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Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | Next PageABE FMaGSthermal | SYSTEM DESIGNthe application, differenttypes of TIMs are availableon the market. In general,this layer should be verythin but able to increase theconducting surface areas byeliminating air gaps thatwould otherwise add to thethermal resistance.Material performance and cost comparison of PCB alternativesPCB materialVirtual testingTesting for thermal performanceis an expensive and time-consumingprocess that requires prototypes to bebuilt and that uses various measurementtechnologies such as infrared cameras.Evaluation programs specifically developedfor solid-state lighting, such as QLED®from Future Lighting Solutions, provideengineers with thermal simulation tools,which can deliver results based on customconditions within minutes. Changes canbe implemented and analyzed to executeAverage thermalresistance (K/W)*Relative cost per “Star”boardMetal-core (MC) PCB 20 100%High performance MCPCB 15 150-200%FR4 open vias 17 18-60%FR4 fi lled and capped vias 13 25-85%Ceramic (AlN) 11 200-300%Ceramic (Al 2O 3) 16 60-70%* Junction to bottom of boarddifferent case studies. Such an approach isalso very useful in applications with pulsedoperating conditions, for example, automotiveturn indicators or cell phone camerafl a s h e s .SummaryThe solid-state lighting industry recognizesthe importance of thermal systems, but thecomplexity of these systems is often underestimated,and the impact on the performance ofpower LEDs is not well documented.However, the mantra“Think thermal first” isbecoming more embeddedin the SSL engineering community.Pushing productperformance and lifetimeby optimizing the drive currentand emitter count isresulting in new materialsand implementation methods.Companies that historicallyfocused on electro-mechanics (i.e. connectorcompanies) now seem to be shifting tothermo-electric systems to meet the SSL industry’sneeds. Materials and methods primarilyused in very advanced, high-volume productsare now becoming available to the SSL engineerand designer. In the end, “Think thermalfirst” may not be just an engineering motto, itpossibly could be a key differentiator that willtrigger development of a successful product inthe emerging SSL industry.______________48 APRIL 2009 LEDsmagazine.comPrevious Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | Next PageABE FMaGS
Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | Next PageABE FMaGScontinued from page 52last wordmove very rapidly. Although this is a positivetrend, it can also create issues. For example,customers may want to wait for the next technologystep before committing themselvesto an LED-based solution. There is tensionbetween the fast pace of technology change,and customer and product requirements.We should be able to provide intelligentupgradeability for customers, to allow theeasy incorporation of new technology. Oneexample is a board layout that can incorporatedifferent Dragon LEDs that operate atdifferent power levels from 1 to 5 W.For cool white LEDs, customers are startingto become satisfied with the efficacy(lm/W value), but for warm white, the performanceis borderline for many applications,and definitely needs improvement. Butin addition to lm/W, there are many aspectsof LED performance that need further work— for example binning, lifetime and reliability.Simultaneously, there is further work todo throughout the whole value chain — forexample in drivers, or thermal management— so that people can realize the full value ofthe LEDs’ high efficacy.We continue to work on many aspects oftechnology, for example new chip technologywith much better linearity of efficiencyversus current density. We can’t share all thedetails of our R&D program, but we certainlyhave enough LED development work to keepus very busy for at least the next five years.OLED lightingOLED lighting is still in the R&D phase,and we are now trying to validate the manypotential applications. Even the simple conceptof a glass plate that emits light createslots of opportunities, and we are workingwith designers to explore these possibilities.For example, we are trying to determineways to use attributes such as a window-likepanel that is transparent when switched off,but can emit light at night.In parallel, we are working on technologyissues, and achieved 62 lm/W last year for awhite emitter. We have to develop low-costencapsulation schemes, for example, andimprove and optimize the substrate andthe emitter stack. The highest priority is toreduce the manufacturing cost of the panels,but we also need to improve features such asefficiency, lifetime and color stability. Andthis work needs to be done in tandem witha consideration for customer-required features.For example, a bottom-emitting structuremight be the easiest to implement inproduction, but does not necessarily offerall the features that customers want.With funding from German and EU bodies,we are progressing along our projecttimeline and passing through variousgates that will eventually move OLED lightingproducts into full production. There is ahealthy community making good progressin this area, with a number of competitorsracing to become leaders in the field.MORE DETAILS: www.osram-os.com_____________________________LEDsmagazine.com APRIL 2009 49Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | Next PageABE FMaGS
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