Title:
Modeling of the Curing Kinetics of No-Flow Underfill in Flip-Chip Applications
Modeling of the Curing Kinetics of No-Flow Underfill in Flip-Chip Applications
Author(s)
Wong, C. P.
Zhang, Zhuqing
Zhang, Zhuqing
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Abstract
No-flow underfill has greatly improved the
production efficiency of flip-chip process. Due to its unique
characteristics, including reaction latency, curing under solder
reflow conditions and the desire for no post-cure, there is a need
for a fundamental understanding of the curing process of no-flow
underfill. Starting with a promising no-flow underfill formulation,
this paper seeks to develop a systematic methodology to study
and model the curing behavior of this underfill. A differential
scanning calorimeter (DSC) is used to characterize the heat
flow during curing under isothermal and temperature ramp
conditions. A modified autocatalytic model is developed with
temperature-dependent parameters. The degree of cure (DOC)
is calculated; compared with DSC experiments, the model gives
a good prediction of DOC under different curing conditions. The
temperature of the printed wiring board (PWB) during solder
reflow is measured using thermocouples and the evolution of DOC
of the no-flow underfill during the reflow process is calculated. A
stress rheometer is used to study the gelation of the underfill at
different heating rates. Results show that at high curing temperature,
the underfill gels at a lower DOC. Based on the kinetic model
and the gelation study, the solder wetting behavior during the
eutectic SnPb and lead-free SnAgCu reflow processes is predicted
and confirmed by the solder wetting tests.
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Date Issued
2004-06
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337894 bytes
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