Dissolution and Interface Reactions between Palladium and Tin(Sn)-Based Solders: Part II. 63Sn-37Pb Alloy

The interface microstructures and dissolution behavior were studied, which occur between 99.9 pct Pd substrates and molten 95.5Sn-3.9Ag-0.6Cu (wt pct, Sn-Ag-Cu) solder. The solder bath temperatures were 513 K to 623 K (240 °C to 350 °C). The immersion times were 5 to 240 seconds. The IMC layer composition exhibited the (Pd, Cu)Sn₄ (Cu, 0 to 2 at. pct) and (Pd, Sn) solid-solution phases for all test conditions. The phases PdSn and PdSn₂ were observed only for the 623 K (350 °C), 60 seconds test conditions. The metastable phase, Pd₁₁Sn₉, occurred consistently for the 623 K (350 °C), 240 seconds conditions. Palladium-tin needles appeared in the Sn-Ag-Cu solder, but only at temperatures of 563 K (290 °C ) or higher, and had a (Pd, Cu)Sn₄ stoichiometry. Palladium dissolution increased monotonically with both solder bath temperature and exposure time. The rate kinetics of dissolution were represented by the expression At ⁿ exp(∆H/RT), where the time exponent (n) was 0.52 ± 0.10 and the apparent activation energy (∆H) was 44 ± 9 kJ/mol. The IMC layer thickness increased between 513 K and 563 K (240 °C and 290 °C) to approximately 3 to 5 μm, but then was less than 3 μm at 593 K and 623 K (320 °C and 350 °C). The thickness values exhibited no significant time dependence. As a protective finish in electronics assembly applications, Pd would be relatively slow to dissolve into molten Sn-Ag-Cu solder. The Pd-Sn IMC layer would remain sufficiently thin and adherent to a residual Pd layer so as to pose a minimal reliability concern for Sn-Ag-Cu solder interconnections.     

Dissolution and interface reactions between the 95.5Sn-3.9Ag-0.6Cu, 99.3Sn-0.7Cu, and 63Sn-37Pb solders on silver base metal

Dissolution and intermetallic compound (IMC) layer development were examined for couples formed between 99.9 silver (Ag) and molten 95.5Sn-3.9Ag-0.6Cu (wt pct), 99.3Sn-0.7Cu, and 63Sn-37Pb solders, using a range of solder temperatures and exposure times. The interface reactions that controlled Ag dissolution were sensitive to the solder composition. The Ag₃Sn IMC layer thickness and interface microstructure as a whole exhibited nonmonotonic trends and were controlled primarily by the near-interface solder composition. The kinetics of IMC layer growth were weakly dependent upon the solder composition. The processes of Ag dissolution and IMC layer growth were independent of one another.     

Effect of Rare-Earth (La,Ce, and Y) Additions on the Microstructure and Mechanical Behavior of Sn-3.9Ag-0.7Cu Solder Alloy

In this article, we report on the microstructure and mechanical properties of Ce- and Y-containing Sn-3.9Ag-0.7Cu solders. The microstructures of both as-processed solder and solder joints containing rare-earth (RE) elements (up to 0.5 wt pct) are more refined compared to conventional Sn-3.9Ag-0.7Cu, with decreases in secondary Sn dendrite size and spacing and a thinner Cu₆Sn₅ intermetallic layer at the Cu/solder interface. These results agree well with similar observations seen in La-containing solders reported previously. The monotonic shear behavior of reflowed Sn-3.9Ag-0.7Cu-X(Ce, Y)/Cu lap shear joints was studied as well as the creep behavior at 368 K (95 °C). The data were compared with results obtained for Sn-3.9Ag-0.7Cu and Sn-3.9Ag-0.7Cu-XLa alloys. All RE-containing alloys exhibited creep behavior similar to Sn-3.9Ag-0.7Cu. Alloys with Ce additions exhibited a small decrease in ultimate shear strength but higher elongations compared with Sn-Ag-Cu. Similar observations were seen in La-containing solders. The influence of the RE-containing intermetallics (CeSn₃ and YSn₃) that form in these alloys on the microstructural refinement, solidification behavior, and mechanical performance of these novel materials is discussed.     

Interfacial Reactions,Microstructure, and Strength of Sn-8Zn-3Bi and Sn-9Zn-Al Solder on Cu and Au/Ni (P) Pads

The Sn-8Zn-3Bi and Sn-9Zn-Al Pb-free solders were used to mount passive components onto printed circuit boards (PCBs) with electroless Ni immersed Au (ENIG) finishing layers using a reflow soldering process. The component mounted boards were aged at 150 °C for 200 to 1100 hours. The interfacial reactions and microstructure of the interfaces between the solders and the pads were observed using scanning electron microscopy and energy-dispersive spectrometry (EDS). Both solder joints on the two pads had similar interfacial microstructures; i.e., a very thin γ ₂-AuZn₃ layer was formed at the interface of the solder and Ni-P layer. The γ ₂-AuZn₃ layer transformed to an ε-AuZn₈ intermetallic compounds (IMC) with a consistent thickness during aging. Zinc atoms redeposited onto the IMC layer increased with increasing aging time. After aging at 150 °C for various times, the shear strengths of the ENIG and organic solderability preservative (OSP) joints were evaluated. The shear strength of the Sn-8Zn-3Bi solder joint was better than that of the Sn-9Zn-Al solder joint. All of the solder joints deteriorated after aging; however, the degradations of the OSP solder joints were more evident than those of the ENIG solder joints.     

The rate of chlorination of metals and oxides: Part I. Fe,Ni, and Sn in chlorine

The rates of chlorination of Fe (528 to 921 K), Ni (890 to 1249 K), and Sn (340 to 396 K) in Cl₂-He andCl₂-Ar mixtures were measured. In the temperature range of the respective investigations the overall reaction products are gaseous: (FeCl₃)₂, NiCl₂, and SnCl₄. Transport through the gas film boundary layer at the surface of the sample plays a major role in controlling the rate of the reactions over large temperature ranges for all three metals. In the high-temperature range for iron (> 680 K) and nickel (> 993 K) as well as for the entire temperature range studied for tin, the transport of Cl2₂(g) through the gas film boundary layer to the surface of the sample controlled the rates for the experimental conditions in the present work. The transport of NiCl₂(g) controlled the rate of the Ni-Cl₂ reaction at lower temperatures. The rate of the Fe-Cl₂ reaction at lower temperatures is controlled by a slow surface reaction between Cl₂(g) and FeCl₂(s) which covers the surface of the iron. The overall activation energy for the formation of the activated complex (FeCl₃)₂‡ is 23 kcal/g-atom Fe.     

Deformation mechanisms in commercial TI-5Al-2.5 Sn (0.5 At. pct Oeq) alloy at intermediate and high temperatures (0.3-0.6 tm)

The plastic flow of the commercial α-alloy Ti 5A1-2.5 Sn (0.5 at. pct Oeq) of 11 to 19 μm grain size was investigated in tension over the temperature range of 600 to 117.3 K (CPH structure) and strain rates of 3x10^-5 to 3 per s employing both constant strain rate and strain rate cycling tests. Dynamic strain aging (due to substitutional solutes) occurred in the temperature range of 600 to 850 K (0.31 to 0.44T _m)with an activation energy of 22.5 KcalJmole (94.1 KjJmol) derived from the start of serrations in the stress-strain curves. At temperatures above 850 K (0.46 to 0.60T _m), the deformation could be described by Dorn’s general equation for diffusion controlled mechanisms with an activation energy of 50 KcalJmole (209 KJJmol).     

Fluid flow in pachuca (air-agitated) tanks: Part I. Laboratory-scale experimental measurements

Gas-agitated reactors are used in a number of process industries, including the metallurgical industry, where they are known as “Pachuca” tanks. In spite of the fact that it is the circulation (i.e., velocity and turbulent kinetic energy distribution) within these tanks that governs the main process requirements,i.e., mass transfer and particle suspension, very little attention has been paid to the question of fluid flow. In the present study, velicity measurements made in a laboratory-scale Pachuca tank have suggested the importance of the fluid flow pattern in governing the performance of air-agitated tanks and have shed some light on the efficient operation of these tanks. Full-center-column tanks with large tank height-to-diameter ratios have a “near-stagnant zone” in the lower section of the annulus. The stagnant zone is a region of low turbulent kinetic energy and is undesirable, since it costs energy and is likely to provide very little in return in terms of mass transfer. An increase in the draft tube diameter, for a given tank diameter, leads to higher velocity and turbulence levels in the annulus, which, in turn, should promote mass transfer. Free-airlift tanks seem to be more vigorously agitated than full-center-column tanks. The present study shows that operating a full-center-column Pachuca tank with the liquid surface at or below the same level as the draft tube top would be disadvantageous in terms of particle suspension and mass transfer and also illustrates that it is erroneous to correlate the turbulence on the liquid surface with the turbulence level within the tank.     

Strengthening in MULTIPHASE (MP35N) alloy: Part I. ambient temperature deformation and recrystallization

The microstructure and mechanical properties of the cobalt-based MP35N alloy (35 pct Co, 35 pct Ni, 20 pct Cr, and 10 pct Mo) were investigated following room-temperature deformation. It was found that the material showed marked work hardening at strains greater than about 0.15 to 0.2, which correlated with the formation of platelike structures on {111} planes. The initial yield strength of 390 MPa was increased to 1385 MPa by cold drawing 48 pct. Electron microscopy showed evidence that the platelike structures were both faulted face-centered cubic (fcc) twins and hexagonal martensite. Secondary strengthening from 1385 to 1935 MPa was achieved by annealing the cold-drawn MP35N at 650 °C for 4 hours. However, no structural change could be detected that could account for this large secondary strengthening. This failure lends indirect support to the proposal that this secondary strengthening could arise from solute partitioning between the fcc matrix and hexagonal martensite. Cold-worked MP35N resisted recrystallization up to a critical softening temperature of 1083 K (810 °C), at which the alloy lost 50 pct of its hardness during a 1-hour anneal. Nucleation occurred readily at and above this temperature. Growth of the new grains at temperatures close to the critical softening temperature appeared to be strongly inhibited by the martensite plates but not by twins. Residual dislocation densities were seen in the recrystallized grains in the vicinity of the disappearing martensite plates. It is proposed that these dislocations arise from local changes in lattice parameters arising from prior solute segregation to the martensite plates. A revision of the earlier solute partitioning model of secondary strengthening is proposed here — that the partitioning occurs locally, adjacent to the preexisting plates. During postanneal deformation, higher stresses are then required for fresh martensite plates (and twins) to be nucleated from the existing plates. Ultrafine grain sizes of only about 1 μm could be produced in MP35N by successive cycles of deformations and anneals at temperatures close to the critical softening temperature.     

The effect of Fe(II) and Fe(III) on the efficiency of copper electrowinning from dilute acid Cu(II) sulphate solutions with the chemelec cell: Part I. Cathodic and anodic polarisation studies

The results are presented from an investigation into the effect of the Fe(III) and Fe(II) concentration on the current efficiency for copper electrowinning using the Chemelec cell. The results are from polarisation studies of acidic sulphate electrolytes containing Cu(II), Fe(II) and Fe(III). The mass transfer coefficients for these cationic species are determined, and the effect of using different anode materials on the overvoltage for the oxidation of Fe(II) and oxygen evolution is also examined.     

Effects of Different Modes of Hot Cross-Rolling in 7010 Aluminum Alloy: Part I. Evolution of Microstructure and Texture

The current study describes the evolution of microstructure and texture in an Al-Zn-Mg-Cu-Zr-based 7010 aluminum alloy during different modes of hot cross-rolling. Processing of materials involves three different types of cross-rolling. The development of texture in the one-step cross-rolled specimen can be described by a typical β-fiber having the maximum intensity near Copper (Cu) component. However, for the multi-step cross-rolled specimens, the as-rolled texture is mainly characterized by a strong rotated-Brass (Bs) component and a very weak rotated-cube component. Subsequent heat treatment leads to sharpening of the major texture component (i.e., rotated-Bs). Furthermore, the main texture components in all the specimens appear to be significantly rotated in a complex manner away from their ideal positions because of non-symmetric deformations in the two rolling directions. Detailed microstructural study indicates that dynamic recovery is the dominant restoration mechanism operating during the hot rolling. During subsequent heat treatment, static recovery dominates, while a combination of particle-stimulated nucleation (PSN) and strain-induced grain boundary migration (SIBM) causes partial recrystallization of the grain structure. The aforementioned restoration mechanisms play an important role in the development of texture components. The textural development in the current study could be attributed to the combined effects of (a) cross-rolling and inter-pass annealing that reduce the intensity of Cu component after each successive pass, (b) recrystallization resistance of Bs-oriented grains, (c) stability of Bs texture under cross-rolling, and (d) Zener pinning by Al₃Zr dispersoids.     

Structure and properties of a rapidly solidified Al-Li-Mn-Zr Alloy for high-temperature applications: Part I. inert gas atomization processing

A new Al-Li alloy containing 2.3 wt pct Li, 6.5 wt pct Mn, and 0.65 wt pet Zr, for high-temperature applications, has been processed by a rapid solidification (RS) technique (as powders by inert gas atomization) and then thermomechanically treated by hot isostatic pressing (hipping) and hot extrusion. As-received and thermomechanically treated powders (of various size fractions) were characterized by X-ray diffraction and scanning and transmission electron microscopy (SEM and TEM, respectively). Phase analyses in the as-processed materials revealed the presence of two Mn phases (Al₄Mn and Al₆Mn), one Zr phase (Al₃Zr), two Li phases (the stable AlLi and the metastable Al₃Li), and the αAl solid solution with high excess in Mn solubility (up to close the nominal composition in the as-atomized powders). Extruded pieces were solutionized at 370 °C and 530 °C for various soaking times (2 to 24 hours). A variety of aging treatments was practiced to check for the optimal (for tensile properties) aging procedure, which was found to be the following: solutioning at 370 °C for 2 hours and water quenching + 1 pct mechanical stretching + one step aging at 120 °C for 3 hours. The mechanical properties, at room and elevated temperatures, of the “hipped” and hot extruded powders are compared following the optimal solutioning and aging treatments. The results indicate that Mn is indeed a favorable alloying element for rapidly solidified Al-Li alloys to retain about 85 to 95 pct of the room-temperature tensile properties even at 250 °C, though room-temperature strength is not satisfactory in itself. However, specific moduli are by 20 to 25 pet higher than those of the 2024 series duralumin-type alloys. Ductilities at room temperatures are in the low 1 to 2.5 pct range and show no improvement over other Al-Li alloys.     

Deformation mechanisms in commercial TI-5Al-2.5 Sn (0.5 At. pct Oeq) alloy at intermediate and high temperatures (0.3-0.6 tm)

The plastic flow of the commercial α-alloy Ti 5A1-2.5 Sn (0.5 at. pct Oeq) of 11 to 19 μm grain size was investigated in tension over the temperature range of 600 to 117.3 K (CPH structure) and strain rates of 3x10^-5 to 3 per s employing both constant strain rate and strain rate cycling tests. Dynamic strain aging (due to substitutional solutes) occurred in the temperature range of 600 to 850 K (0.31 to 0.44T _m)with an activation energy of 22.5 KcalJmole (94.1 KjJmol) derived from the start of serrations in the stress-strain curves. At temperatures above 850 K (0.46 to 0.60T _m), the deformation could be described by Dorn’s general equation for diffusion controlled mechanisms with an activation energy of 50 KcalJmole (209 KJJmol). M. D?NER was formerly with Department of Metallurgical Engineering and Materials Science, University of Kentucky, Lexington, Ky. 40506     

Structure of the welding zone between titanium and orthorhombic titanium aluminide for explosion welding: I. Interface

The structures of the interfaces and transition zones of bimetallic metal-intermetallide joints produced by explosion welding under various conditions have been studied. The welded materials were commercial-purity titanium and orthorhombic titanium aluminide of two alloying schemes. The specific features of the structure and substructure of the zones under study are discussed. Wave formation and formation of isolated vortex zones, as well as tracks of particles related to the transfer of particles of one metal into the other one, were observed. A possible scenario of formation of interfaces, depending on the composition of titanium aluminide and welding conditions, is proposed.     

On social diagnosis and prognosis concerning childhood--experiences in Czechoslovakia. Part I (author's transl)

The term "social" is defined multidimensionally. For the child, the most important structural unit of the social environment is the family, whose normal function influences the child's development significantly. Familiar disturbances threaten or damage it. From these aspects a social prognosis can be derived. The intuitive assessment of a singular case should be replaced by an objective, generalizable method.     

The thermodynamic studies of liquid copper alloys by electromotive force method: Part I. The Cu−O,Cu−Fe−O,and Cu−Fe systems

Oxygen activities in liquid Cu−O and Cu−Fe−O alloys were measured in the temperature range 1100° to 1300°C by the solid oxide electrolyte emf method with mixtures of Ni−NiO and Co−CoO as reference electrodes. The Cu−O and Cu−Fe−O alloys were analyzed for iron and/or oxygen content. The activity coefficient of oxygen at infinite dilution in liquid copper was found to be 0.115, 0.195, and 0.286 at 1100°, 1200°, and 1300°C, respectively. The results are compared with previous investigations on the Cu−O system. Based on this comparison, the best equation for the free energy of solution has been suggested. The standard free energy of formation of CoO(s) has been calculated at the experimental temperatures. In the liquid Cu−Fe−O system at 1200°C, a minima in oxygen solubility is reached at 1.1 at. pct Fe in the alloy. The value of interaction coefficient, , is −565 at 1200°C. Iron activities in the liquid Cu−Fe alloys have been calculated at 1100° and 1200°C, and a strong positive deviation from ideality is observed. Results of this study were combined with literature data at 1550°C to obtain the values of and at infinite dilution in liquid copper. A. D. KULKARNI, formerly with Chase Brass and Copper Co., Cleveland, Ohio     

The effects of composition and carbide precipitation on temper embrittlement of 2.25 Cr-1 Mo steel: Part I. Effects of P and Sn

Temper embrittlement of 2.25 Cr-1 Mo steel doped with P and Sn was studied systematically. Carbide extraction by electrolysis, X-ray diffraction, transmission (replica) electron microscopy, chemical analysis of the matrix, and scanning Auger microprobe analysis were conducted to determine the effect of carbide precipitation and subsequent variation of the Mo concentration in solution on the segregation of P. These analyses were correlated with the ductile-to-brittle transition temperature (measured by use of a slow-bend test), as well as hardness measurements and fractographic information obtained by scanning electron microscopy. The results indicate that the principal role of Mo is to suppress embrittlement by scavenging of P, presumably by a Mo-P compound formation, thereby diminishing P segregation. However, due to the stronger interaction between Mo and C, Mo is precipitated in an M₂C carbide during tempering or aging, and the matrix is depleted of Mo. The P thereby released segregates at a rate consistent with the rate of M₂C precipitation. At a Mo concentration >0.7 pct the beneficial effect of Mo is decreased due to enhanced M₂C precipitation, the content of Mo in solution remaining essentially constant. The M₂C is formed at the expense of Cr-rich M₇C₃; this results in more Cr in solution, thereby permitting more Cr-P cosegregation, and embrittlement increases. Tin was found not to produce temper embrittlement in this steel when present at concentrations up to 0.04 pct.     

TTR-diagrams (time-temperature-reaction) for thermo-mechanical treatments of steels. – Part I: Time-temperature-diagrams and intercritical annealing of deformed Fe-Ni-alloys

Time-temperature-reaction diagrams for thermo-mechanical treatments of steels. As example: formation of coarse two-phase microstructures in Fe-Ni alloys by intercritical annealing.