Cambridge Nanotherm Ltd of Haverhill, Suffolk, UK, a producer of nanoceramic thermal management technology, says that its Nanotherm LC thermal management solution addresses the unique needs of chip-scale packaged (CSP) LEDs.
CSP LEDs have a number of benefits over traditional high-power LEDs (HP LEDs), giving module designers the ability to produce smaller, brighter and more cost-effective luminaires. Market research firm Yole Développment forecasts that CSPs will comprise 34% of the HP LED market by 2020.
However, CSPs also present a significant thermal challenge. Traditional HP LEDs have a ceramic submount onto which the LED die is mounted. This spreads the heat from the die before it reaches the printed-circuit board, helping to keep the junction temperature of the die within its approved operating temperature. CSPs do not use a submount. Instead the P and N contacts are metalized, enabling the die to be soldered directly onto the PCB - usually a metal-clad PCB (MCPCB). This approach reduces the cost and size of the finished LED package.
The downside is that removing the ceramic submount (and its heat-spreading abilities) makes CSPs an intense 'point source' of heat that most MCPCBs simply cannot handle. The challenge is conducting the concentrated thermal flux through the dielectric layer of the PCB and into the metal board where it can be spread and removed by the heat-sink. If the heat is not removed quickly enough then there is a significant risk of the LED overheating and failing catastrophically. This situation is exacerbated by the ability to mount CSP LEDs extremely closely together – a benefit for shrinking module designs, but a major headache when it comes to thermal management as the intensity of the heat is increased significantly.
The key to understanding this challenge is the dielectric layer. MCPCBs are usually made of an epoxy resin mixed with ceramic to create a thermally conductive but electrically isolating barrier. However, there is a limit to how much ceramic can be added before the composite become friable, restricting the thermal conductivity of the layer.
Cambridge Nanotherm says that its approach to thermal management provides a unique solution to this challenge. A patented electro-chemical oxidation (ECO) process converts the surface of an aluminium board into a super-thin alumina dielectric layer. This Nanoceramic alumina has a thermal conductivity of 7.2W/mK which, coupled with being just tens of microns thick, yields a composite thermal performance of 115W/mK (much higher than any competing MCPCB). This means that the heat from the CSP LEDs is conducted efficiently through the dielectric and into the aluminium board, ensuring that the LED junction temperature is kept at a stable temperature.
"CSPs, particularly Nichia's DMC LEDs, bring significant cost and manufacturability benefits to LED designers," says sales & marketing director Mike Edwards. "However, by removing the heat-spreading submount, they push the thermal challenge from the LED manufacturers to the module and luminaire designers who now need new and innovative ways to handle the heat," he adds.
"Epoxy-filled MCPCBs struggle to cope with the thermal profile of CSP designs, particularly when they are mounted close together on a module," Edwards continues. "Nanotherm's unique Nanoceramic MCPCBs overcome these limitations, enabling designers to build increasingly power dense modules," he claims. "This, coupled with our comprehensive manufacturing capabilities, offers designers the optimum route to realizing their CSP designs."
Cambridge Nanotherm also recently expanded its manufacturing capabilities to meet increasing demand for its thermal management technology. The firm says that, in keeping with its wider philosophy, it is pushing to make its technology as easy to implement as possible. Nanotherm has hence established partnerships with a wide network of PCB and thin-film manufacturers to offer a broad and comprehensive range of options for circuitization, quality, volume and standards.
