Correlation between interfacial microstructure and shear behavior of Sn–Ag–Cu solder ball joined with Sn–Zn–Bi paste

Sn–8Zn–3Bi solder paste was applied as a medium to joint Sn–3.2Ag–0.5Cu solder balls and Cu/Ni/Au metallized ball grid array substrates at 210 °C. Sn–Ag–Cu joints without Sn–Zn–Bi addition were also conducted for comparison. The shear behavior of the specimens was investigated after multiple reflow and thermal aging. For each strength test, more than 40 solder balls were sheared. The shear strength of Sn–Ag–Cu specimens kept constant ranging from 15.5 ± 1.3 N (single reflow) to 16.2 ± 1.0 N (ten reflows) and the fractures occurred in the solder. Shear strength of Sn–Ag–Cu/Sn–Zn–Bi specimens fell from 15.9 ± 1.7 N (single reflow) to 13.4 ± 1.6 N (ten reflows). After single reflow, Sn–Ag–Cu/Sn–Zn–Bi specimens fractured in the solder along Ag–Au–Cu–Zn intermetallic compounds and at Ni metallization. After ten reflows, fractures occurred in the solder and at solder/Ni–Sn–Cu–Zn intermetallic compound interface. The shear strengths of the Sn–Ag–Cu and Sn–Ag–Cu/Sn–Zn–Bi packages changed little after aging at 150 °C. Sn–Ag–Cu/Sn–Zn–Bi joints kept higher strength than Sn–Ag–Cu joints. Sn–Ag–Cu joints fractured in the solder after aging. But the fractures of Sn–Ag–Cu/Sn–Zn–Bi specimens shifted to the solder with aging time.     

Subcritical crack growth and power law exponent of Y–Si–Al–O(–N) glasses in aqueous environment

The subcritical crack growth resistance in water of a Y–Si–Al–O and Y–Si–Al–O–N glasses has been investigated with three point bending experiments. It has been shown that the SCG behaviour of the Y–Si–Al–O–N glass is superior to that of the Y–Si–Al–O glass. This is reflected by the power law exponent n which is 21 for the Y–Si–Al–O glass and 63 for the Y–Si–Al–O–N glass. Mechanistic implications of these observations are discussed.     

Properties of SnAgCu/SnAgCuCe soldered joints for electronic packaging

For quad flat packages (QFP256), lead-free soldered joints reliability in service is a critical issue. In this paper, soldering experiments of quad flat package (QFP256) devices were carried out by means of infrared reflow soldering system with Sn–3.8Ag–0.7Cu and Sn–3.8Ag–0.7Cu–0.03Ce lead-free solders, respectively, and the mechanical properties of micro-joints of the QFP devices were tested and studied by STR micro-joints tester. The results indicate that the tensile strength of Sn–Ag–Cu–Ce soldered joints is better than that of Sn–Ag–Cu soldered joints. In particular, the addition of trace Ce to the Sn–Ag–Cu solder can refine the microstructures and decrease the thickness of the intermetallic compound layer of Sn–Ag–Cu solder alloys. In addition, the stress–strain response of Sn–Ag–Cu/Sn–Ag–Cu–Ce soldered joints in quad flat packaging was investigated using finite element method based on Garofalo–Arrhenius model. The simulated results indicate creep distribution of soldered joints is not uniform, the heel and toe of soldered joints, the area between soldered joints and leads are the creep concentrated sites. The creep strain of Sn–Ag–Cu–Ce soldered joints is lower than that of Sn–Ag–Cu soldered joints.     

Influence of arsenic, antimony and phosphorous on the microstructure and corrosion behavior of brasses

The effect of minor additions of As, Sb and P on phase distribution and corrosion behavior has been studied in brasses. The alloys investigated were 60Cu–39Zn–1Pb, 48.95Cu–45Zn–5Pb–1Sn–0.05As, 48.90Cu–45Zn–5Pb–1Sn–0.05As–0.05Sb and 48.85Cu–45Zn–5Pb–1Sn–0.05As–0.05Sb–0.05P. Immersion tests in 1% CuCl₂ solution indicated that the addition of As improved corrosion resistance while the combined addition of As + Sb and As + Sb + P was not beneficial. The hardness increased significantly with the addition of As, Sb and P. Microstructural observations indicated an increase in β phase fraction in the As, Sb and P containing alloys. X-ray diffraction studies confirmed the formation of intermetallic compounds in As, Sb and P containing alloys. Based on the microstructural observations, the intermetallic compounds appear to be primarily precipitated in the β phase with As + Sb and As + Sb + P additions. The lower corrosion resistance of the alloys 48.90Cu–45Zn–5Pb–1Sn–0.05As–0.05Sb and 48.85Cu–45Zn–5Pb–1Sn–0.05As–0.05Sb–0.05P has been related to increase in β phase volume fraction and precipitation of intermetallic compounds in the β phase.     

Microstructure and corrosion properties of as sub-rapid solidification Mg–Zn–Y–Nd alloy in dynamic simulated body fluid for vascular stent application

Magnesium alloy stent has been employed in animal and clinical experiment in recent years. It has been verified to be biocompatible and degradable due to corrosion after being implanted into blood vessel. Mg–Y–Gd–Nd alloy is usually used to construct an absorbable magnesium alloy stent. However, the corrosion resistant of as cast Mg–Y–Gd–Nd alloy is poor relatively and the control of corrosion rate is difficult. Aiming at the requirement of endovascular stent in clinic, a new biomedical Mg–Zn–Y–Nd alloy with low Zn and Y content (Zn/Y atom ratio 6) was designed, which exists quasicrystals to improve its corrosion resistance. Additionally, sub-rapid solidification processing was applied for preparation of corrosion-resisting Mg–Zn–Y–Nd and Mg–Y–Gd–Nd alloys. Compared with the as cast sample, the corrosion behavior of alloys in dynamic simulated body fluid (SBF) (the speed of body fluid: 16 ml/800 ml min⁻¹) was investigated. The results show that as sub-rapid solidification Mg–Zn–Y–Nd alloy has the better corrosion resistance in dynamic SBF due to grain refinement and fine dispersion distribution of the quasicrystals and intermetallic compounds in α-Mg matrix. In the as cast sample, both Mg–Zn–Y–Nd and Mg–Y–Gd–Nd alloys exhibit poor corrosion resistance. Mg–Zn–Y–Nd alloy by sub-rapid solidification processing provides excellent corrosion resistance in dynamic SBF, which open a new window for biomedical materials design, especially for vascular stent application.     

Suppressing the growth of interfacial Cu–Sn intermetallic compounds in the Sn–3.0Ag–0.5Cu–0.1Ni/Cu–15Zn solder joint during thermal aging

Evolution of interfacial phase formation in Sn–3.0Ag–0.5Cu/Cu (wt%), Sn–3.0Ag–0.5Cu–0.1Ni/Cu, Sn–3.0Ag–0.5Cu/Cu–15Zn, and Sn–3.0Ag–0.5Cu–0.1Ni/Cu–15Zn solder joints are investigated. Doping Ni in the solder joint can suppress the growth of Cu₃Sn and alter the morphology of the interfacial intermetallic compounds (IMCs), however it shows rapid growth of (Cu,Ni)₆Sn₅ at the Sn–3.0Ag–0.5Cu–0.1Ni/Cu interface. In comparison with the Cu substrates, the Cu–Zn substrates effectively suppress the formation of Cu–Sn IMCs. Among these four solder joints, the Sn–3.0Ag–0.5Cu–0.1Ni/Cu–15Zn solder joint exhibits the thinnest IMC, and only (Cu,Ni)₆(Sn,Zn)₅ formed at the interface after aging. It is revealed that the presence of Ni acts to enhance the effect of Zn on the suppression of Cu–Sn IMCs in the SAC305–0.1Ni/Cu–15Zn solder joint. The limited formation of IMCs is related to the elemental redistribution at the joint interfaces during aging. The Sn–3.0Ag–0.5Cu–0.1Ni/Cu–15Zn joint can act as a stabilized interconnection due to the effective suppression of interfacial reaction.     

Mechanical properties of rapidly solidified ribbons of some AI–Si based alloys

Continuous uniform ribbons of Al–16 Si, Al–12.5 Si–1 Ni and Al–12.5 Si–1 Mg were prepared by melt spinning. Microhardness was measured. The as-melt spun values were 1280, 1370 and 1500 MN m-2 which relax on thermal ageing to 700, 700 and 800 MN m-2 for Al–16 Si, Al–Si–Ni and Al–Si–Mg, respectively. The hardness values of the melt spun ribbons are higher than the as-cast rods from which the ribbons were produced by a factor ranging from 1.8–2.2 times. Tensile testing at room temperature shows that the load–elongation curves are linear with a change of slope occurring in some of the specimens. These curves also show serrations in the case of as-melt spun and the intermediately annealed Al–Si specimens, while no serration was observed in the fully annealed samples. No serration was observed in the Al–Si–Ni and Al–Si–Mg alloys. UTS values were 420, 270 and 100 MN m-2 for Al–16 Si, Al–Si–Ni and Al–Si–Mg, respectively. These values show that the rapid solidification process improved the tensile properties significantly in Al–16 Si and Al–Si–Ni alloys while no significant improvement can be detected for Al–Si–Mg alloy. A discussion is given on hardness relaxation and tensile testing results in terms of silicon precipitation. This revised version was published online in November 2006 with corrections to the Cover Date.     

Using direct hot-rolling approach to obtain dual-phase weathering steel Cu–P–Cr–Ni–Mo

A weathering steel Cu–P–Cr–Ni–Mo has been developed which exhibits special continuous cooling transformation characteristics which permit the desired dual-phase (DP) microstructure to be obtained by direct hot-rolling. Hot-rolling procedures to obtain DP microstructures have been designed based on the continuous cooling transformation diagram of weathering steel Cu–P–Cr–Ni–Mo. The results show that the microstructures of DP weathering steels Cu–P–Cr–Ni–Mo are characterized by an irregular distribution of island-shaped martensite–austenite in the matrix of polygonal ferrite grains. DP weathering steel Cu–P–Cr–Ni–Mo with favorable corrosion resistant property, weldability and mechanical properties, such as, high strain hardening exponent values, a lower ratio of yield to tensile strength, and higher strengths; and is obtained successfully by direct hot-rolling.     

Phase Diagrams of Pb-Free Solders and their Related Materials Systems

Replacing Pb–Sn with Pb-free solders is one of the most important issues in the electronic industry. Melting, dissolution, solidification and interfacial reactions are encountered in the soldering processes. Phase diagrams contain equilibrium phase information and are important for the understanding and prediction of phase transformation and reactive phase formation at the solder joints. This study reviews the available phase diagrams of the promising Pb-free solders, and their related materials systems. The solders are Sn–Ag, Sn–Cu, Sn–Ag–Cu, Sn–Zn, Sn–Bi, Sn–In and Sn–Sb. The materials systems are the solders with the Ag, Au, Cu, Ni substrates, such as Sn–Ag–Au, Sn–Ag–Ni, Sn–Cu–Au, and Sn–Cu–Ni ternary systems. For the Pb-free solders and their related ternary and quaternary systems, preliminary phase equilibria information is available; however, complete and reliable phase diagrams over the entire compositional and temperature ranges of soldering interests are lacking.     

Room Temperature Impedance and ac Conductivity Studies on Na-, K-Doped Tc-Enhanced High Tc Superconductors

Impedance and ac conductivity studies on parent Y–Ba–Cu–O and Na-, K-doped Tc-enhanced and other superconductors indicate that either the mechanism of ac conductivity or nature of charge carriers or both in the Na-, K-doped Y–Ba–Cu–O differ from the parent Y–Ba–Cu–O and other superconductors. This is indicated by the random walk type (RWT) model curve fittings.     

Effects of samarium on microstructure and mechanical properties of Mg–Y–Sm–Zr alloys during thermo-mechanical treatments

Microstructure and mechanical properties of Mg–4Y–xSm–0.5Zr (x = 1, 4, 8) alloys during thermo-mechanical treatments were investigated in this study. Mg–4Y–4Sm–0.5Zr alloy exhibits higher tensile strength but lower elongation than Mg–4Y–1Sm–0.5Zr alloy during the thermo-mechanical treatments. Large amount of intermetallic phases still remained at grain boundaries in Mg–4Y–8Sm–0.5Zr alloy after solution. These undissolved phases can strengthen the grain boundaries at temperatures higher than 573 K. But the room temperature mechanical properties of Mg–4Y–8Sm–0.5Zr alloy during the thermo-mechanical treatments were greatly weakened for the brittleness of these undissolved intermetallic phases.     

Tuning the stress induced martensitic formation in titanium alloys by alloy design

Two novel titanium alloys, Ti–10V–2Cr–3Al and Ti–10V–1Fe–3Al (wt%), have been designed, fabricated, and tested for their intended stress-induced martensitic (SIM) transformation behavior. The results show that for Ti–10V–1Fe–3Al the triggering stress for SIM transformation is independently affected by the β domain size and β phase stability, when the value of the molybdenum equivalent is higher than ~9. The triggering stress was well predicted using the equations derived separately for the commercial Ti–10V–2Fe–3Al alloy. For samples containing β with a lower molybdenum equivalence value, pre-existing thermal martensite is also present and this was found to have an obstructive effect on SIM transformation. In Ti–10V–2Cr–3Al, the low diffusion speed of Cr caused local gradients in the Cr level for many heat treatments leading even to martensite free zones near former β regions.     

The effect of preparation method on the activities of Pd–Fe–O<Emphasis Type="Italic">x</Emphasis>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts for CO oxidation

The Pd–Fe–Ox/Al₂O₃ catalysts were prepared by co-impregnation (co-Pd–Fe–Ox/Al₂O₃) and sol–gel method (sol–gel–Pd–Fe–Ox/Al₂O₃) and characterized by N₂ adsorption–desorption, X-ray diffraction (XRD), H₂-temperature programmed reduction (H₂-TPR), and X-ray photoelectron spectroscopy (XPS). The CO catalytic oxidation was investigated over Pd–Fe–Ox/Al₂O₃ catalysts prepared by different methods. The 100% conversion temperature (T ₁₀₀) over pre-reduced co-Pd–Fe–Ox/Al₂O₃ (co-Pd–Fe–Ox/Al₂O₃–R) and pre-reduced sol–gel–Pd–Fe–Ox/Al₂O₃ (sol–gel–Pd–Fe–Ox/Al₂O₃–R) is 90 and 25 °C when fed with the reaction mixture containing 1 vol.% CO and a balance of air, respectively. XRD results indicate that the sol–gel method is favorable for the high dispersion of PdO particles compared with co-impregnation method. H₂-TPR results suggest that the interaction between Pd and Fe is existent over both sol–gel–Pd–Fe–Ox/Al₂O₃ and co-Pd–Fe–Ox/Al₂O₃ catalysts, while the interaction in former catalyst is stronger than that in the latter. The XPS results show that the Pd species on the surface of both sol–gel–Pd–Fe–Ox/Al₂O₃–R and co-Pd–Fe–Ox/Al₂O₃–R catalysts are the mixture of oxide and metal state, leading to the high activity for CO oxidation. Furthermore, the different Pd²⁺/Pd⁰ ratio may be the reason for the different activity between sol–gel–Pd–Fe–Ox/Al₂O₃–R and reduced co-Pd–Fe–Ox/Al₂O₃–R catalysts.     

Wear characteristics of a new type austenitic stainless steel

In order to solve the problem of the poor wear resistance in conventional austenitic stainless steels, a new type austenitic stainless steel was designed based on Fe–Mn–Si–Cr–Ni shape memory alloys in this article. Studies on its wear resistance and wear mechanism have been carried out by comparison with that of AISI 321 stainless steel using friction wear tests, X-ray diffraction, scanning electron microscope. Results showed that the wear resistance of Fe–14Mn–5.5Si–12Cr–5Ni–0.10C alloy was better than that of AISI 321 stainless steel both in dry and oily friction conditions owing to the occurrence of the stress-induced γ → ε martensitic phase transformation during friction process. This article also compared the corrosion performance of the two stainless steels by testing the corrosion rate. Results showed that the corrosion rate of Fe–14Mn–5.5Si–12Cr–5Ni–0.10C alloy was notably lower in NaOH solution and higher in NaCl solution than that of AISI 321 stainless steel.     

Influence of granulated blast furnace slag on the reaction,structure and properties of fly ash based geopolymer

Ground granulated blast furnace slag (GBFS) has been used to alter the geopolymerisation behaviour of fly ash. The influence of varying amount of GBFS (5–50%) on the reaction kinetics has been studied using isothermal conduction calorimetry. It was observed that the reaction at 27 °C is dominated by the GBFS activation, whereas the reaction at 60 °C is due to combined interaction of fly ash and GBFS. The reaction product of geopolymerisation has been characterised using X-ray diffraction and scanning electron microscopy–X-ray microanalysis. Alumino–silicate–hydrate (A–S–H) and calcium–silicate–hydrate (C–S–H) gels with varying Si/Al and Ca/Si ratio are found to be the main reaction products. Coexistence of A–S–H and C–S–H gel further indicates the interaction of fly ash and GBFS during geopolymerisation. Attempt has been made to relate the microstructure with the properties of the geopolymers.     

TLP bonding of SiCp/2618Al composites using mixed Al–Ag–Cu system powders as interlayers

Mixed Al–Ag–Cu and Al–Ag–Cu–Ti powders were used as interlayers for transient liquid phase diffusion bonding (TLP bonding) of SiC particulate reinforced 2618 aluminum alloy matrix composite (SiCp/2618Al MMC). The results show that by using mixed Al–Ag–Cu powder with the eutectic composition as an interlayer, SiCp/2618Al MMC can be TLP bonded at 540 °C, however, the joining layer is porous. Adding a certain amount of titanium into the Al–Ag–Cu interlayer, the TLP bonding quality can be improved. The titanium added into the Al–Ag–Cu interlayer has an effect of shortening the solidification time of the joining layer, thus decreasing SiC particles from the parent materials entering into the joining layer. The joints bonded using Al–Ag–Cu–Ti interlayers have a maximum shear strength of 101 MPa when 2.1% titanium is added.     

Wettability of NiAl by a liquid Ni–Si–B alloy

An investigation of the wettability of the intermetallic compound NiAl by a liquid Ni–4.5 wt% Si–3.2 wt% B filler metal is presented in this paper. Dynamic observations of spreading of Ni–Si–B droplets, conducted using hot-stage light microscopy, are correlated with post-cooling microscopy and analysis. The paper examines the influence of the oxide layer on the NiAl substrates, on the progression of spreading of the Ni–Si–B liquid. Termination of spreading of the Ni–Si–B droplets by the onset of isothermal solidification at the spreading front is considered. Spreading of the Ni–Si–B droplets was found to be rapid until the onset of isothermal solidification at the spreading front. However, once isothermal solidification commenced, negligible further spreading was observed. The Ni–Si–B filler metal was observed to spread by undermining of the substrate oxide. However, a marked reaction occurred between the substrate oxide and the Ni–Si–B filler metal. This reaction served to remove the substrate oxide layer. The paper contrasts the mechanisms of substrate oxide undermining and isothermal solidification of liquid Ni–Si–B droplets on NiAl with those occurring during the spreading of the same liquid on pure nickel and Ni–Cr alloys. This revised version was published online in November 2006 with corrections to the Cover Date.     

Microstructure,tensile properties,and creep behavior of high-pressure die-cast Mg–4Al–4RE–0.4Mn (RE = La,Ce) alloys

High-pressure die-cast (HPDC) Mg–4Al–4RE–0.4Mn (RE = La, Ce) magnesium alloys were prepared and their microstructures, tensile properties, and creep behavior have been investigated in detail. The results show that two binary Al–Ce phases, Al₁₁Ce₃ and Al₂Ce, are formed mainly along grain boundaries in Mg–4Al–4Ce–0.4Mn alloy, while the phase composition of Mg–4Al–4La–0.4Mn alloy contains only α-Mg and Al₁₁La₃. The Al₁₁La₃ phase comprises large coverage of the grain boundary region and complicated morphologies. Compared with Al₁₁Ce₃ phase, the higher volume fraction and better thermal stability of Al₁₁La₃ have resulted in better-fortified grain boundaries of the Mg–4Al–4La–0.4Mn alloy. Thus higher tensile strength and creep resistance could be obtained in Mg–4Al–4La–0.4Mn alloy in comparison with that of Mg–4Al–4Ce–0.4Mn. Results of the theoretical calculation that the stability of Al₁₁La₃ is the highest among four Al–RE intermetallic compounds supports the experimental results further.     

Evaluation of Cobalt–Carbon and Palladium–Carbon Eutectic Point Cells for Thermocouple Calibration

Two cobalt–carbon (Co–C) eutectic point (1,324 °C) cells and one palladium–carbon (Pd–C) eutectic point (1,492 °C) cell were constructed for thermocouple calibration. The lengths of the Co–C and Pd–C cells were 297 mm, 140 mm, and 140 mm, respectively. The melting and freezing plateaux at the Co–C and Pd–C eutectic points were observed using Pt/Pd thermocouples. The repeatability of the plateau, the effect of the surrounding temperature, and the temperature profile in the cell were measured, and the heat flux effect along the thermometer well was evaluated. When the plateaux of Co–C (297 mm height), Co–C (140 mm height), and Pd–C cells, were measured three times, seven times, and six times, respectively, the standard deviations of the melting points were 0.1 μV, 0.1 μV, and 0.4 μV, respectively. According to the temperature profiles along the thermometer well during the melting plateaux, it was found that the Pt/Pd thermocouple should be inserted at least 9.5 cm, 5 cm, and 6 cm below the surface of the eutectic alloys in the Co–C (297 mm height), Co–C (140 mm height), and Pd–C cells with the furnace set-point 16 °C above the melting point.     

Reliability studies of Sn–9Zn/Cu and Sn–9Zn–0.3Ag/Cu soldered joints with aging treatment

In this study, the interfacial reactions and joint reliabilities of Sn–9Zn/Cu and Sn–9Zn–0.3Ag/Cu were investigated during isothermal aging at 150 °C for aging times of up to 1,000 h. Cu₅Zn₈ IMCs layer is formed at the as-soldered Sn–9Zn/Cu interface. Adding 0.3wt.% Ag results in the adsorption of AgZn₃ on the Cu₅Zn₈ IMCs layer. The as-soldered Sn–9Zn/Cu and Sn–9Zn–0.3Ag/Cu joints have sufficient pull strength. The thickness of the IMCs layer formed at the interface of Sn–9Zn/Cu and Sn–9Zn–0.3Ag/Cu both increase with increasing aging time. Correspondingly, both the pull forces of the Sn–9Zn and Sn–9Zn–0.3Ag soldered joints gradually decrease as the aging time prolonged. However, the thickness of the IMCs layer of Sn–9Zn–0.3Ag/Cu increases much slower than that of Sn–9Zn/Cu and the pull force of Sn–9Zn–0.3Ag soldered joint decreases much slower than that of Sn–9Zn soldered joint. After aging for 1,000 h, some Cu–Sn IMCs form between the Cu₅Zn₈ IMC and the Cu substrate, many voids form at the interface between the Cu₅Zn₈ layer and solder alloy, and some cracks form in the Cu₅Zn₈ IMCs layer of Sn–9Zn/Cu. The pull force Sn–9Zn soldered joint decreases by 53.1% compared to the pull force measured after as-soldered. Fracture of Sn–9Zn/Cu occurred on the IMCs layer on the whole and the fracture micrograph implies a brittle fracture. While the pull force of Sn–9Zn–0.3Ag soldered joint decreases by 51.7% after aging at 150 °C for 1,000 h. The fracture mode of Sn–9Zn–0.3Ag soldered joint is partially brittle at the IMCs layer, and partially ductile at the outer ring of the solder.