The topic of whether a CPU heat sink should be a copper heat sink or aluminum heat sink comes up in every thermal management design. And the short answer as to which material to use is:
There are many variables in designing the right heat sink, some of which include:
- Thermal management cost budget relative to BOM cost
- Orientation of boards (vertical or horizontal)
- How much weight or stress can be applied to the target chip
- How much keep out around a chip exists
- Air flow to the chip
- Air flow in and through the system (maybe you don’t need a heat sink at all as noted in an earlier ATS White Paper)
- Component dimensions
- Component height
- Target junction temperature
- Target case temperature
Let’s just focus on the material question though, copper heatsink vs. aluminum heatsink. Chris Soule, Engineering Director at Thermshield, has done a nice one page write up on the topic. Some of his key points include:
- Pure copper has about two times the conductivity of aluminum but that inherent advantage is only helpful when
- Air Flow speeds are 800 LFM
- The hot spot on the CPU or other semiconductor is small in comparison to the size of the chip itself.
- When air flow is 400 LFM or lower or the hot spot on the CPU or semiconductor is spread throughout the chip, then Aluminum is a better choice.
- The cost of a copper heat sink is often up to three times the equivalent sized aluminum heat sink
In our labs here at ATS, we’ve found that if an aluminum heatsink by itself does not have the necessary thermal condutivity, then using phase change thermal interface material (such as those listed in our Thermal Interface Roundup Post) with the proper pressure applied can make the difference in cooling.
So which do you use? Copper or Aluminum? It depends on the variables noted including your budget. One thing is for sure, there is no clear, one sized fits all answer and the thermal engineer should carefully decide. Hopefully before the electrical design is complete!