FEM Modeling of Temperature Distribution of a Flip-Chip No-Flow Underfill Package During Solder Reflow Process

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Date
2004-01Author
Wong, C. P.
Zhang, Zhuqing
Sitaraman, Suresh K.
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Show full item recordAbstract
Flip chip on organic substrate has relied on underfill
to redistribute the thermomechanical stress and to enhance
the solder joint reliability. However, the conventional flip-chip
underfill process involves multiple process steps and has become
the bottleneck of the flip-chip process. The no-flow underfill is
invented to simplify the flip-chip underfill process and to reduce
the packaging cost. The no-flow underfill process requires the
underfill to possess high curing latency to avoid gelation before
solder reflow so to ensure the solder interconnect. Therefore, the
temperature distribution of a no-flow flip-chip package during
the solder reflow process is important for high assembly yield.
This paper uses the finite-element method (FEM) to model the
temperature distribution of a flip-chip no-flow underfill package
during the solder reflow process. The kinetics of underfill curing
is established using an autocatalytic reaction model obtained by
DSC studies. Two approaches are developed in order to incorporate
the curing kinetics of the underfill into the FEM model
using iteration and a loop program. The temperature distribution
across the package and across the underfill layer is studied. The
effect of the presence of the underfill fillet and the influence of
the chip dimension on the temperature difference in the underfill
layer is discussed. The influence of the underfill curing kinetics
on the modeling results is also evaluated.