Dr. Shahrom Mahmud

Universiti Sains Malaysia


Talk Title
Impact of Thermal Interface Material and Substrate on Luminous Flux Curve of InGaAlP Low-Power LEDs
Talk Abstract

One of the major problems in the lighting industry is the thermal management of the lighting device. Work on thermal management is a crucial area of research and development since device heat dissipation affects light output, reliability, and lifespan of light emitting diode (LED) packages. Handling of thermal resistance from the LED solder point to the ambiance is linked to the external thermal management that comprises a selection of cooling mode, heatsink design, and thermal interface material (TIM). Among the factors that help to increase the light output of the LED system are efficient substrate and thermal interface material (TIM). Many LED manufacturer datasheets display the value of the “maximum luminous flux” at the maximum input current whereby the luminous flux values are dependent on the LED system design. In this work, we investigated the impact of thermal interface material (TIM) and substrate on commercial indium gallium aluminum phosphide (InGaAlP) low-power light-emitting diodes (LEDs) with foci on complete luminous flux curve, thermal conductivity and junction temperature. Many low-power LED datasheets specify a typical luminous flux value of 9.5 lm measured at 0.107 W electrical power. One batch of commercial low-power LEDs was mounted directly onto different substrates that were FR4 and aluminum (Al)-based metal-core printed circuit boards (MCPCBs) with a dielectric layer of different thermal conductivity (2 W/m.K and 5 W/m.K). Another batch of LEDs was prepared with similar way but a layer of thermal interface material (TIM) was applied between the LED and substrate whereby two TIM materials were used namely thermally conductive epoxy (TCE) and thermally conductive adhesive (TCA). The thermal conductivities of TCE and TCA were 1.67 and 1.78 W/m.K, respectively. The LED parameters were measured using a combined system of T3Ster (the thermal transient tester) and TeraLED (thermal and radiometric characterization of LEDs) at various input currents. The luminous flux curve was explicated using the photoelectrothermal (PET) theory. It was found that the “maximum luminous flux” values in this work were much higher than that specified in the LED manufacturer datasheet in that the samples with thermal interface material (TIM) had the maximum electrical power shifted to higher values (higher than the specified 0.107 W as in the datasheet). We obtained the best results for the LED sample mounted on FR4 substrate with TCA layer whereby the “maximum luminous flux” value was 33 lm compared to that specified in the LED manufacturer datasheet (9.5 lm). The three-fold increase in the “maximum luminous flux” value was attributed to efficient LED heat removal via thermal conduction path through the TIM-substrate resulting in a much improved LED light emission. By using suitable combinations of TIM and substrate, LED customers can have great flexibility in designing efficient and cheaper low-power LED systems that not only work in low-power regimes but also possibly in high-power systems. We believe the results of this work are novel and not reported elsewhere.

Short Biography

Shahrom Mahmud obtained a BSc. degree in Materials/Ceramic Engineering from Iowa State University, and MSc-PhD degrees from Universiti Sains Malaysia. Having worked as an Engineer for a decade at Thomson, Sumitomo, Nippon Steel & IBM, Dr Mahmud was involved in the manufacturing and research of many electronic components. His research team has been actively engaging in transdiscplinary research involving electronic components, semiconductors, nanoparticles, biomedicine and thermal management. Currently Dr Mahmud is serving as an Associate Professor at the School of Physics, Universiti Sains Malaysia.

Talk Keywords
Light-emitting diodes; luminous flux; thermal management; substrate; thermal interface material; electrical power.
Target Audience
Students, Post doctoral, Industry, Doctors and professors
Speaker-intro video

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