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The increasing utilization of Al‐matrix composites in electronics packaging industry raises demands of solder materials with melting temperature at 400‐500°C. The purpose of this paper is to determine the thermal properties of two Ag‐Cu‐Sb alloys with the composition close to two eutectic points, and two Au‐Ag‐Ge alloys along the eutectic line, to observe the microstructures and to investigate the wettability of the alloys, and to evaluate the possibility for them to be used as medium temperature solders.

Four candidates of solder alloys in the Au‐Ag‐Ge (AAG1, AAG2) and Ag‐Cu‐Sb systems (ACS1, ACS2) were studied to reveal microstructures, melting points, wettabilities, and the interfaces between the solder and Al/SiC substrate coated with Au and Ni.

The paper finds that the ACS1 and ACS2 alloys possess small temperature gaps between solidus and liquidus: 422.9°C/429.2°C and 483.3°C/488.1°C, respectively. For two AAG alloys, the temperature ranges between solidus and liquidus are larger than 40°C. The wettability tests showed that two ACSs and AAG1 alloys have good wettability to the substrate. Similarly, except ACS2 alloy, the other alloys exhibit good adhesion with the substrate.

The paper shows that the ACS1 alloy and the AAG1 alloy could be used as the optimum solder materials for 400‐500°C owing to the good wettability and proper melting point.

The purpose of this paper is to evaluate the influence of solder powders sizes applied in soldering materials used for Package-on-Package (PoP) system manufacture as well as other factors on reliability and mechanical strength of created solder joints in three-dimensional (3D) PoP structures.

The design of experiments based on the Genichi Taguchi method were used in the investigation. The main factors covered different printed circuit board (PCB) coatings, soldering materials with solder powders sizes from Types 3 to 7 and soldering profiles. The reliability of 3D PoP structures was determined by measurements of resistance of daisy-chain solder joints systems during thermal shocks (TS) cycles. The mechanical strength of solder joints in 3D PoP structures was determined by measurements of a shear force of “Top” layer of 3D structures at T0 and after 1,500 TS. The ANOVA was used for results assessment.

The size of solder powders applied in soldering materials had small (10 per cent) influence on mechanical strength of solder joints in 3D PoP structures. Small size of solder powder had positive effect on solder joints reliability in 3D PoP structures. Especially important was the selection of solder paste for “Bottom” layer of 3D PoP system (influence 17 per cent). Incorrect soldering profile (influence 46 per cent) or wrong selected PCB coating (influence 35 per cent) can very easily reduce the positive impact of soldering materials on solder joints reliability. It was stated that as low as possible soldering profile and organic solderability preservative (OSP) coating in the case of single-sided PCB are the best for 3D PoP structures due to their reliability.

This paper explains how different sizes of solder powders used nowadays in solder pastes influence on reliability and mechanical strength of the solder joints in 3D PoP structures. The contribution, in numerical values, of soldering materials, soldering profile and PCB coating on 3D PoP structures solder joints reliability as well as recommendations improving reliability of 3D PoP structures solder joints were presented.

The purpose of this paper is to assess the effect of different temperature cycling profiles on the reliability of lead‐free 388 plastic ball grid array (PBGA) packages and to deeply understand crack initiation and propagation.

Temperature cycling of Sn‐3.8Ag‐0.7Cu PBGA packages was carried out at two temperature profiles, the first ranging between −55°C and 100°C (TC1) and the second between 0°C and 100°C (TC2). Crack initiation and propagation was analyzed periodically and totally 7,000 cycles were run for TC1 and 14,500 for TC2. Finite element modeling (FEM), for the analysis of strain and stress, was used to corroborate the experimental results.

The paper finds that TC1 had a characteristic life of 5,415 cycles and TC2 of 14,094 cycles, resulting in an acceleration factor of 2.6 between both profiles. Cracks were first visible for TC1, after 2,500 cycles, and only after 4,000 cycles for TC2. The crack propagation rate was faster for TC1 compared to TC2, and faster at the package side compared to the substrate side. The difference in crack propagation rate between the package side and substrate side was much larger for TC1 compared to TC2. Cracks developed first at the package side, and were also larger compared to the substrate side. The Cu tracks on the substrate side affected the crack propagation sites and behaved as SMD. All cracks propagated through the solder and crack propagation was mainly intergranular. Crack propagation was very random and did not follow the distance to neutral point (DNP) theory. FEM corroborated the experimental results, showing both the same critical location of highest creep strain and the independence of DNP.

Such extensive work on the reliability assessment of Pb‐free 388 PBGA packages has never been performed. This work also corroborates the results from other studies showing the difference in behavior between Pb‐free and Pb‐containing alloys.

This study aims to provide guidance for the reliability of electronic packaging. The reliability of solder joints at extremely temperature thermal shock is critical for electronic equipment operating in the field of deep space exploration. In this study, the Sn3.0Ag0.5Cu (SAC305)/Cu solder joints were prepared and thermally shocked with temperatures ranging from −110°C to 110°C, to investigate the effects of extreme temperature thermal shock on the microstructural evolution and property deterioration of the solder joints.

The interfacial intermetallic compound (IMC) stress gradient was calculated through thermal stress theory, mechanism of voids/cracks initiation was clarified, and prediction of the service life was analyzed with the energy-based model.

It is found that the Ag₃Sn, IMC and cracks/voids had evolved significantly with the increase in the cycle period. The microstructure of the IMC changed from short rod-like morphology to scallop shape, the voids in the Cu₃Sn IMC layer continued to increase and integrate, forming larger diameter voids, etc. In addition, the shear strength of SAC305/Cu solder joints decreased gradually with the increase in thermal shock cycles, the fracture mode changes from ductile fracture mode to ductile-brittle mixed fracture mode after 500 cycles. The characteristic lifetime of the SAC305/Cu solder joints under the action of extreme thermal shock is about 1427.86 cycles.

This work provides guidance for the reliability of the solder joints at extremely temperature thermal shock.

The purpose of this paper is to study the rheological behaviours of lead‐free solder pastes used for flip‐chip assembly applications and to correlate rheological behaviours with the printing performance.

A range of rheological characterization techniques including viscosity, yield stress, oscillatory and creep‐recovery tests were carried out to investigate the rheological properties and behaviours of four different solder paste formulations based on no‐clean flux composition, with different alloy composition, metal content and particle size. A series of printing tests were also conducted to correlate printing performance.

The results show that in the viscosity test, all solder pastes exhibited a shear thinning behaviour in nature with different highest maximum viscosity. The yield stress test has been used to study the effect of temperature on the flow behaviour of solder pastes. A decrease in yield stress value with temperature was observed. The results from the oscillatory test were used to study the solid‐ and liquid‐like behaviours of solder pastes. Creep‐recovery testing showed that the solder paste with smaller particle size exhibited less recovery.

More extensive research is needed to simulate the paste‐roll, aperture‐filling and aperture‐emptying stages of the stencil printing process using rheological test methods.

Implementation of these rheological characterization procedures in product development, process optimization and quality control can contribute significantly to reducing defects in the assembly of flip‐chip devices and subsequently increasing the production yield.

The paper shows how the viscosity, yield stress, oscillatory and creep‐recovery test methods can be successfully used to characterize the flow behaviour of solder pastes and also to predict their performance during the stencil printing process.

The resource parameter in life cycle assessments is used to evaluate present efficiency in resource recovery from printed circuit boards. It is shown that only a fraction of the resources held by PCBs are recovered today, and that in order to improve resource recovery a good knowledge of the chemical content of electronic components is necessary. Analytical techniques specially suited to the analysis of electronic components are discussed, and it is concluded that critical resources are indeed concentrated in certain electronic components. Finally, an automated system for removing components from the boards and for recognising and sorting the components is discussed.

This study aims to review the effect of copper percentage in Sn-based solder alloys (Sn-xCu, x = 0–5 Wt.%) on intermetallic compound (IMC) formation and growth after laser soldering.

This study reviews the interfacial reactions at the solder joint interface, solder joint morphology and the theory on characterizing the formation and growth of IMCs. In addition, the effects of alloying and strengthening mechanism, including wettability, melting and mechanical properties are discussed.

This paper presents a comprehensive overview of the composition of tin-copper (Sn-Cu) solders with a potential to enhance their microstructure, mechanical characteristics and wettability by varying the Cu percentage. The study found that the best Cu content in the Sn-xCu solder alloy was 0.6–0.7 Wt.%; this composition provided high shear strength, vibration fracture life value and ideal IMC thickness. A method of solder alloy preparation was also found through powder metallurgy and laser soldering to improve the solder joint reliability.

This study focuses on interfacial reactions at the solder joint interface, solder joint morphology, modelling simulation of joint strength and the theory on characterising the formation and growth of IMC.

The paper comprehensively summarises the useful findings of the Sn-Cu series. This information will be important for future trends in laser soldering on solder joint formation.

The purpose of this paper is to produce and investigate the interfacial reaction between Sn‐3.0Ag‐0.5Cu (SAC305) thin films and Cu substrates by solder reflow at various temperatures and times.

SAC305 thin films were deposited on copper substrates using a thermal evaporation technique. The as‐deposited SAC305/Cu was then reflowed on a hot plate at temperatures of 230, 240, 250 and 260°C for 30 s. In addition, solder reflow was conducted at a constant temperature of 230°C for 5, 10, 15 and 20 s. The microstructure, phase and thickness of the intermetallic compounds (IMCs) formed were determined after cross‐sectional metallographic preparation.

Cu₆Sn₅ and Cu₃Sn were observed at the as‐reflowed SAC305/Cu interfacial region. The IMC thicknesses increased with the higher reflow temperature and longer reflow times.

Up to now, studies on the thin film characteristics of SAC305 lead‐free solder have been very limited. Thus, this paper presents the deposition of SAC305 thin film by a thermal evaporation technique and its characteristics after solder reflow.

The purpose of this paper is to investigate the influence of silver nanoparticle additions on the wetting properties of Sn‐Ag‐Cu (SAC) solder paste. In this investigation, the basic solder paste contained 85 wt.% of commercial Sn 96.5 Ag 3 Cu 0.5 powder (with the particle sizes in the range of 20‐38 μm) and 15 wt.% of self‐prepared middle activated rosin flux. To this paste was added 0.5, 1, 2 and 4 wt.% of self‐prepared silver nano‐powders of different grain sizes (from 9 to 138 nm). After the pastes had stabilized, their wetting properties were tested. The main goal of these investigations was to improve the wetting properties of SAC solder paste and to find correlations between the results of the wetting of solder paste with nanoparticles on the copper substrate with the microstructure of the solder joints.

The following methods were applied for the wetting solder paste investigation: spreading on the copper substrate, contact angle measurement on the copper and wetting on a FR‐4 laminate double sided with an 18‐μm thick copper foil. The investigations were performed at temperatures of 220, 230, 240 and 250°C. Cross‐sectioning was performed on the solder paste after reflow on the copper substrate. For the microstructural analysis of the “nano” modified solder joints obtained at 250°C, standard metallographic procedures were applied. Changes in the microstructure, the thickness of the inter‐metallic compounds (IMCs) and their chemical compositions were observed by means of scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS).

As expected, a higher silver nanoparticle addition to the SAC solder paste resulted in better wetting properties on copper. The results indicated the possibility of an improvement of the reflow soldering process by using SAC solder paste with silver nanoparticles and by lowering its soldering temperature. An improvement was also observed in the wettability with a decrease in the silver nanoparticle grain size. Also, the wettability proceeded at a lower temperature (20°C lower) than that for the SAC paste, without the nano‐additives. For the 4 per cent silver nanoparticle addition, Ag₃Sn star‐like IMCs were also found, which grew with the lowering of the silver nanoparticle grain size.

Further studies are necessary for confirmation of the practical application, especially of the mechanical properties, as well as the reliability properties of the solder joints, for the chosen solder paste with silver nanoparticles.

Taking into account the wetting data, the best results of the “nano” SAC solder pastes were obtained for the highest addition of the silver nanoparticles. It was found that the spreading on copper was higher and the contact angles were lower for the SAC solder paste with 4 per cent (by wt.) of 138‐nm grain size silver nanoparticles. A comparison of SAC solder pastes with a 4 per cent silver nanoparticle addition but of a different grain size (138‐9 nm), suggested a further improvement in wetting properties with lowering of the silver nanoparticle grain size. The results suggested the possibility of an improvement in the reflow soldering process by using SAC solder paste with silver nanoparticles and by lowering its soldering temperature.

Spreading, wetting and contact angle measurement methods were used for the wetting determination of the SAC solder paste with the silver nanoparticles on copper under the same temperature conditions. Also, the microstructure of the solder joints obtained at 250°C was determined with the use of SEM and EDS methods. The results obtained made it possible to draw conclusions regarding the correlation between the output of the wetting results and the amount and the grain size of the added silver nanoparticles, and also the microstructure and thickness of the IMCs of the “nano” solder joints.

Impressions gained from two visits to Japan, discussing with representatives of industry and academe the current status regarding the implementation of lead‐free technology, are presented. Driven by the commercial rewards of lead‐free goods, Japan appears to have more clearly articulated targets for the removal of lead, in advance of the expected timescales in EU legislation. Various strategies for combating problems associated with the higher melting point of lead‐free solder alloys have been investigated. Design and development generally involve a broader approach than in Europe, involving stress analysis, materials properties and life prediction to underpin empirical data obtained by thermal cycling of boards. Despite the existence of several committees to facilitate the introduction of lead‐free solders, a lack of cohesion is sometimes apparent, particularly regarding heat treatment of materials prior to testing. It is proposed that a challenge as demanding as this would benefit from greater collaboration internationally.

The purpose of the present study was to review the thermo-mechanical challenges of reflowed lead-free solder joints in surface mount components (SMCs). The topics of the review include challenges in modelling of the reflow soldering process, optimization and the future challenges in the reflow soldering process. Besides, the numerical approach of lead-free solder reliability is also discussed.

Lead-free reflow soldering is one of the most significant processes in the development of surface mount technology, especially toward the miniaturization of the advanced SMCs package. The challenges lead to more complex thermal responses when the PCB assembly passes through the reflow oven. The virtual modelling tools facilitate the modelling and simulation of the lead-free reflow process, which provide more data and clear visualization on the particular process.

With the growing trend of computer power and software capability, the multidisciplinary simulation, such as the temperature and thermal stress of lead-free SMCs, under the influenced of a specific process atmosphere can be provided. A simulation modelling technique for the thermal response and flow field prediction of a reflow process is cost-effective and has greatly helped the engineer to eliminate guesswork. Besides, simulated-based optimization methods of the reflow process have gained popularity because of them being economical and have reduced time-consumption, and these provide more information compared to the experimental hardware. The advantages and disadvantages of the simulation modelling in the reflow soldering process are also briefly discussed.

This literature review provides the engineers and researchers with a profound understanding of the thermo-mechanical challenges of reflowed lead-free solder joints in SMCs and the challenges of simulation modelling in the reflow process.

The unique challenges in solder joint reliability, and direction of future research in reflow process were identified to clarify the solutions to solve lead-free reliability issues in the electronics manufacturing industry.

This paper aims to identify a variety of binary system solders by alloying, and relevantly derive multiple system Pb-free solders from the former, attempting to replace the high temperature Sn-Pb solder.

The basis of the paper is the synthesis of previous studies. In terms of some binary high temperature solder alloys, such as Au-20Sn, Bi-2.5Ag, Sn-5Sb, Au-12.5Ge, Zn-6Al and Zn-Sn, taking the alloy phase diagram as the starting point, the melting characteristics, microstructure, mechanical properties, wetting ability and reliability of solder joint are analysed and the prospect is consequently indicated.

Based on the analysis of the six groups of Pb-free solders, the present binary system solder alloys, from the perspective of melting properties, mechanical properties, soldering or reliability of solder joint, rarely meet the comprehensive requirements of replacing the high-temperature Sn-Pb solder. It is assumed to be a solution that multiple-system Pb-free solders derive from a variety of binary system solders by means of alloying. The future development of high temperature Pb-free solder may focus on some factors such as physical properties, mechanical properties, processing, reliability of solder joint, environmental performance and expense.

The paper concentrates on the issue of Pb-free solders at high temperature. From a specific perspective of binary system solders, the presently available Pb-free solders are suggested from the starting point of the alloy phase diagram and the prospect of alternatives of Sn-Pb solders at high temperature are indicated.

An investigation has been performed on the improved solder wettability of oxidized aluminum (Al) with lead-free solder (96.5Sn-3.5Ag) using Ar-H₂ plasmas. The lead-free solder wettability was raised from 62.2 per cent wetting for Al oxidized in air at 250 C for 4 h to 98.4 per cent wetting of oxidized Al modified by Ar-H₂ plasmas at a certain H₂ flow rate. This study aims to gain insight on the surface characteristics of Al affecting the solder wettability with a liquid lead-free solder.

Ar-H₂ plasmas at certain H₂ flow rates are intended to reduce Al oxides on the surfaces of oxidized Al substrates both by physical bombardments via Ar plasmas and chemical reductions with H₂ plasmas, while Al substrates are exposed in Ar-H₂ plasmas to improve the solder wettability with a liquid lead-free solder.

Surface characteristics of oxidized Al substrates have been identified to play key roles for enhanced lead-free solder wettability using Ar-H₂ plasmas. A decrease in polar surface free energy and an increase in dispersive surface free energy on the surfaces of oxidized Al substrates are exploited to advance the lead-free solder wettability. Decreased composition ratios of O to Al, detected by X-ray photoelectron spectroscopy (XPS) for oxidized Al substrates, are crucial for improved lead-free solder wettability.

XPS is typically used to analyze the surface compositions of Al oxides. To provide a rapid and non-expansive method to identify the surfaces of Al substrates prior to soldering to assure lead-free solder wettability, this study proposes a measurable skill, a so-called sessile drop test method, to investigate surface free energies such as total, polar and dispersive surface free energy on the surfaces of Al substrates, to illuminate how the lead-free solder wettability of oxidized Al is improved by Ar-H₂ plasmas.

This paper aims to summarise the effects of ZnO nanoparticles (0.1, 0.3, 0.5, 0.7 and 1.0 Wt.%) on the structure, mechanical, electrical and thermal stability of Sn–3.5Ag–0.5Cu (SAC355) solder alloys for high-performance applications.

The phase identification and morphology of the solders were studied using X-ray diffraction and scanning electron microscopy. Thermal parameters were investigated using differential scanning calorimetry. The elastic parameters such as Young's modulus (E) and internal friction (Q⁻¹) were investigated using the dynamic resonance technique, whereas the Vickers hardness (Hv) and creep indentation (n) were examined using a Vickers microhardness tester.

Microstructural analysis revealed that ZnO nanoparticles (NPs) were distributed uniformly throughout the Sn matrix. Furthermore, addition of 0.1, 0.3 and 0.7 Wt.% of ZnO NPs to the eutectic (SAC355) prevented crystallite size reduction, which increased the strength of the solder alloy. Mechanical parameters such as Young's modulus improved significantly at 0.1, 0.3 and 0.7 Wt.% ZnO NP contents compared to the ZnO-free alloy. This variation can be understood by considering the plastic deformation. The Vickers hardness value (Hv) increased to its maximum as the ZnO NP content increased to 0.5. A stress exponent value (n) of approximately two in most composite solder alloys suggested that grain boundary sliding was the dominant mechanism in this system. The electrical resistance (ρ) increased its maximum value at 0.5 Wt.% ZnO NPs content. The addition of ZnO NPs to plain (SAC355) solder alloys increased the melting temperature (T_m) by a few degrees.

Development of eutectic (SAC355) lead-free solder doped with ZnO NPs use for electronic packaging.

The author proposed a friction plunge micro-welding (FPMW) method and applied it to column grid array packaging to realize the connection of copper columns without precision molds assisted positioning. The purpose of this paper is to study the flow behavior of the solder undergoing frictional thermo-mechanical action during the FPMW and to determine the source of the solders in the micro-zones with different microstructure characteristics near the solder/Cu column friction interface.

Three kinds of Sn58Bi/SAC305 and SAC305/Pb90Sn composite solder samples were designed to study the flow behavior of the solder during FPMW using Bi and Pb as tracer elements.

The results show that most of the solders in the position occupied by the copper column was softened and plasticized during the welding process and was extruded to side of the copper column, flowing axially, circumferentially and radially along a trajectory similar to a conical spiral line. Under the drive of the tangential friction force and the radial hold-tight force, the extruded out visco-plastic solders fully mixed with the visco-plastic solders on the sides of the copper column, and bonded with the solders that deformed plastically on the periphery, so that a stir zone and a dynamic recrystallization zone finally evolved. The outside plastically deformed solders evolved into a thermo-mechanical affected zone.

The flow behavior of the solder during the FPMW was determined, as well as the source of the solders in micro-zones with different microstructure characteristics.

The purpose of this paper is to carry out a study of the evolution of the microstructure and the microhardness of Sn-Cu-Ag alloys from as-cast condition and under artificial isothermal aging at different temperatures (100ºC and 180ºC) for a treatment time up to 500 h. A comparison with Sn-37% Pb eutectic solder samples was also made.

Sn-3.5%Ag, Sn-0.7%Cu and Sn-3.5%Ag-0.9%Cu were poured in two different cooling rate conditions and then aged at 100ºC (373ºK) and 180 °C (453ºK) during 500 h. Microstructural changes were observed by optical microscopy, scanning electron micrograph and energy dispersive X-ray microanalysis. Differential scanning calorimetry technique (DSC) was also used to confirm the obtained results.

A decrease up to 20% in microhardness respect to the value of the as-cast alloy was observed for both aging temperatures. These changes can be explained considering the coarsening and recrystallization of Sn dendrites present in the microstructures of all the systems studied.

There is no evidence of dissolution or precipitation of new phases in the range of studied temperatures that could be detected by DSC calorimetry technique. The acting mechanisms must be the result of coarsening of Sn dendrites and the residual stresses relaxation during the first stages of the isothermal aging.

Overall, selection maps about the extent of the eutectic growth projects the solidification velocities leading to given microstructures. This is because of limitations of most of the set of results when obtained for single thermal gradients within the experimental spectrum. In these cases, associations only with the solidification velocity could give the false impression that reaching a given velocity would be enough to reproduce a result. However, that velocity must necessarily be accompanied by a specific thermal gradient during transient solidification. Therefore, the purpose of this paper is to not only project velocity but also include the gradients acting for each velocity.

Compilation of solidification velocity, v, thermal gradient, G, and cooling rate, Ṫ, data for Sn-Cu and Sn-Bi solder alloys of interest is presented. These data are placed in the form of coupled growth zones according to the correlated microstructures in the literature. In addition, results generated in this work for Sn-(0.5, 0.7, 2.0, 2.8)% Cu and Sn-(34, 52, 58)% Bi alloys solidified under non-stationary conditions are added.

When analyzing the cooling rate (Ṫ = G.v) and velocity separately, in or around the eutectic composition, a consensus cannot be reached on the resulting microstructure. The (v vs. G) + cooling rate diagrams allow comprehensive analyzes of the combined v and G effects on the subsequent microstructure of the Sn-Cu and Sn-Bi alloys.

The present paper is devoted to the establishment of (v vs. G) + cooling rate diagrams. These plots may allow comprehensive analyses of the combined v and G effects on the subsequent microstructure of the Sn-Cu and Sn-Bi alloys. This microstructure-processing mapping approach is promising to predict phase competition and resulting microstructures in soldering of Sn-Cu and Sn-Bi alloys. These two classes of alloys are of interest to the soldering industry, whereas manipulation of their microstructures is considered of utmost importance for the metallurgical quality of the product.

Heavy metals play a crucial role in the economic development of any nation. Industries utilizing heavy metals, consequently, emanate a large volume of metal-containing liquid effluents. Since metals are non-renewable and finite resources, their judicious and sustainable use is the key. Hazardous metal-laden water poses threat to human health and ecology. Apart from metals, these industrial effluents also consist of toxic chemicals. Conventional physical–chemical techniques are not efficient enough as it consumes energy and are, therefore, not cost effective.

It is known that biomaterials namely microorganisms, plants, and agricultural biomass have the competence to bind metals, in some cases, selectively, from aqueous medium. This phenomenon is termed as “metal biosorption.” Biosorption has immense potential of becoming an effective alternative over conventional methods. The authors in the present chapter have used secondary data from their previous research work and attempted to develop few strategic models through their feasibility studies for metal sustainability.