Wafer-Level Flip Chip Packages Using Preapplied Anisotropic Conductive Films (ACFs)

Abstract

Recently, wafer-level packaging (WLP) has become 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 developments 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 a lower cost, higher performance, and environmentally green packaging process, anisotropic conductive film (ACF) flip chip assembly has been widely used, such as in ultrafine-pitch flat panel display (FPD) and general semiconductor packaging applications, too. However, there has been no previous attempt on the wafer-level flip chip assembly using ACFs. In this paper, wafer-level flip chip packages using preapplied ACFs were investigated. After ACF prelamination on an electroplated Au bumped wafer, and subsequent singulation, singulated chips were flip-chip assembled on an organic substrate using a thermocompression bonding method. Au-plated bumps were well assembled on Ni/Au pads of organic substrates. The electrical, mechanical properties and the reliabilities of wafer-level flip chip assemblies (WL-FCAs) were evaluated and compared with conventional ACF flip chip assemblies using the thermocompression method. Contact resistance measurement was performed after thermal cycling, high temperature/humidity, and pressure cooker test. ACF joints between electroplated Au bumps and substrate metal pads showed stable contact resistance of 5 m per a bump, strong bump adhesion, and similar reliability behaviors compared with conventional ACF flip chip joints using a thermocompression bonding. As a summary, new wafer-level packages using preapplied ACFs were successfully demonstrated for flip chip assembly. The new wafer-level packages using preapplied ACFs can be widely used for many nonsolder flip chip assembly applications such as chip-on-board (COB), chip-on-flex (COF), and chip-on-glass (COG).Index Terms-Anisotropic conductive film (ACF) prelamination, flip chip assembly, reliability, wafer-level flip chip packages, waferlevel package.

Development of a 3-D Process Technology for Wafer-Level Packaging of MEMS Devices

“…Unlike ordinary devices, most MEMS devices with moving parts cannot be directly molded with engineering plastic and require unique packaging structures. In addition, hermetic vacuum sealing between the MEMS device and its packaging is important in order to improve the reliability of these devices [8]- [10]. These requirements result in a higher cost and lower throughput.…”

Wafer level packages (WLPs) using anisotropic conductive adhesives (ACAs) solution for flip-chip interconnections

“…In this wafer level packaging process, after ACF pre-lamination on an electroplated Au bumped wafer, and subsequent singulation was performed, and then, singulated chip was assembled on an organic substrates using thermo-compression bonding method. It can reduce several processing steps such as ACF slitting, ACF pre-lamination and removal of releasing film on each substrate of the conventional single chip package (SCP) process [4]. In this process, after ACF lamination on an entire wafer and chip singulation, ACF pre-applied chips are flip-chip assembled on substrates.…”