Title :
Reliability of interfaces for lead-free solder bumps
Author :
Shih, Richard L H ; Lau, Danny Y K ; Kwok, Raymund W M ; Li, M. ; Sun, Mandy K W
Author_Institution :
Dept. of Chem., Chinese Univ. of Hong Kong, Shatin, China
Abstract :
This study aims at a better understanding of the reliability of lead-free solder bumps for flip-chip applications. Without the presence of lead, copper in the under bump metal (UBM) layer dissolves extensively into the molten solder during reflow, which forms a thick intermetallic layer at the interface. It was found that with a annealing step before reflow, the thickness of the intermetallic layer can be reduced. When nickel is used as the UBM and SnAgCu is used as the bump material, (Cu,Ni)6Sn5 ternary intermetallic is formed at the interface. The ternary intermetallic increased the chance of failure at the interface during ball shear test. After thermal cycling, the probability of failure at the interface further increased.
Keywords :
annealing; copper; copper alloys; failure analysis; flip-chip devices; integrated circuit interconnections; integrated circuit packaging; interface structure; mechanical testing; microassembling; nickel; probability; reflow soldering; silver alloys; solders; surface chemistry; tin alloys; (CuNi)6Sn5 ternary intermetallic; Cu; SnAgCu bump material; SnAgCu-Ni; annealing; ball shear test; copper dissolution; failure probability; flip-chip applications; interface reliability; intermetallic interface layer; intermetallic thickness; lead-free solder bumps; molten solder reflow; nickel UBM; thermal cycling; under bump metal layer; Argon; Copper; Environmentally friendly manufacturing techniques; Intermetallic; Lead; Nickel; Ovens; Scanning electron microscopy; Sputtering; Tin;
Conference_Titel :
Thermal and Mechanical Simulation and Experiments in Microelectronics and Microsystems, 2004. EuroSimE 2004. Proceedings of the 5th International Conference on
Print_ISBN :
0-7803-8420-2
DOI :
10.1109/ESIME.2004.1304100
