The cooling system that used to be installed on the Radeon X1950 XTX is deservedly regarded as one of the best reference coolers combing excellent noise characteristics with high cooling performance. The developer drew upon that old design to create the cooler for the Radeon HD 3870.
It even doesn’t seem to differ from the Radeon X1950 XTX’s cooler at all, but its design is simpler because the RV670 generates less heat than the R580+.
Particularly, the heatsink is a monolithic thing milled out of a chunk of copper and lacking any advanced features like heat pipes or something. Such a heatsink was used in the cooler of GeForce 6800 in both copper and aluminum versions as well as in the legendary coolers Thermaltake Volcano 7+ and Cooler Master Aero 7+.
The monolithic heatsink is free from the main drawback of composite heatsinks, the additional thermal resistance in the place of connection of the ribs with the sole. The heatsink of the Radeon HD 3870’s cooler is rather small, not requiring a heat pipe for a uniform distribution of heat. It is cooled with a 7.2W centrifugal fan (12V, 0.6A) with a 75mm impeller.
The developer even saw to such small things as the slits under the fan: it is there that the power circuit heatsink is located. So, the hot air is exhausted by the fan through these slits avoiding a “heat bag” that might lead to overheat of the MOSFETs. Passing through the main heatsink and taking heat off the GPU, the hot air is exhausted out of the system case to keep better thermal conditions inside the PC. The memory chips are cooled by a separate L-shaped copper heatsink with good ribbing. That’s a proper solution for chips clocked at 1125 (2250) MHz.
Traditional dark-gray thermal grease is used between the heatsink and the GPU die. There is just the necessary amount of it here, unlike on the GeForce 8800 GT. The other components of the cooling system use elastic rubber-like thermal pads. The heatsinks on the memory and load-bearing transistors are fastened to the card separately from the main heatsink. The latter uses a four-pole fastening mechanism with a metallic back-plate and spring-loaded screws. This mechanism prevents the PCB from bending and the heatsink from misaligning. The profiled casing the fan resides in is attached to the main heatsink with six small screws. It is rather light, being no burden for the PCB.
By our estimate, the cooling system of the Radeon HD 3870 should be able to cope with 80-90 watts of heat at low noise level – that’s the amount of power the RV670 should dissipate when clocked at 775MHz. This thought-through cooler design is overall better than the reference cooler of the GeForce 8800 GT. Its only drawback is the dual-slot form-factor, but it’s a normal thing for every advanced graphics card today.