Screwed-on copper heatspreaders - what's at the interface?

[FMann]

I was reading some product info on some various CPU heatsinks and noticed that some low to mid-priced solutions (e.g., Thermaltake TR2 M1) have a copper heatspreader attached via screws.

So I'm wondering if there is any interface material between the copper and aluminum to facilitate heat transfer or are the two pieces just press-fit/mated to each other?

If it's just screwed on w/o any interface material, I wonder what would be the result if you were to add some thermal compound between the two pieces.

 

[Fallen Kell]

Thermal compound has lower conductivity then the metal does. The only reason we use thermal compound between the heatsink and the CPU (or other chip) is because they are not matted to each other during manufacturing.

 

[madcow235]

probably a little Solder because with just pure force, like 200lbs+, the copper would start to mold into the aluminum but aluminum bends way before that so it cant be sheer force and therefore must be solder or something.