Thermal Management
Leading edge thermal
management
A panelised die array (144 die per unit) on Nanotherm MBPCB material
Cambridge Nanotherm introduces a next generation thermal management substrate that uses nano-ceramic dielectrics. Steven Curtis explains this new technology to CIE
T
he use of ceramics in the electronics industry is by no means new - ceramic tiles for both the thick- and thin-film substrate markets have been around for many years. However, over the past decade, materials research has shifted its focus to find an
alternative to these fragile and costly substrates. The latest methods use an inexpensive base material, such as aluminium, and apply a ceramic coating to form a thermally conductive dielectric layer. Circuitry can then be formed on the dielectric layer resulting in the formation of a metal-backed PCB.
In the case of a nano-ceramic substrate, the surface of an aluminium panel is converted to alumina (aluminium oxide) using an electrochemical process; a complex electrical waveform is applied to the panel while it is held in an electrolyte solution. On the face of it, this may seem very similar to anodising, plasma electrolytic oxidation or micro-arc oxidation, but the reality is that none of these methods provide a dense enough layer to give good electrical isolation. Nano-ceramics have a crystallite size of about 20-40nm which, when combined with their density and interfacial properties, provide an excellent electrically isolative layer.
In 2010, Cambridge Nanotherm Ltd began to commercialise its coating technology for use in the electronics industry. The coating technology had been developed by the company founders Dr. Pavel Shashkov and Sergey Usov and had already been proven in other applications, such as motorsport and aerospace. The nano-ceramic layer, formed by a Nanotherm proprietary process, not only provides excellent dielectric strength but is also more thermally conductive that conventional polymer based PCB technologies.
Figure 1: Table of thermal conductivities of dielectrics 12 March 2013 Components in Electronics
The Nanotherm Metal-backed PCB is formed by taking a nano-ceramic coated aluminium panel and using conventional multilayer bonding processes to apply a layer of metallisation, i.e. copper. Nanotherm material
is processed through a PCB fabricator or PCB assembly facility in the same way that industry standard metal-clad PCBs and insulated metal substrate materials are. The difference is in its thermal performance.
Figure 2: Lay-up of Nanotherm MBPCB
Thermal performance There are two elements to the thermal impedance of a substrate - the thermal impedance of its individual layers and the thermal impedance at the interface between layers. Cambridge Nanotherm’s coating technology converts the surface of the aluminium panel to alumina, creating a composite which has a very low thermal impedance at the interface of the two materials. The thermal conductivity of the alumina dielectric is 7W/mK, which is higher than conventional filled epoxy dielectrics. Thermal impedance is also a function of layer thickness – the nano-ceramic layer can be grown in thicknesses as low as 10 micron
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