Copper films of different thicknesses of 0.2, 0.5, 1 and 2 microns were electroplated on top of the adhesion-promoting barrier layers on <100> single crystal silicon wafers. Controlled Cu grain growth was achieved by annealing films in vacuum.The Cu film microstructure was characterized using Atomic Force Microscopy and Focused Ion Beam Microscopy. Elastic modulus of 110 to 130 GPa and hardness of 1 to 1.6 GPa were measured using the continuous stiffness option (CSM) of the Nanoindenter XP. Thicker films appeared to be softer in terms of the lower modulus and hardness, exhibiting a classical Hall-Petch relationship between the yield stress and grain size. Lower elastic modulus of thicker films is due to the higher porosity and partially due to the surface roughness. Comparison between the mechanical properties of films on the substrates obtained by nanoindentation and tensile tests of the freestanding Cu films is made.

When mobile electronic devices drop during service, solder interconnects are loaded under intermediate to high strain rates. Therefore, the strain response of solders at elevated strain rates is critical to reliability prediction. This paper presents the plastic flow behavior of Sn-3.8Ag-0.7Cu solder under compression over strain rates ranging from 0.1 s -1 to 30 s -1 at several different temperatures and under various aging conditions. Both yield strength and work hardening rate were observed to increase substantially with increasing strain rate, with the strain rate sensitivity at higher temperatures being greater. Empirical expressions capturing the strain rate and temperature dependence of the yield and work hardening parameters are presented. Microstructural observations revealed greater strain localization following testing at higher strain rates, with the development of distinct flow patterns and localized kinking of dendrites due to twin formation. Low-temperature aging (35°C) appeared to enhance yield strength slightly relative to the as-reflowed condition, but decreased the work hardening rate. With aging at higher temperatures (100°C and 180°C), and commensurate coarsening of the precipitate structure, both yield strength and work hardening rate decreased dramatically.

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.

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 toward material selection for reliable ACF packages. This approach has very good correlation with experimental results and reliability testing of various ACF materials.

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