Wafer-Level Packages Using Anisotropic Conductive Adhesives (ACAs) Solution for Flip-Chip Interconnections

In this paper, wafer-level packages (WLPs) using an anisotropic conductive adhesives (ACAs) solution have been newly developed for flip-chip interconnections. WLPs using ACAs (ACA-WLPs) reduce processing steps compared to WLPs using anisotropic conductive films (ACFs), because ACA solution is directly coated on a wafer without an ACF formation process on the releasing film and an ACF lamination process on the wafer. The effects of ACA coating process parameters, such as blade gap and temperature, were first investigated for a uniform thickness coating without voids on an Au-bumped wafer. After solvent drying and subsequent singulation of a B-stage ACA-coated wafer, a singulated chip was flip-chip assembled on an organic substrate using a thermo-compression bonding method. The reliabilities of flip-chip assemblies using ACA-WLPs were evaluated in terms of a high temperature/humidity test, thermal cycling test, and pressure cooker test (PCT) and compared with corresponding results of conventional ACF flip-chip assemblies. In the high temperature/humidity reliability test and thermal cycling test, there was no difference in the flip-chip reliabilities between the two types of flip-chip assemblies. Furthermore, the flip-chip assemblies using ACA-WLPs showed better PCT reliability than the conventional ACF flip-chip assemblies.