Ultrasonic brazing of Zr-based bulk metallic glasses (Zr-BMG) and 1060-Al alloy dissimilar was realized by using a Zn-3Al filler metal. A firm metallurgical bonding was obtained at the dissimilar joint interfaces. In the initial stage, a single-phased Zn50Al25Zr25 IMC layer was found on the Zr-BMG surface. Prolonging the brazing time, the excessive growth of the Zn50Al25Zr25 IMC layer inhibited the diffusion of Al from brazing seam to the reaction front, which induced the composition fluctuation of Al and thus the formation of Zn50Al25Zr25/Zn-rich phase composite layers on the Zr-BMG surface. The shear strength of joints was affected by the interfacial reaction phase, and the highest value obtained was 68 MPa.

Low-temperature bonding of 7075 Al alloy with metal foam/Sn composite solder was achieved under ultrasound conditions. The effects of metal foam compositions and soldering temperatures on the microstructure were investigated, together with the shear strength of joints. Results indicated that employing Ni-Cu alloy foam could accelerate the reactive rate of solder layers compared with Ni foam. Discontinuous networks composed of fine particles could be observed in the joints produced with composite solders, which were dense with adding Cu. The increase in dispersed particles was attributed to the excessive nucleation and loose structure of the (Ni, Cu)(3)Sn-4 phases. Meanwhile, the increased dispersed particles also contributed to inhibiting the growth of Al3Ni phases, thereby regulating the microstructure of solder layers. The above results induced a significant improvement in the mechanical properties of joints. The highest shear strength of joints was 78.3 MPa, which was more substantial than the generally reported results of Al alloys joints soldered at low temperature.

Ultrasound-assisted fluxless brazing of Zr based Bulk metallic glasses (Zr-BMG) joint using Zn-3Al filler metal was performed in this study. The effect of ultrasonic vibration time on the microstructure and mechanical properties of Zr-BMG joints were investigated. Results showed that excellent metallurgic bonding could be obtained in ultrasonically brazed Zr-BMG joints. The interfacial reaction between liquid Zn-3Al filler metal and Zr-BMG substrate showed a mutation characteristic, which could be distinguished into incubation period and acceleration period. In the incubation period, Zn50Zr25Al25 intermetallic compounds (IMCs) with small ellipsoidal shape were slowly formed and distributed randomly on Zr-BMG surface. However, in the acceleration period, Zn50Zr25Al25 ellipsoids developed rapidly into a wavy-structured IMCs layer with a thickness of 17 pm, which was comprised of alternate Zn50Zr25Al25 and Zn22Zr sublayers. The microstructure evolution of Zn-3Al/ZrBMG interface was ascribed to the combined effects of acoustic cavitations and Al element controlled interfacial metallurgic reactions. The average shear strength of joint was increased firstly then decreased slightly with increasing ultrasonic vibration time, and a highest strength value of approximately 100 MPa was obtained for joints brazed for 96 s. The shearing failure was inclined to occur at the Zn-3Al/Zr-BMG interface then transferred into the interfacial IMCs layer with increasing ultrasonic vibration time.

In this study, Cu alloy joints were fabricated with a Ni-foam reinforced Sn-based composite solder with the assistance of ultrasonic vibration. Effects of ultrasonic soldering time on the microstructure and mechanical properties of Cu/Ni-Sn/Cu joints were investigated. Results showed that exceptional metallurgic bonding could be acquired with the assistance of ultrasonic vibration using a self-developed Ni-foam/Sn composite solder. For joint soldered for 5 s, a (Cu,Ni)(6)Sn-5 intermetallic compound (IMC) layer was formed on the Cu substrate surface, Ni skeletons distributed randomly in the soldering seam and a serrated (Ni,Cu)(3)Sn-4 IMC layer was formed on the Ni skeleton surface. Increasing the soldering time to 20 s, the (Ni,Cu)(3)Sn-4 IMC layer grew significantly and exhibited a loose porous structure on the Ni skeleton surface. Further increase the soldering time to 30 s, Ni skeletons were largely dissolved in the Sn base solder, and micro-sized (Ni,Cu)(3)Sn-4 particles were formed and dispersed homogeneously in the soldering seam. The formation of (Ni,Cu)(3)Sn-4 particles was mainly ascribed to acoustic cavitations induced erosion and grain refining effects. The joint soldered for 30 s exhibited the highest shear strength of 64.9 +/- 3.3 MPa, and the shearing failure mainly occurred at the soldering seam/Cu substrate interface.

Ultrasound-assisted dipping was performed to fabricate a Sn coating layer on the Al2O3 ceramic, then the as-coated Al2O3 ceramics were ultrasonically soldered with Ni-foam reinforced Sn and Sn-9Zn composite solders, respectively. Effects of ultrasonic soldering time on the microstructure and mechanical properties of joints were investigated. A pure Sn metallization layer which exhibited excellent metallurgic bonding with Al2O3 ceramic was fabricated by ultrasonic dipping for more than 40s. For Al2O3 joints soldered with composite solders for 4s, Ni skeletons distributed irregularly in the soldering seam and some pores existed in the base solders. A thin Ni3Sn4 intermetallic compound (IMC) layer was formed at the Sn/Ni interface while no reaction phase was found at the Sn-9Zn/Ni interface. Increasing the ultrasonic soldering time to 12s the Ni skeletons were compressed into a strip type. In the Al2O3/Ni-Sn/Al2O3 joint, the gaps among Ni skeletons were filled with Ni3Sn4 layers with some reaction cavities trapped in them. However, in the Al2O3/Ni-Sn9Zn/Al2O3 joint, the Ni skeletons gaps were mainly filled with (Ni,Zn)3Sn4 bulks with some (Ni,Zn)3Sn4 particles dispersed between them. The Al2O3/Ni-Sn9Zn/Al2O3 joint soldered for 12s exhibited the highest shear strength of 53.45MPa with the joint shear failed at the interface of filler metal layer and Al2O3 ceramic.

Ultrasound-assisted dipping of ZrO2 ceramics into molten Sn solder was performed to realize the low-temperature joining of ZrO2 ceramics in this study. Scanning electron microscopy with energy dispersive spectrometer, X-ray diffraction and X-ray photoelectron spectroscopy were employed to study the effects of ultrasonic vibration on the microstructure of Sn/ZrO2 interface, and to elucidate the joining mechanism between Sn coating layer and ZrO2 ceramic. Results showed that, after ultrasonically dipping in molten Sn for 1200s, a pure Sn solder layer with a thickness of approximately 8–9µm was coated on the ZrO2 surface. The Sn coating layer exhibited excellent metallurgic bonding with ZrO2 ceramic. A nano-sized ZrSnO4 ternary phase, which was beneficial to the smooth transition of the lattice from Sn solder to ZrO2 ceramic, was formed at the Sn/ZrO2 interface. The formation of ZrSnO4 interlayer was ascribed to the acoustic cavitation induced high-temperature reaction of Sn, O and ZrO2 at the molten Sn/ZrO2 ceramic interface. The tested average shear strength of ZrO2/Sn/ZrO2 joints was approximately 32MPa, and the shearing failure mainly took place within the Sn solder layer.

Ultrasound-assisted fluxless brazing of Cu/Zn-Al/Cu joint was performed in this study. Evolutions of the microstructure and mechanical properties of Cu alloy joints ultrasonically brazed with Zn-3Al and Zn-14Al filler metals were investigated. Results showed that excellent metallurgic bonding between the Zn-3Al filler metal and the Cu substrate could be obtained by brazing at 450 degrees C for 4 s, accompanied with the creation of thick CuZn5 and Cu5Zn8 intermetallic compounds (IMCs) layers on the Zn-3Al/Cu interface. Compared with the Zn-3Al/Cu system, much longer ultrasonic vibration time was needed for the completely wetting of the Zn-14Al filler metal on the Cu substrate, but the thick Cu5Zn8 IMC layer was replaced with a thin Cu based diffusion layer on the Zn-14Al/Cu interface. The wetting of Zn-3Al filler metal on the Cu substrate was attributed to the combined effects of ultrasound-induced cavitation and Cu/Zn metallurgic reaction, while the wetting of Zn-14Al filler metal on the Cu substrate was mainly attributed to the ultrasound-induced cavitation effects. The shear strength of the Cu/Zn-3Al/Cu and Cu/Zn-14Al/Cu joint was 37.9 MPa and 92.1 MPa, respectively; the shearing failure took place within the Cu interfacial layer in all case. (C) 2015 Elsevier Ltd. All rights reserved.

This paper has introduced the status of retired home appliances reverse logistics industry in China, elaborated the key technologies which need to be focused on to enhance the development level of reverse logistics industry, including product life cycle information tracing technology, retired product quality detection technology, inventory optimization control technology, to build efficient reverse logistics information system and lead the industry to develop in the direction of informationization and standardization.

The growth behavior of Cu6Sn5 grains formed at an Sn3.5Ag/Cu interface was investigated. During soldering, Cu6Sn5 grains formed at the interface, showing a flattened ovoid shape. During solidification, Cu precipitated from molten solder in the form of Cu6Sn5, forming faceted surfaces on existing interfacial grains. The interfacial Cu6Sn5 morphology was unrelated to its crystal orientation, which was primarily dependent on reaction temperature. A reaction temperature of 240°C led to an increase in (002) growth and a decrease in (101) growth with time. However, the (002) plane peak was not detected in the interfacial grains formed at a higher reaction temperature (280°C).

Interfacial reactions in a SnAg3.0Cu0.5/Cu lap joint for naked and encompassed specimens were investigated contrastively under electric current stressing. After applying a constant direct current at 6.5 A for 144 h, an abnormal accumulation of bulk Cu6Sn5 intermetallic compound was found at the cathode for the naked specimen. But normal polarization phenomenon arose for the encompassed specimen at the same current density for 504 h. The abnormal accumulation phenomenon was explained by the mechanism that thermomigration and stress migration induced by temperature gradient dominated the migration process. A three-dimensional joint simulation model was designed to demonstrate how current crowding and temperature gradient can enhance the local atomic flux.

The morphologies of Cu6Sn5 grains formed at the interface between Sn-3.5Ag (wt.% unless otherwise specified) and Cu substrates were studied in this work. Reflow experiments were performed for 60 s at peak temperatures of 513 K, 533 K, 543 K, and 553 K. Two morphologies of interfacial Cu6Sn5 grains were observed in wetting reactions: prism type, above 543 K, and scallop type, below 533 K. During aging, the two morphologies gradually transitioned to layer type. These three morphologies could be transformed into each other as long as the corresponding condition changed. The morphology transition of Cu6Sn5 in the wetting reaction was explained by the change in Jackson's parameter with temperature. In addition, the effect of the Cu content in molten solder on interfacial Cu6Sn5 grains was examined. Significant differences in shear strength were observed for solder joints with different interfacial Cu6Sn5 morphologies in the case of a lower shear height. Joint strength is discussed in terms of the microstructure of the solder matrix and the morphology of interfacial Cu6Sn5 grains.

A novel lead-free bumping technique using an alternating electromagnetic field (AEF) was investigated. Lead-free solder bumps reflowed onto copper pads through AEF have been achieved. A comparison was conducted between the microstructures of the lead-free solder joints formed by the conventional thermal reflow and AEF reflow. Keeping the substrate temperature lower than that of the solder bumps, AEF reflow successfully created metallurgical bonding between the lead-free solders and metallizations through an interfacial intermetallic compound (IMC). The AEF reflow could be finished in several seconds, much faster than the conventional hot-air reflow. Considering the morphology of the interfacial Cu6Sn5 IMC, a shorter heating time above the melting point would be a better choice for solder joint reliability. The results show that AEF reflow is a promising localized heating soldering technique in electronic packaging.

Purpose - The aim of the paper is to control the height and shape of solder interconnects employed in electronic packaging applications by an induction heating reflow method, which can achieve the solder bumping and interconnecting process in a simple way.Design/methodology/approach - Through the application of a designed induction heating system, a new methodology was forced to exhibit its certain qualities of forming and geometry controlling in the process. The corresponding temperature distribution has been analyzed based on a discussion of skin effects in metal spheres. The local melt phenomenon is observed and identified via the microstructures taken by scanning electron microscope (SEM).Findings - In this work, barrel-shaped solder joints with high heights and hourglass-shaped solder joints can be obtained, which is good for improving the solder joint lifetime. The mechanism of solder joint height and shape control, which can be explained by the local melt phenomenon, is discussed and demonstrated via the different morphologies of Ag3Sn intermetallic compound (IMC).Originality/value - The findings of this paper will help the understanding of the whole solder interconnecting process during induction heating reflow and the effects of electromagnetic fields on solder joint shape control.

The effect of the anode and cathode on the electrochemical corrosion behavior of lead-free Sn-Ag-Cu and Sn-Ag-Cu-Bi solder joints in deionized water was investigated. Corrosion studies indicate that SnO crystals were generated on the surfaces of all lead-free solder joints. The constituents of the lead-free solder alloys, such as Ag, Cu, and Bi, did not affect the corrosion reaction significantly. In contrast to lead-free solders, PbO x was formed on the surface of the traditional 63Sn-37Pb solder joint in deionized water. A cathode, such as Au or Cu, was necessary for the electrochemical corrosion reaction of solders to occur. The corrosion reaction rate decreased with reduction of the cathode area. The formation mechanism of SnO crystals was essentially a galvanic cell reaction. The anodic reaction of Sn in the lead-free solder joints occurred through solvation by water molecules to form hydrated cations. In the cathodic reaction, oxygen dissolved in the deionized water captures electrons and is deoxidized to hydroxyl at the Au or Cu cathode. By diffusion, the anodic reaction product Sn2+ and the cathodic reaction product OH− meet to form Sn(OH)2, some of which can dehydrate to form more stable SnO·xH2O crystals on the surface of the solder joints. In addition, thermodynamic analysis confirms that the Sn corrosion reaction could occur spontaneously.

PurposeThe purpose of this paper is to describe a local melt process of solder bumping employed in electronic packaging applications by an induction heating reflow method, for a combined numerical and experimental study involving a temperature measurement using an infrared thermometer during the reflow process and microstructural observations after reflow, which can be used to control the height and shape of solder interconnects.Design/methodology/approachIn the induction heating reflow process, the temperature distribution within the solder ball during the heating phase is of prime importance for the success of the process and the geometry control quality of final joints. This paper investigates the local melt process of solder balls reflowed onto Cu/Ni/Au pads, and focuses on the effect of the inductive heat on the thermal distribution during the melting process. A finite‐element model is applied to simulate the thermal field in a solder bump during the induction heating period in a reflow process. The effects of the coil current and the electromagnetic frequency on the thermal performance are investigated by using the validated thermal model. The local melt phenomenon in the solder joint is observed and identified by the microstructures taken using scanning electron microscopy.FindingsIn this paper, the numerical results match the experimental results quite well to validate the finite element modeling model. The local melt phenomenon predicted by simulation, and verified by experiments, is demonstrated to be capable of controlling the solder joint shape. Several parametric studies are carried out to understand the effects of different frequencies during assembly, and to suggest that a higher frequency is easier to get a greater temperature gradient, thus a more obvious local melt phenomenon, which is good for achieving the geometry control for solder joints.Originality/valueThe findings of this paper will help to understand the detailed solder bumping process during induction heating reflow and the effects of electromagnetic field frequency on solder joint shape controlling.

Ball grid array (BGA) solder interconnecting is one of the key technologies in electronic packaging and assembly. Legislation of lead-free process has made the application of lead-free solder become wider in electronic products. Compared to the lead-tin solder, the relatively higher melting points of most lead-free solders call for a higher reflow temperature. Thus conventional integral-heating process at an elevated temperature would induce severe warpage of components and substrates and reduce the in-service reliability of solder joint. In this dissertation, a new concept of selective heating was proposed to address the reliability issues of integral heating process in lead-free BGA interconnection. By using this concept a novel BGA interconnection technology, named as induction heating reflow, is developed. The significance of this research lies in the potentials of acceleration of the lead-free process in electronic productions, promotion in the applicability of lead-free BGA packaging, and the enhancement of the reliability of BGA components. Compared with conventional hot-air reflow, the thermal characteristics of liquid-solid interfacial reaction and solid-solid interfacial reaction, the formation of interfacial intermetallic compound (IMC) and their growth kinetics were all studied. The result shows that with the increasing of temperature, Cu 6 Sn 5 grains change from scallop-type into prism-type. In the solid-state aging process the evolution of interfacial IMC is merely controlled by the diffusion of Cu atoms from pad, and its thickness grows linearly with the square root of aging time.

Due to the legislations and environment concerns, the applying of lead free technology is the trend in electronic manufacturing industry. Roadmap of Guangdong’s lead free technology was established within the framework of industrial roadmapping technology. Reliability is one of the most important features in lead free electronic manufacturing. The corresponding roadmap was formulated in accordingly. This paper presents the methodologies which were employed in the roadmapping of reliability aspect in Guangdong’s lead free technology. The employed methodologies include Delphi’s method, Brain Storming method and SWOT analytic method. The roadblocks were estimated and the necessary R&D activities were forecasted finally.