NDLI: Reliability and Au-concentration in OLB solder fillets of TAB-devices having a 75 /spl mu/m pitch

Content Provider	IEEE Xplore Digital Library
Author	Zakel, E. Villain, J. Reichl, H.
Copyright Year	1994
Abstract	TAB-OLB contacts having 75-/spl mu/m pitch were applied in a detailed long-term reliability test program. A variation of the Au-concentration in the OLB solder fillet was made using tapes with different thicknesses of the Au-tape metallization of 0.2, 0.5, 0.8, and 1.2 /spl mu/m. Pull tests and corresponding metallurgical investigations were performed in order to determine the optimal Au-thickness for best reliability performance. Compared to the OL-bonds having high Au-concentrations (0.8 and 1.2 m Au-tape metallization), the samples with low Au-concentrations (0.2 and 0.5 /spl mu/m Au) show lower mechanical pull test values after bonding, thermal aging, and thermal cycling. From the variation of Au-metallization thickness the tapes with 0.8 /spl mu/m have the best reliability performance. This can be attributed to the improvement of solder wetting behavior due to higher Au-concentrations. Additionally the improved solder fillet formation leads to a better mechanical performance of the whole contact. The presence of intermetallic Au-Sn phases does not affect the reliability even after severe thermal cycling treatment. The Au-concentration in the solder fillet of the present study are all well below the critical value of 10 at.%, so that Kirkendall pore formation in the ternary Cu-Sn-Au system is not the main failure mechanism. The formation of ternary Cu-Au-Sn intermetallic compounds causes a continuous decrease of the copper lead thickness. A new aspect is the growth limitation of the compounds due to the limited amount of Sn in the fillet. The formation of Kirkendall-voids and the growth of the ternary compounds of the type (CuAu)/sub 6/Sn/sub 5/ stop when Sn in the solder fillet is totally consumed. This is accompanied with a coagulation of already formed Kirkendall-pores causing an annealing effect of pull-test values after extended thermal aging treatments (155/spl deg/C, 500-1000 h).
Sponsorship	IEEE Computer Society
Starting Page	138
Ending Page	147
Page Count	10
File Size	2461183
File Format	PDF
ISSN	10709894
Volume Number	19
Issue Number	1
Language	English
Publisher	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Publisher Date	1996-02-01
Publisher Place	U.S.A.
Access Restriction	Subscribed
Rights Holder	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Subject Keyword	Testing Tin Metallization Aging Lead Intermetallic Performance evaluation Gold Bonding Failure analysis
Content Type	Text
Resource Type	Article
Subject	Engineering

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