Wafer level packages using anisotropic conductive adhesive for flip chip assembly

Abstract

Anisotropic conductive adhesives/films (ACAs/ACFs) have been widely used not only to display IC packaging but also to semiconductor packaging in forms of chip-on-glass (COG), chip-on-flex (COF), and chip-on-board (COB). In this study, wafer level packages (WLP) using ACAs solution for flip-chip interconnections have been developed and the effects of process parameters on the wafer level package performance were investigated. At first, the effect of several coating process parameters, such as coating speed, blade gap and temperature were investigated for the uniform thickness coating without voids and bubbles on a Au bumped wafer. After solvents drying and the subsequent singulation of a B-stage ACA solution coated wafer, singulated chips were flip-chip assembled on organic substrates using a thermo-compression bonding method. The reliabilities of flip chip assemblies using WLP were evaluated in terms of high temperature/humidity, and pressure cooker test and compared with those of conventional SCPs. In high temperature/humidity reliability test, there was no difference of flip chip reliabilities among two types of flip chip assemblies. However, in pressure cooker test, WLP using ACAs solution showed better PCT reliability than conventional ACF package. As a conclustion, new WLP using ACAs solution were developed and successfully demonstrated with reduced processing steps for flip chip interconnections. WLP using ACAs solution can provide cost-effective ACA flip chip assemblies by the reduction of processing steps and times because they can eliminate several processes such as ACF slitting, ACF chip-size cutting, ACF prelamination on a substrate.