Failure Mechanism Study of Anisotropic Conductive Film (ACF) Packages

Abstract

Anisotropic Conductive Film (ACF) consists of an adhesive polymer matrix with dispersed conductive particles. In Flip-Chip technology, ACF has been used in place of solder and underfill for chip attachment to glass or organic substrates. The filler particles establish the electrical contacts between the interconnecting areas. ACF Flip-Chip bonding provides finer pitch, higher package density, reduced package size and improved lead-free compatibility. Nevertheless, the interconnection is different from traditional solder joints, the integrity and durability of the ACF interconnects have major concerns. Failures in Anisotropic Conductive Film (ACF) parts have been reported after temperature cycling, moisture preconditioning and autoclave. The failures have not been well understood and have been attributed to a wide variety of causes. This paper investigates the failure mechanism of ACF using finite element simulation. From a failure-initiation point of view, the response of ACF packages to environmental (temperature and humidity) exposure is very different from standard underfilled packages. These differences cause the ACF package to fail in different ways from an underfilled package. Simulation results have shown that moisture-induced ACF swelling and delamination is the major cause of ACF failure. With moisture absorption, the loading condition at the interface is tensile-dominant, which corresponds to lower interface toughness (or fracture resistance). This condition is more prone to interface delamination. Therefore, the reliability of ACF packages is highly dependent on the ACF materials. The paper suggests a new approach towards material selection for reliable ACF packages. This approach has very good correlation with experimental results and reliability testing of various ACF materials.

Reliability of adhesive joined thinned chips on flexible substrates under humid conditions

“…This swelling due to humidity typically increases with temperature. Swelling due to moisture differed significantly between the materials used in the test samples causing the formation of hygroscopic stresses in the structure [30,31].…”

Electrically conducting film of silver sub-micron particles as mechanical and electrical interfaces for transfer printed micro- and nano-pillar devices

“…In this technology, the receiver matrix provides both the physical adhesion and the electrical conductivity. When the metal particles are in the nanometer range, ECF offers the advantages of low processing temperature with a fine interconnect pitch capability [50][51][52]. We discuss the method of forming an ECF layer using a monolayer of AgSP as the polymer conductive filler.…”

Microscopic stress simulation of non-planar chip technologies

“…Finite element modeling (FEM) of chip and package systems is widely used for design and optimization studies in the field of micro-electronics [1]. Continuing demands result in complex ICs with structural miniaturization and material mixture.…”

“…Owing to these advantages, microelectronic manufactures prefer products with non-planar technologies over planar, where few or no planarization processes such as chemical mechanical polishing (CMP) are employed. Typically, finite element simulation studies in micro-electronics ignore the complicated geometries, thereby affect the accuracy of these simulations [1,3]. Hence, it is crucial to include the actual geometry data in order to effectively apply simulation in technology and product development.…”