass). This doesn't leave much, other than the
motherboard and the case itself :-) A little less kicking of the
computer with your shoes helps too :-))

If you want to do more research, a good search term (include the quotes)

"heatsink design considerations"

There is an AMD document here:
http://www.amd.com/us-en/assets/content_type/white_pape...

It says the clip load target is 16lbf, which in your case would equal
4lbf per screw. I doubt Thermalright provides any design data for
you to look at.

HTH,
Paul
September 6, 2004 12:28:12 AM

Archived from groups: alt.comp.periphs.mainboard.asus (More info?)

thanks Paul,

I don't plan to ship or transport it. the computer will stay put.
since it has a backplate, do you think i'm ok?

it's not trauma from a bump or fall i'm worried about. it's the
constant weight over time finally making something overflex or break
that i'm worried about (including solder points).
!