Stereological Analysis of Microstructural Evolution Due to Aging in SnAgCu Solder Alloys

• Published in: Journal of electronic materials Vol. 53; no. 3; pp. 1399 - 1413
• Main Authors: Chavali, S., Ganti, S. S., Liao, H., Subbarayan, G., Dutta, I., Dayananda, M.
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.03.2024; Springer Nature B.V
• Subjects: Aging; Aging (metallurgy); Characterization and Evaluation of Materials; Chemistry and Materials Science; Creep (materials); Electronics and Microelectronics; Eutectics; Instrumentation; Intermetallic compounds; Lineal analysis; Materials Science; Mechanical properties; Microstructure; Oblate spheroids; Optical and Electronic Materials; Original Research Article; Precipitates; Soldered joints; Solders; Solid State Physics; Tin base alloys; microstructural parameters; stereological techniques; isothermal aging; SnAgCu alloys
• ISSN: 0361-5235; 1543-186X
• DOI: 10.1007/s11664-023-10885-x

Due to its high homologous temperature (0.4 - 0.8  T m ), isothermal aging of Sn3.0Ag0.5Cu solder alloy causes microstructural changes that significantly affect its observed macroscopic creep behavior. In order to characterize such changes in mechanical behavior of the macroscale solder joint, a stereological description of the microstructural changes due to aging is needed. The microstructure of the as-reflowed solder joint mainly consists of primary Sn dendrites surrounded by a eutectic microconstituent consisting of Sn, Ag 3 Sn, and Cu 6 Sn 5 phases. Upon aging, the microstructure evolves with the growth of the Ag 3 Sn precipitates within the eutectic microconstituent and change in relative volume fractions of dendritic and eutectic regions. In this study, microstructural changes that occur in Ag 3 Sn precipitate during aging at temperatures of 25°C, 75°C, and 125°C are monitored for various aging times ranging from 1 to 90 days by employing areal and lineal analysis stereological techniques. The Ag 3 Sn precipitates are treated as oblate spheroids in shape and their size distributions for all microstructures are determined on the basis of Saltykov–DeHoff analysis. The various microstructures are characterized in terms of Sn dendrite cell size and Ag 3 Sn particle size. The importance of the developed stereological model for microstructurally adaptive creep modeling is finally discussed.