W. Dong

Formation of highly preferred orientation of β-Sn grains in solidified Cu/SnAgCu/Cu micro interconnects under temperature gradient effect

β-Sn grain orientation and configuration are becoming crucial factors to dominate the lifetime of solder interconnects in three-dimensional integrated circuit packaging. In this paper, we found that a temperature gradient during solidification significantly dominated the orientation and configuration of the final β-Sn grains in Cu/SnAgCu/Cu micro interconnects. Being different from the random orientations and growth fronts meeting or cyclic twin boundary forming near the center after homogeneous temperature bonding, the β-Sn grains solidified under a certain temperature gradient were observed to follow a highly preferred orientation with their c-axis departing from the direction of temperature gradient by about 45°–88°. Meanwhile, these preferred oriented β-Sn grains consisted of low angle grain boundary structures with misorientation in the range of 0°–15°. The mechanism was explained in terms of the anisotropy and directional growth of β-Sn grains. The results pave the way for grain orientation control ...

Continuous epitaxial growth of extremely strong Cu6Sn5 textures at liquid-Sn/(111)Cu interface under temperature gradient

As the diameter of solder interconnects in three-dimensional integrated circuits (3D ICs) downsizes to several microns, how to achieve a uniform microstructure with thousands of interconnects on stacking chips becomes a critical issue in 3D IC manufacturing. We report a promising way for fabricating fully intermetallic interconnects with a regular grain morphology and a strong texture feature by soldering single crystal (111) Cu/Sn/polycrystalline Cu interconnects under the temperature gradient. Continuous epitaxial growth of η-Cu6Sn5 at cold end liquid-Sn/(111)Cu interfaces has been demonstrated. The resultant η-Cu6Sn5 grains show faceted prism textures with an intersecting angle of 60° and highly preferred orientation with their ⟨ 11 2 ¯ 0 ⟩ directions nearly paralleling to the direction of the temperature gradient. These desirable textures are maintained even after soldering for 120 min. The results pave the way for controlling the morphology and orientation of interfacial intermetallics in 3D packagin...

Formation of preferred orientation of Cu 6 Sn 5 grains in Cu/Sn/Cu interconnects by soldering under temperature gradient

The anisotropic behaviors of micro solder interconnects have been recognized as a crucial reliability concern due to the continuous trend of miniaturization in high-performance electronic devices. The hexagonal structure η-Cu6Sn5 with highly anisotropic phase structure has considerable influence on its growth behavior during soldering and performance in service. In the present work, synchrotron radiation real-time imaging technology was used to in situ investigate the growth behavior of η-Cu6Sn5 intermetallic compound (IMC) in Cu/Sn/Cu solder interconnects during soldering under temperature gradient. The microstructure of the Cu/Sn/Cu micro interconnects and the orientation of η-Cu6Sn5 IMC grains after soldering were characterized. The electron backscattered diffraction (EBSD) analysis revealed that the η-Cu6Sn5 grains showed a preferred orientation, with their [0001] direction being nearly parallel to the direction of temperature gradient. The results pave the way for controlling the orientation of the small number of interfacial IMC grains in three-dimensional (3D) packaging technology.

Synchrotron radiation in situ study on the solidification of Cu/Sn-58Bi/Cu solder joint under temperature gradient

Synchrotron radiation real-time imaging technology was conducted to in situ investigate the thermomigration and solidification behavior of Cu/Sn-58Bi/Cu solder joint during reflow under temperature gradient. The high concentration of Bi in solder retarded the thermomigration of Cu atoms and the interfacial reaction of the solder joint. Both the growth of the interfacial intermetallic compounds (IMCs) and the dissolution of the Cu substrates in the solder joints were inconspicuous. During the solidification, Bi-rich phase nucleated in the bulk solder and grew fast in the shape of triangular or quadrangular prism. Subsequently, the Sn-rich phase nucleated and dendritically grew in a high speed. Finally, the biphase separation in the bulk solder was clearly observed. The growth mechanism of both Bi-rich and Sn-rich grain under temperature gradient was discussed.

Study on precipitation and dissolution of interfacial Cu6Sn5 during thermomigration

Synchrotron radiation real-time imaging technology was used to in situ study the precipitation and dissolution behavior of interfacial Cu₆Sn₅ under temperature gradient during soldering. At the cold end, the pre-formed Cu₆Sn₅ grains continued to grow at a fast rate with increasing aspect ratio. Whereas at the hot end, the pre-formed Cu₆Sn₅ grains dissolved into the liquid solder rapidly then maintained as an extremely thin, scallop-like IMC layer. The thermomigration of Cu atoms from the hot end towards the cold end was responsible for the asymmetrical morphology of the interfacial Cu₆Sn₅ between the cold and hot ends.

Simulation of 63Sn-37Pb BGA packaging particle formation based on pulsated orifice ejection method (POEM)

A simulation method was used to investigate the effects of experiment parameters on particle formation of 63Sn-37Pb based on POEM. The results show that stable particles could be obtained only with adequate clearance. Particles with various sizes are obtained by rationally controlling the diameter of orifice, rod velocity and applied pressure. 63Sn-37Pb mono-sized sphere micro particles with different sizes were prepared by POEM, the experimental results are consistent with that of simulation.

Fabrication of BGA solder balls by pulsated orifice ejection method

A new method named Pulsated Orifice Ejection Method (POEM) is proposed for fabrication of BGA solder balls with narrow size distribution and high sphericity. As for an orifice with a certain diameter, the diameter of solder balls is mainly affected by rod displacement and gas pressure. The size of solder ball linearly increases with the increase of both the rod displacement and the gas pressure within a certain range. The analysis of size distribution and sphericity shows that solder ball fabricated by POEM meets the requirements of BGA packaging. In addition, the solidification behavior of the droplets prepared by POEM is also discussed by theoretical calculation.