• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2003.11a
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• pp.84-87
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• 2003

Since Pb-free solder alloys have been used extensively in microelectronic packaging industry, the interaction between UBM (Under Bump Metallurgy) and solder is a critical issue because IMC (Intermetallic Compound) at the interface is critical for the adhesion of mechanical and the electrical contact for flip chip bonding. IMC growth must be fast during the reflow process to form stable IMC. Too fast IMC growth, however, is undesirable because it causes the dewetting of UBM and the unstable mechanical stability of thick IMC. UP to now. Ni and Cu are the most popular UBMs because electroplating is lower cost process than thin film deposition in vacuum for Al/Ni(V)/Cu or phased Cr-Cu. The consumption rate and the growth rate of IMC on Ni are lower than those of Cu. In contrast, the wetting of solder bumps on Cu is better than Ni. In addition, the residual stress of Cu is lower than that of Ni. Therefore, the alloy of Cu and Ni could be used as optimum UBM with both advantages of Ni and Cu. In this paper, the interfacial reactions of Sn-3.5Ag-0.7Cu solder on Ni-xCu alloy UBMs were investigated. The UBMs of Ni-Cu alloy were made on Si wafer. Thin Cr film and Cu film were used as adhesion layer and electroplating seed layer, respectively. And then, the solderable layer, Ni-Cu alloy, was deposited on the seed layer by electroplating. The UBM consumption rate and intermetallic growth on Ni-Cu alloy were studied as a function of time and Cu contents. And the IMCs between solder and UBM were analyzed with SEM, EDS, and TEM.

• Transactions of Materials Processing
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• v.7 no.5
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• pp.481-488
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• 1998

The active metal brazing was applied to bond Alumina and Ni-Cr steel by Ag-Cu-Zr-Sn alloy and the interfacial microstructure and reaction mechanism were investigated. Polycrystalline monoclinic $ZrO_2$ with a very fine grain of 100-150 nm formed at the alumina grain boundary contacted with Zr segregation layer at the interface. The $ZrO_2$ layer containing the inclusions and cracks were developed at the boundary of inclusion/$ZrO_2$ due to the difference in specific volume. The development of $ZrO_2$ at the interface was successfully explained by the preferential penetration of $ZrO_2$ at the interface was successfully explained by the preferential penetration of Zr atoms a higher concentration of oxygen and a high diffusion rate of Al ions into molten brazing alloy.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.21 no.11
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• pp.968-972
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• 2008

Ni/Ti/Al multilayer system ('/'denotes the deposition sequence) was tested for low-resistance ohmic contact formation to Al-implanted p-type 4H-SiC. Ni 30 nm / Ti 50 nm / Al 300 nm layers were sequentially deposited by e-beam evaporation on the 4H-SiC samples which were implanted with Al (norminal doping concentration = $4\times10^{19}cm^{-3}$) and then annealed at $1700^{\circ}C$ for dopant activation. Rapid thermal anneal (RTA) temperature for ohmic contact formation was varied in the range of $840\sim930^{\circ}C$. Specific contact resistances were extracted from the measured current vs. voltage (I-V) data of linear- and circular transfer length method (TLM) patterns. In constrast to Ni contact, Ni/Ti/Al contact shows perfectly linear I-V characteristics, and possesses much lower contact resistance of about $2\sim3\times10^{-4}\Omega{\cdot}cm^2$ even after low-temperature RTA at $840^{\circ}C$, which is about 2 orders of magnitude smaller than that of Ni contact. Therefore, it was shown that RTA temperature for ohmic contact formation can be lowered to at least $840^{\circ}C$ without significant compromise of contact resistance. X-ray diffraction (XRD) analysis indicated the existence of intermetallic compounds of Ni and Al as well as $NiSi_{1-x}$, but characteristic peaks of $Ti_{3}SiC_2$, a probable narrow-gap interfacial alloy responsible for low-resistance Ti/Al ohmic contact formation, were not detected. Therefore, Al in-diffusion into SiC surface region is considered to be the dominant mechanism of improvement in conduction behavior of Ni/Ti/Al contact.

• Journal of the Korean Society for Heat Treatment
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• v.12 no.2
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• pp.145-156
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• 1999

The distribution of the second phase, the change of transformation temperature and mechanical properties with thermomechanical treatment conditions were investigated by metallography, calorimetry, EDS, tensile test and fractography in a Cu-Al-Ni-Ti-Mn alloy. The cast structure revealed Ti-rich precipitates($X_L$ phase) between dendrite arms, which have been identified as $(Cu,Ni)_2TiAl$ intermetallic compounds. By homogenizing above $900^{\circ}C$, the $X_L$ phase was melted in the matrix, while the Xs phase was precipitated in matrix and the volume fraction of it was increased. When hot-rolled specimen was betatized below $750^{\circ}C$, recrystallization could not be observed. However, the specimen betatized above $800^{\circ}C$ was recrystallized and the grain size was about $50{\mu}m$, while Xs phase was precipitated in matrix. With raising betatizing temperature, $M_s$ and $A_s$ temperatures were fallen and transformation hysteresis became larger. The strain of the specimen betatized at $800^{\circ}C$ was 8.2% as maximum value. The maximum shape recovery rate could be obtained in the specimen betatized at $800^{\circ}C$ but it was decreased due to the presence of Xs phase with increasing betatizing temperature.

• Corrosion Science and Technology
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• v.15 no.3
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• pp.129-134
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• 2016

The effects of Ti on the high temperature oxidation of Ni-based superalloys were investigated by cyclic oxidation at $850^{\circ}C$ and $1000^{\circ}C$. The oxide scale formed at $850^{\circ}C$ consists of $Cr_2O_3$, $Al_2O_3$, and $NiCr_2O_4$ layers, while a continuous $Al_2O_3$ layer was formed at $1000^{\circ}C$. The oxidation rate of the alloy with higher Ti content was higher than the alloy with less Ti content at $850^{\circ}C$, possibly due to the increase in the metal vacancy concentration in the $Cr_2O_3$ layer involved by incorporation of $Ti^{4+}$. However, Ti improved the oxidation resistance of the superalloy at $1000^{\circ}C$ by reducing oxygen vacancy concentration in $Al_2O_3$ layer.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.6
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• pp.634-641
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• 2001

Shape memory alloy has been used to improve the tensile strength of composite by the occurrence of compressive residual stress in matrix using its shape memory effect. In order to fabricate shape memory alloy composite, TiNi alloy and A16061 were used as reinforcing material and mix, respectively. In this study, TiNi/A16061 shape memory alloy composite was made by using hot press method. However, the specimen fabricated by this method had the bonding problem at the boundary between TiNi fiber and Al matrix when the load was applied to it. A cold rolling was imposed to the specimen to improve the bonding effect. It was found that tensile strength of specimen subjected to cold rolling was more increased than that of specimen which did not underwent cold rolling. In addition, acoustic emission technique was used to quantify the microscopic damage behavior of cold rolled TiNi/A16061 shape memory alloy composite at high temperature.

• Journal of the Korean Society for Heat Treatment
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• v.23 no.2
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• pp.96-103
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• 2010

$Ni_3Al$ is known as a good high temperature structural material because of high yield strength at ambient temperature. However, it is too brittle to use as a structural material because of their weak grain boundary. In this work, orientation measurement and related mechanical properties of directionally solidified NiAl/$Ni_3Al$ two-phase alloys with various compositions (Ni-23~27 at.%Al) were investigated for developing multi-phase DS-processed alloys with the growth rates of 10, 50 and 100 ${\mu}m/s$ in a modified Bridgeman type furnace. It was found that the multi-phase microstructures such as the $\gamma$ dendrite +${\gamma}'$ matrix duplex microstructure was formed in the hypoeutectic composition of 23 at.%Al, $\beta$ dendrite +${\gamma}'$ matrix duplex microstructure in the hypereutectic composition of 26 and 27 at.%Al. And ${\gamma}'$ single phase was formed in the composition of 24.5 and 25 at.%Al. The hypoeutectic alloy including $\gamma$ dendrites with ${\gamma}'$ matrix showed a large elongation of over 70% at room temperature. However, the room-temperature tensile elongation decreased with increasing Al contents because the volume fraction of brittle $\beta$ dendrites in the ductile ${\gamma}'$ matrix increased.

• Journal of Korea Foundry Society
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• v.27 no.6
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• pp.243-249
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• 2007

The effect of Re addition and solidification rate on the directional solidification behavior of Ni-Al model alloy has been investigated. Directional solidification (DS) were carried out using the modified Bridgman furnace with various solidification rates. The solid/liquid interface during directional solidification was preserved by quenching the specimen after the desired volume fraction of original liquid was solidified. The equilibrium partition coefficients of Al and Re Were estimated by measuring the compositions at the quenched solid/liquid interface. Then, the effect of Re addition on the elemental segregation behavior was carefully analyzed. The differential scanning calorimetry results showed that the Re addition results in increased ${\gamma}'$ solvus and freezing range of the alloy. It was also shown that the primary dendrite arm spacing gradually decreases with increasing the Re content, while the secondary dendrite arm spacing appears to be independent on the Re content. The compositional analyses clearly revealed that the segregation of Al increased with increasing the Re content and solidification rate, while that of Re was found to be independent on the solidification rate in the range of $10{\sim}100{\mu}m/s$ due to its sluggish diffusion rate in the Ni solid solution.

• Journal of the Korean Society for Heat Treatment
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• v.8 no.2
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• pp.127-136
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• 1995

The simultaneous addition of Al and Cr to the surface of Ni-and Fe-base alloy provides enhanced resistance to oxidation and corrosion in high temperatures. However, because of the large differences in thermodynamic stabilities of the volatile halides of Al and Cr, the codeposition of Al and Cr by halideactivated pack cementation is only possible for very specific, limited combinations of conditions. In this study, the experiments on the combinations of various metallic source powders and activators were conducted in order to obtain codeposition layers of Al and Cr on Ni with adequate composition by pack cementation. When Cr-Al masteralloy was used as a source powder, it was not easy to control Al and Cr content sensitively in the coating layers. On the other hand, when pure Cr and Al powder was used, ${\beta}$-NiAl layer containing about 20wt % Cr was obtained.

• Journal of Korea Foundry Society
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• v.17 no.2
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• pp.195-206
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• 1997

AC8A matrix composites reinforced with Ni-aluminide were fabricated by squeeze casting process, and the characteristics and nature of the growth of Ni-aluminide phases at the interface between nickel and aluminurn were investigated. In the as-cast composites, the reaction layer between Ni skeleton and aluminum matrix was found to be $NiAl_3$, regardless of the casting temperatures and the kinds of preforms. During high temperature solution treatment the $NiAl_3$ layer grew and formed new $Ni_2Al_3$ layer. Because of presence of the porosity formed by Kirkendall effect at the interface between $NiAl_3$ and aluminum matrix, the tensile strength of composites was inferior to that of AC8A matrix alloy. However, the composites exhibited superior wear resistance due to the formation Ni-aluminide intermetallic phases. Composite A, of which Ni skeleton was fully transformed into Ni-aluminide, shows better wear resistance than that of composite B which still possessed some unreacted Ni skeleton.