Pan Pacific Symposium Conference Proceedings


Authors: Kyung-Wook Paik, Il Kim, Ho-Young Son, and Chang-Kyu Chung
Company: Korea Advanced Institute of Science and Technology
Date Published: 1/24/2008   Conference: Pan Pacific Symposium

Abstract: Wafer level package (WLP) is one of the promising packaging technologies due to its advantages such as fewer processing steps, lower cost, and enhanced device performance compared to conventional single chip packaging. Many reports on new WLP design, material and process have been accomplished according to performance and reliability requirement of the devices to be packaged [1, 2]. For, anisotropic conductive films (ACFs) flip chip assembly has been widely used for flat panel display (FPD) and general semiconductor packaging applications because of lower cost, higher performance and environmentally green packaging process.

In this study, wafer level flip chip packages using pre-applied ACAs (denoted as ACA-WLPs) including ACFs(films) and ACPs(pastes) were investigated. In case of ACF-WLPs, after ACF pre-lamination on an electroplated Au bumped wafer, and subsequent singulation, and singulated chips were flip-chip assembled on an organic substrate using a thermo-compression bonding method. In addition, in case of ACP-WLPs, ACPs were also directly coated on an entire wafer, and then dried as ACFs. After the ACFs coating on a Si wafer, subsequent dicing and assembly processes are the same as the ACF-WLPs case. For both ACF-WLPs and ACP-WLPs, Au plated bumps were well assembled on Ni/Au metal pads of organic substrates. The electrical, mechanical properties and the reliabilities of ACA-WLPs were evaluated and compared with conventional ACF flip chip assemblies using ACFs applied on a substrate followed by a flip chip assembly using a thermo-compression method. A single bump contact resistance measurement was performed after thermal cycling, high temperature/humidity, and pressure cooker test. ACA-WLPs showed stable contact resistance of 5mohm per a bump, strong bump adhesion, and similar reliability behaviors compared with conventional ACF flip chip joints using a thermo-compression bonding.

As a summary, new ACA-WLPs were successfully demonstrated for flip chip assembly, and ACA-WLPs can be widely used for many flip chip assembly applications such as COB (Chip-on-Board), COF (Chip-on-Flex), COG (Chip-on-Glass), embedded chips, and 3-D chip stacking.

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