Novel Reworkable Fluxing Underfill for Board-Level Assembly

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Title: Novel Reworkable Fluxing Underfill for Board-Level Assembly
Author: Wong, C. P. ; Zhang, Zhuqing ; Li, Haiying
Abstract: Underfills are traditionally applied for flip-chip applications. Recently, there has been increasing use of underfill for board-level assembly including ball grid arrays (BGAs) and chip scale packages (CSPs) to enhance reliability in harsh environments and impact resistance to mechanical shocks. The no-flow underfill process eliminates the need for capillary flow and combines fluxing and underfilling into one process step, which simplifies the assembly of underfilled BGAs and CSPs for SMT applications. However, the lack of reworkability decreases the final yield of assembled systems. In this paper, no-flow underfill formulations are developed to provide fluxing capability, reworkability, high impact resistance, and good reliability for the board-level components. The designed underfill materials are characterized with the differential scanning calorimeter (DSC), the thermal mechanical analyzer (TMA), and the dynamic mechanical analyzer (DMA). The potential reworkability of the underfills is evaluated using the die shear test at elevated temperatures. The 3-point bending test and the DMA frequency sweep indicate that the developed materials have high fracture toughness and good damping properties. CSP components are assembled on the board using developed underfill. High interconnect yield is achieved. Reworkability of the underfills is demonstrated. The reliability of the components is evaluated in air-to-air thermal shock (AATS). The developed formulations have potentially high reliability for board-level components.
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Type: Article
Citation: IEEE Transactions on Advanced Packaging, Vol. 27, no. 3, August 2004, 525-532
Date: 2004-09
Publisher: Georgia Institute of Technology
Institute of Electrical and Electronics Engineers, Inc., New York
Subject: Assembly
Material properties

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