Elger G.,Ingolstadt University of Applied Sciences |
Kandaswamy S.V.,Ingolstadt University of Applied Sciences |
Liu E.,Ingolstadt University of Applied Sciences |
Hanss A.,Ingolstadt University of Applied Sciences |
And 3 more authors.
Microelectronics Journal | Year: 2015
An innovative sensitive test method is developed to detect solder joint cracking for high power LED packages. The method is based on transient thermal analysis and can fully replace the still dominating light-on test. For experimental application of the model, test groups of LED packages were soldered with two different lead free solders (SnAgCu305 and Innolot FL-640) on Aluminum Insulated Metal Substrate (Al-IMS) and exposed to temperature cycles. Transient thermal measurements were performed directly after assembly and after specific cycle numbers. After data processing the increase of the relative thermal resistance between the initial signal at "0" cycles and ". n" cycles is obtained and correlated with cracks in the solder joint by cross sections. Based on the CAD and material data of the LED package a finite element (FE) model is set up. The time-resolved temperature curves are properly reproduced by transient thermal simulation. The measured "0" cycle curves are fitted using the FE model by adjusting a few material parameters within their allowed tolerance range. A parameter sensitivity analysis is performed. The impact of a crack in the solder joint between package and printed circuit board (PCB) on the time resolved temperature curve is simulated. The simulated crack propagates from the corner of the package to its center. The experimental measured curves are reproduced. Based on the simulation a failure criteria is defined, representing a crack length between 20% and 30% of the solder joint area, and Weibull curves are calculated. A higher creep resistance for the test group soldered with Innolot FL-640 compared to the test group soldered with SAC305 is observed. © 2015 Elsevier Ltd.
Marchuk A.,Ludwig Maximilians University of Munich |
Wendl S.,Ludwig Maximilians University of Munich |
Imamovic N.,Ludwig Maximilians University of Munich |
Tambornino F.,Ludwig Maximilians University of Munich |
And 3 more authors.
Chemistry of Materials | Year: 2015
The isotypic nitridophosphates Ba3P5N10X (X = Cl, I) have been synthesized by high-temperature reaction under pressures between 1 and 5 GPa. The crystal structures of both compounds were solved and refined using single-crystal X-ray diffraction data. Accuracy of the structure determination as well as phase purity of the products were confirmed by Rietveld refinement and FTIR spectroscopy. The band gap values (4.0-4.3 eV) for the direct transitions were determined from UV-vis data using the Kubelka-Munk function and were confirmed by DFT calculations. Both compounds crystallize in the Ba3P5N10Br structure type (space group Pnma (No. 62), Z = 8; Ba3P5N10Cl, a = 12.5182(5) Å, b = 13.1798(5) Å, c = 13.7676(6) Å, R1 = 0.0214, wR2 = 0.0526; Ba3P5N10I, a = 12.6311(7) Å, b = 13.2565(8) Å, c = 13.8689(8) Å, R1 = 0.0257, wR2 = 0.0586) with a tetrahedra network being analogous to the topology of the JOZ zeolite structure type. The crystal structure is built up of all-side vertex-sharing PN4 tetrahedra leading to a zeolite-like framework with three-dimensional achter-ring channels containing alternately Ba and respective halide atoms. The condensed dreier-, vierer-, and sechser-rings form two different composite building units made up of 344286-cages. Upon being doped with Eu2+, the title compounds exhibit intriguing luminescence properties, which were compared with that of Ba3P5N10Br:Eu2+. Upon excitation by near-UV light, nonsaturated color luminescence from multiple emission centers was observed in the orange (X = Cl) and cyan to amber (X = I) spectral range of the visible spectrum. © 2015 American Chemical Society.
Strobel P.,Ludwig Maximilians University of Munich |
Schmiechen S.,Ludwig Maximilians University of Munich |
Siegert M.,Ludwig Maximilians University of Munich |
Tucks A.,Lumileds Germany GmbH |
And 2 more authors.
Chemistry of Materials | Year: 2015
Eu2+- as well as Ce3+-doped Ba[Li2(Al2Si2)N6] and its related Mg-substituted compounds Ba[(Mg2-xLix) (Al4-xSix)N6]:Eu2+ (x = 0-2) with x = 1.6, 1.8 have been synthesized by metathesis reactions in tantalum ampules. Crystal structures were solved and refined from single-crystal X-ray diffraction data. All three compounds crystallize in tetragonal space group P4/ncc (no. 130) (Z = 4, Ba[Li2(Al2Si2)N6]:Eu2+: a = 7.8282(4), c = 9.9557(5) Å, R1 = 0.0144, wR2 = 0.0366). Their crystal structures, exhibiting the novel framework topology whj, consist of a highly condensed anionic tetrahedra network of disordered (Li/Mg)N4 and (Al/Si)N4 units connected to each other by common edges and corners. The degree of condensation (i.e., atomic ratio (Al,Li,Mg,Si):N) is κ = 1. The Ba2+-position is coordinated eight-fold by N3- in form of a truncated square pyramid. Upon doping with Eu2+, narrow-band emission in the green to yellow spectral range is observed (λem = 532-562 nm, fwhm ≈ 1962 cm-1). Ce3+-doped crystals of Ba[Li2(Al2Si2)N6] show blue emission (λem = 468; 507 nm). According to the tunability of the narrow-band green emission, application in LED-backlight liquid crystal displays appears promising. (Figure Presented). © 2015 American Chemical Society.
Durach D.,Ludwig Maximilians University of Munich |
Neudert L.,Ludwig Maximilians University of Munich |
Schmidt P.J.,Lumileds Germany GmbH |
Oeckler O.,University of Leipzig |
Schnick W.,Ludwig Maximilians University of Munich
Chemistry of Materials | Year: 2015
Due to the relationship between structure and luminescence properties, detailed crystal structure determination for microcrystalline phosphors is necessary for a profound understanding of materials properties. The yellow phosphor La3BaSi5N9O2:Ce3+ (λmax = 578 nm; fwhm ∼4700 cm-1) was characterized by a combination of transmission electron microscopy (TEM) and synchrotron microfocus diffraction as only agglomerates of crystals with a maximum size of a few μm could be obtained yet. La3BaSi5N9O2:Ce3+ was synthesized from LaF3, La(NH2)3, BaH2, Si(NH)2, and CeF3 in a radio frequency furnace. It crystallizes in space group Pmn21 (no. 31) with a = 9.5505(8), b = 19.0778(16), c = 12.1134(9) Å, and Z = 8. Its interrupted three-dimensional tetrahedra network contains zehner and dreier rings of vertex-sharing SiN4 and SiN2O2 tetrahedra. The crystal structure was confirmed by high-resolution TEM and Z-contrast scanning TEM. The element distribution was derived by bond-valence sum calculations. The infrared spectrum proves the absence of N-H bonds (Figure Presented). © 2015 American Chemical Society.
Wagatha P.,Ludwig Maximilians University of Munich |
Pust P.,Ludwig Maximilians University of Munich |
Weiler V.,Lumileds Germany GmbH |
Wochnik A.S.,Ludwig Maximilians University of Munich |
And 4 more authors.
Chemistry of Materials | Year: 2016
Highly efficient red-emitting luminescent materials deliver the foundation for next-generation illumination-grade white light-emitting diodes (LEDs). Recent studies demonstrate that the hardly explored class of nitridoaluminates comprises intriguing phosphor materials, e.g., Sr[LiAl3N4]:Eu2+ or Ca[LiAl3N4]:Eu2+. Here, we describe the novel material Ca18.75Li10.5[Al39N55]:Eu2+ with highly efficient narrow-band red emission (λem ≈ 647 nm, full width at half-maximum, fwhm ≈ 1280 cm-1). This compound features a rather uncommon crystal structure, comprising sphalerite-like T5 supertetrahedra that are composed of tetrahedral AlN4 units that are interconnected by additional AlN4 moieties. The network charge is compensated by Ca2+ and Li+ ions located between the supertetrahedra. The crystal structure was solved and refined from single-crystal and powder X-ray diffraction data in the cubic space group Fd3m (No. 227) with a = 22.415(3) Å and Z = 8. To verify the presence of Li, transmission electron microscopy (TEM) investigations including electron energy-loss spectroscopy (EELS) were performed. Based on the intriguing luminescence properties, we proclaim high potential for application in high-power phosphor-converted white LEDs. (Figure Presented). © 2016 American Chemical Society.
O'Connor A.P.,Max Planck Institute for Nuclear Physics |
Becker A.,Max Planck Institute for Nuclear Physics |
Blaum K.,Max Planck Institute for Nuclear Physics |
Breitenfeldt C.,Max Planck Institute for Nuclear Physics |
And 25 more authors.
Physical Review Letters | Year: 2016
We have studied the photodissociation of CH+ in the Cryogenic Storage Ring at ambient temperatures below 10 K. Owing to the extremely high vacuum of the cryogenic environment, we were able to store CH+ beams with a kinetic energy of ∼60 keV for several minutes. Using a pulsed laser, we observed Feshbach-type near-threshold photodissociation resonances for the rotational levels J=0-2 of CH+, exclusively. In comparison to updated, state-of-the-art calculations, we find excellent agreement in the relative intensities of the resonances for a given J, and we can extract time-dependent level populations. Thus, we can monitor the spontaneous relaxation of CH+ to its lowest rotational states and demonstrate the preparation of an internally cold beam of molecular ions. © 2016 American Physical Society.
Bhardwaj J.,Trimble |
Peddada R.,Trimble |
Spinger B.,Lumileds Germany GmbH
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2016
High power LEDs were introduced in automotive headlights in 2006-2007, for example as full LED headlights in the Audi R8 or low beam in Lexus. Since then, LED headlighting has become established in premium and volume automotive segments and beginning to enable new compact form factors such as distributed low beam and new functions such as adaptive driving beam. New generations of highly versatile high power LEDs are emerging to meet these application needs. In this paper, we will detail ongoing advances in LED technology that enable revolutionary styling, performance and adaptive control in automotive headlights. As the standards which govern the necessary lumens on the road are well established, increasing luminance enables not only more design freedom but also headlight cost reduction with space and weight saving through more compact optics. Adaptive headlighting is based on LED pixelation and requires high contrast, high luminance, smaller LEDs with high-packing density for pixelated Matrix Lighting sources. Matrix applications require an extremely tight tolerance on not only the X, Y placement accuracy, but also on the Z height of the LEDs given the precision optics used to image the LEDs onto the road. A new generation of chip scale packaged (CSP) LEDs based on Wafer Level Packaging (WLP) have been developed to meet these needs, offering a form factor less than 20% increase over the LED emitter surface footprint. These miniature LEDs are surface mount devices compatible with automated tools for L2 board direct attach (without the need for an interposer or L1 substrate), meeting the high position accuracy as well as the optical and thermal performance. To illustrate the versatility of the CSP LEDs, we will show the results of, firstly, a reflector-based distributed low beam using multiple individual cavities each with only 20mm height and secondly 3x4 to 3x28 Matrix arrays for adaptive full beam. Also a few key trends in rear lighting and impact on LED light source technology are discussed. © COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.