Modelling of ICA creep properties

Flip chip bonding with isotropically conducting adhesives is gaining in popularity since it can simplify and reduce the cost of the interconnecting process. To effectively estimate the reliability of ICA flip chip joints, one needs to model the viscoelastic behaviour of the adhesives. Creep is an important property because it enables stress relaxation through non-recoverable strain. Ignoring ICA creep in FE-simulations will result in overestimation of stress and underestimation of strain in a joint. This paper proposes that ICAs can be modelled as a Maxwell element to calculate creep compliance rates. The creep compliance rates are needed for simulating stress-strain hysteresis curves during a thermal cycle. The calculated non-recoverable creep strains are also used to estimate the fatigue lifetime of a joint. Results suggest that the lifetime of ICA joints is influenced less by non-recoverable strain than the lifetime of tin-lead solder joints.