Passive alone won’t work well, since the air against the heat sink will itself get hot and you end up with nothing. Gotta have a fan.
Also be aware that thermal tape is, while better than nothing, really is terrible at transferring heat. Proper thermal epoxy is an order of magnitude more conductive.
But while air flow is critical to making the cooling work well, it doesn’t need much air flow. A gentle breeze or a hurricane – makes no difference as long as the total amount of heat that you need to dissipate (which means the total amount of heat that actually makes it through the RAM) doesn’t exceed the capacity of the air to transfer away.
So that “dual fan” thing is just silly.
And note that with that thing stuck on, its game over as far as any mezzanine board goes.
And of course, you’re doing nothing to cool the BOARD – your heat sink will actually block air from reaching the board, which is responsible for a large portion (most?) of the cooling.
What I actually did, if you would read the description rather than just click the link, is;
- Cleaned off the crummy tape from the heat sink and glued it on with thermal epoxy,
- Added a fan that is perpendicular to the board standing beside it, blowing air across the heat sink and both sides of the board,
- Added PWM fan control via the ATMEGA on the sensor mezzanine board.
I have it set to turn the fan ON minimum speed when the CPU temperature reached 40 C, and scale up to maximum at 65. Each step shuts off 5 degrees below its startup temperature, so it steps down from full speed when it crosses below 60, and it shuts off when it crosses 35.
The fan is most of the time off, and you have to really beat on it before it throttles at all, which really means that you have to run a stress test on it.