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

Xing Fu,Yunfei En,Xiaoqi He,Bin Zhou,Yun Huang,Hongtao Chen,Ruohe Yao,Si Chen

doi:10.3390/ma12101593

Abstract

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.

Highlights

Deep-space exploration necessitates an astrovehicle of great reliability over an extensive range of temperatures, for instance, under the conditions of Moon (77–423 K), Mars (133–293 K) and GiantPlanets (133–653 K) [1,2]
Sn-based microbumps undergo a transition from ductile to brittle at cryogenic temperatures (CT), resulting in brittle cracks that can lead to catastrophic failure of electronic components
Electron backscatter diffraction (EBSD) technology was utilized to investigate the effect of grain orientation and grain boundaries on the migration of Pb atoms and intermetallic compound (IMC)

Summary

Introduction

Deep-space exploration necessitates an astrovehicle of great reliability over an extensive range of temperatures, for instance, under the conditions of Moon (77–423 K), Mars (133–293 K) and Giant. Sn-based microbumps undergo a transition from ductile to brittle at CT, resulting in brittle cracks that can lead to catastrophic failure of electronic components. Due to increasing current densities required for high-performance, multi-functional, and miniaturized electronic devices, electromigration (EM) is becoming a crucial issue for the reliability of solder interconnects [10,11,12]. In the actual engineering application process, the tin-based solder micro-interconnect structure changes its internal lattice structure during the process of temperature drop, resulting in a so-called gray tin or tin pest (α-Sn) parasitic phase [25]. The low temperature factor can reduce the thermal energy of the lattice and the atom migration speed [26]. Self-mixed Pb-containing solder joints are used to characterize electromigration inside interconnected solder joints of an α-Sn lattice structure. Electron backscatter diffraction (EBSD) technology was utilized to investigate the effect of grain orientation and grain boundaries on the migration of Pb atoms and IMCs

Experiment

Results and Discussion

Conclusions