ATI R300 Package: Thermal Problems Caused by the Shim
put it bluntly, there is problem with the ATI R300 processor package that impacts just how well heatsinks
can cool on the Radeon 9700 Pro.
|The root of the problem is the shim, but is this gap thermally significant, or simply unimportant?
area around the R300's silicon core populated by ultra small capacitors and resistors, the manufacturer has placed something there for protection. That
protection comes in the form of a 4mm wide band of copper which runs
around the perimeter of the 40mm square package. It helps to prevent the tiny components from
getting crushed, or the core from being chipped.
This copper shim is glued to the surface of the PCB,
and if it were installed flush to the height of the silicon core,
it would actually be very useful.
Unfortunately, the problem is that the copper shim is
actually slightly thicker than the
silicon core by about 0.0023". This makes it impossible for the flat bottomed heatsink ATI use
to actually come in contact with the R300 core for optimal
In the retail package, ATI
have gotten around this by using a thick yellow thermal interface material (TIM) between the extruded
aluminum heatsink and the silicon core. That yellow TIM bridges the
most users looking to push their ATI Radeon 9700 card a little farther with the
stock heatsink will tend to want to remove the thermal interface material, and
replace it with a good quality thermal compound. TIM's are generally not known
for possessing the best thermal conducting properties.
You will of course remember that for a
thermal compound to work well, the smallest possible amount should be used.
After all, the material is just meant to fill in the microscopic voids between the
silicon and the relatively "rough" aluminum base of a heatsink. [Please see "Heatsink Fundamentals: Contact
Resistance" for more explanation on this topic]
With the ATI R300 FC-BGA packaging, the shim necessitates the use of a
rather thick layer of thermal compound just for the heatsink to make some sort of
contact with the core, and that isn't good. Several web
sites have even gone so far as to remove the shim with a sharp X-Acto
knife, but I'm not too keen on taking a chance in scratching (cutting) a trace
line on an expensive videocard, rendering it useless.
We can only guess that someone perhaps miscalculated
the thickness of the copper shim used on the R300 FC-PGA processor package,
or forgot to include the height of the adhesive in their calculations. If
you look very closely, there is a very small gap between the copper and the
Since it is
unlikely that ATI will make any changes in their manufacturing process to even
out the heights between the shim and the R300 core, the real question
that remains for us is what kind of temperature
hit are we talking about here? Is the gap caused by the shim thermally significant,
or simply unimportant? And what's more, if the stock heatsink were able to sit flush to the
silicon core, instead separated by a thermal interface material, what would the
this question we decided not to remove the shim (though some people have without
any problems other than a voided warranty), but rather to mill out a small area
from the base of the stock heatsink. Once we cut away some of the metal,
the heatsink would be able to sit squarely on the core.