Analyses and design for electrochemical migration suppression by alloying indium into silver

Abstract

Silver electrochemical migration (ECM) is a serious reliability issue for fine pitch as well as power electronic devices that employ silver as interconnection materials. In this study, a method to suppress the ECM behavior of silver was proposed and implemented. Solid solutions of Ag-In and intermetallic compounds were fabricated and their ECM properties were studied through the water drop test (WDT). The WDT was performed on alumina substrate in deionized water at 3 V, where the leakage current was measured. The results show that Ag-In alloy samples have considerably longer lifetime before reaching short circuit than pure silver samples. As indium concentration in Ag-In solid solution increases, the resistance to ECM also increases. The migration process is completely inhibited when the indium concentration reaches 19 at.%. The morphologies of the dendrites and surfaces of the anode and cathode were also investigated. A model was established to explain the anti-ECM mechanism of Ag-In alloys. By forming indium oxide on the surface of the anode under electric field in a humid environment, the anode gets passivated and the silver dissolution path is completely blocked, and thus inhibiting the ECM process. It was discovered that the quality of electrode surfaces is essential in realizing the full potential of the inherent anti-ECM ability of Ag-In alloys. In conclusion, the results of this investigation have shown that Ag-In alloys can be promising and valuable candidates for conductors, metallization, and interconnect materials in fine pitch and high power electronic devices.

Review—Electrochemical Migration in Electronic Materials: Factors Affecting the Mechanism and Recent Strategies for Inhibition

“…Alloying elements can also affect the passivation behavior of a material which in turn affect the anodic dissolution step, either by an increase in the passive range or by the formation of new passive oxide film with the solders involved. 30,35 This passive oxide layer prevents a metal anode from being oxidized to form metal ions. Previous investigations showed that alloying elements such as Cu, Ag, Bi and Pb affect the passivation behavior of Sn-based materials.…”

“…It was suggested that the formation of PdO also acted as a barrier to Ag dissolution. A recent finding by Yang et al 35 also reported that incorporating 19 at % of indium (In) into pure Ag creates Ag-In alloy that is completely resistant to ECM due to the formation of a passive indium oxide layer (suggested to be In 2 O 3 ).…”

Size-Controlled Low-Melting-Point-Alloy Particle-Incorporated Transient Liquid-Phase Epoxy Composite Conductive Adhesive with High Performances

“…Therefore, it is expected that the LMPA particles can be fully transformed into IMCs with higher melting points, such as Ag 9 In 4 and Ag 3 Sn, during the curing process of TLP-ECA. From the knowledge of previous research, with Ag 9 In 4 and Ag 3 Sn IMCs in TLP-ECA composites, the antielectrochemical migration performance of Ag-based TLP-ECA is expected to be considerably improved, possibly owing to the alternating 4d valence band structure of Ag-based alloys . However, if we increase the size of the LMPA particles to the level of traditional preparation methods (25–50 μm), improper size matching between the Ag flakes (7–10 μm) and LMPA particles would lead to a different diffusional reaction scenario.…”

“…From the knowledge of previous research, 33 with Ag 9 In 4 and Ag 3 Sn IMCs in TLP-ECA composites, the antielectrochemical migration performance of Ag-based TLP-ECA is expected to be considerably improved, possibly owing to the alternating 4d valence band structure of Ag-based alloys. 32 However, if we increase the size of the LMPA particles to the level of traditional preparation methods (25−50 μm), improper size matching between the Ag flakes (7−10 μm) and LMPA particles would lead to a different diffusional reaction scenario. Furthermore, the LMPA content would be locally oversupplied because the large LMPA is 2−4 times larger than Ag flakes.…”

“…Moreover, the diffusional reactions mechanism of LMPA particles filled TLP-ECAs has been systematically investigated and unveiled with solid experimental evidence from differential scanning calorimetry (DSC), X-ray diffraction (XRD), and high-resolution scanning transmission electron microscopy in high-resolution high-angle annular dark-field mode (STEM-HAADF) studies. Accordingly, the antielectrochemical-migration 32 and antitarnishing 33 properties of Ag-based TLP-ECAs are expected to be considerably enhanced. Finally, combining their advantages in terms of electrical, mechanical, and electrochemical stability, the sonochemical LMPA particleincorporated Ag-based TLP-ECAs have been suggested as promising interconnection material candidates in the emerging field of SiC/GaN power electronics packaging.…”