How to make great Heat Sinks

Let’s start with the definition of the requirements of an ideal heat sink. So, what properties are usually needed?

High thermal conductivity
Leak tightness for any media
Good corrosion resistance
Sufficient mechanical properties

So, take an aluminium block and machine the heat sink out of it. It will have great thermal conductivity and good corrosion resistance!? True, but machining that much material becomes very cost-intensive.
Casting is the obvious solution. The typical HPDC alloys are all high in silicon, which is a major disadvantage for thermal conductivity.

The heat conductivity for pure aluminium is around 220 W/mK. In metals, the Wiedemann-Franz-law describes the correlation between electric and heat conductivity. In essence, a good electronic conductor is a good thermal conductor. Therefore, everything that harms the flow of electrons harms the thermal properties. These are:

Grain boundaries
Foreign atoms
Inclusions
Different phases
High temperatures

Taking these factors all into account, the limit for HPDC is around 150 to 160 W/mK of thermal conductivity. Many heat sinks require thermal conductivities above 170 W/mK. Otherwise, a cooling fan is needed. For large 5G antennas heat sinks the warm stream of air attracts wildlife that builds their nest in the stream until it fails. That kills the electronics quite quickly, and replacing an antenna in the wild is a lot of work.

So, the solution reduces the elements in the casting alloy as much as possible. Going below 7% of silicon massively reduces the castability in HPDC massively. But in Rheocasting, an alloy with 1.7% silicon is perfectly castable. Here, you can reach peak values over 190 W/mK, whereas the average is around 170 to 180 W/mK.

Because of the good feeding behaviour of Rheocasting, a several millimetre thick base and fins below 0.5 mm can be cast in good condition. So there won’t be leakage passages to find, which keeps the electronics safe.

If you would like more information on heat sinks, I have an in-depth case study on the Download page. Check out that article and schedule a free consultation below to learn how to use Rheocasting as a tool to acquire new business.