Microstructure and Grain Orientation Evolution in Sn-3.0Ag-0.5Cu Solder Interconnects Under Electrical Current Stressing

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The grain orientation of Sn-based solder joints on copper pillars under the combined action of electron wind force and temperature gradient greatly affects their electromigration damage. The copper pillars with Sn-1.8Ag lead-free solder on the top was subjected to a current density of 1.5 × 104 A/cm2 at 125 °C to study the electromigration behaviors. The grain orientation was characterized by scanning electron microscopy (SEM) equipped with electron backscattered diffraction (EBSD) detector. Metal dissolution and voids formation in the cathode as well as massive intermetallic compounds(IMC) accumulation in the anode were observed after electromigration. Closer examination of solder joints revealed that the Sn grain whose c-axis perpendicular to electric current may have retarded Cu diffusion to anode and IMC accumulation. In addition, the newly formed Cu6Sn5 exhibited preferred orientation related to the electric current direction.

Section: Introductionmentioning

confidence: 99%

The Effect of Grain Orientation of β-Sn on Copper Pillar Solder Joints during Electromigration

Wang

et al. 2021

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“…The schematic unit cell of a Sn grain represents the orientation of an Sn grain in Figure 5d. It has been reported in previous studies that the metal atoms diffuse much faster along the c-axis than the other two long axes (a-axis or b-axis) in a β-Sn grain lattice [19]. The microbump (β-Sn) has a body-centered tetragonal grain structure at RT.…”

Section: Resultsmentioning

confidence: 99%

“…The resistivity along the a and b axes is 13.25 μΩ-cm, while the c-axis is 20.27 μΩ-cm. [19]. For instance, the calculated anisotropy ratio for Ni could reach as high as 30,000 [34].…”

Section: Resultsmentioning

confidence: 99%

“…EM is affected by the crystallographic structure of Sn-based solder interconnects [17,18]. The most widely used lead-free solders in electronic packaging are Sn-based solder alloys with a β-Sn matrix, such as Sn–Ag and Sn–Ag–Cu [19,20]. Therefore, the characteristics of the interconnects are determined by β-Sn, which exhibits strong anisotropy in multiple aspects, such as mechanical, thermal, electrical, and diffusion properties, due to its body-centered tetragonal crystal structure [21,22,23,24].…”

Section: Introductionmentioning

confidence: 99%

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Microstructure and Grain Orientation Evolution in SnPb/SnAgCu Interconnects Under Electrical Current Stressing at Cryogenic Temperature

En²,

Zhou³

et al. 2019

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Electromigration was characterized at the cathode Cu/solder interface—without the effect of Joule heating—by employing scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) analyses. Rapid (Cux,Ni1−x)6Sn5 intermetallic compound (IMC) growth was observed at the anomalous region at the cathode end due to the effect of current crowding. The abnormal isotropic diffusion and parallel distribution of Pb were characterized in an ultra-low temperature environment in a monocrystalline structure stressed at −196 °C. The interesting results were attributed to crystallographic transformation due to the simultaneous effect of cryogenic and electrical stressing. The diffusion behavior of Pb atoms in face-centered cubic lattices performed isomorphism. As a result, Pb atoms of the bump gathered at the high-energy grain boundaries by diffusing through the face-centered cubic lattices around the long grain boundary, eventually forming a long-range distribution and accumulation of Pb elements. Our study may provide understanding of cryogenic electromigration evolution of the Cu/solder interface and provide visual data for abnormal lattice transformation at the current stressing.

“…Shen [24] investigated the evolution of grain orientation during EM by synchrotron microdiffraction and the results indicated that the grain rotation occurred only in the current crowding region and the grain rotation led to a little decrease of resistivity. Chen [25] found that grain orientations at the neck region of the Sn-3.0Ag-0.5Cu (SAC305) solder joints tended to be identical after EM, which was due to the grain rotation and the grains merged in the direction of decreasing resistivity.…”

Section: Introductionmentioning

confidence: 99%

The In-Situ Observation of Grain Rotation and Microstructure Evolution Induced by Electromigration in Sn-3.0Ag-0.5Cu Solder Joints

Chen

et al. 2020

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The in-situ observation of Sn-3.0Ag-0.5Cu solder joints under electromigration was conducted to investigate the microstructure and grain orientation evolution. It was observed that there was a grain rotation phenomenon during current stressing by in-situ electron backscattered diffraction (EBSD). The rotation angle was calculated, which indicated that the grain reorientation led to the decrease of the resistance of solder joints. On the other hand, the orientation of β-Sn played a critical role in determining the migration of Cu atoms in solder joints under current stressing migration. When the angle between the electron flow direction and the c-axis of Sn (defined as α) was close to 0°, massive Cu6Sn5 intermetallic compounds were observed in the solder bulk; however, when α was close to 90°, the migration of the intermetallic compound (IMC) was blocked but many Sn hillocks grew in the anode. Moreover, the low angle boundaries were the fast diffusion channel of Cu atoms while the high grain boundaries in the range of 55°–65° were not favorable to the fast diffusion of Cu atoms.