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18 The PCB Design Magazine • August 2017 You may think that none of this provides an answer to Andy's simple question, because in none of these cases did the board reach the client; this all happened inside the production stage. Who was at fault when a defect of the airbag system forced Nissan to withdraw cars from the market due to a bug in the cruise con- trol deactivation switch manufactured by Texas Instruments? The PCB designer? The electronic module manufacturer? The car manufacturer? Everyone? Why, despite the many DfX initiatives (in- cluding Design for Zero Defects and Design for Six Sigma), do these errors still happen? Basi- cally, rules are for humans. I read an opinion column recently that de- scribed robotization as the single best way for America to bring back electronics production from China. If this happens, will the mistakes disappear? No, not if the robots are controlled by hu- mans. As another old Latin saying goes, "Errare humanum est." PCBDESIGN Gaudentiu Varzaru is a researcher at the Politehnica University of Bucharest and a show manager for the TIE PCB design conference. WHOSE FAULT IS THAT BAD BOARD? The color of the light emitted by an LED can be tuned by altering the size of their semi- conductor crystals. LMU researchers have now found a clever and economical way of doing just that, which lends itself to industrial-scale production. Unlike the incandescent light bulb, LEDs pro- duce light of a defined color within the spectral range from the infrared to the ultraviolet. The exact wavelength of the emission is determined by the chemical composition of the semiconduc - tor employed, which is the crucial component of these devices. In the case of some semi-con- ducting materials, the color can also be tuned by appropriately modifying the size of the crystals of which the light-emitting layer is composed. In crystals with dimensions on the order of a few nanometers, quantum mechanical effects begin to make themselves felt. LMU researchers in collaboration with col- leagues at the University of Linz (Austria) have now developed a method for the production of semi-conducting nanocr ystals of defined size based on the cheap mineral oxide known as perovskite. These crystals are extremely stable, which ensures that the LEDs exhibit high color fidelity—an important criterion of quality. More - over, the resulting semiconductors can be print- ed on suitable surfaces, and are thus predestined for the manufacture of LEDs for use in displays. The crucial element in the new method is a thin wafer, only a few nanometers thick, which is patterned like a waffle. The depressions serve as tiny reaction vessels, whose shape and volume ultimately determine the final size of the nanocrystals. "Optimal measurements of the size of the crystals were obtained using a fine beam of high-energy X-radiation at the Deutsche Elektronen- Synchrotron (DESY) in Hamburg," says LMU researcher Dr. Bert Nickel, member of the Nanosystems Initiative Munich (NIM), a Cluster of Excellence. Moreover, the wafers are produced by means of an economical electro- chemical process, and can be fash- ioned directly into LEDs. LMU Finds New Way to Tune LED Colors

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