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50 SMT Magazine • September 2017 by Lauren Cummings and Priyanka Dobriyal, Ph.D. INTEL CORP. Abstract With increasing consumer demand for smartphones, wearable devices, and Internet of Things applications, there is a growing trend in package and printed circuit board miniaturiza- tion. In particular, wafer-level packages (WLPs) have garnered recent popularity for their af- fordable cost, small footprint, and thin pro- file. Component suppliers must be prepared to support failure analysis (FA) for PCB-assembled WLPs, including fault isolation (FI), nonde- structive screening, as well as destructive analy- sis techniques. If a board- or package-level fail- ure is subtle or cannot be detected non-destruc- tively, the WLP requires rework and reball be- fore proceeding with further component-level testing and destructive FA. Due to their fragili- ty and small form factor, the rework and reball process steps pose considerable risks for WLPs. The component lacks a package substrate and is easily damaged using traditional rework tool- ing and handling. On high-density boards and modules, there is also a risk for adjacent board- side passives or packages to be bumped and damaged during package removal from the PCB. The present work addresses the rework and re- ball challenges of a specific WLP case study, and suggests improvements for maintaining the true failure signature. Rework and reball reci- pes were successfully developed for a WLP, and optical microscopy (OM) and C-mode scanning acoustic microscopy (CSAM) were used to in- spect for thermally or mechanically-induced ar- tifacts. By implementing enhanced WLP rework and reball methods, the industry will be better poised to improve the quality and reliability of small form factor devices. Introduction There is a growing consumer demand for smart wearable products, including watch- es, fitness bands, eyewear, and headphones. Barriers to the market still exist, as many con- sumers are concerned with style, battery life, functionality, and cost. The mature smartphone market faces similar challenges, with consumers FEATURE

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