Title :
A study in flip-chip UBM/bump reliability with effects of SnPb solder composition
Author :
Wu, J.D. ; Zheng, P.J. ; Lee, C.W. ; Hung, S.C. ; Lee, J.J.
Author_Institution :
Adv. Semicond. Eng., Inc., Kaohsiung, Taiwan
fDate :
30 March-4 April 2003
Abstract :
This paper aims to investigate electromigration phenomena of under-bump-metallization (UBM) and solder bumps of a flip-chip package under a high temperature operation life test (HTOL). UBM is a thin film Al/Ni(V)/Cu metal stack of 1.5 μm, while the bump material consists of Sn/37Pb, Sn/90Pb, and Sn/95Pb solders. Current densities of 2,500 and 5,000 A/cm2 and ambient temperatures of 150 to 160°C are applied to study their impact on electromigration. It is observed that bump temperature has a more significant influence than current density on bump failures. Owing to its higher melting point characteristics and lower Sn content, high-lead bumps are observed to have an 8 to 12-fold improvement in Mean-Time-To-Failure (MTTF) compared with eutectic Sn/37Pb. Individual bump resistance history is used to evaluate UBM/bump degradation. The measured resistance increase is from bumps with electrical current flowing upward into the UBM/bump interface (cathode), while bumps with opposite current polarity cause only minor resistance change. The identified failure sites and modes reveal structural damage at the region of UBM and UBM/bump interfaces in the form of solder cracking or delamination. The effects of current polarity and crowding are key factors in the observed electromigration behavior of flip-chip packages.
Keywords :
aluminium; ball grid arrays; copper; delamination; electromigration; environmental testing; failure analysis; flip-chip devices; integrated circuit metallisation; integrated circuit packaging; integrated circuit reliability; lead alloys; life testing; nickel alloys; soldering; thermal stress cracking; tin alloys; vanadium alloys; 1.5 micron; 150 to 160 C; Al-NiV-Cu; FCBGAs; MTTF; SnPb; SnPb solder composition; ambient temperatures; bump failures; bump temperature; current crowding; current densities; current polarity; delamination; electromigration phenomenon; failure sites; flip-chip UBM/bump reliability; flip-chip package; high temperature operation life test; mean-time-to-failure; melting point characteristics; solder bumps; solder cracking; structural damage; thin film Al/Ni(V)/Cu metal stack; under-bump-metallization; Current density; Electric resistance; Electromigration; History; Inorganic materials; Life testing; Packaging; Temperature; Tin; Transistors;
Conference_Titel :
Reliability Physics Symposium Proceedings, 2003. 41st Annual. 2003 IEEE International
Print_ISBN :
0-7803-7649-8
DOI :
10.1109/RELPHY.2003.1197733
