An alumina coating process fit for service in space

A nanoceramic alumina coating process for aluminium printed circuit board (PCB) components was presented by Cambridge Nanotherm Ltd at the recent Electronic Materials and Processes for Space (EMPS) workshop which took place in April 2015 at the German Space Operations Centre near Munich, Germany.

Giles Humpston, Field Applications Manager at Suffolk-based Cambridge Nanotherm Ltd, opened proceedings with his company’s nanoceramic alumina coating process for aluminium printed circuit board (PCB) components, which enhances the material’s thermal and electrical properties.

Established methods for applying alumina coatings to a metal, such as anodising, plasma electrolytic oxidation and spray coating can already produce effective mechanical coatings. But their high surface roughness, low breakdown voltage and unpredictable deposition make them unsuitable for electronic applications.

Rather than simply coating, Nanotherm’s process converts the surface of aluminium itself into alumina, through electrochemical processing in an electrolytic cell filled with a benign alkaline solution, which can be safely disposed of down the drain. ‘It’s important to mention that this is a green technology,’ said Humpston – ‘one of the company’s founders demonstrated that it’s safe by putting a cup into the tank and drinking it, and he’s still alive!’

The resulting nanoceramic material maintains the robust mechanical properties of aluminium, but with thermal performance comparable with aluminium nitride – the boards survived thermal cycling from -40°C to 250°C without degradation, and PCBs with a thermal conductivity of 152W/mK can be manufactured by adhering copper foil to the top surface of the converted aluminium, Humpston said.

‘It’s alumina, but not as you know it’, he said. The composition of the nanoceramic layer is affected by the other elements present in the aluminium alloy, with chemical differences visible in the material’s colour – a purer grade produces an ivory finish, while alloys containing copper can be almost jet-black.