NEWS ANALYSIS
Claiming breakthrough performance with its metal-clad PCB substrates, Nanotherm, has already made inroads into LED markets, reports Rebecca Pool.
cool Keeping LEDs
AS THE LED INDUSTRY SHIFTS to ever-higher brightness LEDs, the race is on to develop better thermal management strategies to dissipate heat. During LED operation a hefty 75 percent of applied electrical power is converted to waste heat, and be it by heatsink, heatpipe or cooling fan, how this heat is removed drastically affects LED performance and lifetime.
UK-based start-up, Nanotherm, claims to have the answer. Founded in 2010 by Pavel Shashkov and Segey Usov, former researchers at the Moscow State University, the company has developed a range of novel aluminium PCB substrates to act as heatsinks for electronics devices.
Currently targeting high performance LED markets, the substrates comprise an aluminium sheet, in which the surface – the top 10 to 30 microns – has been electrochemically converted to an alumina dielectric layer. A layer of copper is then epoxy-bonded or deposited to the dielectric layer, depending on customer budget, creating a circuit layer on the sheet, ready for PCB processing on industry-standard lines.
Shashkov and Usov claim their alumina dielectric layer provides excellent isolation with much improved thermal performance over the standard epoxies used as conventional dielectrics. The alumina layer is also up to ten times thinner than conventional epoxy layers and boasts a bulk thermal conductivity of
7 W m-1 K-1 in at some 3 W m-1
whereas high thermal conductivity epoxies come K-1
. And pleasingly for Nanotherm, its
independent tests indicate the thermal resistance of the overall PCB substrates is 20 percent less than today’s metal- backed PCBs, reducing LED operating temperatures by as much as 20 °C. As recently-appointed chief executive, Ralph Weir puts it: “I think this is a product that when engineers see it they say ‘wow, I really love that’.”
Patented process
The key to success is the conversion of the metal surface to an extremely thin dielectric layer. This process has roots in so- called plasma electrolytic oxidation (PEO), an electrochemical process similar to anodising, and developed by Shashkov and Usov more than a decade ago, to harden metal alloys for engineering applications.
Like anodisation, metal alloys, such as magnesium and aluminium, are dipped into a liquid electrolyte with an electric potential than applied to form an oxide-based ceramic – magnesia and alumina – at the alloy surface. However, PEO employs higher potentials so voltage discharges occur with the resulting plasma modifying the structure of the oxide layer. For example, sequences of voltage pulses can alter the surface roughness and porosity of the coating to produce harder- wearing surfaces.
Shashkov and Usov spent the best part of the 1990s developing the hardness treatment, setting up Cambridge-based Keronite, in 2000, to exploit the technology. But while the treatment produces a hard-wearing, as well as thermally conductive and electrically insulating surface layer, porosity within this layer renders the treatment useless for electronic applications.
With a thin dielectric layer, Nanotherm materials have a short thermal path from the source – a semiconductor device soldered to the copper surface – to the heatsink. [Nanotherm]
With this in mind, the pair went on to develop a new process that delivers an oxide ceramic surface layer comprising very densely-packed crystals with a lot less porosity, and launched Nanotherm in 2010. Details on how the surface layer is formed are scant although patent searches reveal a colloidal alkaline electrolyte is likely used, containing ceramic particles less than 100 nm in diameter.
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www.compoundsemiconductor.net Issue VI 2014 Copyright Compound Semiconductor
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