Cold Gas Dynamics Spraying (CGDS for short) is a relatively new process which was invented in the mid-1980's by Anatolii Papyrin, a researcher at the Institute of Theoretical and Applied Mechanics of the Russian Academy of Sciences. The process involves accelerating fine metal powders of 1-50µm in size to speeds of 300 to 1200 m/s within a stream of Helium gas.

The fine stream of metal powder is sprayed onto substrate where the impact causes deformation of both materials. In the above example copper powder is sprayed onto aluminum substrate where both materials subsequently bond by micro welding. As the powder impacts against the substrate at up to 1200m/s surface oxides are broken open and the substrate contact surface temperatures rises and leads to micro welding. The temperature of the entire process hovers around 300 degrees Celsius which is well below the melting point of either substrate or metal powder.

If we look at the construction of the Verax P14Cu heatsink, the process goes something like this... The aluminum heatsink extrusion forms the substrate to which copper power is bonded through CGDS technology. The copper layer formed on the base of the aluminum heatsink measures on the order of 0.2 mm thick, with an oxide content of less than 0.2%.

This oxide content is significant for a couple of reasons which we'll get to in just a moment. The copper section is then coated to about 0.02mm thickness with tin solder to facilitate attaching the actual copper base plate. The tin solder fills in the hair-line gaps which may exist between the Cold Gas Dynamic Sprayed layer of copper which acts as a solderable interface for the aluminum heatsink, and the 3mm thick copper plate.

You might be wondering what the point of all this is? Well, the other option of using silicon based thermal compound to act as an interface between the 3mm copper base plate and the aluminum doesn't really present the best option in terms of thermal conductivity. While silicon compound is significantly more thermally conductive than air (or any voids between the two pieces of metal), when compared to a true metal-to-metal bond it falls substantially short.

The point we were making about oxide percentages relates to the second most common process used to bond copper with dissimilar aluminum, and that is nickel plating to facilitate a solder joint. While there is nothing wrong with this process, Cold Gas Dynamic Spraying nets an advantage by the fact that is destroys most of the oxide layers which cover metal surfaces. For example aluminum can be anodized to protect its surface from the surrounding environment.

Anodizing basically creates a transparent oxide layer over the surface of the aluminum, and this is why anodized aluminum can be coloured black, gold, or a whole rainbow of colours. Anodized aluminum is not as thermally conductive as untreated aluminum, and so the same sort of situation stands here. By breaking up the natural oxide layer which forms on aluminum through the metal-to-metal micro welding brought about by Cold Gas Dynamic Spraying engineers are able to create nearly oxide and alloy-free bonds between copper and aluminum (and a whole host of other metals). The end result is that a better thermal interface is created between the copper and aluminum which means any heatsink making use of this technology should conduct heat energy from the copper base to the aluminum fins with less thermal resistance.

Cold Gas Dynamic Spraying is a process by which fine metal powder is accelerated to through a high velocity gas stream and impacted onto substrate surface to create a nearly oxide and alloy-free metal-to-metal forge bond. For example these four aluminum plates at left have had a thin layer of copper deposited via CGDS to form an aluminum-to-copper bond. No other materials like solder, glue, or even high heat are required, and the metal powder remains solid to prevent further oxidization. More information on the process is available through this site at the Universität der Bundeswehr Hamburg, and here.