Impact of Thermal Cycling on Sn-Ag-Cu Solder Joints and Board-Level Drop Reliability

• Published in: Journal of electronic materials Vol. 37; no. 6; pp. 880 - 886
• Main Authors: Xu, Luhua, Pang, John H. L., Che, Faxing
• Format: Journal Article
• Language: English
• Published: Boston Springer US 01.06.2008; Institute of Electrical and Electronics Engineers; Springer Nature B.V
• Subjects: Applied sciences; Brazing. Soldering; Characterization and Evaluation of Materials; Chemistry and Materials Science; Electronics; Electronics and Microelectronics; Exact sciences and technology; Impact tests; Instrumentation; Intermetallic compounds; Joining, thermal cutting: metallurgical aspects; Lead free solders; Materials; Materials Science; Metals. Metallurgy; Microelectronic fabrication (materials and surfaces technology); Optical and Electronic Materials; Reliability; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Solid State Physics; Thermal cycling; Kirkendall void; Drop impact; Pb-free solder; thermal cycling; intermetallic compound; ball grid array; Thermal ageing; Brittle fracture; Thermal cycle; Kirkendall effect; Crystal defect; BGA technology; Electronic packaging; Lead free solder; Void; Copper; Bonding; Gold; Intermetallic compound; Durability; Surface treatment; Lifetime; Soldered joint; Nickel; Reliability; Impact test; Interface; Fracture mode
• ISSN: 0361-5235; 1543-186X
• DOI: 10.1007/s11664-008-0400-0

The electronic packaging industry uses electroless nickel immersion gold (ENIG) or Cu-organic solderability preservative (Cu-OSP) as a bonding pad surface finish for solder joints. In portable electronic products, drop impact tests induce solder joint failures via the interfacial intermetallic, which is a serious reliability concern. The intermetallic compound (IMC) is subjected to thermal cycling, which negatively affects the drop impact reliability. In this work, the reliability of lead-free Sn-3.0Ag-0.5Cu (SAC) soldered fine-pitch ball grid array assemblies were investigated after being subjected to a combination of thermal cycling followed by board level drop tests. Drop impact tests conducted before and after thermal aging cycles (500, 1000, and 1500 thermal cycles) show a transition of failure modes and a significant reduction in drop durability for both SAC/ENIG and SAC/Cu-OSP soldered assemblies. Without thermal cycling aging, the boards with the Cu-OSP surface finish exhibit better drop impact reliability than those with ENIG. However, the reverse is true if thermal cycle (TC) aging is performed. For SAC/Cu-OSP soldered assemblies, a large number of Kirkendall voids were observed at the interface between the intermetallic and Cu pad after thermal cycling aging. The void formation resulted in weak bonding between the solder and Cu, leading to brittle interface fracture in the drop impact test, which resulted in significantly lower drop test lifetimes. For SAC/ENIG soldered assemblies, the consumption of Ni in the formation of NiCuSn intermetallics induced vertical voids in the Ni(P) layer.