Cure kinetics modeling and process optimization of the vialux 81 epoxy photodielectric dry film (PDDF) material for microvia applications

Abstract

AbstractThe cure kinetics of a photodielectric dry film (PDDF) material called ViaLux 81 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). 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 are used to predict the degree‐of‐cure (DOC) evolution. Two approaches have been developed based on the dynamic DSC data: (1) a “model‐free” approach, which only requires information about the cure‐dependence of the activation energy; and (2) a practical scheme to deconvolute the two curing peaks. Excellent agreement is observed for the heating rate experiments, but the methods are inadequate for predicting the DOC evolution under isothermal conditions. Therefore, a modified autocatalytic model with temperature‐dependent kinetic parameters has been developed based on the isothermal DSC data. This model predicts the DOC evolution for isothermal curing profiles very well. However, some discrepancy is evident in predicting the DOC evolution for heating rate experiments, due to the underestimation of the activation energy. With appropriate corrections, excellent predictive capability is illustrated for complex cure schedules with combined heating rate and isothermal segments. In addition, a cure process optimization strategy has been suggested, and the fabrication of fine features and microvias is demonstrated. © 2002 John Wiley & Sons, Inc. J Appl Polym Sci 84: 691–700, 2002; DOI 10.1002/app.2345