Subgrain Rotation Behavior in Sn3.0Ag0.5Cu-Sn37Pb Solder Joints During Thermal Shock

• Published in: Journal of electronic materials Vol. 47; no. 1; pp. 124 - 132
• Main Authors: Han, Jing, Tan, Shihai, Guo, Fu
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.01.2018; Springer Nature B.V
• Subjects: Axes (reference lines); Ball grid packaging; Characterization and Evaluation of Materials; Chemistry and Materials Science; Continuity (mathematics); Electronics and Microelectronics; Grain orientation; Instrumentation; Materials research; Materials Science; Microstructure; Misalignment; Optical and Electronic Materials; Polycrystals; Recrystallization; Soldered joints; Solid State Physics; Thermal shock; Mixed solder joints; recrystallization; subgrain rotation; thermal fatigue
• ISSN: 0361-5235; 1543-186X
• DOI: 10.1007/s11664-017-5864-3

Ball grid array (BGA) samples were soldered on a printed circuit board with Sn37Pb solder paste to investigate the recrystallization induced by subgrain rotation during thermal shock. The composition of the solder balls was Sn3.0Ag0.5Cu-Sn37Pb, which comprised mixed solder joints. The BGA component was cross-sectioned before thermal shock. The microstructure and grain orientations were obtained by a scanning electron microscope equipped with an electron back-scattered diffraction system. Two mixed solder joints at corners of the BGA component were selected as the subjects. The results showed that recrystallization occurred at the corner of the solder joints after 200 thermal shock cycles. The recrystallized subgrains had various new grain orientations. The newly generated grain orientations were closely related to the initial grain orientations, which indicated that different subgrain rotation behaviors could occur in one mixed solder joint with the same initial grain orientation. When the misorientation angles were very small, the rotation axes were about Sn [100], [010] and [001], as shown by analyzing the misorientation angles and subgrain rotation axes, while the subgrain rotation behavior with large misorientation angles in the solder joints was much more complicated. As Pb was contained in the solder joints and the stress was concentrated on the corner of the mixed solder joints, concaves and cracks were formed. When the adjacent recrystallized subgrains were separated, and the process of the continuous recrystallization was limited.