May_EDFA_Digital

edfas.org ELECTRONIC DEV ICE FA I LURE ANALYSIS | VOLUME 24 NO . 2 4 EDFAAO (2022) 2:4-10 1537-0755/$19.00 ©ASM International ® CHALLENGES FOR SYSTEM SUPPLIER FAILURE ANALYSIS ON SUBSYSTEM COMPONENTS Xuming Deng 1 , Weidong Huang 1 , Changhong Yu 1 , Xiongjian Wu 1 , Yang Xu 1 , Xiaole Zhao 1 , and Qing Gu 2 1 Device Analysis Engineering, Microsoft China, Suzhou, China 2 Device Analysis Engineering, Microsoft Corp., Redmond, Washington frhuang@microsoft.com INTRODUCTION It is always a challenge for a systemsupplier to investi- gate the root cause and failuremechanismon subsystems or component-level issues. Traditionally, systemsuppliers mainly do an A-B-A swap to find out which components have the issue, then rely on their subsystemsuppliers todo failure analysis (FA) and take corrective actions on compo- nent level failures. The A-B-A swap is a simple crosscheck test, whichmeans the suspect component in failed system A is installed in a known good systemB to check if it passes or not. In addition, the corresponding good component in a known good systemB is installed in the failed systemA to check if this, in turn, passes or not. However, it is not easy for a subsystem supplier to reproduce the failure and to perform the right failure analysis to identify the real root cause without system-level information and solid failure analysis capability. In this article, failure analysis of awhite LED back-light module in a portable computer device was studied as an example to compare the different FAmindsets and results between systemsupplier and component supplier. Failure mechanisms, an FA cooperation work model, root cause, and lessons learned are also discussed. Figure 1 shows the supply chain for the white light- emitting diodes (WLEDs) used in a portable computer. From Tier 5 WLED supplier to Tier 4 LED bar supplier, to Tier 3 back-lightmodule/unit (BLU), to Tier 2 liquid crystal module (LCM), toTier 1.5 touchdisplaymodule (TDM), and finally to Tier 1 finished goods assembly supplier. Wide color gamut displays include a greater number of colors than what most conventional flat panel displays (FPD) can show. The greater a display’s coverage of awide color gamut, the more colors it will be able to reproduce. Expanding the color gamut is one of the exciting new developments in display technology and should help to create more colorful and lifelike images. As the successor of cold cathode fluorescent lamp (CCFL) light source, WLEDs are wildly used as the light source of liquid crystal display (LCD) back-light systems, where blue light is generated on a GaN die and then part of blue light is converted into yellow or green/red light to form white light. [1] White light generated from the WLEDs goes through a light-guiding plate, diffusers, prism layers, polarizers, and a liquid crystal cell. Other than the absorp- tion spectrum of the component in the optical path, two major contributors for color performance are the color fil- ter (CF) layer inside of the liquid crystal cell and theWLEDs. To achieve a wider color gamut, WLEDs with separate green and red phosphor materials are used instead of conventional single yellowYAGphosphor. [2] As fluorescent Fig. 1 LED supply chain. Fig. 2 Photo taken in darkroom showing the defect symptom: hotspot at bottom of display.