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Abstract Flip chip has
become interest to electronic package because of its gang
bonding and high I/O capability. This present study
investigated the flip chip solder bump produced by reflow
process and its properties. It has been investigated in a series
of study on the solder bump structure of solder / nickel /
copper / aluminum, the interaction among these metal combination
during reflow. In addition, investigations also made on the
shear strength of solder bump when reflowed at temperatures of
210℃, 250℃ and for five, ten times cyclic reflow. The aluminum
and copper were sputtered on silicon wafer. The electroless
nickel was applied as a barrier layer and wetting layer. The
tin-lead solder was deposited on the electroless nickel with
electroplating. The reflow interaction behavior was investigated
with SEM on the cross section of the bump. The experimental
results revealed that the aluminum layer did not penetrate
through the 2μm electroless nickel barrier layer at reflow
temperatures of 210℃and 250℃for a period of 15 sec. In
addition, the copper layer diffuses and penetrates through the
2μm, 3.9μm electroless nickel barrier layer and interacts with
the tin-lead solder, but not diffuses and penetrates through
the 6.5μm, 10μm. Meanwhile, nickel also reacts with solder. An
intermetallic compound layer was formed at the interface between
solder and electroless nickel barrier layer. The results of the
average solder bump shear strength at reflow temperature 250℃
is better than 210℃；for five and ten times cyclic reflow, the
average shear strengths are around 35.4~40.6g.
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