My arduino started to overheat, after working for about a half-hour, even with a fan blowing directly on the IC chip.
How can a attach a heat sink be attached to the IC chip on an Arduino Uno SMD that can be taken on and off.
The '328 should not be running hot. If so, that's usually a good sign that you have damaged an output pin thru excess current draw, or are sinking/sourcing too much current in total.
Is it the '328 that is running hot, or is it the voltage regulator running hot from a mix of high input voltage and high current draw by the board and attachments?
You can get something like this http://search.digikey.com/us/en/products/274-2AB/345-1087-ND/655555
and stuff like this to hold it on http://search.digikey.com/us/en/products/BP100-0.011-00-1010/BER160-ND/307782
but you shouldn't need it.
What are you powering the Arduino with? 9V wall-wart, 12 V wall wart?
What do you have connected to the 5V and IO pins?
The lower the voltage of the external supply the less power the voltage regulator has to 'burn-off' to drop the voltage.