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edfas.org 9 ELECTRONIC DEV ICE FA I LURE ANALYSIS | VOLUME 24 NO . 2 Compared to conventional LEDdie design, this LEDhas a passivation layer removed on top of n-GaN and p-GaN layers to improve the side outcoupling efficiency. When silver dendrite grows from n-GaN layer toward p-GaN under the electric field, because Ag is conductive, the dendrite will become a leakage path when it reaches the P-GaN layer, as shown in Figs. 13a, b, and c. Based on the failuremechanism, the T5 LED supplier agreed to the cor- rective action to add a passivation layer to better insulate the P-GaN and N-GaN. CONCLUSION From this LED failure analysis case study, it is clear that subsystem suppliers need to understand how their subsystems are utilized, assembled, and tested in the system level. Subsystem suppliers should either build up full FA capability in house or utilize third-party labs for fault isolation and physical failure analysis. As for system suppliers or designers, their FA teams should engage early with the subsystemsupplier FA team with the following strategy: Firstly, the system supplier needs to build up a world class FA capability and clear FA process flow to demonstrate critical and complicated component failure analysis; secondly, the systemsupplier FA team must have the capability to guide and train the subsystem FA team how to set up specific capability and metrology to reduce analytical mistakes; and lastly, the system supplier needs to take care of the FA capability of the whole supply chain and get involved early during the new subsystem supplier set up. In this LED case, WLED suppliers tried their best to increase the EQE, and a small improvement of EQE trans- lates to a large advantage in competitiveness. However, those efforts could be risky in some specific applications. In this occurrence, the WLED’s EQE drop is caused by an electrical leakage path that is formed by migrated Ag+ cations. If this WLED is used in PWM dimming applica- tions, the user impact would be negligible; but it became a serious issuewith analog dimming. Understanding each other is a challenge for both LED suppliers and system designers. Meanwhile, failure isolation steps are always impor- tant to identify the root-cause. Lack of failure isolation steps could lead to wrong decisions and faulty corrective actions. ACKNOWLEDGMENT The authors would like to express acknowledgments to the cross functional teams, including reliability, quality, NPI, factory management, and development, for their great teamwork in this LED failure analysis and problem solving. Special thanks to themanagement, J.P. Peterson and Krishna Darbha, for their support and review of this analysis and paper. REFERENCES 1. P.F. Smet, A.B. Parmentier, and D. Poelman: “Selecting Conversion Phosphors for White Light-Emitting Diodes,” J. Electrochem. Soc., 2011, 158, p. R37-R54. 2. C.C. Tsai, et al.: “Investigation of Ce:YAG Doping Effect on Thermal Aging for High-Power Phosphor-Converted White-Light-Emitting Diodes,” IEEE Trans. Device Mater. Reliab., 2009, 9, p. 367−371. 3. J.E. Murphy, et al.: “PFS, K 2 SiF 6 :Mn 4+ : the Red-line Emitting LED Phosphor Behind GE’s TriGain Technology Platform,” SID Symp. Dig. Tech. Pap., 2015, 46, p. 927-930. 4. P.G.J. Barten: Contrast Sensitivity of the Human Eye and its Effects on Image Quality, The International Society for Optical Engineering Press, 1999. 5. R. Verstraete, et al.: “Red Mn 4+ -Doped Fluoride Phosphors: Why PurityMatters,” ACS Appl. Mater. Interfaces, 2018, 10, p. 18845−18856. 6. H. Weidong, et al.: “Capacitor Dendrite Failure Analysis for Lidless CPU Testing,” 19th IEEE Intl. Symp. Phys. Failure Anal. Integr. Circuits, 2012, DOI: 10.1109/IPFA.2012.6306253. ABOUT THE AUTHORS Xuming Deng is a principal hardware engineer working for Microsoft China since 2012. Prior to joining Microsoft, Deng worked as a system design engineering manager in NVidia for graphic card products aswell as an exchange research scholar at UC Irvine’s civil engineering department for sensor technologies. He holds a B.S. in automation systems from Shanghai JiaoTong University. WeidongHuang is adirector of device analysis engineering atMicrosoftChina leading the Materials and Physical Analysis Team for Microsoft hardware prod- ucts. Before joiningMicrosoft in 2012, Huangworked in a technical manager role in previous companies such as Espec, DaimlerChrysler, and AMD. Huang holds a Ph.D. degree fromShanghai Institute of Microsystem& Information Technology, Chinese Academy of Science, majoring in electronic packaging and its reliability, materials science.