What are bonded fin heat sinks?

Bonded fin heat sink: what is it and how does it compare to other heat sinks?

A bonded fin heat sink consists of 3 main parts: a base with grooves, fins and an adhesive to bond the fins to the base.

Bonded fin bases:

Extruded bases from a multi-ton extrusion press

The base can be made in a variety of ways. In thermal management and production, extruded bases are the preferred method. Extruded aluminum alloys have great thermal conductivity and extrusion is easy to manage when it comes to production and labor.

Machined heat sink bases

Another option for making bases is to machine out grooves for the fins. Compared to extruded bases, using a sawed base is less accurate or a milled based is more time and labor intensive. Generally, these methods are solely used for prototype or small quantity runs.

Cast aluminum heat sink bases

Casting is also an option for large quantities or complex base geometries in addition to the fin grooves. But casting requires a large upfront investment in a die and you sacrifice thermal performance by using a die cast aluminum. These alloys have less thermal conductivity than it’s extruded or machined counterparts.

Fin options

For the most part, all fins are cut from coil stock. A progressive punch cuts off short pieces of a huge coil of thin metal to make the fins. Another machine straightens the fins so they fit into the grooves of the heat sink base. The coil stock can come in a variety of standard thicknesses and standard heights, so these can be mixed and matched with base options.

The bonding process

When you have your base and your fins, you’re ready to put them together to make your bonded fin heat sink assembly. Typically, a thermally conductive epoxy is used to bond the fins into the grooves of the base. These grooves are specially designed to balance the need for adhesion while minimizing the amount of epoxy between the fins and base. While the epoxies used for bonding are created to transfer as much heat as possible, they still aren’t as conductive at aluminum. The effectiveness of this design relies on keeping this layer as thin as possible. Once you put everything together and let the epoxy cure, you have a bonded fin heat sink.

Benefits of bonded fin heat sinks

A bonded fin heat sink has a few advantages over other heat sink technologies. The aspect ratio between the fin gap and fin height exceeds anything you can produce with extrusion. You can get a 60:1 ratio with a bonded fin assembly, where extrusions can only get up to a 20:1 ratio. Besides the aspect ratio, you have additional height compared to other technologies. Applications that have more vertical height available can take advantage of fins up to 6″ tall to generate more surface area for heat transfer. Where tooling costs are similar to extruded heat sinks, you pay more for the added design flexibility with labor and assembly time. Compared to other assembled fin types, bonded fins are economical. Reach out to Eaton design engineers to discuss if a bonded fin heat sink is right for your application.