Effects of ACFs adhesion on the bending reliability of Chip-in-Flex Packages for Wearable Electronics Applications

Abstract

In this paper, the effects of adhesion properties of ACFs on CIF bending reliability were investigated by enhancing the adhesion between ACFs and Si chip or flexible substrate by an oxygen plasma treatment. In order to analyze the enhanced adhesion properties of CIF packages, several techniques such as contact-angle, surface-energy, surface-roughness, and SEM Digital image correlation (DIC) were used. The contact angle measurements indicate that the surface energies of Si chip and flexible substrate can be increased by an oxygen plasma treatment. And the Digital Image Correlation technique also measures the degree of deformation and strain mathematically by comparing the reference and deformed configuration digital images. As a result, by increasing adhesion strength using a plasma treatment, the stress concentration reduced at the ACF interface and the delamination location also changed. Moreover, when the oxygen plasma was treated on the Si chip and flexible substrate, stress concentration changed from the ACF interface to the ACF resin itself. With the optimized plasma treatment conditions and the ACF materials, the bending reliability of the CIF package was successfully demonstrated up to 160,000 bending cycles.