Effect of strain rate on adhesion strength of Anisotropic Conductive Film (ACF) joints

Advantages of Anisotropic Conductive Films (ACF) technology, especially the low bonding temperature, fine pitch capability, elimination of lead and low cost, have resulted in ACF interconnects being widely used in contemporary portable electronic devices. Such products are exposed to various types of mechanical loadings, such as shock and impact during handling and accidental drops, throughout their life-cycle. Such impacts involve a risk of a mechanical damage to the electronic components and their interconnections to the PWAs inside the product housing. Evidence indicates that damage to the ACF matrix can directly result in instability of the contact resistance of the bonding. This study evaluates the ACF adhesive strength under mechanical loading conditions. ACF adhesive strength with three selected width and pitch, two kinds of surface finishes: ENIG and OSP surface finish is studied at different dynamic load velocities for tensile and shear tests. ACF/ENIG interface is found to exhibit higher adhesion strength than ACF/OSP interface. Furthermore, some rate dependency in adhesive strength is observed. ACF adhesion strength is captured in a rate-dependent traction-separation constitutive response in Finite Element (FE) Cohesive Zone Models (CZM), to model the damage initiation and evolution in the ACF during tensile and shear tests.