Thermal Behavior Characterization and Mechanical Property Degradation of Sn-1Ag-0.7Cu-5BixIn/Cu Joints

Publication Date

5-27-2026

Document Type

Article

Publication Title

International Journal of Advanced Manufacturing Technology

Volume

145

Issue

1-2

DOI

10.1007/s00170-026-18377-y

First Page

425

Last Page

437

Abstract

Based on calculation of phase diagrams (CALPHAD)-assisted phase fraction calculations, Sn-1Ag-0.7Cu-5Bi-xIn (x = 4, 8, 15, 17 wt%, hereafter denoted as xIn) alloys were designed to meet long-term high-temperature service requirements in solder joints. Bi and In were added to offset performance losses resulting from reducing Ag content. With Bi fixed at 5 wt%, this study investigated the effects of varying In content on melting behavior, microstructure, mechanical properties, and fracture mechanisms. Results showed that increasing In content eliminated Bi-rich particles, and at ≥ 15 wt% In, InSn₄ phases appeared. The interfacial IMC transformed from Cu₆Sn₅ to Cu₆(Sn, In)₅, with the amount of InSn₄ and secondary phases increasing with In content. During isothermal aging at 170 °C, the 4In joints formed Cu-rich layers, causing stress concentration and interfacial cracking. In the 8In joints, Cu and In diffusion converted Cu₆(Sn, In)₅ to Cu₃(Sn, In), generating residual stresses and interfacial cracks. Higher In contents lowered melting points, accelerated diffusion, and stabilized Cu₆(Sn, In)₅, thereby improving joint reliability. These findings provide valuable insights for controlling interfacial intermetallic compounds and designing solder joints.

Funding Number

202301BC070001-001

Funding Sponsor

Yunnan Provincial Science and Technology Department

Keywords

IMC, In-doped low silver SAC joints, Mechanical properties, Microstructure

Department

Aviation and Technology

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