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Transient Liquid Phase Bonding (TLPB) makes use of the isothermal solidification of a liquid interlayer through the formation of intermetallic compounds (IMC). This work investigates the Ag3Sn IMC formation in a thin, electroplated Ag–Sn interlayer system appropriate for TLPB – while covering as-coated conditions, growth initiation up to a few minutes of holding time – with experimental and numerical methods. Both solid-state and solid–liquid reactions at 200, 250 and 300 °C, respectively, were covered under identical and near-isothermal conditions with a novel experimental setup. Morphological aspects like the lateral IMC grain size or the scallop roughness were proven to strongly depend on temperature. Growth kinetics were captured by power laws, growth exponents n were determined as 0.24, 0.36 and 0.29, parabolic growth constants k as 1.32 ⋅ 10−11, 4.04 ⋅ 10−10 and 7.24 ⋅ 10−10 cm2/s at 200, 250 and 300 °C, respectively, and the activation energy Q as 30.6 kJ/mol. Predominant diffusion mechanisms, i.e. volume or GB diffusion, as well as coarsening effects were identified as temperature and time dependent at early stages. A mathematical model was developed based on the Arrhenius relationship including a growth correction function zIMC,corr to calculate and predict IMC growth as a function of temperature and time. The study was completed by multiphase-field simulations which targeted to mimic kinetic and morphological features of Ag3Sn IMC under various conditions. Good agreement between experiments and simulations was found for a limited set of parameters which allowed drawing conclusions about the dominant transport mechanisms for the reacting elements.

This work addresses the microstructure evolution during transient liquid phase bonding (TLP) of high-density (small volume) interconnects, which are relevant for 3D packaging in the microelectronics industry. Specifically, the intermetallic compound (IMC) growth in the Cu/Sn/Cu sandwiched soldering joint configuration is characterized through predicted processing maps. These maps are derived from phase-field modeling simulations that incrementally vary geometrical and thermal conditions (i.e., initial solder thicknesses ranging from 4 μm to 28 μm and system temperatures ranging from T = 240 °C to 310 °C). The calculations consider the concurrent evolution of the Cu3Sn and Cu6Sn5 IMC layers at the expense of the liquid solder (i.e., Sn) and the substrates (i.e., α -Cu) given their respective chemical potentials and associated driving forces for diffusion and phase transformation. Additionally, materials properties (e.g., diffusivity, interfacial energy, and mobility) are adjusted in order to account for varying processing temperatures that are relevant to the transient liquid phase (TLP) joining process. Through this study, it is shown how temperature, initial liquid solder thickness, and hold time influence (1) how the IMC phases evolve, (2) whether or not IMC phases are eliminated, and (3) how IMC grains coarsen. These results make it possible to develop practical strategies for the use of TLP joining process in high-density interconnects.

In this work, we present a preliminary model based on the multiphase-field formalism that is used to investigate the evolution of intermetallic compound (IMC) layers in the Cu/Sn solder system under electromigration conditions. The simulation considers the concurrent evolution of the Cu3Sn and Cu6Sn5 IMC layers under electrochemical driving forces. We use CALPHAD descriptions for the thermodynamics of the bulk phases (Cu, Sn and both IMCs) and incorporate electrochemical contributions to the total free energy of the microstructure in order to simulate the evolution of the interfacial microstructure due to mass–current couplings. The simulation considers grain-boundary diffusion as the dominant mechanism for chemical-potential-driven mass flux. The simulation considers the effect of current density and polarity on the growth of IMCs. The simulations are in turn compared to experimental measurements of growth rates, morphology of IMC grains and evolution of interface roughness. The analysis of experiments and simulations suggest that back-stress resulting from the non-equilibrium vacancy generation due to diffusive flux imbalance among the individual diffusants (Cu and Sn) plays a fundamental role in the evolution of the IMC layers. Overall, the simulations and experiments show good qualitative agreement.

The microstructural evolution of η(Cu6Sn5) and e(Cu3Sn) in a Cu/Sn/Cu structure under transient liquid phase bonding conditions is numerically investigated through the use of the multiphase-field method. The material parameters and reaction conditions were adopted from relevant experimental research. Simulation results were then analyzed and compared with the experiments in terms of morphology of intermetallic compound (IMC) grains, growth ratio of the η layer with respect to the e layer, evolution of each layer and roughness of each interface. Additionally, it is shown through the use of simulation data that, while liquid Sn is present, the growth of the η IMC layers is dominant and that, upon the exhaustion of liquid Sn, the η grains of the upper and lower layers impinge on one another, at which time the larger grains continue to coarsen at the expense of the smaller grains. Concurrently, the growth of the e layers becomes significant and continues to increase until the η layer is fully consumed or the reaction is thermally arrested. Overall, the simulations were found to be in good qualitative agreement with experiments for morphology of the IMC grains, while showing good quantitative agreement, in spatial extent and elapsed time frames, for the evolution of each of the IMC layers and the derived growth ratio of the η layer with respect to the e layer. Furthermore, it is shown that the results corresponding to different thickness values for the initial Sn layer suggest that the IMC evolution can be reasonably predicted in advance of experimental studies.

Cu/Sn soldering alloys have emerged as a viable alternative to Pb-based solders, and thus have been extensively explored in the past decade, although the fine-scale behavior of the resulting intermetallic compounds (IMCs), particularly during the early stages of interface formation, is still a source of debate. In this work, the microstructural evolution of Cu6Sn5, in a Cu/Sn soldering reaction at 523 K, was experimentally investigated by dipping a single Cu sample into molten Sn at a near-constant speed, yielding a continuous set of time evolution samples. The thickness, coarsening and morphology evolution of the Cu6Sn5 layer is investigated through the use of scanning electron microscopy. The experimental results are also compared to phase-field simulations of the microstructural evolution of the Cu6Sn5 layer. The influence of model parameters on the kinetics and morphological evolution of the IMC layer was examined. In general, good qualitative agreement is found between experiments and simulations and for a limited parameter set there appears to be good quantitative agreement between the growth kinetics of the Cu6Sn5 layer, the grain boundary (GB) effect on grain coarsening, and the substrate/IMC interface roughness evolution. Furthermore, the parametric investigations of the model suggests that good agreement between experiments and simulations is achieved when the dominant transport mechanism for the reacting elements (Cu and Sn) is GB diffusion.

This study investigates the concurrent nucleation, formation and growth of two intermetallic compounds (IMCs), Cu 6 Sn 5 ( η ) and Cu 3 Sn ( e ), during the early stages of soldering in the Cu–Sn system. The nucleation, formation and growth of the IMC layers is simulated through a multiphase-field model [1,2] in which the concurrent nucleation of both IMC phases is considered to be a stochastic Poisson process with nucleation rates calculated from classical nucleation theory [3] . CALPHAD thermodynamic models are used to calculate the local contributions to the free energy of the system and the driving forces for precipitation of the IMC phases. The nucleation parameters of the η phase are estimated from experimental results [4] and those of the e phase are assumed to be similar. A parametric investigation of the effects of model parameters (e.g. grain boundary (GB) diffusion rates, interfacial and GB energies) on morphological evolution and IMC layer growth rate is presented and compared with previous works in which nucleation was ignored [5] . In addition, the resulting growth rates are compared with the available literature and it is found that, for a certain range in the model parameters, the agreement is quite satisfactory. This work provides valuable insight into the dominant mechanisms for mass transport as well as morphological evolution and growth of IMC layers during early stages of Pb-free soldering.

Computational investigations of the morphological evolution and growth kinetics for intermetallic compounds (IMCs, Cu 6 Sn 5 and Cu 3 Sn) formed during reaction and aging between Sn-based solder and a copper substrate are presented. Cu-substrate, Cu 3 Sn ( ɛ phase) and Cu 6 Sn 5 ( η phase) layers (or grains), as well as the Sn-liquid phase (or Sn-solid phase) are considered during the soldering (solid-state aging) process. In the simulation, interface regions are defined by the coexistence of two or more phases (at triple points) at a computational grid point. The simulation is performed through the multiphase-field approach. In the phase-field simulation, the grain boundary (GB) diffusion of the η phase as well as the interfacial energy between this phase and the solder alloy are treated as model parameters. Variation of these parameters allows the investigation of the effects of short-circuit diffusion paths and GB wetting on the morphological evolution of the IMC layers. The simulations addresses the growth kinetics of the two IMC layers (Cu 6 Sn 5 and Cu 3 Sn) during the two processes up to 14 h, illustrating the variation of η and ɛ IMC thickness and the number of η and ɛ grains as the microstructure coarsens.

We investigate the early stages of the morphological evolution of intermetallic compounds (IMCs) during lead-free soldering involving liquid Sn-based solder and Cu substrate considering the heterogeneous nucleation of the IMCs. The simulation is performed through the multi-phase-field approach [20,25]. Initially, the liquid Sn-based solder and the Cu substrate are considered to be at metastable local equilibrium. Nucleation at the solder/substrate interface is modeled by considering it to be a Poisson process. The phase-field simulation accounts for variations in grain boundary diffusion in the g phase and interface energies between the g phase and liquid solder, and uses these variations to investigate the multiplicity of soldering reactions, and make comparisons with previous work [23]. The simulations address the kinetics of the IMC growth during lead-free soldering under the effect of nucleation at an early stage, illustrating the variation in Cu substrate thickness, IMC thickness and number of grains that nucleate or disappear due to grain growth-induced coalescence.

The dynamics of two horizontal inviscid liquid layers induced by a vertical wavemaker is studied analytically, followed by a numerical analysis. The focus is put on the time dependent motion of the two interfaces, formed between the two liquid layers and between the upper layer and the air above. The singularities that would appear in the two contact lines (the three-phase lines formed by the wavemaker, the liquids, and the air) in most variable-separating techniques are suppressed by a Fourier-integral method, which generates uniformly valid solutions; the surface elevations at the contact lines remain finite for all time. Various wavemaker velocities are considered for realistic applications of the results. The study is initially prompted by the oil-skimming problem, one of the main issues of which is to determine the optimum speed of the oil skirt, without leaving the spilt oil behind. By obtaining the locations of the two interfaces though this study, the motion of the oil layer (upper liquid) can be determined precisely, based on conservation laws.

The dynamics of a vapor bubble between its liquid phase and a heated plate is studied in relation to the breakdown and recovery of the film boiling. By examining the expansion and the contraction of the vapor bubble the film boiling and transition boiling states are predicted. Conservation laws in the vapor, solid, and liquid phases are invoked along with fully nonlinear, coupled, free boundary conditions. These coupled system of equations are reduced to a single evolution equation for the local thickness of the vapor bubble by using a long-wave asymptotics, which is then solved numerically to yield the transient motion of the vapor bubble. Of the numerous parameters involved in this complex phenomenon we focus on the effects of the degree of superheat from the solid plate, that of the supercooling through the liquid, and the wetting/dewetting characteristics of the liquid on the solid plate. A material property of the substrate thus is incorporated into the criteria for the film boiling based on hydrodynamic models.

Prenatal ethanol exposure has various deleterious effects on neuronal development. As GABA B receptor is known to play an important role during the development of the CNS, we now focused on its mRNA expression pattern in the rat brain during the late gestational days (GD) from 15.5 to GD 21.5. Ethanol’s effect was also observed from GD 11.5 to GD 21.5. GABA B1 receptor mRNA showed a high expression level in GD 15.5 and 19.5, while GABA B2 receptor mRNA did in GD 15.5 and 21.5. The mRNAs levels depended on age and area during development. Ethanol exposure decreased GABA B1 receptor from GD 11.5 to GD 19.5 with slight increases in GD 21.5. The decreasing effects were area dependent, with the highest effects in the forebrain including cortex, whereas slight effects were observed in the midbrain and hindbrain. The present results suggest an important role of GABA B receptor in the effects of ethanol on prenatal brain developmental processes.

The characteristics of lithium/manganese-dioxide cells using Li powder or Li foil as the negative electrode (anode) are compared at high-rate discharge. Lithium powders with a mean diameter of 20 μm are produced by forming a dispersion of molten Li metal in inorganic carrier fluids. Cells using Li powder anodes show larger capacity and lower internal resistance than cells using Li foil anodes. Based on BET (Brunauer–Emmett–Teller) measurements, a reduction of effective current density due to the large surface area of the Li powder is considered to be responsible for the superior higher-rate discharge characteristics.

Endurable water-repellent coated layers have been formed on safety glasses for automobiles via a sol-gel based spray coating process. Coated films are composed of a silica underlayer (∼800 A) and a fluorocarbon layer in which the formed silica shows a definite surface roughness and acts as the enhancement factor for chemical and mechanical durability. Durability is a function of the degree of surface roughness, structural fineness and homogeneity. Dual stage aging in silica sol controls a wide range of surface roughness. Water-repellency is degraded gradually by a combination of sunlight (ultraviolet), water, and abrasion. Spray coating on large size and curved safety glasses was successfully carried out.

A search for charm hadron decays into two muons plus one or more hadrons has been carried out using a hybrid emulsion spectrometer. This technique is sensitive to modes with missing neutrals, e.g. π0μ+μ− and ϱ±μ+μ−, as well as to constrained modes having visible invariant masses equal to those of charm states. No evidence for any such decays has been found, which allows upper limits at the 90% confidence level as low as 1.8 × 10−4 to be placed on the branching fractions for charm-changing neutral-current and lepton-number violating decay modes.

Several efficient programs written in C that handle large scaled matrices, which are usually stored out of the core memory, are provided. A compacted sky-line matrix storage scheme is used for the symmetric coefficient matrices and Crout elimination is used for the solution of linear systems without core blocks. Scalar machine matrix multiplication, canonical multiplication and solutions of non-symmetric augmented linear system routines are provided, which are easily modified to the vectorized machines. Numerical tests are done by personal computers and engineering workstations. Efficiency of storage and time is considered good, compared to the full in-core routines.

The relative branching fraction RK = Γ(D0 → K−μ+v)/Γ(D0 → μ−X) has been measured by Fermilab experiment E653, using D0 mesons produced by 600 GeV π−. The semimuonic decay sample of 232 events was identified by the decay chain D ∗+ → D 0 π + , D 0 → μ + h − X , where h is a hadron. The Kμv component was extracted from the joint distribution of these events in the D0 decay variables Mmin and pTh. We find RK = 0.472 ± 0.051 (stat) ± 0.040 (sys), and use a world average of the D0 → Klv branching fraction to obtain the D0 inclusive semimuonic branching fraction B(D0 → μ+X) = (7.67 ± 1.13)%.

A new method, called graphic scanning, was developed by the Nagoya University Group for emulsion analysis in a hybrid experiment. This method enhances both speed and reliability of emulsion analysis. Details of the application of this technique to the analysis of Fermilab experiment E653 are described.

Heat and mass transfer with a uniformly distributed falling liquid desiccant film in a cross-flow parallel plate gas-liquid heat exchanger is predicted, and the results compared with experiment. The process air is in cross-flow over the desiccant film. Refrigerant flows through the heat exchanger tubes and removes the heat of absorption for dehumidification and supplies the heat for regeneration. The governing equations, boundary conditions, and interfacial equilibrium conditions for the concentration, temperature and pressure are presented. The problem is more complex than for cocurrent or countercurrent flow, as it is fully three-dimensional.

A search for charm production in the coherent diffractive dissociation reaction pSi→XSi was carried out for the modes D0→K−π+, D0→K−π+π+π−, and D+→K−π+π+. No charm signals were observed, and the 90% confidence level upper limit for coherent charm pair production was determined to be 26 μb per silicon nucleus. The results are interpreted as an upper limit of 0.2% on the amount of intrinsic charm in the proton.

Upper limits at the 90% confidence level are presented for four- and five-prong semimuonic decays of charm mesons. From a study of four-prong vertices we find B ( D 0 → K − π + π − μ + ν )/ B ( D 0 → K − μ + ν ) B (D 0 → ( K ∗ (892)π) − μ + ν)/B(D 0 → K − μ + ν) . The five-prong vertices yield the result B ( D S + → η ′ μ + ν ) / B ( D S + → φμ + ν )

We present a study of the Cabibbo-allowed semimuonic decay modes of the DS+ produced in 600 GeV c π − -emulsion interactions. From a signal of 18.7±4.9−0.7+0.4 events in the DS+ → oμ+υ channel, the product of production cross section and partial width is measured with respect to that for D + → K ∗0 μ + υ to be ( σ(D S + ) σ(D + )) . (Λ(D S + → oμ + ν)Λ(D + → K ∗0 μ + ν)) = 0.56 ± 0.14 ± 0.12. The form factor ratios in the decay, obtained by fitting to the decay angles and q2, are A 2 (0) 1 (0) = 2.1 −0.5 +0.6 ± 0.2 and V (0) A 1 (0) = 2.3 −0.9 +1.1 ± 0.4 , where A1 (0) and A2 (0) are the axial vector form factors and V(0) is the vector form factor, evaluated at q2 = 0. The first observation of DS+ → (ημ+υ + η'μ+υ) is also reported, and Γ (D S + → (ημ + υ + η'μ + υ)) Γ (D S + → oμ + υ) is determined to be 3.9 ± 1.6.

We report on the production characteristics and total cross section for 9 beauty hadron pairs produced by a 600 GeV/ c π − beam, the first such information in this energy region. The events were detected in the hybrid emulsion spectrometer of Fermilab Experiment E653. The measured pair cross section for all χ F , assuming linear A dependence, is 33±11 (stat.)±6(syst.) nb/nucleon. Fits of the inclusive single-hadron production distribution to the forms d σ d χ F ∝ (1−|χ F −χ 0 |) n and d σ d p T 2 ∝ exp (−bp t 2 ) give n=5.0 −2.1−1.7 +2.7+1.7 , χ 0 =0.06 −0.07−0.03 +0.06+0.02 , and b=0.13 −0.04−0.02 +0.05+0.02 ( GeV /c −2 . .The pairs tend to be produced back-to-back.

The branching ratio for the decay mode D + → K ∗0 μ + ν has been measured with two methods. The first uses D0→K−μ+ν for normalization, and yields the result B( D + → K ∗0 μ + ν)=(3.25±0.71±0.75)% . From this method we also obtain the direct measurement Γ( D + → K ∗0 μ + ν)/Γ( D 0 → K − μ + ν)=0.43±0.09±0.09 . The second method uses the mode D+→K−π+π+ for normalization and yields B( D + → K ∗0 μ + ν)=(4.18±0.66±0.96)% . Combining the results of the two methods yields B( D + → K ∗0 μ + ν)=(3.57±0.96)% .

We present total and differential cross sections for charm mesons produced in 600 GeV/c π- emulsion interactions. Fits to d2σ/dxF dpT2∞ (1−|xF|)nexp (-bpT2) for 676 electronically reconstructed D mesons with xF>0 give n=4.25±0.24 (stat.)±0.23 (syst.) and b=0.76±0.03±0.03 (GeV/c)-2. The total inclusive D+ and D0 cross sections are σ(π-N→D±; xF>0) = 8.66±0.46±1.96μb nucleon and σ(π - N→D 0 D 0 ; x F >0)=22.05±1.37±4.82μb nucleonk, where a linear dependence on the mean atomic weight of the target is assumed. These results are compared to next-to-leading order QCD predictions.

A measurement of the form factor ratios in the decay D + → K ∗ (892) 0 μ + ν is obtained by fitting to the decay angles and q2 of 305 events. The results, evaluated at q2 = 0, are A2(0)/A1(0) = 0.82+0.22−0.23 (stat.)±0.11 (sys.) and V(0)/A1(0) = 2.00+0.34−0.32±0.16, where A1 and A2 are the axial vector form factors and V is the vector form factor. The corresponding ratio of the longitudinal to transverse polarization of the K ∗0 is 1.18±0.18±0.08. These results are compared with other experimental results and with theoretical predictions.