Intermetallic Compound

In situ scanning tunneling microscopy (STM) and reflection high energy electron diffraction (RHEED) were used to characterize mercury film electrodeposited onto a Pt(1 1 1) electrode at room temperature. Depending on the amount of Hg deposit, two different growth modes were observed. At low Hg coverage, crystalline (0 0 0 1)Hg adlayer accompanied by 30 •-rotated (1 1 1)-Pt patches was found on Pt(1 1 1). Deposition of multilayer Hg resulted in layered PtHg 2 and PtHg 4 amalgams, which grew epitaxially by aligning their (2 0 1) and (11 0) planes, respectively, parallel to the Pt(1 1 1) substrate. The preference of these epitaxial relationships for the electrochemically formed Pt-Hg intermetallic compounds on Pt(1 1 1) could result from minimization of the surface energy.

The intermetallic compound MnGaGe, which crystallizes in the Fe2As structure shows a large and positive pressure dependence of the Curie temperature. To study this behaviour we perform band structure calculations whose results enter a spin fluctuation model. It is shown that the peculiar properties of MnGaGe can be traced back to the quasi two-dimensional magnetism of the Mn layers.

A common joining method in microelectronics is thermosonic bonding of gold wires to aluminium pads deposited on the integrated circuit. In the interface between the wire and the pad a number of intermetallic compounds Al x Au y can develop, which significantly affect the mechanical properties and corrosion resistance of the bonds. Based on Onsager's extremal principle of irreversible thermodynamics, the present paper describes the evolution of the intermetallic phases. This macroscopic model contains several thermodynamic and kinetic parameters, some of which are not available from databases. As an alternative to often cumbersome experiments, density functional theory is applied to calculate the formation energies of the phases and of atomic vacancies, as well as the vacancy migration energies in AlAu 4. To derive tracer diffusion coefficients from the atomistic vacancy jump rates, one must take peculiarities of the AlAu 4 lattice into account: the vacancy migration energy between certain gold sites is found to be rather low, but these low-energy jumps are arranged in closed triangles and, therefore, do not provide paths for long-range diffusion of gold atoms. However, together with two other types of jumps with still moderate migration energies, a contiguous network of diffusion paths for gold becomes possible. Since the diffusion of aluminium in AlAu 4 requires the generation of high-energy anti-site defects (at least temporarily), aluminium is expected to move very slowly, but no final solution is provided.

We report on the structural and magnetic properties of the YCo 4 Al and PrCo 4 Al intermetallic compounds. Both phases crystallize in the hexagonal CaCu 5 -type structure with P6/mmm space group. Neutron powder diffraction experiments demonstrate that the Al atoms preferentially occupy the 3g crystallographic site of the CaCu 5 structure. Al substitution in RCo 5 induces remarkable changes of the magnetic properties: a drastic decrease of the mean Co magnetic moment, the saturation magnetization, and the Curie temperature. The magnetic anisotropy field at room temperature has been measured on field-oriented powder using magnetization measurements. A spin reorientation transition was observed in PrCo 4 Al at low temperature by susceptibility measurements on a field-oriented sample. A detailed analysis of this phenomenon is completed by polar magnetic measurements and neutron thermodiffraction experiment. First-order magnetization process occurs in PrCo 4 Al up to 60 K at a critical field of about 6 T. r

Electroless Ni-P layers with three different P contents (6.1 wt.%, 8.8 wt.%, and 12.3 wt.%) were deposited on copper (Cu) substrates. Multilayered samples of Sn-3.5Ag/Ni-P/Cu stack were prepared and subjected to multiple reflows at 250°C. A tensile test was performed to investigate the effect of P content on the solder joint strength. The low P samples exhibited the highest joint strength after multiple reflows, while the strength of medium and high P samples decreased more rapidly. From interfacial analysis, the Ni 3 Sn 4 intermetallic compound (IMC) formed at the interface of low P sample was found to be more stable, while the one of medium and high P samples spalled into the molten solder. The IMC spallation sped up the consumption of electroless Ni-P, leading to the large formation of Cu-Sn IMCs. Fractographic and microstructural analyses showed that the degradation in solder joint strength was due to the formation of layers of voids and growth of Cu-Sn IMCs between the solder and the Cu substrate.

Electroless Ni-P layers with three different P contents (6.1 wt.%, 8.8 wt.%, and 12.3 wt.%) were deposited on copper (Cu) substrates. Multilayered samples of Sn-3.5Ag/Ni-P/Cu stack were prepared and subjected to multiple reflows at 250°C. A tensile test was performed to investigate the ...

The crystal structure of the intermetallic compound Nb6Sn5 has been determined. The space-group symmetry was found to be Immm (D22~), and lattice parameters were measured as a--5.656+ 0.002, b= 9.199 _+ 0.003, e= 16.843 + 0"004 A. The compound shows pronounced layering normal to the short axis.

High fluence Fe implantations were performed in commercial aluminium samples using two different iron isotopes, Fe q 56 q and Fe. The implanted layers were studied by Rutherford backscattering spectrometry, conversion electron Mossbauer 57 qs pectroscopy, grazing incidence X-ray diffraction, and scanning electron microscopy with energy dispersion spectroscopy. There is clear evidence for the direct formation of the Al Fe intermetallic compound during ion implantation. The thermal stability of 5 2 such an intermetallic phase was studied by means of annealing treatments, and it was found that it disappears after 1 h annealing at 630 8C and a new intermetallic compound, Al Fe , is formed.

This paper is concerned with the mechanics of interfacial fracture that are active in two common testing configurations of solder joint reliability. Utilizing eutectic Pb-Sn/Cu as a reference system and assuming the presence of a predefined crack size in the intermetallic compound (IMC) layer, stress intensity factors (K I and K II) at the crack are numerically calculated for the two given configurations. The analysis of the tensile test configuration reveals that the fracture occurs by the crack-opening mode (K I mode), as anticipated, but that it is greatly assisted by the viscoplasticity of the solder. With nonuniform viscoplastic deformation across the joint, K I is found to increase much more rapidly than it would without the solder, decreasing the critical crack size to the micron scale. The same mechanism is also responsible for the development of a K II comparable to K I at the crack tip, that is, |K I /K II | $ 1. It is also found that the predominant fracture mode in the bump shear configuration is crack opening, not crack shearing. This is an unexpected result, but numerical analyses as well as experimental observations provide consistent indications that fracture occurs by crack opening. During shear testing, bump rotation due to nonzero rotational moment in the test configuration is found to be responsible for the change in the fracture mode because the rotation makes K I become dominant over K II. With rotational moment being affected by the geometry of the bump, it is further found that the fracture behavior may vary with bump size or shape.

The new antimonides MFe_1-xSb can be synthesized by arc-melting of M, Fe, and MSb_2 (M=Zr, Hf). All title compounds crystallize in the TiNiSi structure type (space group Pnma, Z=4). The lattice parameters of the new phases MFe_1-xSb, as obtained from the bulk samples of the nominal compositions MFeSb, are (a=681.4(1) pm, b=417.87(7) pm, c=740.3(1) pm for ZrFe_1-xSb and a=674.0(1) pm, b=412.0(2) pm, c=729.7(2) pm for HfFe_1-xSb. Under the reaction conditions used, the occupancy factors of the iron position content of ZrFe_1-xSb does not exceed 68(1)% (i.e. x=0.32(1)). Extended Hückel calculations, performed on the hypothetical model structures ``ZrFeSb'' and ``ZrFe_0.75Sb'', point to the phase ZrFe_1-xSb being metallic, independent of the x value. The band structure of ``ZrFeSb'', obtained with ab initio LMTO calculations, reveals a three-dimensional metallic conductivity and a nonmagnetic ground state.

This paper consid,ers the influence of _composite pulse eleclToplated nickel/tin WVS"j iayering: o" lft" mitigation of Sn whiskei growttr. The performance of ih".o-porit. p"ulsed plating-method in the mitigation of Sn whisker growth is also .o*pu".d with t'wo otf,er plating procedures. The results indicate that, uit.r a period of 6 months, the compoiite pulsed ptating-technique demonstrates much better resistance to Sn whisker growth than other plating t..ftttiq"es such as pure Sn plating and Sn plating \^Tth a Ni.underlayer onto a brass substrate subjected to various envirbnmental conditions. The primalY conclusions are based on the analysis of microstructural characteristics, the u"""ugu residual stress distribution in the film over different time periods .o*p,it"a by x-ray diffraction, the formation of intermetallic compounds, and the amounf of Sn whisker growth in each case.

The solid + liquid phase equilibria between α-Al and β-AlLi were determined using differential thermal analysis (DTA), metallography, and chemical analysis. Boron nitride (BN), which was found to be inert to these alloys, was used as the container. These measurements were carried out in order to resolve the discrepancies reported in the literature. The α-Al+β-AlLi eutectic temperature and composition were

General properties of aluminium alloys of the rare earth metals are briefly summarised. Their phase equilibria and the crystal structures of the different intermediate phases are presented and discussed. The results obtained in the experimental investigation of the Y-Al and Sm-Al systems are reported. The formation enthalpies of YA12 and SmAlz have been re-measured, resulting in-50.5kJ/(mol at) and-55.0kJ/(mol at) at room temperature, in a good agreement with literature data. Phase equilibria investigation in the Sm-Al system has been carried out and the results obtained via thermal analysis, micrographic examination, microprobe and X-ray diffraction analyses described and discussed in the framework of the general behaviour of the rare earth alloys. The experimental Sm-Al phase diagram, collated with previous literature data, is compared with the results of a thermodynamic optimisation. The following inter-metallic compounds exist: Sm2Al (peritectic decomposition, at 860°C) SmAl (per.dec.960"Q SmAl2 (melting point 148O"Q SmAls (peritectoidal decomposition at 113o"C), SmsAlr , (melting point-1380°C). The following eutectic equilibria have also been determined or confirmed: 20 at% Al and 760°C 75 at% Al and 134O"C, 97.0 at%Al and 635°C. A eutectoidal equilibrium occurs at 10 at% Al and 700°C.

Single crystals of uranium intermetallic compound UCo 0:5 Sb 2 were grown by means of the antimony-flux technique. The characterization of the samples has been carried out utilizing single crystal X-ray diffraction and magnetization measurements. UCo 0:5 Sb 2 is found to crystallize in the tetragonal HfCuSi 2-type structure, space group P4=nmm with Z ¼ 2 formula units per cell, and the lattice parameters a ¼ 0:4300ð1Þ and c ¼ 0:8958ð2Þ nm: The refinement of the occupancy parameters and the energy dispersive X-ray analysis have indicated a distinct deficiency on the cobalt sites. The results of magnetization measurements showed that UCo 0:5 Sb 2 orders ferromagnetically below 65 K with a huge magnetocrystalline anisotropy with the c direction being the easy magnetization axis.

In this investigation, the effect of manganese as an alloying element in the range 0.01%–0.53 wt.%, on the hardness, 0.2% yield, tensile and impact strength, and creep properties of a gravity cast Zn–Al based ZA-8 alloy has been investigated. It was found that addition of Mn over the entire range of concentrations has a useful effect on the hardness of the alloy. Also, the 0.2% yield and ultimate tensile strength (UTS) of the samples did not change significantly with Mn additions up to 0.045 wt.% but decreased with a further increase in Mn content. Furthermore, the impact strength of the alloy improved with increasing Mn up to 0.045 wt.% and then decreased gradually with a further increase in Mn content. On the other hand, the creep resistance of the alloy increased continuously with increasing Mn content up to 0.53 wt.% Mn. Metallographic studies showed that addition of Mn resulted in microstructural modifications of the alloy involving the formation of complex intermetallic compound identified as MnAl6. The increase in creep resistance and decrease in tensile and impact strength were thought to have been caused by the changing morphology and amount of the intermetallic.

The high-intensity, high-resolution x-ray source at the European Synchrotron Radiation Facility (ESRF) has been used in x-ray diffraction (XRD) experiments to detect intermetallic compounds (IMCs) in lead-free solder bumps. The IMCs found in 95.5Sn3.8Ag0.7Cu solder bumps on Cu pads with electroplated-nickel immersion-gold (ENIG) surface finish are consistent with results based on traditional destructive methods. Moreover, after positive identification of the IMCs from the diffraction data, spatial distribution plots over the entire bump were obtained. These spatial distributions for selected intermetallic phases display the layer thickness and confirm the locations of the IMCs. For isothermally aged solder samples, results have shown that much thicker layers of IMCs have grown from the pad interface into the bulk of the solder. Additionally, the XRD technique has also been used in a temperature-resolved mode to observe the formation of IMCs, in situ, during the solidification of the solder joint. The results demonstrate that the XRD technique is very attractive as it allows for nondestructive investigations to be performed on expensive state-of-the-art electronic components, thereby allowing new, lead-free materials to be fully characterized.

In IC packages, thermosonic wire bonding is the preferred method for making electrical connections between the die pad and lead frame. These interconnect are made using fine metal wires. On thermal aging (under 175 8C for 5 h) gold aluminide easily forms in gold ball bonds while formation of intermetallic compound is absent in case of copper ball bonds. An analysis of the atomic property of the elements bonded explains that atomic radii and electronegativity factors favor gold aluminide formation. #

In the next generation nanoelectronics and SiC based electronic packaging, current density and temperature gradient will be larger in orders of magnitude. Electromigration and thermomigration are considered to be major road blocks leading to realisation of nanoelectronics and SiC based high temperature power electronics. In this paper, damage mechanics of 95.5Sn4Ag0.5Cu (SAC405) lead-free solder joints under high temperature gradients have been studied. This paper presents observations on samples which were subjected to 1000°C/cm thermal gradient for two hours, 286 hours, 712 hours and 1156 hours. It was observed that samples subjected to thermal gradient did not develop a Cu 3 Sn intermetallic compound (IMC) layer at the hot side due to Cu migration to the cold side thus causing insufficient Cu mass concentration to form Cu 3 Sn. On the other hand, in samples subjected to isothermal annealing exhibited IMC growth. In samples subjected to thermomigration, near the cold side the Cu concentration is significantly higher, compared to hot side. Extensive surface hardness testing showed increase in hardness from the hot to cold sides, which indicates vacancy migration and Sn grain coarsening are in the opposing direction.

Laser diodes (LD) are usually bonded onto heat sinks for the purposes of heat dissipation, mechanical support and electrical interconnect. In this study, energy dispersive X-ray analysis (EDX) and electron backscatter diffraction (EBSD) are employed to investigate the microstructure evolution of 80Au/20Sn solder joint in LD package. During reflow, Pt-Sn and (Au, Ni)Sn IMCs were formed at the respective LD/solder and solder/heatsink interfaces, while d, b and f 0 phases of Au/Sn intermetallics were found in the solder joint. The Au-rich b and f 0 phases in the solder joint limit the growth of interfacial IMCs. Chip shear testing showed that the failure occurred within the LD, with partial brittle fracture at the GaAs substrate and partial interfacial delamination at the GaAs/SiN interface. The strong solder bond can be attributed to the high mechanical strength of 80Au/20Sn solder, which provides improved stability for high temperature applications.

Interface evolution caused by thermal aging under different temperatures and durations was investigated by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was found that approximately 30-nm-thick and discontinuous Cu-Al intermetallic compounds (IMCs) were present in the initial bonds before aging. Cu-Al IMCs grew under thermal aging with increasing aging time. The growth kinetics of the Cu-Al IMCs was correlated to the diffusion process during aging; their combined activation energy was estimated to be 1.01 eV. Initially, Al-rich Cu-Al IMCs formed in the as-bonded state and early stage of aging treatment. Cu 9 Al 4 was identified by selected-area electron diffraction (SAD) as the only type of Cu-Al IMC present after thermal aging at 250°C for 100 h; this is attributed to the relatively short supply of aluminum to the interfacial reaction.

The size and morphology of intermetallic compounds of Sn–Ag solder alloys can have a significant influence on the mechanical strength of solder joints. The aim of the present study is to characterize the as-cast microstructure of a Sn–2 wt.% Ag solder alloy, and to correlate the resulting scale of the dendritic matrix and the morphology of the Ag3Sn intermetallic compound (IMC) with the corresponding solidification cooling rate. Pre-heated low-carbon steel molds and a water-cooled solidification apparatus were used permitting a significant range of solidification cooling rates to be experimentally examined. It is shown that under very slow cooling conditions (0.02 °C/s) the microstructure of the sample is formed by a coarse dendritic matrix and a mixture of fiber and plate-like Ag3Sn IMC in the interdendritic region with the fibers located along the board line separating the matrix. For cooling rates from 0.15 to 1.15 °C/s a mixture of spheroid and fiber-like IMC and secondary dendrite arm spacings between 15 and 40 μm, with the spheroids located in the center of the interdendritic region. At higher cooling rates, of about 8 °C/s only Ag3Sn spheroids (of about 0.5 μm in diameter) prevail in the eutectic mixture.► 3D characterization of the morphology of Ag3Sn by an over-etching technique. ► Ag3Sn spheroids are associated with fine dendrite spacings, λ2, of Sn-rich phase. ► A mixture of Ag3Sn (spheroids + fiber-like) is associated with λ2 from 10 to 45 μm. ► A mixture of Ag3Sn (fibers + plate-like) is associated with λ2 of about 100 ± 15 μm. ► Pb-free solder manufacturers can control the microstructure by the cooling rate.

The global transition to lead-free (Pb-free) electronics has led component and equipment manufacturers to transform their tin-lead (SnPb) processes to Pb-free. At the same time, Pb-free legislation has granted exemptions for some products whose applications require high long-term reliability. However, due to a reduction in the availability of SnPb components, compatibility concerns can arise if Pb-free components have to be utilized in a SnPb assembly. This compatibility situation of attaching a Pb-free component in a SnPb assembly is generally termed "backward compatibility." This paper presents the results of microstructural analysis of mixed solder joints which are formed by attaching Pb-free solder balls (SnAgCu) of a ball-grid-array component using SnPb paste. The experiment evaluates the Pb phase coarsening in bulk solder microstructure and the study of intermetallic compounds formed at the interface between the solder and the copper pad.

Nanoscale interfacial evolution in Cu-Al wire bonds during isothermal annealing from 175°C to 250°C was investigated by high resolution transmission electron microscopy (HRTEM). The native aluminum oxide film ($5 nm thick) of the Al pad migrates towards the Cu ball during annealing. The formation of intermetallic compounds (IMC) is controlled by Cu diffusion, where the kinetics obey a parabolic growth law until complete consumption of the Al pad. The activation energies to initiate crystallization of CuAl 2 and Cu 9 Al 4 are 60.66 kJ mol À1 and 75.61 kJ mol À1 , respectively. During IMC development, Cu 9 Al 4 emerges as a second layer and grows together with the initial CuAl 2 . When Al is completely consumed, CuAl 2 transforms to Cu 9 Al 4 , which is the terminal product. Unlike the excessive void growth in Au-Al bonds, only a few voids nucleate in Cu-Al bonds after long-term annealing at high temperatures (e.g., 250°C for 25 h), and their diameters are usually in the range of tens of nanometers. This is due to the lower oxidation rate and volumetric shrinkage of Cu-Al IMC compared with Au-Al IMC.

Purpose -The purpose of this paper is to investigate the effects of reflow time, reflow peak temperature, thermal shock and thermal aging on the intermetallic compound (IMC) thickness for Sn3.0Ag0.5Cu (SAC305) soldered joints. Design/methodology/approach -A four-factor factorial design with three replications is selected in the experiment. The input variables are the peak temperature, the duration of time above solder liquidus temperature (TAL), solder alloy and thermal shock. The peak temperature has three levels, 12, 22 and 328C above solder liquidus temperatures (or 230, 240 and 2508C for SAC305 and 195, 205, and 2158C for SnPb). The TAL has two levels, 30 and 90 s. The thermally shocked test vehicles are subjected to air-to-air thermal shock conditioning from 2 40 to 1258C with 30 min dwell times (or 1 h/ cycle) for 500 cycles. Samples both from the initial time zero and after thermal shock are cross-sectioned. The IMC thickness is measured using scanning electron microscopy. Statistical analyses are conducted to compare the difference in IMC thickness growth between SAC305 solder joints and SnPb solder joints, and the difference in IMC thickness growth between after thermal shock and after thermal aging. Findings -The IMC thickness increases with higher reflow peak temperature and longer time above liquidus. The IMC layer of SAC305 soldered joints is statistically significantly thicker than that of SnPb soldered joints when reflowed at comparable peak temperatures above liquidus and the same time above liquidus. Thermal conditioning leads to a smoother and thicker IMC layer. Thermal shock contributes to IMC growth merely through hightemperature conditioning. The IMC thickness increases in SAC305 soldered joints after thermal shock or thermal aging are generally in agreement with prediction models such as that proposed by Hwang. Research limitations/implications -It is still unknown which thickness of IMC layer could result in damage to the solder. Practical implications -The IMC thickness of all samples is below 3 mm for both SnPb and SAC305 solder joints reflowed at the peak temperature ranging from 12 to 328C above liquidus temperature and at times above liquidus ranging from 30 to 90 s. The IMC thickness is below 4 mm after subjecting to air-to-air thermal shock from 2 40 to 1258C with 30 min dwell time for 500 cycles or thermal aging at 1258C for 250 h. Originality/value -The paper reports experimental results of IMC thickness at different thermal conditions. The application is useful for understanding the thickness growth of the IMC layer at various thermal conditions.

Thermosonic bonding process is a viable method to make reliable interconnections between die bond pads and leads using thin gold and copper wires. This paper investigates interface morphology and metallurgical behavior of the bond formed between wire and bond pad metallization for different design and process conditions such as varying wire size and thermal aging periods. Under thermal aging, the fine pitch gold wire ball bonds (0.6-and 0.8-mil-diameter wires) show formation of Kirkendall voids apart from intermetallic compound growth. With 1-and 2-mil-diameter gold wire bonds, the void growth is less significant and reveals fine voids. Studies also showed that void formation is absent in the case of thicker 3-mil wire bonds. Similar tests on copper ball bonds show good diffusional bonding without any intermetallic phase formation (or with considerable slow growth) as well as no voids on the microscopic scale and thus promises to be a better design alternative for elevated temperature conditions. D

Stainless steel-zirconium alloys have been developed at Argonne National Laboratory to contain radioactive metal isotopes isolated from spent nuclear fuel. This article discusses the various phases that are formed in as-cast alloys of type 304 stainless steel and zirconium that contain up to 92 wt pct Zr. Microstructural characterization was performed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), and crystal structure information was obtained by Xray diffraction. Type 304SS-Zr alloys with 5 and 10 wt pct Zr have a three-phase microstructure-austenite, ferrite, and the Laves intermetallic, Zr(Fe,Cr,Ni)z+x, whereas alloys with 15, 20, and 30 wt pct Zr contain only two phases-ferrite and Zr(Fe,Cr,Ni)2+x. Alloys with 45 to 67 wt pct Zr contain a mixture of Zr(Fe,Cr,Ni)z+x and Zr2(Ni,Fe), whereas alloys with 83 and 92 wt pet Zr contain three phases-a-Zr, Zr2(Ni,Fe), and Zr(Fe,Cr,Ni)z+x. Fe3Zr-type and Zr3Fe-type phases were not observed in the type 304SS-Zr alloys. The changes in alloy microstructure with zirconium content have been correlated to the Fe-Zr binary phase diagram.

We review studies of the electromagnetic response of various classes of correlated electron materials including transition metal oxides, organic and molecular conductors, intermetallic compounds with d-and f -electrons as well as magnetic semiconductors. Optical inquiry into correlations in all these diverse systems is enabled by experimental access to the fundamental characteristics of an ensemble of electrons including their self-energy and kinetic energy. Steady-state spectroscopy carried out over a broad range of frequencies from microwaves to UV light and fast optics timeresolved techniques provide complimentary prospectives on correlations. Because the theoretical understanding of strong correlations is still evolving, the review is focused on the analysis of the universal trends that are emerging out of a large body of experimental data augmented where possible with insights from numerical studies. arXiv:1106.2309v1 [cond-mat.str-el]

This study examines the growth mechanism of micro void called ''Kirkendall voids'' within NiSnP nanocrystalline layer between (Cu,Ni) 6 Sn 5 intermetallic compound (IMC) and Ni 3 P formed during two double reflow processes. The micro voids in NiSnP layer formed at the first reflow grow faster under the elevated reflow temperature than under the standard lead-free reflow, during the second reflow process. Despite the diffusion barrier Ni(P), the inward diffusion flux of Sn from (Cu,Ni) 6 Sn 5 into NiSnP layer is much slower than the outward flux of Sn from NiSnP layer into Ni 3 P, consequently leaving voids as NiSnP thickness increases. Results show that the thermal activation energy through the elevated reflow temperature has a higher influence in micro void growth than the number of reflows for the inward and outward diffusion flux difference of Sn within NiSnP layer in electroless Ni(P)/immersion Au and SnAgCu reaction system.

Abstrac~MMC with intermetallic matrices (NLAI, NiAI) reinforced with continuous AI:O~ fibres were investigated with regard to interfacial reactions during diffusion bonding, by means of TEM, EDS and HRTEM. The specimens were fabricated by hot pressing for 2 h. at 1200 1280C for the Ni;AI matrix and at 130(~1450 C for the NiA1 matrix. Experimental results revealed a diffusion of Ni from the Ni~AI matrix into the fibres during diffusion bonding. As a consequence of the diffusion process a chemical reaction took place at the interfacial area: thin films of about 5 20 nm thickness appeared in some sections of the interface, in which the lattice planes were disordered and porous compared with matrix and fibre: in other sections spinels with compound oxides of AI and Ni or (Ni, Mg)AI:O4 were formed as interracial reaction products. In contrast to the results on Ni~A1, specimens with NiAI matrix showed good stability during hot pressing: no obvious diffusion of Ni from the matrix into the fibre could be detected, and no interaction products were apparent in the interface. The potential influence of these interfacial behaviours on the properties of the composites will be discussed.

In this study, UBM material systems for flip chip solder bumps on Cu pads were investigated using the electroless copper (E-Cu) and electroless nickel (E-Ni) plating methods; and the effects of the interfacial reaction between UBMs and Sn-36Pb-2Ag solders on the solder bump joint reliability were also investigated to optimize UBM materials for flip chip on Cu pads. For the E-Cu UBM, scallop-like Cu 6 Sn 5 intermetallic compound (IMC) forms at the solder/E-Cu interface, and bump fracture occurred along this interface under a relatively small load. In contrast, at the E-Ni/E-Cu UBM, E-Ni serves as a good diffusion-barrier layer. The E-Ni effectively limited the growth of the IMC at the interface, and the polygonal-shape Ni 3 Sn 4 IMC resulted in a relatively higher adhesion strength compared with the E-Cu UBM. As a result, electroless deposited UBM systems were successfully demonstrated as low cost UBM alternatives on Cu pads. It was found that the E-Ni/E-Cu UBM material system was a better choice for solder flip chip interconnection on Cu pads than the E-Cu UBM.

Microstructures and hardness of aluminum alloy ductile iron were investigated by SEM, XRD, EPMA and hardness measurement techniques. The results show, increasing the Al-alloying element leads to decrease of free ferrite and carbide, as well as increase in the pearlite volume fraction. It is also has been found that in the higher values of Al, about 85% of the matrix would be pearlite. It is indicated that an increase in the aluminum content also leads to a decrease in the spacing between pearlite layers. XRD results show, in the presence of Al, intermetallic compounds such as Al 6 Fe, AlFe 3 C 0.5 , Fe 3 Al and FeAl were produced. Furthermore the hardness measurements illustrate that by increasing the Al content, the microhardness of ferrite and pearlite and specimens hardness have been significantly increased.

The objective of this review is to study interfacial reactions between pure Sn or Sn-rich solders, and common base metals used in Pb-free electronics production. In particular, the reasons leading to the observed interfacial reactions products and their metallurgical evolution have been analyzed. Results presented in the literature have been critically evaluated with the help of combined thermodynamic-kinetic approach based on the concept of local equilibrium and microstructural knowledge. The following conclusions have been reached: Firstly, the formations of intermetallic compounds in solid/liquid reaction couples are primarily controlled by the dissolution processes of base metals. Other factors that need be considered are the thermodynamic driving force for the formation of intermetallic compounds, their structures and concentration profiles in liquid. Secondly, annealing of solder interconnections in solid state can drastically change the microstructures formed in the solid/liquid reactions, especially if only one of the components in the solder takes part in the interfacial reactions. Thirdly, additional elements can have three major effects on the binary reactions between a base metal and Sn: (i) they can increase or decrease the reaction/growth rates, (ii) the additives can change the physical properties of the phases formed, and (iii) they can form additional reaction products or displace the binary equilibrium phases by forming new reaction products. Finally, if the local stable or metastable equilibrium is established at the interface, stability information together with kinetic considerations can provide a feasible approach to analyze interfacial reactions, which can have significant impact on the reliability of soldered electronics assemblies. #

Electroplated Ni/Au over Cu is a popular metallization for PCB finish as well as for component leads, especially wirebondable high frequency packages, where the gold thickness requirement for wirebonding is high. The general understanding is that less than 3 wt% of Au is acceptable in SnPb solder joints. However, little is known about the effect of Au content on the reliability of SnAgCu solder joints. The purpose of this study is to determine the acceptable level of Au in SAC305 solder joints. Three different package platforms with different Au thicknesses were assembled on boards with two different Au thicknesses using a standard surface mount assembly line in a realistic production environment. The assembled boards were divided into three groups: as-built, isothermally aged at 125°C for 30 days, and isothermally aged at 125°C for 56 days. All boards were then subjected to accelerated mechanical reliability tests including random vibration and drop testing. The results show that solder joints with over 10 wt% Au are unacceptable. If Cu is available to dissolve in the solder joint, then an Au content under 5 wt% will not significantly degrade the reliability of the solder joint. When Ni layers are present on both the board and component sides of the interface, this limits the ability of Cu to dissolve into the solder joint and hence an Au content under 3 wt% is acceptable. The failure mechanism for solder joints with high Au content is fractures through the AuSn 4 IMC. Our comprehensive long-term reliability study did not confirm the finding by that the weak interface between (Au, Ni)Sn 4 and Ni 3 Sn 4 results in brittle interfacial failure. Additional findings confirmed the danger of placing parts near high stress areas and that a high level of voiding reduced reliability.

The present work demonstrates that friction stir welding (FSW) is a feasible route for joining 6061 aluminium (Al) alloy to AISI 1018 steel. The weld has a good weld quality and is free of cracks and porosity. The tensile failure happened at the boundary between the nugget and thermomechanically affected zone of the base Al alloy, indicating that the weld has a higher joining strength. Despite the fact that the hardness fluctuates strongly within the nugget, the average hardness of the nugget is substantially higher than that of the base Al alloy. During FSW, localized melting of the Al alloy in the nugget occurred, and the molten Al alloy reacted strongly with steel pieces spread through the nugget, which resulted in the formation of the Al-Fe intermetallic compounds, Al 13 Fe 4 and Al 5 Fe 2 . The nugget consists of secondary phases including coarse steel pieces and Al-Fe intermetallic compounds, and an Al alloy matrix. These secondary phases contribute to the hardness of the weld.

We have investigated the hydrogenation and dehydrogenation properties of binary RNi 5 (R: La, Pr, Nd, Sm, Gd, Tb and Dy) intermetallic compounds in the pressure range of 0.1-35 MPa and temperature range of 223-298 K. Pressure-composition isotherms demonstrated that as the atomic number of R increased in RNi 5-H systems, the single pressure plateau (LaNi 5) split into two plateaux (PrNi 5 , NdNi 5 , SmNi 5 and GdNi 5), and then into three plateaux (TbNi 5 and DyNi 5), indicating the presence of two hydrides (β 2 and γ 2 phases) and then three hydrides (β 3 , γ 3 and δ 3 phases). The β 3-γ 3 and γ 3-δ 3 phase transitions in the TbNi 5-H system corresponded, respectively, to the α 2-β 2 and β 2-γ 2 transitions in the RNi 5-H (R: Pr, Nd, Sm and Gd) systems having two plateaux.

We investigated element-specific magnetic moments and the spin-resolved unoccupied density of states ͑DOS͒ of polycrystalline Co 2 TiZ ͑Z =Si, Ge, Sn, Sb͒, Co 2 Mn x Ti 1−x Si and Co 2 MnGa 1−x Ge x Heusler alloys using circular dichroism in x-ray absorption spectroscopy ͑XMCD͒. We find a small ͑Ͻ0.03 B ͒ Ti moment oriented antiparallel and a large ͑Ͼ3 B ͒ Mn moment oriented parallel to the Co moment of approximately 1 B per atom in the investigated compounds. Orbital magnetic moments are increased for quaternary compounds compared to the corresponding ternary compounds with x =0 or x = 1. The unoccupied spin-resolved partial DOS at the Co atom was extracted from the XMCD data. In the case of Co 2 TiSi, Co 2 TiGe, and Co 2 TiSn, the Co minority DOS reveals a maximum at 0.5 eV above E F and very low values at E F in agreement with the expectation for half-metallic ferromagnetism. In contrast, Co 2 TiSb shows a large minority DOS at the Fermi energy like a normal metal. A substitution of Ti by Mn in Co 2 TiSi shifts the minority DOS maximum from 0.5 to 0.9 eV with respect to the Fermi energy. For the series Co 2 MnGa 1−x Ge x we observe a gradual shift of the minority DOS maximum from 0.7 eV for x = 1 to 1.0 eV for x = 0, indicating half-metallic ferromagnetism for the whole series. Our results, revealing the distribution of magnetic moments and the relative position of the Fermi energy as a function of the number of valence electrons, confirm the predicted possibility of tailoring the minority band gap using substitutional quaternary Heusler compounds. The results maybe of general importance for the understanding of the electronic structures in complex intermetallic compounds.

A large number of ab-initio calculations of energies of formation of intermetallic compounds have been performed in the last 15 years. The currently used methods are listed. The paper presents a review of the aluminium based compounds which have been studied. Comparisons of calculated and experimental enthalpies of formation are provided for aluminim-3d and-4d transition metal alloys at equiatomic composition. The modelling of the enthalpies of mixing of solid solutions based on a given lattice is described.

Lead-free Sn -Ag -Cu(SAC) solder joint on Cu -OSP and ENIG subject to thermal testing leads to IMC growth and causes corresponding reliability concerns at the interface. Modulus and hardness of these IMCs were characterized by Nanoindentation CSM from plan view in this study. A plan-view IMC surface was prepared by deep etching and slight polishing method. When SAC/Ni(Au) solder joint were subject to thermal aging, elastic modulus of the NiCuSn IMC at SAC/ENIG specimen changed from 207 to 146 GPa with different aging time up to 500 h. The hardness decreased from 10.0 to 7.3 GPa. For SAC/Cu -OSP reaction couple, elastic modulus of Cu 6 Sn 5 kept constant at 97.0 GPa and hardness about 5.7 GPa. The modulus of Cu 3 Sn after 500 h thermal aging was 115.7 GPa. The change of modulus is caused by solid state diffusion process during thermal aging where the morphology and crystal structure of Ni, -Cu -Sn IMC is changing. The calculation of modulus and hardness for IMC layers was based on nanoindentation CSM test results and was compared with reported results. D

This paper presents thermal simulations for reliability-oriented design of planar transformers for medium-power, high-frequency DC-DC converters. The modeling approach is based on accurate 3D finite-element thermal simulation of the transformer structure; inputs to the finite-element thermal model are the magnetic and electrical power losses extracted by experimental characterization of a planar transformer test-bench we designed and assembled. The simulation results are compared with those of infra-red thermal measurements. The simulations allowed to evaluate the effect of frequency and output current on the temperature distribution inside the transformer, thus setting limits for reliable operation, and to analyze alternative designs aimed at improving thermal management and, consequently the transformer reliability.

The interfacial reactions and the resultant intermetallics between lead free solders, i.e., Sn-3.8Ag-0.7Cu, Sn-3.5Ag and Sn-0.7Cu, and substrates with different metallisation, namely, Cu, electroless Ni (EN), immersion Ag on Cu (CuImAg) and electroless Ni immersion gold (ENIG), were investigated after multiple reflows and subsequent ageing. For Cu and CuImAg substrates, the intermetallic compounds (IMCs) Cu3Sn and Cu6Sn5 formed at the interface were identified, compared to Ni3Sn4 IMC in the case of EN or ENIG substrates reacting with Sn-3.5Ag. However, for EN or ENIG substrates, when using Sn-3.8Ag-0.7Cu and Sn-0.7Cu solders, the IMCs formed at the interface was (Cu,Ni) 6Sn5. It has been revealed that the growth of Cu6Sn5 was faster than that of (Cu,Ni) 6Sn5 and Ni3Sn4, which indicates the introduction of Ni into the Cu6Sn5 IMC may provide an optimised solution to enable the stability of the interfaces formed during soldering. As for the morphology of the IMCs, when they formed at the interface, the (Cu,Ni) 6Sn5 IMCs were needle- or facet-like, the Cu6Sn5 and Ni3Sn4 IMCs were facet-like and Ag3Sn IMCs were plate- or pebble- or needle-like. In the solder, the Cu6Sn5 IMC had prism-like shape with some of them appearing hollow with the Ag3Sn IMCs embedded inside. Kirkendall voids were found in the Cu3Sn and Ni3P layers, and the formation of Kirkendall voids in the Cu3Sn layer is likely related to the immersion Ag surface finish.