Mingliang Huang

Role of Cu in dissolution kinetics of Cu metallization in molten Sn-based solders

The focus of this study is on the role of Cu content in the dissolution kinetics of Cu in high-Sn solders during the solid/liquid reaction accompanied by interfacial intermetallic compound formation. Small additions of Cu (0.7%, 1.5%) in high-Sn solders dramatically decrease the dissolution rate of Cu at low temperatures. Sn-3.5Ag, as expected, has a dissolution rate similar to that of pure Sn. The difference in dissolution rate of Cu in various molten solders is explained in terms of the solubility limit of Cu in molten solders based on the Cu-Sn phase diagram. The correlation between the metallurgical aspects of interfacial η(Cu6Sn5) phase formation and dissolution kinetics of Cu in molten solders leads to an understanding of the mechanism that controls the dissolution rate of Cu in molten solders.

Improvement of wettability and tensile property in Sn–Ag–RE lead-free solder alloy

Abstract The influence of mixture (La, Ce) rare earth elements (RE) on wettability and tensile property in Sn–3.5Ag solder alloy was investigated. The wetting property was improved by 0.25–0.5% addition of (La, Ce) rare earth elements into the Sn–3.5Ag solder alloy, while over addition of the rare earth elements up to 1.0 wt.% reduced the beneficial influence. The ultimate strength and ductility were also enhanced by 0.25–0.5% addition of (La, Ce) rare earth elements, while the change of melting temperature was negligible.

In situ study on the effect of thermomigration on intermetallic compounds growth in liquid-solid interfacial reaction

Synchrotron radiation real-time imaging technology was carried out in situ to observe and characterize the effect of thermomigration on the growth behavior of interfacial intermetallic compounds (IMCs) in Cu/Sn/Cu solder joint during soldering. The thermomigration resulted in asymmetrical formation and growth of the interfacial IMCs. Cu6Sn5 and Cu3Sn IMCs formed at the cold end and grew rapidly during the whole soldering process. However, only Cu6Sn5 IMC formed at the hot end and remained relatively thin until solidification. The IMCs at the cold end were nearly seven times thicker than that at the hot end after solidification. The Cu dissolution at the cold end was significantly restrained, while that at the hot end was promoted, which supplied Cu atoms to diffuse toward the cold end under thermomigration to feed the rapid IMC growth. Moreover, the thermomigration also caused asymmetrical morphology of the interfacial IMCs at the cooling stage, i.e., the Cu6Sn5 IMC at the cold end transformed into facet ...

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 ...

Drop failure modes of Sn–3.0Ag–0.5Cu solder joints in wafer level chip scale package

Abstract To reveal the drop failure modes of the wafer level chip scale packages (WLCSPs) with Sn–3.0Ag–0.5Cu solder joints, board level drop tests were performed according to the JEDEC standard. Six failure modes were identified, i.e., short FR-4 cracks and complete FR-4 cracks at the printing circuit board (PCB) side, split between redistribution layer (RDL) and Cu under bump metallization (UBM), RDL fracture, bulk cracks and partial bulk and intermetallic compound (IMC) cracks at the chip side. For the outmost solder joints, complete FR-4 cracks tended to occur, due to large deformation of PCB and low strength of FR-4 dielectric layer. The formation of complete FR-4 cracks largely absorbed the impact energy, resulting in the absence of other failure modes. For the inner solder joints, the absorption of impact energy by the short FR-4 cracks was limited, resulting in other failure modes at the chip side.

On the thickness of Cu6Sn5 compound at the anode of Cu/liquid Sn/Cu joints undergoing electromigration

In the electromigration tests performed with the Cu/liquid Sn/Cu samples of effective Sn lengths

Formation mechanism and kinetic analysis of the morphology of Cu6Sn5 in the spherical solder joints at the Sn/Cu liquid–solid interface during soldering cooling stage

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The effect of laser-soldering parameters on the Sn-Ag-Cu/Cu interfacial reaction

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