Ralf Schmidt

Ultraviolet Pumped Tricolor Phosphor Blend White Emitting LEDs

Near-UV and violet emitting AlGaInN single quantum well LED structures were grown by MOCVD on sapphire substrates. On-wafer tests before processing gave an output power at 40 mA between 1.4 mW at 380 nm and 6.7 mW at 420 nm. LED chips with wavelengths between 380 and 404 nm were selected for manufacturing radial UV LEDs and white emitting LEDs. The UV to white converters were prepared from broad band red, green and blue emitting powder phosphors with individual luminescence peaks near 610, 550 and 460 nm, respectively. White luminescence conversion (LUCO) LEDs with a warm hue and color temperatures in the range 4000-4300 K are demonstrated.

Effects of additional elements (Fe, Co, Al) on SnAgCu solder joints

The electronics industry has successfully transitioned to lead free soldering for computer and consumer products while in the automotive industry due to the very high reliability requirements this step is still in an ongoing process. In order to ensure or even to enhance the reliability of electronics the improvement of lead free solder joints based on Sn-Ag-Cu (SAC) solder has been the focus of many research projects already. One approach to improve the thermal fatigue properties of these alloys is to add a further alloying element SAC + X. Until now, further elements have mainly been added by metallurgical alloying, requiring special equipment and conditions. The powder production is even more difficult. In this paper a new way how to add minor amounts around 0.1 wt.-% of a forth element to SAC solder joints is presented. One possibility is to do the doping during the reflow process adding the additional elements via the flux by incorporating Co-, Fe-, Al- or other metal compounds into the flux. Experiments have shown that Co and Fe were successfully added while for certain other elements like for example Al this was not possible until now. In comparison to standard SAC solder the Co containing solder shows a refined microstructure and Co is found in the intermetallic phase Cu6Sn5. Fe which has been found at grain boundaries is not only attractive as alloying element but as metallization layer, too. It is possible to deposit Fe on printed circuit boards using electroplating. During soldering the slowly growing FeSn2 phase forms between the solder and the Fe layer.

Laminated electrochromic device for smart windows

An electrochromic device using tungsten oxide as an electrochromic electrode, cerium- titanium oxide as an optically passive counter electrode, laminated by a polymer based ion conductor has been fabricated and characterized. The fabrication technology as well as the optical switching behavior and cyclability show that this device is a promising system for smart windows in automotive and building application.

Nanowires in Electronics Packaging

In the light of continuous miniaturization of traditional microelectronic components, the demand for decreasing wire diameters becomes immediately evident. The observation of metallic conductor properties for certain configurations of carbon nanotubes (CNT) and their current carrying capability [1] set the minimal diameter of a true wire to about 3 nm (compare Chap. 15). Investigations are in progress even below that diameter on nanocontacts, formed by single metal atoms, i.e., quantum wires. Quantum wires can be produced by mechanical wire breaking [2], its combination with etching and deposition [3], or other techniques. The properties of quantum wires are only about to be understood theoretically [4]. Doubtless, they are worth considering for packaging solutions in molecular electronics to come [5]. In this chapter, we focus on metal wires and rods in the size range above 10 nm up to submicron diameters, evaluated already to be attractive for microelectronic packaging purposes. Techniques to generate, to characterize, and to handle them, as well as their interaction with electromagnetic fields will be useful for packaging applications in the age of nanotechnology. With the wealth of information available, this review focuses on general trends and starting points for deeper study. Although the cited references are representative, they cannot be complete, since numerous activities are ongoing to produce and to characterize new kinds of wire-like geometries from different materials.