Many ideas and industry best practices are used to help meet the design goals of a properly configured heat sink.  One theme that is often considered but has historically been too expensive or impractical to manufacture is to make the part as a solid piece.  A heat sink made as one piece as a solid offers many advantages.  A heat sink from a solid piece of metal will often outperform heat sinks when the fins are mechanically joined at the base via bonding, brazing, soldering, etc.  These methods of building the heat sink often add thermal resistance and inhibit the thermal transfer.  Some of the more common methods that are used to build a heat sink from a solid include:

• Machining
• Casting
• Extrusion
• Forging

The chart below compares the thermal performance of three identical shapes; one formed by die casting, one formed by extruding and one formed by forging.  (Maching is not considered because the thermal performance is similar to forging but this option is discounted because it is often not an economical option for large scale production.)

Secondary machining operations increase production time and add to the cost.

An extrusion is made via a linear manufacturing process.  This process limits the design of the heat sink because the fins are often the full length of the extruded part and then must be machined and cross-cut to finish the final design.  Often the machining operations will require holes to be added to the part for mechanical fastners such as screws and push-pins, chamfers, cut-outs and more.  All of these actions will add to the production process and create long lead times and added costs for production runs.

The forging process has fewer limitations and allows for efficient production of complex shapes and fin structures.  A forged part is often pressed into shape within the tool and helps minimize or eliminate secondary machining operations because these extra features can be built into the tool and help maximize the efficiency for production.  Details such as holes, chamfers, pin fin, elliptical fins, variable heights, complex fin structures, etc are often created in the tool and allow the part to be made from one operation.

Increasing the surface area of a heat sink will often improve the thermal performance of a heat sink design.  However, care must be taken to make sure the increased fin density of surface area does not degrade performance of the heat sink due to increased pressure drop across the fin structure.  This pressure drop is often a result of low air flow caused by the higher fin density or other inhibitors of efficient air flow through the heat sink fins.

As part of designing the heat sink fins one is often limited by the manufacturing process being used.  For example, extruded fins must be tapered so that the material will pass through the tool without breaking. The number of fins in an extrusion will always be limited by the width at the base and the aspect ratio of the fins. These restrictions inherently limit the surface area.

Forged fins can be made almost perfectly straight allowing for more fins per square inch. The fins can also be formed into many different shapes, such as elliptical, pin and straight shapes. The resulting increase in surface area can be an important factor in improving thermal performance.

The pictures below illustrate this concept.

The forged heat sink pictured above increases the surface area by 18% without increasing size or weight. The result is increased thermal performance.