NDLI: Transmission electron microscopy characterization of the porous structure induced by high current density in the flip-chip solder joints

Content Provider	IEEE Xplore Digital Library
Author	Ming-Yen Tsai Yen-Liang Lin Kao, C.R.
Copyright Year	2009
Description	Author affiliation: Department of Material Science and Engineering, National Taiwan University, Taiwan (Ming-Yen Tsai; Yen-Liang Lin; Kao, C.R.)
Abstract	There are several identified failure mechanisms such as void formation and propagation, the local melting mechanism and the underbump metallization (UBM) dissolution in flip chip solder joints. In our previous studies Ni(V) UBM consumption was also found to cause the failure. The flip chip solder joint used in this study was with Al/Ni(V)/Cu UBM on the chip side and an Au/Ni surface finish on the substrate side. The solder was used by eutectic PbSn. The aging temperature was constant 150°C and a 0.32A current stressing was applied to make a nominal current density of 5 x $10^{3}A/cm^{2}.$ Owing to the combined effects of current crowding and local Joule heating, the microstructure of the Ni(V) UBM near the entrance of the electrons into the joints was transformed to a porous structure after 550 hours. Afterwards the porous structure propagated all over the UBM to make the solder joints fail since the porous structure was non-conductive. The microstructure was firstly observed by field emission scanning electron microscopy (FE-SEM) and subsequently focused ion beam (FIB) was used to fabricate specimens for transmission electron microscopy (TEM) observation. The porous structure was composed of many voids near the interface of Ni(V)/(Cu,Ni)6Sn5 and a void-free area near the interface of Ni(V)/Al. Energy dispersion X-ray (EDX) analysis on TEM was performed for composition analyses. In the porous structure almost no Ni signal was detected except for the region near the interface of Ni(V)/Al. Pb-rich dark patches observed in the porous structure revealed that a severe diffusion behavior was occurred during electromigration. Selected area diffraction patterns (SADPs) were derived to identify phases. The results showed that the matrix of the porous structure was amorphous. Fine grains of Cu6Sn5 and V2Sn3 were randomly distributed in the matrix of the porous structure and a thin layer of Ni3Sn4 was located at the interface of Ni(V)/Al.
Starting Page	444
Ending Page	447
File Size	6283284
Page Count	4
File Format	PDF
ISBN	9781424443413
DOI	10.1109/IMPACT.2009.5382212
Language	English
Publisher	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Publisher Date	2009-10-21
Publisher Place	Taiwan
Access Restriction	Subscribed
Rights Holder	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Subject Keyword	Scanning electron microscopy transmission electron microscopy(TEM) Flip-Chip solder joint electromigration Transmission electron microscopy Flip chip solder joints Electron beams Failure analysis Tin Electron emission Performance analysis Microstructure Current density
Content Type	Text
Resource Type	Article

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