Investigation of the curing behavior of a novel epoxy photo‐dielectric dry film (ViaLux™ 81) for high density interconnect applications

Abstract

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.

Thermal and mechanical characterization of ViaLUX/sup TM/ 81: a novel epoxy photo-dielectric dry film (PDDF) for microvia applications

“…The glass transition temperature, from Fig. 10(a) or 10(b), is at approximately 110 C, which is consistent with that from DSC experiments ( [4]) and DMA experiments (see Section IV-C). The large increase in CTE above the is due to the softening of the material, i.e., significant plastic deformation will occur at temperatures above the .…”

“…As can been observed from the subsequent DSC scan data in Fig. 3(b), isothermal curing is incomplete up to 170 C. However, when the isothermal cure temperature was increased to 175 C, no residual exotherm was obtained indicating complete cure of the material at 175 C. As has been reported earlier in [4], these results suggest that a cure duration of approximately 15 minutes at temperatures above 165 C could result in a DOC greater than 90%. This implies that faster fabrication is possible with either rapid thermal curing (RTC) equipment or continuous belt furnaces.…”

“…Thereafter, is calculated from , and the rate constant is computed by transposing the reaction model to the left hand side in (3). All the results for the temperature-dependent kinetic parameters are summarized as (4) Solution of the cure rate equation using the 4th order Runge Kutta method yields the DOC evolution with time. Excellent agreement is evident at the selected isothermal temperatures from Fig.…”

“…However, the lack of material composition information makes the kinetic analysis presented here strictly phenomenological in nature. 1521-3331/01$10.00 ©2001 IEEE Earlier work by the authors on this material described a complex curing mechanism, with two distinct curing peaks observed in dynamic DSC scan experiments ( [4]). The two peaks were caused due to the long lifetime of the photoinitiator catalyst, and could not be separated at lower heating rates.…”

“…2). A "model-free" method suggested by [11] was implemented, which required information only about the cure-dependence of the activation energy ( [4]). Excellent agreement was observed for the heating rate experiments, but the method was inadequate for predicting the DOC evolution under isothermal conditions.…”