Microstructure evolution and microimpact performance of Sn-Ag-Cu solder joints under thermal cycle test
- PDF / 2,152,840 Bytes
- 9 Pages / 584.957 x 782.986 pts Page_size
- 89 Downloads / 235 Views
S. Liu Department of Mechanical Engineering, National Chung Cheng University, Chia-Yi, Taiwan 62102, Republic of China (Received 2 December 2009; accepted 23 February 2010)
The microstructure and microimpact performance of Sn1Ag0.1Cu0.02Ni0.05In (SAC101NiIn)/AuNi/Cu solder ball joints were investigated after a thermal cycle test (TCT). The joints show complete bulk fracture behavior before TCT. Moreover, TCT facilitated interfacial fracture behavior with lower fracture energy. The intermetallic compounds (IMCs) formed in the solder joints before and after TCT were investigated. TCT induces a variety of structural variations in the solder joints, including slipping bands, whisker formation, the squeezing of the IMC layer, the formation of cavities, the rotation and pop-up of grain, and the deformation and rotation of the entire joint. The variations in fracture behavior induced by TCT are correlated with the structural variations in the solder joints. I. INTRODUCTION
Tin-based lead-free solders have been widely used in electronic packaging such as ball grid arrays (BGA) and flip chips (FC). An important concern for electronic devices is the service lifetime, and the mechanical behavior of solder alloys is extremely important, because solder joints must retain their mechanical integrity under myriad conditions, such as creep, thermal fatigue, mechanical shock, and drop resistance.1 Hence, thermal and mechanical reliability tests are used to evaluate the lifetimes of electronic devices. Recently, it has been reported that the thermal reliability of electronic packaging strongly depends on the geometry of the solder joint and the crystal structure of the solder material.2,3 Thermal treatment not only induces the coarsening of precipitates and grain growth, but also induces changes in crystal structure. Coarsening of precipitates (Ag3Sn, b-Sn, or AuSn4) during cycling results in strength reduction. Some evidence shows that variations in the microstructure, particularly in the Sn grain size and crystal orientation, affect the corresponding deformation properties of the solder joints.4,5 The grain size and crystal structure affect joint strength and the deformation ability of the solder ball joint, respectively. However, as yet there is no evidence to prove the relation between fracture behavior in the solder joint system and the grain orientation.6,7 Consequently, variations in the microstructure, a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2010.0162
1312
http://journals.cambridge.org
J. Mater. Res., Vol. 25, No. 7, Jul 2010 Downloaded: 24 Mar 2015
particularly in the Sn grain size and crystal orientation, need further investigation with regard to their possible effects on the properties of SAC solder joints. It was reported that Sn–3Ag–0.5Cu exhibits longer thermal fatigue life than Sn–1Ag–0.5Cu.8,9 The large amount of fine tin grain in high-silver-content solders (x ¼ 3 to 4 wt%) restricts crack propagation and grain boundary sliding in the solder joint during t
Data Loading...
