Multilayered high density interconnect (HDI) processing on organic substrates typically introduces warpage and residual stresses. The magnitude of the warpage and the residual stresses depends on, among other factors, the processing temperatures and the thermomechanical properties of the dielectric and substrate materials. In this work, a prospective epoxy-based dielectric material for such sequentially built up (SBU) high density-interconnect printed wiring boards (HDI-PWB) is considered. The polymer is a photo-dielectric dry film (PDDF) material called ViaLux™ 81, which exhibits a complicated curing behavior due to the long lifetime of the cationic photoinitiators generated by ultraviolet (UV) exposure. The objectives of this work are 1) to conduct differential scanning calorimetry (DSC) experiments and develop a cure kinetics model; 2) to develop a cure shrinkage model based on thermal and chemical shrinkage experiments; 3) to determine the thermomechanical properties of partially and fully cured Vialux™ 81 dry film. All of these experimental characterizations are necessary to select suitable process parameters and to obtain a consistent product with the desired physical and mechanical properties.

An integrated process modeling methodology using a coupled cure-thermal-stress analysis approach has been developed to determine the evolution of warpage and stresses during the sequential fabrication of high-density electronic packaging structures. The process modeling methodology has been demonstrated, for example, with a bi-layer structure consisting of a 3 mil (76. m) thick Vialux 81 photo-definable dry film (PDDF) polymer on a Silicon substrate. Extensive material characterization of the thermo-mechanical properties of the thin film polymer is presented, including the development of a viscoelastic material model. The predicted warpage values have been validated with Shadow Moiré experiments, while the predicted stress values have been validated with experimental data using the Flexus Thin Film Stress Measurement Apparatus. Good agreement is seen between the predicted and the experimental warpage and stressvalues during the entire cure cycle. Finally, the importance of incorporating viscoelastic polymer behavior and processing history is emphasized in the context of developing the multi-layered high-density wiring integrated substrate fabrication process.

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The objective of this work was to determine the cure kinetics of ViaLux™ 81 photo‐dielectric dry film and to optimize its curing schedule for the fabrication of sequentially built up high density interconnect‐printed wiring boards. Photosensitive epoxy materials such as the photo‐dielectric dry film studied herein have complicated curing regimes. This is attributed to the long lifetime of the curing catalyst that is generated by ultraviolet exposure. Dynamic differential scanning calorimetry (DSC) experiments revealed a two‐peak curing mechanism, which could not be separated at lower heating rates. The activation energies for the two cure events, calculated using the Kissinger method, were found to be 129 and 124 kJ/mol, respectively. A cure‐dependent activation energy was also determined using the isoconversional method, and a “model‐free” approach was adopted to simulate the evolution of degree‐of‐cure under dynamic and isothermal conditions. The results suggest that cure cycles of approximately 15 min at temperatures above 165°C can result in a degree‐of‐cure of 90% and above. This implies that faster fabrication is possible with either rapid thermal curing equipment or continuous cure surface mount technology furnaces. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 430–437, 2000

The objective of this work was to determine the cure kinetics of ViaLux™ 81 photo-dielectric dry film and to optimize its curing schedule for the fabrication of sequentially built up high density interconnect-printed wiring boards. Photosensitive epoxy materials such as the photo-dielectric dry film studied herein have complicated curing regimes. This is attributed to the long lifetime of the curing catalyst that is generated by ultraviolet exposure. Dynamic differential scanning calorimetry (DSC) experiments revealed a two-peak curing mechanism, which could not be separated at lower heating rates. The activation energies for the two cure events, calculated using the Kissinger method, were found to be 129 and 124 kJ/mol, respectively. A cure-dependent activation energy was also determined using the isoconversional method, and a "model-free" approach was adopted to simulate the evolution of degree-of-cure under dynamic and isothermal conditions. The results suggest that cure cycles of approximately 15 min at temperatures above 165°C can result in a degree-of-cure of 90% and above. This implies that faster fabrication is possible with either rapid thermal curing equipment or continuous cure surface mount technology furnaces.