(Georgia Institute of Technology, 1998-09)
Wong, C. P.; Shi, Songhua; Jefferson, G.
Underfill encapsulant is critical to the reliability of the flip-chip solder joint interconnects. Novel no-flow underfill
encapsulant is an attractive flip-chip encapsulant due to the simplification of the no-flow underfilling process. To develop the no-flow underfill material suitable for the no-flow underfilling
process of flip-chip solder joint interconnects, we have studied
and developed a series of metal chelate latent catalysts for the no-flow underfill formulation. The latent catalyst has minimal
reaction with the epoxy resin cycloaliphatic type epoxy) and the
crosslinker (or hardener) at the low temperature (< 180 ℃) prior
to the solder reflow and then rapid reaction takes place to form
the low-cost high performance underfills. The effects of the concentration
of the hardener and catalyst on the curing profile and
physical properties of the cured formulations were studied. The
kinetics and exothermic heat of the curing reactions of these formulations
were investigated by differential scanning calorimetry
(DSC). Glass transition temperature (T[subscript g]) and thermal coefficient
of expansion (TCE) of these cured resins were investigated by
thermo-mechanical analyzer (TMA). Storage moduli (E′; E″)
and crosslinking density of the cured formulations were measured
by dynamic-mechanical analyzer (DMA).Weight loss of these formulations
during curing was investigated by thermo-gravimetric
analyzer (TGA). Additionally, some comparison results of our
successful novel generic underfills with the current commercial
experimental no-flow underfills are reported.
(Georgia Institute of Technology, 1998-06)
Wong, C. P.; Vincent, Michael Brien; Shi, Songhua
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.