Effect of Ni and Sb additions and testing conditions on the mechanical properties and microstructures of lead-free solder joints

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• 作者：Q.B. Tao^a ; L. Benabou^a ; ^{lahouari.benabou@uvsq.fr" class="auth_mail" title="E-mail the corresponding author} ; L. Vivet^b ; V.N. Le^a ; F.B. Ouezdou^a
• 关键词：Pb-free solder ; Alloy element ; Mechanical characterization ; Deformation and fracture ; Intermetallics ; Finite element method
• 刊名：Materials Science & Engineering A
• 出版年：2016
• 出版时间：4 July 2016
• 年：2016
• 卷：669
• 期：Complete
• 页码：403-416
• 全文大小：2150 K

文摘

Nowadays, one of the strategies to improve the reliability of lead-free solder joints is to add minor alloying elements to solders. Therefore, the aims of this study are to investigate the effect of Ni and Sb, as well as that of the testing conditions (temperature and strain rate), on the mechanical properties of two new lead-free solder joints, Sn-3.8Ag-0.7Cu-3Bi/Cu and Sn-3.8Ag-0.7Cu-3Bi0.2Ni1.54Sb/Cu. The changes, after testing, in their respective microstructure will also be investigated. The procedure to fabricate appropriate joint samples is described in this research. The shear tests were conducted by micro-tensile machine at temperatures between room temperature and 125 °C and strain rates between 2.0×10⁻⁴ s⁻¹ and 2.0×10⁻² s⁻¹. The experimental results indicate that, with additions of Ni and Sb in Sn-3.8Ag-0.7Cu-3Bi, the ultimate tensile strength (UTS) and the yield stress (σ_y${\sigma }_y$) are improved. Moreover, both temperature and strain rate may have substantial effects on the mechanical behavior and the microstructural features of the solder alloys. During the shear tests, the strength decreases with the increase of the test temperature and/or the decrease of the strain rate. The enhanced strength is attributed to the solid solution hardening effects of Sb in the Sn matrix and the refinement of the microstructure with the addition of Ni. Ni and Sb additions lead to the formation of new (Cu, Ni)₆Sn₅ and Ag₃(Sn, Sb) IMCs. Needle-like (Cu, Ni)₆Sn₅ appeared in the Sn-3.8Ag-0.7Cu-3Bi0.2Ni1.54Sb/Cu, instead of the globular-like Cu₆Sn₅ inSn-3.8Ag-0.7Cu-3Bi/Cu. In addition, the nine Anand material parameters are identified using the shear stress-strain data and a non-linear least square fitting and its validity is checked by means of the experimental data. The findings found that these Anand parameters are also in good agreement with data given in literature for other solder alloys. The obtained material parameters of the Anand constitutive model were utilized to analyze the stress-strain response of an Insulated Gate Bipolar Transistor (IGBT) under thermal cycling. Furthermore, the SEM analysis of as-fabricated joint specimens as well as fractured specimens at different testing conditions was done to observe the effects of these factors on the microstructure of the solder alloys.