Linearly elastic finite element analyses were used to examine the effects of fiber orientation, notch angle and notch root radius on the stress distribution in Arcan specimens in order to optimize the specimen geometry for the unidirectional, fiber reinforced composite AS4/PEEK under shear and biaxial loadings. Two fiber orientations, three notch angles and five notch root radii were examined. A comparison between butterfly-shaped and circular S-shaped specimens was also made. For specimens with fibers running across the specimen from grip to grip (1-2 orientation), a 1340 notch angle was found to be the best choice due to superior stress uniformity along the gage section and minimum transverse normal stress along the notch flank. However, specimens with fibers running from notch to notch (2-1 orientation), required a 900 notch angle for optimum stress uniformity along the gage section and minimum transverse normal stress along the specimen notch. It was also found that, along the gage section, the largest shear stress concentration occurred near the notch roots of the 1-2 specimen, yet it was not seen in the 2-1 specimen. This made the 2-1 specimen a better candidate for determining the shear properties of fiber reinforced composites. It was also found that the butterfly-shaped specimen bonded to steel grips provided much more uniform normal stresses than the original circular S-shaped specimen did. As a result, a butterfly-shaped Arcan specimen with a 2-1 fiber orientation, a 900 notch angle, a 2.38 mm root radius and bonded to steel grips was found to be very suitable for examining the longitudinal deformation behavior of this particular fiber reinforced composite under both shear and biaxial loading. Strain distributions from the finite element analyses were also compared to those obtained from moire measurements. At low load levels, there was excellent agreement between the two. Nonlinear effects mitigated stress concentrations at higher load levels.

ABSTRACT--Moir6 interferometry was used to examine the strain distributions in Arcan-type specimens under shear loading. The compact geometry allowed longitudinal and transverse shear behavior to be considered. The best results for longitudinal moduli were obtained with fibers running from notch to notch. As with the Iosipescu configuration, strain averaging or correction factors were required for modulus determination in all fiber orientations. None of the bending problems that have been encountered in the Iosipescu specimen were observed. Some twisting was noticed, but its extent (less than 2 percent) was much less than has been noted in shear testing with Iosipescu specimens.

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This paper aims to investigate the electromigration phenomenon of under-bump-metallization (UBM) and solder bumps of a flip-chip package under high temperature operation life test (HTOL). UBM is a thin film AIMi(V)/Cu metal stack of 1.5 pm; while bump material consists of Sn/37Pb, Sn/90Pb, and Sd95Pb solder. Current densities of 2,500 and 5,000 Ncm2 and ambient temperatures of 150 to 160 "C are applied to study their impact on electromigration. It is observed that hump temperature has more significant influence than current density does to bump failures. Owing to its higher melting point characteristics and less content of Sn phase, high-lead bumps are observed to have 8-12-fold improvement in Mean-Time-To-Failure (MTTF) than that of eutectic Sd37Pb. Individual bump resistance history is calculated to evaluate UBMibump degradation. The measured resistance increase is from bumps with electrical current flowing upward into UBMibump interface (cathode), while bumps having opposite current polarity cause only minor resistance change. The identified failure sites and modes from aforementioned high resistance bumps reveal structural damages at the region of UBM and UBMhump interface in forms of solder cracking or delamination. Effects of current polarity and crowding are key factors to observed electromigration behavior of flip-chip packages. I CellNo. I Current I CurrentDensitv 1 Temp. I 0-7803-7649-8/03/$17.00 02003 IEEE

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