Cure kinetics modeling of ViaLux/sup TM/ 81: a novel epoxy photodielectric dry film (PDDF) for microvia applications

The cure kinetics of a photo-dielectric dry film (PDDF) material, ViaLux 81/sup TM/, has been studied, with the aim of understanding and optimizing its curing schedule for the fabrication of sequentially built up (SBU) high density interconnect printed wiring boards (HDI-PWB). This knowledge is useful to ensure the accuracy and registration of the fine interconnect features and the thermomechanical integrity of the finished multilayered structure. Initial dynamic Differential Scanning Calorimetry (DSC) scans on the material revealed a two-stage curing mechanism due to the long lifetime of the photoinitiator catalyst, which could not be separated at lower heating rates. On the other hand, the heat flow exotherm from isothermal DSC experiments showed a rapid reaction rate at the beginning with only a single peak. Therefore, to capture the complexity of the process, the faster multiple heating rate DSC experiments were used to predict the degree-of-cure (DOC) evolution. Excellent agreement was observed for the heating rate experiments, but the method was inadequate for predicting the DOC evolution under isothermal conditions. Therefore, a modified auto-catalytic model with temperature-dependent kinetic parameters was developed based on isothermal DSC data.