Tag Archives: copper

What is Micro-porous Copper Foam Technology?

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.

Graphene Metal Sandwich Improves Electronics

Heat conducting properties of the metal Copper are well known. However, scientists have been able to improve this property even further. By creating a sandwich of graphene with copper, scientists have found that the heat conducting properties of copper are strongly enhanced. Expectedly, this discovery could lead to further downscaling of electronic products.

This pioneering discovery is the work of two professors – Alexander A. Balandin and Konstantin S. Novoselov. Balandin is a professor of electrical engineering at the Bourns College of Engineering at the University of California, Riverside. Novoselov is a professor of physics at the University of Manchester in the United Kingdom. Both are corresponding authors for the paper they have published in the journal Nano Letters.

In their experiments, the researchers added a one-atom thick graphene layer on both sides of a copper film. The graphene layer had highly desirable mechanical, thermal and electrical properties. The researchers found that the addition of graphene layers on the two sides of the copper film increased the heat conducting properties of the sandwich by up to 24 percent.

According to Balandin, who initially discovered the unusual heat conducting properties of graphene in 2013, the enhancement of the ability of copper to conduct heat was an important discovery. Hybrid copper-graphene interconnects in electronic chips could now be made much smaller.

Copper is the most popular metal used for semiconductor interconnects and it replaced aluminum because of its better electrical conductivity. Layering copper with graphene and increasing the heat conducting properties of copper, therefore, became an important factor for the electronic industry.

Manufacturers tend to downscale the size of interconnects and transistors in computer chips with the intention of increasing the number of transistors therein. This puts an enormous strain on the performance of the copper interconnects they use. Downscaling had reached a point where there is little room for further improvement. Therefore, manufacturers were actively seeking improved interconnect structures with better conduction properties for current and heat.

Initially, even the researchers were surprised at the significant improvement in the thermal conduction properties of copper film despite the thickness of the graphene coating being only one atom thick. However, they soon realized that the improvement was not from the graphene acting as an additional heat-conducting channel. Rather, the improvement came about as changes occurred in the copper’s Nano- and microstructure because of the graphene layer deposition.

Researchers used microscopes to examine the grain sizes within the copper film both before and after adding graphene. They found that the high temperature deposition of graphene, in vapor form, stimulated the growth of grain sizes in the copper film. Ultimately, it was found the larger grain sizes in the copper coated with graphene that caused the improvement in heat conduction.

Another finding of the research was the improvement in heat conduction of copper was limited to thin copper films alone. This is a significant find since the future copper interconnects will be scaling down to the nanometers range. A nanometer is one-thousandth of a micrometer. Balandin and his team will be researching the heat conduction properties in copper films of nanometer thickness coated with graphene.