Cambridge Nanotherm of London reported that its Nanotherm LC thermal management solution addresses the unique requirements of chip-scale packaging (CSP) LEDs. This news comes just after the company expanded its manufacturing capabilities to meet the increasing demand for its thermal management technology.
Using CSP LEDs gives LED lighting designers several benefits over using conventional high-power LEDs (HP LEDs). CSP LEDs enable module developers to produce smaller, brighter and more cost-effective luminaires. For this reason, the market for CSP LEDs is growing rapidly and is projected to make up 34% of the HP LED market by 2020 according to Yole Développment.
However, using CSP LEDs also introduces a significant thermal challenge. Unlike conventional HP LEDs that employ a ceramic submount onto which the LED die is mounted, CSPs do not use a submount.
The ceramic submount of traditional LEDs enables the heat from the die to spread before it reaches the printed circuit board, helping to keep the die’s junction temperature within its approved range. Instead of using a submount, in CSP LEDs, the P and N contacts are metalized so the die can be soldered directly onto the PCB (usually a metal-clad PCB — MCPCB). This approach of metalizing the contacts reduces the cost, and size, of the, finished LED package.
The downside of removing the ceramic submount with its heat spreading capabilities is that it makes CSPs an intense ‘point source’ of heat that most MCPCBs cannot handle. A well-designed CSP LED module needs to conduct the concentrated thermal flux through the PCB’s dielectric layer and into the metal board where the heatsink can spread and removed it. If however, the heat is not removed quickly enough, the LED has a significant risk of overheating and failing catastrophically.
This thermal situation is exacerbated when designers mount CSP LEDs closely together to shrink modules and get higher flux density. Close mounting increases the heat intensity significantly, and thermal management must compensate.
MCPCBs are usually composed of an epoxy resin mixed with ceramic to form a thermally conductive, but electrically isolating, barrier. However, adding too much ceramic can make the composite friable, restricting the thermal conductivity of the layer.
Cambridge Nanotherm asserts that its thermal management provides a unique solution to this challenge. The company employs a heavily patented electrochemical oxidation (ECO) process that converts the surface of an aluminum board into a super-thin alumina dielectric layer. According to the firm, this nanoceramic alumina has a thermal conductivity of 7.2 W/mK while being just tens of microns thick. The thermal conductivity of the nanoceramic alumina translates to a composite thermal performance of 115 W/mK, which the company notes are much higher than any competitive MCPCB. This thermal performance allows the heat from the CSP LEDs to be conducted efficiently through the dielectric and into the aluminum board, thus ensuring a stable LED junction temperature.
Cambridge Nanotherm sales and marketing director Mike Edwards said, “CSPs, particularly Nichia’s D.M.C. LEDs, bring significant cost and manufacturability benefits to LED designers. 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.
“Epoxy-filled MCPCBs struggle to cope with the thermal profile of CSP designs, particularly when they are mounted close together on a module. Nanotherm’s unique nanoceramic MCPCBs overcome these limitations, enabling designers to build increasingly power dense modules. This, coupled with our comprehensive manufacturing capabilities, offers designers the optimum route to realizing their CSP designs.”