Designing an Extrudable Aluminium Heat Sink Profile

As electronics become smaller and more powerful, the space available for thermal management tends to decrease while the amount of heat that needs to be dissipated increases.

This makes designing an extruded aluminium heat sink more of a challenge, because you want enough surface area to achieve the required cooling performance, but you also want it to be possible to manufacture the aluminium profile reliably.

There's a balance to strike between improving the performance of your heat sink and avoiding aluminium extrusion pitfalls.

Fin design for an extruded aluminium heat sink

The fins on a heat sink increase the surface area available to transfer heat into the surrounding air. So, when space is limited, it seems logical to make the fins thinner, taller and more closely spaced, but actually, there are limits both in terms of thermal performance and extrusion.

Firstly, the smaller the gaps between fins, the more difficult it becomes for air to move between them. While taller fins provide more surface area, it doesn't mean the heat will efficiently travel from the base to the end of each fin.

Then, from an extrusion perspective, thin, tall, and closely spaced fins also make an aluminium profile more challenging to manufacture. During the extrusion process, heated aluminium is pushed through a die containing the shape of the profile, and the aluminium needs to flow through every part of that die correctly. As fins become increasingly thin and deep, controlling this flow and maintaining the required geometry becomes more difficult. Things like cantilever length, push zones, alloy, and generally how extrusion works must be considered alongside the cooling performance you need.

Understanding the limits of aluminium extrusion

There is no single minimum fin thickness, maximum fin height or minimum gap that applies to every aluminium heat sink extrusion. What can be manufactured depends on the complete profile, like size, alloy, fin geometry, base thickness, tolerances, and the extrusion press used.

One particularly important consideration is the relationship between fin height and fin thickness. As a fin becomes taller relative to its thickness, it becomes progressively more challenging to extrude and keep within tolerance.

Compact heat sinks can push these limits because designers naturally want to fit as much cooling surface as possible into a small space. But an aluminium profile that is theoretically possible to extrude isn't necessarily the most economical one to manufacture repeatedly. Sometimes, just a slight increase in fin thickness or gap is enough to make production considerably more reliable, and cheaper for you.

The base of your aluminium heat sink profile

It isn't just the fins that need to be considered careful. The base is important, too.

The base is the section of the heat sink that sits between the electronic component and the fins, and it is the part of the heat sink that allows heat to spread into the rest of the profile.

From a manufacturing perspective, its thickness can have an important effect on the aluminium extrusion. A very thick base combined with very thin fins creates large differences in material thickness within the same cross-section, which can make it more difficult to control how the aluminium flows through the die.

The contact surface may also require more precision than the extrusion process alone can provide.

If specific flatness, surface-finish or dimensional tolerances are required where the heat sink contacts the electronic component, the surface can be machined after extrusion. Mounting holes, threads, slots and other features can also be added during secondary machining.

So, there's also an element of machining as well as extrusion that should be considered, therefore designing the heat sink as a finished, machined aluminium component rather than only ensuring extrusion is possible.

Designing compact aluminium heat sinks that are possible to manufacture

The final aluminium heat sink profile therefore needs to balance its thermal requirements with the realities of extrusion.

Thin and tall fins can provide additional surface area but become increasingly challenging to manufacture. A thicker base may be required for thermal reasons, but that then creates another consideration for material flow. Tight tolerances may be necessary in some areas, while others may not require the same level of precision.

This is why it can be useful to involve your aluminium extrusion supplier before the heat sink design is completely finalised, to have them take a look and see whether it is designed for manufacture as well as robust thermal management.

Get in touch with us if you're looking for a supplier of aluminium profiles, manufactured to your specifications.