Binary Pb-Sn Research Articles

The influence of Pb content on the interfacial free energy of solid Sn in eutectic Pb–Sn liquid mixtures using molecular dynamics simulations

ABSTRACT The solid–liquid interfacial free energy (γ) for binary Pb–Sn systems at different concentrations and crystal orientations is calculated using molecular dynamics (MD) simulation that employs a modified-embedded atom method interatomic potential. First, the solid–liquid interface is constructed in MD simulations according to its calculated phase diagram. Then, the capillary fluctuation method (CFM) is employed for the calculation of the solid–liquid interfacial stiffness. A novel systematic approach is proposed that eliminates the error in the linear approximation of the CFM. The results show that orientation of the solid Sn crystal does not have a significant influence on the value of the stiffness, which explains the experimentally observed spherical shape of Sn particles in eutectic liquid Pb–Sn mixtures. The calculated γ for pure Sn is in good agreement with experimental counterparts. In addition, this study finds that γ slightly increases with increasing the concentration of Pb in the eutectic liquid Pb–Sn mixture, which agrees with available experimental data.

Solidification Morphology and Bifurcation Predictions with the Maximum Entropy Production Rate Model

The use of the principle of maximum entropy generation per unit volume is a new approach in materials science that has implications for understanding the morphological evolution during solid–liquid interface growth, including bifurcations with or without diffuseness. A review based on a pre-publication arXiv preprint is first presented. A detailed comparison with experimental observations indicates that the Maximum Entropy Production Rate-density model (MEPR) can correctly predict bifurcations for dilute alloys during solidification. The model predicts a critical diffuseness of the interface at which a plane-front or any other form of diffuse interface will become unstable. A further confidence test for the model is offered in this article by comparing the predicted liquid diffusion coefficients to those obtained experimentally. A comparison of the experimentally determined solute diffusion constant in dilute binary Pb–Sn alloys with those predicted by the various solidification instability models (1953–2011) is additionally discussed. A good predictability is noted for the MEPR model when the interface diffuseness is small. In comparison, the more traditional interface break-down models have low predictiveness.

Size-dependent thermodynamic description of the binary Pb-Sn system

Recently, a new thermodynamic description of the binary Pb - Sn system was proposed and it seems to be interesting to extend this description on the system, where size of particles plays a key-role. To obtain this goal a set of surface Gibbs energies was calculated and added to Gibbs energies describing bulk phases. The extended thermodynamic description was used for calculation of size-dependent phase diagram of binary Pb-Sn system. Comparison of calculation with limited literature information allows for statement that the proposed model is in good agreement with experiment.

Element‐free Galerkin method for thermosolutal convection and macrosegregation

AbstractIn the present work, the element‐free Galerkin (EFG) method is applied to a continuum solidification model that calculates thermosolutal convection and macrosegregation during dendritic solidification of multicomponent alloys. Simulations for directional solidification of a binary Pb–Sn alloy and a Ni‐base quaternary alloy have been performed in a rectangular two‐dimensional domain. In both calculations, the alloy melt is cooled from below and the growth of the mushy zone is followed in time. The formation of macrosegregation defects known as ‘freckles’ has been successfully simulated using the meshless EFG method. A varying degree of sensitivity of results to the number and distribution of meshfree particles was obtained. The potential of the method for a broader range of solidification models is discussed. Copyright © 2009 John Wiley & Sons, Ltd.

A flip chip process based on electroplated solder bumps

Compared to wire bonding and TAB, flip chip technology using solder joints offers the highest pin count and packaging density and superior electrical performance. The chips are mounted upside down on the substrate, which can be made of silicon, ceramic, glass or - in some cases - even PCB. The extra processing steps required for chips are the deposition of a suitable thin film metal layer(s) on the standard Al pad and the formation of bumps. Also, the development of new fine line substrate technologies is required to utilize the full potential of the technology. In our bumping process, bump deposition is done by electroplating, which was chosen for its simplicity and economy.Sputter deposited molybdenum and copper are used as thin film layers between the aluminum pads and the solder bumps. A reason for this choice is that the metals can be selectively etched after bumping using the bumps as a mask, thus circumventing the need for a separate mask for etching the thin film metals. The bumps are electroplated from a binary Pb-Sn bath using a thick liquid photoresist.An extensively modified commercial flip chip bonder is used for alignment and bonding. Heat assisted tack bonding is used to attach the chips to the substrate, and final reflow joining is done without flux in a vacuum furnace.

Creep in Shear of Experimental Solder Joints

Thermal fatigue failures of solder joints in electronic devices are a great concern in the electronics industry. Since the fatigue load is often in shear the details of thermal fatigue failure in shear are of particular interest. Recent work indicates that similar failure mechanisms operate in both thermal fatigue in shear and unidirectional creep in shear. Additionally, since the operative temperatures during thermal fatigue represent high solder homologous temperatures, creep deformation is certainly involved. These factors and the relative case of conducting creep experiments encourage the study of solder joints under shear creep conditions. This work presents steady state shear creep rate vs. shear stress data for several solder compositions, including the binary eutectic alloy and Pb-Sn alloyed with small amounts of Bi, Cd, In, and Sb, in a joint configuration. These data indicate that conventional creep mechanisms operate in the temperature and shear strain rate ranges studies. Extensive microstructural information is also reported. The microstructural evolution under creep conditions indicates that the instability of the as-cast binary Pb-Sn eutectic microstructure initiates creep failure. Changes of the as-solidified microstructure with the third element addition are reported as are the microstructural responses of each of these alloys to creep deformation. The efficacy of postponing the microstructural instability with the addition of small amounts of ternary elements is discussed.

Investigation op the binary Pb-Sn system by DTA

The phase diagram of the binary Pb-Sn system was determined by a modified DTA aparatus. The heat of mixing in liquid and solid state were also determined by quantitative DTA.

Channel formation in Pb-Sn, Pb-Sb, and Pb-Sn-Sb alloy ingots and comparison with the system NH4CI-H2O

The formation of segregation channels during the unidirectional solidification of base chilled ingots has been studied as a function of composition in binary Pb-Sn and Pb-Sb and ternary Pb-Sn-Sb alloys. The patterns of channel distribution were characterized in the binary and ternary systems and are described as functions of temperature gradients, growth rates, dendrite spacings, and interdendritic permeabilities. Channels appear to nucleate at random across a dendritic front and subsequently to interact as they propagate, decreasing in density across the front. Assuming that the interdendritic spacing is the characteristic distance for a liquid perturbation, yields critical effective Rayleigh numbers which lie within a factor of x40 for both metallic and aqueous systems. This correlation is close, considering the sensitivity to any assumed dimension and the range of material properties involved, and is taken to support a model for channel nucleation occurring close to the dendritic growth front.

Corrosion of Pb-Sn alloys in alkaline solutions

The corrosion behaviour of binary Pb-Sn alloys in sodium hydroxide solutions was studied by the loss in weight technique and by recording the variation in the corrosion potential of the alloy with time. It was found that the rate of alloy corrosion decreases with increasing tin content in the alloy. Thiourea was found to inhibit the corrosion of Pb-Sn alloys in sodium hydroxide by a maximum of 92%. The inhibition efficiency decreases with increasing tin content in the alloy.

Cu-Pb-Sn Ternary System: Low Cu Additions to Pb-Sn- Binary System

ABSTRACTA portion of the Cu-Pb-Sn ternary diagram was determined experimentally. The investigation was concentrated on the high Pb corner and, to a lesser extent of alloys from Sn to the binary Pb-Sn eutectic. The experimental techniques used were thermal analysis, metallography, and electron microprobe analysis. A new technique for determining liquidus temperatures was used. For the high Pb region the proposed ternary eutectic at 0.06 Cu 0.02% SnPb (all compositions are in weight %) was not observed. For most alloys the primary crystallization phase was Cu3Sn. It was shown that Cu6Sn5 exists in the solid state; for high Sn alloys, it was observed that the addition of Pb reduced the decomposition temperature of Cu6Sn5. A ternary eutectic reaction near the binary Pb-Sn eutectic was confirmed, and the temperature of the ternary eutectic was 1°K below that of the binary eutectic. Liquidus temperatures as well as other reactions detected by thermal analysis will be presented.