Fast-Flow Underfill Encapsulant: Flow Rate and Coefficient of Thermal Expansion

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Date
1998-06Author
Wong, C. P.
Vincent, Michael Brien
Shi, Songhua
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Show full item recordAbstract
In the flip-chip on board assembly method, an
underfill encapsulant material is applied in the gap between
the integrated circuit (IC) chip and substrate to distribute the
shear stresses at the solder interconnects. These shear stresses
are imposed on the solder interconnects due to a coefficient of
thermal expansion (CTE) mismatch between the IC chip and
substrate. Different technologies such as fast-flow, no-flow, and
reworkable underfills are currently being studied for flip-chip
underfill encapsulant materials. This paper looks at the underfill
encapsulant used in the fast-flow method of underfilling the IC
chip/substrate gap. The effect of filler loading, particle size, and
particle size distribution on the flow rate and CTE of the fastflow
underfill material are discussed in this work. The material
used for the experiments is an epoxy resin with added silica filler
to decrease the CTE. This study focuses on what effect different
filler characteristics have on the underfill encapsulant. Also, an
underfill encapsulant that can compete with one of industry’s
faster fast-flow underfills was developed as a result of this work.