Apart from Aluminum, Copper is the most widely used material for making heat sinks, because properties of copper make it suitable for the purpose. Chief among them is its superior thermal conductivity and malleability. That means copper conducts heat better than most other materials and it is easy to form into different shapes that a heat sink necessitates. However, latest research has revealed another form of copper that promises still better thermal conductivities.
In today’s high-density electronics, thermal management plays a significant role. Reducing heat generation and removing heat from tight spaces is a constant challenge for electronics engineers designing smartphones, laptops, tablets and other space-constrained gadgets.
Engineers manage the heat generated in such high-density electronic designs by deploying optimized heat sinks. Versarien, a materials specialist, has found that using a micro-porous structure of copper maximizes its surface area enabling the heat sink become more effective in dissipating heat.
Micro-porous copper or copper foam has pores that vary in size from 300 to 600µm. The pores also make it lighter than solid copper, with a relative density of around 37%. Most importantly, the pores increase the surface area much more than that in traditional copper foam. A lost carbonate sintering process is responsible for generating the micro-pores.
Metallurgists compact and sinter a mixture of pure copper powder with a carbonate powder. This makes a matrix of copper ligaments, with the carbonate powder sandwiched in between. Once the mixture cools, water dissolves the carbonate, which is then recovered for recycling. The remaining copper forms a regular and uniform structure, which is highly rigid, porous and permeable and whose density per unit volume the manufacturer can easily control.
At present, Versarien makes heat sinks in form factors ranging from 10x10x2 to 40x40x5 mm. The company anticipates micro-porous copper foam heat sink usage in VOIP equipment, broadband routers, cable modems, flat panel displays, set top boxes and Gigabyte Passive Optical Network communication infrastructure.
Micro-porous copper foam is like an open cell structure, with an extraordinarily large number of interconnected pores distributed uniformly throughout the base copper material. To enhance its radiant properties, the manufacturer deposits a thin but exceedingly hard copper oxide coating at a high temperature. That gives the copper its high emissivity so desirable in a heat sink. Overall, you can have a significant height reduction in a passive heat sink footprint, without any compromise on its capacity to remove heat.
Testing provides evidence of its superior efficiency in heat removal. Micro-porous copper foam heat sinks outperform traditional solutions by more than 6°C/W. That means for every Watt of heat removed by a micro-porous copper foam heat sink, there is an additional temperature drop of about 6°C above what is offered by traditional heat sinks. For example, the thermal resistance of a 40x40x5 mm micro-porous copper foam heat sink is 17.4°C/W for an applied load of 5W. For a 20x20x5 mm heat sink, the thermal resistance is 35.8°C/W for an applied load of 2W.
Conventional heat sinks require special appendages such as pins, fins or micro-channels to increase their surface area. That increases the space taken up by the heat sink and makes it less efficient. When available space is limited, it is more practicable to use micro-porous copper foam heat sinks.