Aluminum and copper connection - thermal paste?

[Asiram]

Hello, I'll be making a custom passive CPU cooler soon, and this will require me to connect two flat surfaces, an aluminum and copper one. Do I use standard CPU thermal paste between aluminum and copper? Or should I use something specific for best thermal conductivity between those metals?

 

[Mr Evil]

Thermal paste will work fine. You could get better thermal conductivity by soldering, but soldering aluminium is tricky.

 

[Pick2]

The thermal expansion of copper and aluminum is different , soldering or thermal epoxy will cause problems. Use a good TIM / paste and be happy.
You cannot solder aluminum. TIG welding aluminum to aluminum works , but it takes an artist to do it right

 

[Mr Evil]

...You cannot solder aluminum....

It is possible with a little trickery, or by using special solder, or by nickel plating the aluminium, or by using ultrasonic soldering