Phase Stability, Phase Transformations, and Reactive Phase Formation in Electronic Materials XX: Properties and Microstructures of Electronic Materials
Sponsored by: TMS Functional Materials Division, TMS Structural Materials Division, TMS: Alloy Phases Committee
Program Organizers: Hiroshi Nishikawa, Osaka University; Shih-kang Lin, National Cheng Kung University; Chao-Hong Wang, National Chung Cheng University; Chih-Ming Chen, National Chung Hsing University; Jaeho Lee, Hongik University; Zhi-Quan Liu, Shenzhen Institutes of Advanced Technology; Ming-Tzer Lin, National Chung Hsing University; Dajian Li, Karlsruhe Institute of Technology; Yu Zhong, Worcester Polytechnic Institute; Yee-wen Yen, National Taiwan University of Science and Technology; A.S.Md Abdul Haseeb, Bangladesh University of Engineering and Technology (BUET); Ligang Zhang, Central South University; Sehoon Yoo, KITECH; Vesa Vuorinen, Aalto University; Yu-Chen Liu, National Cheng Kung University

Wednesday 2:00 PM
March 17, 2021
Room: RM 21
Location: TMS2021 Virtual

Session Chair: A.S. Md. Abdul Haseeb, University of Malaya; Chih-Ming Chen, National Chung Hsing University


2:00 PM  Keynote
Effect of Initial Volume Ratio and Reflow Temperature on the Microstructure of SnBiAg-SAC Mixed Solder Joints: Eric Cotts1; Faramarz Hadian1; Randy Owen1; Mohammed Genanu1; 1Binghamton University
    Significant phase transformations occur in mixed assembly SAC/Bi-Sn solder joints (e.g., SAC305/Sn57Bi1Ag) during standard processing procedures. The changes in microstructure of these mixed assemblies during reflow (140C to 215C) depend upon the peak temperature, and on the initial ratio of the volume of the SnBiAg paste to the volume of the SnAgCu solder ball. The final volume ratio between the volumes of the SnAgCu and SnBiAg phases can be predicted as a function of the peak reflow temperature. Prolonged heating of such mixed assemblies accelerates diffusion of Bi in to the SAC region, resulting in recrystallization of the Sn in the SAC. The newly formed, high energy grain boundaries provide pathways for relatively rapid diffusion of Bi. Transformation rates are characterized and reported. Values of the shear strength of the mixed assemblies as a function of peak reflow temperature and initial volume ratio are also reported.

2:40 PM  
Effect of Low Bi Content on Mechanical Property of Sn-Bi-Zn Alloy before and after Thermal Aging: Hiroshi Nishikawa1; Shiqi Zhou1; Chih-han Yang2; Yu-An Shen2; Shih-kang Lin2; 1Osaka University; 2National Cheng Kung University
     Recently, eutectic Sn-58Bi alloy is becoming one of the candidates of the low-temperature lead-free solders. High joint strength, large creep resistance, and good wettability were recognized as advantages. However, the brittleness of eutectic Sn-58Bi alloy is one of the unsolved issues. To address the issue, Zn was selected as the element to control the liquidus temperature of the Sn-Bi-Zn ternary system. In this study, Sn-Bi-Zn alloy with low Bi content was examined by tensile tests before and after aging. A fine microstructure containing Sn-Bi-Zn ternary structure and higher volume fraction of Sn-rich phase were observed. Before aging, approximately 112 % elongation improvement for the Sn-Bi-Zn alloy was obtained compared to that of eutectic Sn-58Bi alloy. After aging, the elongation was still superior than that of eutectic Sn-58Bi alloy owing to the higher volume fraction of Sn-rich phase.

3:00 PM  
High-throughput Calculations for Sn-Bi-Ag and Sn-Bi-Ag-In Low-temperature Lead-free Solders: Chih-Han Yang1; Yuki Hirata2; Hiroshi Nishikawa2; Shih-kang Lin1; 1National Cheng Kung University; 2Osaka University
    Low-temperature lead(Pb)-free solders with low cost and high reliability are in demand in the electronic industry. Eutectic Sn-58Bi with high mechanical properties and low melting temperature at 139 °C has drawn significant interest in the industry. However, the coarsened (Bi)-rich phase deteriorated the reliability of the solder joint. The goal is to supress (Bi)-rich phase grain growth, while keeping their low melting temperatures. In this study, CALPHAD-type thermodynamic high-throughput calculations (HTC) using the PANDAT software and corresponding key experiments were performed to design Sn-Bi-Ag (SBA) and Sn-Bi-Ag-In (SBAI) systems. Thousands of calculated solidification paths based on the Scheil model was employed. As for the mechanical properties of the SBA and SBAI solder, high yield strength, high ultimate tensile strength, and slightly better elongation were obtained. This study shows that CALPHAD calculations make a good agreement with experimental results in phase fraction, melting point, and paths of solidification.

3:20 PM  
Solid-liquid Interfacial Reaction between Cu and In-48Sn Alloy: Fu-Ling Chang1; C. Robert Kao1; H. T. Hung1; S. Y. Lin1; 1National Taiwan University
    Soldering temperature below 200℃ is required to avoid the warpage of bonding chips for many applications. Low temperature alloys, such as In-48Sn and Sn-58Bi, are receiving the most attentions. Sn-58Bi alloy, with superior fatigue resistance and tensile strength, has been widely used in the industry. However, the brittle property of Bi-containing phases restricts its application. On the other hand, In-48Sn alloy, with good mechanical properties and excellent thermal conductivity, has not yet been fully investigated. Therefore, the present study focused on the interfacial reactions between Cu and molten In-48Sn solder alloy at 150℃. To overcome the difficulty of polishing In-containing samples and to obtain artifact-free microstructures, cryogenic broad Ar beam ion polishing was applied. Electron probe micro-analyzer and X-Ray diffractometer were also used to identify the phase structure at the interface.

3:40 PM  
Using Machine Learning to Predict Hardness of Sn-based Alloys: Yu-Chen Liu1; Chih-han Yang1; Hannah Carillo1; Chuan-cheng Lin1; Shih-kang Lin1; 1National Cheng Kung University
    In this study, we employed the machine learning method with gaussian kernel ridge regression (GKRR) to develop a model for predicting the as-casted Sn-based alloy hardness. The 5-fold (leave-out (LO)-alloy-group) cross-validation (CV) test showed RMSE/σ of 0.43 ± 0.02 (0.38 ± 0.28) and R2 of 0.81 (0.79). The LO-element CV test suggested that our model was able to fully or partially extrapolate to some of the unknown elements space which were not shown in the data set, but was still difficult to do so without the information of some elements. The cross-plot analysis showed that our model was able to predict well within the composition range of the training data set. By using this model, we were able to design solders with hardness as high as 40.7 and as low as 2.7 Hv, and to explore the hardness change vs. types of doping elements in technology-relevant systems for future applications.