Development and Application of the Moisture-Dependent Viscoelastic Model of Polyimide in Hygro-Thermo-Mechanical Analysis of Fan-Out Interconnect

A moisture-dependent viscoelastic model of polyimide dielectric thin film was developed from experimental characterizations of the moisture diffusion and the moisture-dependent viscoelastic behaviors. In the moisture diffusion characterization, a series of moisture absorption experiments were carried out by using vapor sorption analyzer. A dual-stage diffusion model was established from the experimental results. The constitutive behaviors of PI thin film under various ambient humidity conditions were obtained from dynamic mechanical analyzer. A master curve of the hygro-thermo-viscoelastic modulus was constructed by fitting to the characterization results with a time-temperature-moisture superposition model. In the hygro-thermo-viscoelastic model of PI thin film, a vertical scale factor was introduced to represent both temperature and moisture effects on the viscoelastic modulus in the glassy regime below the glass transition point. For investigating the influence of moisture on the stress development in fan-out package, a global-local finite element model was developed to consider moisture absorption and the corresponding stress in redistribution-layer interconnect.