Low-Temperature Cu-Cu Bonding Process Based on the Sn-Cu Multilayer and Self-Propagating Reaction Joining
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Transient liquid phase bonding can be realized at a relatively low temperature through building an intermetallic interconnection. A self-propagating reaction joint can achieve a low temperature bond by confining the heat at the bonding interface and reduce the thermal effect on other components. In this work, a Sn-Cu alternating multilayer was combined with an Al-Ni self-propagating reaction joint to develop a highly efficient low-temperature Cu-Cu hybrid bonding process. The Sn-Cu alternating multilayer was directly prepared on the Cu substrates by an alternating electroplating process. The Al-Ni multilayer film was sandwiched between two Cu substrates under a pressure of 5 MPa and ignited with a 15-V spark at room temperature. Cu-Cu bonds with three different Sn/Cu thickness ratios were studied. It was found that the Cu6Sn5 layer within the three Sn layers had different thicknesses and decreased with increasing distance from the heat source of the Al-Ni nanofoil. The thickness difference between adjacent Cu6Sn5 layers at first decreased with the increasing Sn/Cu thickness ratio in these three groups and then remained constant. The shear strength of the bonds varied with the thickness of Cu6Sn5 layer and achieved a high shear strength with a Sn/Cu thickness ratio of 1.6 μm/1 μm, where fracture occurred within the Cu6Sn5 layer near the Cu substrate. The combination of the Sn-Cu multilayer and self-propagating reaction joining process can achieve a good low-temperature bond between Cu substrates with an optimized Sn/Cu thickness ratio, which has a strong influence on the quality of bonds, the Cu6Sn5 morphology, and shear strength.
KeywordsLow-temperature Cu-Cu bonding self-propagating reaction joining Sn-Cu alternating multilayer Cu6Sn5 IMC layer shear strength
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The authors are grateful for the financial support from the National Key Basic Research Special Fund of China [Grant No. 2015CB057205]; and the Program for Changjiang Scholars and Innovative Research Team in University [Grant No. IRT13017].
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