Jay.. thanks!
If Im reading this right,
A: copper is a better conductor electrically.
B: Alu expands and contracts slightly more than CU with temperature variances.
C: Copper draws energy into itself faster than alu.
However, I am wondering why manufacturers use a combination of these 2 metals instead of just solid CU? What advantage are they achieving buy this combination. With such small quantities used?
http://www.tp-e.com/TPEPres.pdf page 8
This shows the most efficent forced convection heat sinks to have a copper base with aluminium fins.
However
http://www.flotherm.com/technical_papers/t275.pdf
Page 3 shows copper having an advantage when it is thin, but is almost the same is the thickness of the sample approaches 1 mm X .8 mm.
http://www.flotherm.com/technical_papers/t281.pdf
There appears to be a 7% variance per 50 W of power in an air cooled environment in favor of CU
The last link showed very little difference between CU and AL. The most advantageous benifits of CU are the highest performance, however I see that the change is very small and AL is 3 times lighter and much cheaper per pound.
However, for with a watercooled block with water reaching both the copper and aluminum fins or posts of the block.. and the fluid addition to absorb the heat.. I think the differences will be negligible. What is then left is the design of the material and the efficiency in which it can transfer the heat to the liquid.
Conclusion. Manufacturers use the most expensive material in the most crucial area of the chip. After that the AL and CU similarities thermally void themselves out, as surface area to fluid contact is what will be transferring the heat. This brings the waterblock maker to use copper for the base, and freedom to use whatever they need for the top, as long as they are bonded in a favorable way to transfer heat between the two.
jaydee116 is right!
What do you guys think?