Eveliina Juntunen

Effect of Phosphor Encapsulant on the Thermal Resistance of a High-Power COB LED Module

With their many advantages, such as small size, energy efficiency, and long lifetime, light emitting diodes (LEDs) are conquering the lighting world. Blue LEDs, because of their high efficiency, are commonly used and a phosphor is used to convert blue light into white light. The remote phosphor concept has gained attention since it promises to deliver better efficacy than solutions in which the phosphor is applied directly on the LEDs. In this paper, the effect of phosphor packaging on the thermal performance of a high-power chip-on-board LED module is studied. Both simulations and measurements show that, despite the added thermal load caused by white light conversion losses in the phosphor, the average temperature of the phosphor-coated LEDs matches with that of noncoated LEDs. The phosphor encapsulant generates a parallel heat conduction path which reduces the thermal resistance from the LED chips to ambient and compensates the thermal power increase.

Fiber-Optic Transceiver Module for High-Speed Intrasatellite Networks

High-speed intrasatellite networks are needed to interconnect units such as synthetic aperture radars, high-resolution cameras, and fast image-compression processors that produce data beyond gigabits per second. We have developed a fiber-optic link, named SpaceFibre, which operates up to 3.125 Gb/s and is compatible with the existing SpaceWire network. The link provides symmetrical, bidirectional, full-duplex, and point-to-point communication. It employs 850-nm vertical-cavity surface emitting lasers, radiation-hardened laser-optimized 50/125 mum graded-index fibers, and GaAs p-i-n photo diodes. The transceiver electronics is realized using a multilayer-ceramic-substrate technology that enables the passive alignment of optical fibers to active devices. The SpaceFibre link demonstrator was tested to transfer data at 2.5 Gb/s over 100 m with a bit error rate of less than 1.3middot10-14. Fiber-pigtailed modules were stressed with temperature variations from -40degC to +85degC, vibrations up to 30 g, and mechanical shocks up to 3900 g. The test results of 20 modules show that the SpaceFibre link is a promising candidate for the upcoming high-speed intrasatellite networks

Thermal Performance Comparison of Thick-Film Insulated Aluminum Substrates With Metal Core PCBs for High-Power LED Modules

Evolution of lumens per watt efficacy has enabled exponential growth in light-emitting diode (LED) lighting applications. However, heat management is a major challenge for an LED module design due to the necessity to conduct heat away from the LED chip. Elevated chip temperatures cause adverse effects on LED performance, lifetime, and color. This paper compares the thermal performance of high-power LED modules made with two types of circuit boards: novel substrates based on insulated aluminum material systems (IAMSs) technology that inherently allows using thermal vias under the LEDs and traditional metal core printed circuit boards (MCPCBs) commonly used with high-power LED applications. IAMS is a thick-film insulation system developed for aluminum that cannot handle temperature higher than 660 °C. The coefficient of thermal expansion of IAMS pastes is designed to match with aluminum, which minimizes any bowing. The thermal via underneath the LED enables excellent thermal performance. More than 7°C reduction in LED junction temperature at 700-mA drive current and 27% reduction in the total thermal resistance from the LED junction to the bottom of the substrate were demonstrated for the IAMS technology when compared with MCPCB. When considering only the thermal resistance of the substrate, reductions of around 70% and 50% were obtained. This versatile and low-cost material system has the potential to make LEDs even more attractive in lighting applications.

Copper-Core MCPCB With Thermal Vias for High-Power COB LED Modules

To improve thermal performance of high-power chip-on-board multichip LED module, a copper-core metal core printed circuit board (MCPCB) substrate with copper filled microvias is introduced. As a reference, the performance is compared with alumina module with the same layout by means of thermal simulations and measurements. Up to 55% reduction in the thermal resistance from the LED source to the bottom of the substrate is demonstrated. The excellent performance of the Cu MCPCB module is due to copper-filled microvias under the blue LED chips that occupy the majority of the multichip module. The conclusion was verified by measuring increased thermal resistances of red chips without thermal vias on the Cu MCPCB module. However, as the blue LEDs dominate the thermal power of the module, they also dominate the module thermal resistance. The thermal resistance was demonstrated to correspond with the number of vias as lower thermal resistance was measured on modules with larger number of vias. The Cu MCPCB was processed in standard PCB manufacturing and low cost material, FR4, was utilized for the electrical insulation. Thus, the solution is potentially cost-effective despite the higher cost of copper in comparison with aluminum that is the most commonly used MCPCB core material.

Optical transceivers for interconnections in satellite payloads

The increasing data rates and processing on board satellites call for the use of photonic interconnects providing high-bitrate performance as well as valuable savings in mass and volume. Therefore, optical transmitter and receiver technology is developed for aerospace applications. The metal-ceramic-packaging with hermetic fiber pigtails enables robustness for the harsh spacecraft environment, while the 850-nm VCSEL-based transceiver technology meets the high bit-rate and low power requirements. The developed components include 6 Gbps SpaceFibre duplex transceivers for intra-satellite data links and 40 Gbps parallel optical transceivers for board-to-board interconnects. Also, integration concept of interchip optical interconnects for onboard processor ICs is presented.

High-speed ADC and DAC modules with fibre optic interconnections for telecom satellites

The flexibility required for future telecom payloads calls for the introduction of more and more digital processing capabilities. Aggregate data throughputs of several Tbps will have to be handled onboard, thus creating the need for effective, ADCDSP and DACDSP highspeed links. ADC and DAC modules with optical interconnections is an attractive option as it can solve easily the transmission and routing of the expected huge amount of data. This technique will enable to increase the bandwidth and/or the number of beams/channels to be treated, or to support advanced digital processing architectures including beam forming. We realised electrooptic ADC and DAC modules containing an 8 bit, 2 GSa/s A/D converter and a 12 bit, 2 GSa/s D/A converter. The 4channel parallel fibre optic link employs 850nm VCSELs and GaAs PIN photodiodes coupled to 50/125μm fibre ribbon cable. ADCDSP and DSPDAC links both have an aggregate data rate of 25 Gbps. The paper presents the current status of this development.

R2R process for integrating LEDs on flexible substrate

Injection overmoulding enables cost-efficient and fully integrated manufacturing of sealed flexible electronics devices with complex optical and mechanical functionalities. Furthermore, the electrical performance of the system can be improved by adding inorganic components on printed, flexible foil before in mould integration of the structure. The development of such the manufacturing process combining hybrid integrated structures with injection overmoulding is introduced in this paper. Contrary to traditional process of overmoulding the electronics label in sheet format, the flexible foil is processed roll-to-roll throughout the full manufacturing chain providing high-efficiency manufacturing. The paper discusses the manufacturing process development and results with a manufacturing trial of demonstrator processed in roll-to-roll hybrid manufacturing with good yield.

Injection moulded lens array for high power LED modules

Light emitting diodes (LED) are increasingly replacing traditional light sources due to their better energy efficiency and potential for reliable operation with long lifetime. The price of LED-based luminaires is still fairly high. One way to decrease the manufacturing cost is to use single lens optics for many LEDs. Optics should provide high efficiency together with low cost and excellent reliability. This paper introduces injection moulded lens array designed for high power LED modules. The lenses were employed with a series of modules containing 4 × 4 white LEDs whose total luminous flux varied from 660 to 2280 lm. The lens had dimensions of 73.4 mm × 73.4 mm × 13.9 mm and it included alignment pins and sides that could be used for sealing. The lens optics gave elliptical 30° × 90° lighting pattern with the uniformity of the illuminance on plane surface better than 3∶2. The lens was optimized for Philips Lumileds Luxeon Rebel, but it was tested also with Cree X-Lamp, Luxeon K2, OSRAM Golden Dragon Plus, OSRAM Diamond Dragon and Seoul Z-power LEDs. This paper presents goniometer measurements of the luminous intensity and compares them to the simulations. Two different lens materials, namely cyclo olefin polymer (COP) and polyamide (PA), was used. The paper lists experiences obtained using these lenses. Especially the reliability of the lens and its attachment is discussed. In total, 24 LED modules were stressed in environmental tests including thermal cycling, thermal shock, moisture and corrosion. Observations made on the lens materials as well as lens attachment materials are depicted. Moisture and corrosion was not a problem but high temperatures challenged both the lens and adhesive materials. 22 modules were subjected to a life test of 6000 h where they were driven with a constant current of 700 mA and monitored continuously. The life test revealed failures in both lens materials. The results challenge the reliability of the plastic lenses in high power LED modules operating in high temperature applications.

Improved infrared temperature sensing system for mobile devices

An infrared (IR) temperature measurement system consists of not only a sensor module and electronics, but also an optomechanical system that guides IR radiation onto the sensor. The geometry and emissivity of the parts affects the reading, if the detector sees not only the target but parts of the measuring system itself. In normal industrial applications, the optics is designed so that the surfaces stabilize to the same temperature as the sensor. This allows the error caused by the device temperature to be easily calibrated away. The correction is valid for stationary conditions and usually near the calibration temperature, which is typically at room temperature. However, we show that if the sensor is embedded into a mobile (hand-held) device which has heat sources, such as power electronics, the normal conditions are no longer valid and the calibration fails. In order to improve infrared temperature sensing for mobile devices, the optics concept was studied and detailed design was performed. In addition, the optics performance was modelled and verified by measurement sensor prototyping. A calibration procedure noticing operational temperature variations was applied. The repeatability of the implemented IR temperature sensor using on a correct transferred calibration curve was better than plusmn0.5degC in an operational temperature range from +12.6 to +49.3degC and target range from +10 to +90degC.