Search Results (111)

This study investigates the electroplating characteristics of Co-Zn alloy coatings with varying Zn contents (0.55 wt.%~8.8 wt.%) and their influence on intermetallic compound (IMC) formation during reactions with Sn solder. Co-Zn alloy coatings were successfully fabricated by electroplating using cobalt plating solutions with different concentrations of zinc sulfate. The results reveal anomalous co-deposition behavior, where the less noble Zn preferentially deposits over Co. Surface morphologies and microstructures evolve significantly with increasing Zn content, transitioning from columnar to dendritic structures. Zn incorporation into the Co lattice disrupts its crystallinity, leading to decreased crystallinity and partial amorphization. Liquid-state and solid-state interfacial reactions with Sn solder demonstrate that Zn content considerably influences IMC formation. In liquid-state reactions at 250 °C, lower Zn contents (0.55–4.8 wt.%) slightly enhance CoSn₃ growth. It exhibits a dense layered-structure without IMC spallation. In contrast, a higher Zn content (8.8 wt.%) significantly reduces IMC formation by approximately 50% and produces a duplex structure with two distinct layers. In solid-state reactions at 160 °C, the suppression effect becomes even more pronounced. The Co-0.55Zn deposit exhibits significant inhibition of CoSn₃ growth, while the Co-8.8Zn sample forms only a thin IMC layer, achieving a suppression rate exceeding 85%. These findings demonstrate that Zn doping effectively limits CoSn₃ formation during solid-state reactions and improves interfacial stability. Full article

This study investigates the interfacial reactions of FeCoNiCr and FeCoNiMn medium-entropy alloys (MEAs) with Sn and Sn-3Ag-0.5Cu (SAC305) solders at 250 °C. The evolution of interfacial microstructures is analyzed over various aging periods. For comparison, the FeCoNiCrMn high-entropy alloy (HEA) is also examined. In the Sn/FeCoNiCr system, a faceted (Fe,Cr,Co)Sn₂ layer initially forms at the interface. Upon aging, the significant spalling of large (Fe,Cr,Co)Sn₂ particulates into the solder matrix occurs. Additionally, an extremely large, plate-like (Co,Ni)Sn₄ phase forms at a later stage. In contrast, the Sn/FeCoNiMn reaction produces a finer-grained (Fe,Co,Mn)Sn₂ phase dispersed in the solder, accompanied by the formation of the large (Co,Ni)Sn₄ phase. This observation suggests that Mn promotes the formation of finer intermetallic compounds (IMCs), while Cr facilitates the spalling of larger IMC particulates. The Sn/FeCoNiCrMn system exhibits stable interfacial behavior, with the (Fe,Cr,Co)Sn₂ layer showing no significant changes over time. The interfacial behavior and microstructure are primarily governed by the dissolution of the constituent elements and composition ratio of the HEAs, as well as their interactions with Sn. Similar trends are observed in the SAC305 solder reactions, where a larger amount of fine (Fe,Co,Cu)Sn₂ particles spall from the interface. This behavior is likely attributed to Cu doping, which enhances nucleation and stabilizes the IMC phases, promoting the formation of finer particles. The wettability of SAC305 solder on MEA/HEA substrates was further evaluated by contact angle measurements. These findings suggest that the presence of Mn in the substrate enhances the wettability of the solder. Full article

This study presents a novel approach to manufacture a rigid printed circuit board (PCB) using sustainable polymers. Current PCBs use a fossil-fuel-based substrate, like FR4. This presents recycling challenges due to its composite nature. Replacing the substrate with an environmentally friendly alternative leads to a reduction in negative impacts. Polylactic acid (PLA) and Polyhydroxybutyrate (PHB) biopolymers are used in this study. These two biopolymers have low melting points (130–180 °C, and 170–180 °C, respectively) and cannot withstand the high temperature soldering process (up to 260 °C for standard SAC (SnAgCu, tin/silver/copper) lead free solder processes). Our approach for replacing the PCB substrate is applying the PLA/PHB carrier substrate at the end of the PCB manufacturing process using injection molding technology. This approach involves all the standard PCB processes, including wet etching of the Cu conductors, and component assembly with SAC solder on a thin flexible polyimide (PI) foil with patterned Cu conductors and then overmolding the biopolymer onto the foil to create a rigid base. This study demonstrates the functionality of two test circuits fabricated using this method. In addition, we evaluated the adhesion between the biopolymer and PI to achieve a durable PCB. Moreover, we performed two different end-of-life approaches (debonding and composting) as a part of the end-of-life consideration. By incorporating biodegradable materials into PCB standard manufacturing, the CO₂ emissions and energy consumption are significantly reduced, and installation costs are lowered. Full article

With the enhancement of environmental protection awareness and the implementation of related regulations, lead-free soldering materials are gradually replacing the traditional leaded soldering materials in the field of electronics manufacturing. Sn–Ag soldering materials have become a research hotspot because of their good mechanical properties, solderability, and thermal fatigue reliability, but their high cost limits their large-scale application. The low silver content of the Sn–Ag solder reduces the cost while maintaining an excellent performance. However, as the size of electronic components shrinks and the package density increases, the solder joint spacing decreases, the potential gradient increases, and electrochemical migration (ECM) becomes a key factor affecting the reliability of solder joints. In this study, the ECM failure process was simulated by the water droplet method, and the SEM and XPS analyses were utilized to investigate the ECM mechanism of Sn1.0Ag solder alloys, and the effects of different concentrations of NaCl solutions on their ECM were investigated. The results showed that the ECM of the Sn1.0Ag solder occurred in a 0.01 M NaCl solution, the dendritic composition was pure Sn, and the white precipitate was a mixture of Sn(OH)₂ and Sn(OH)₄. With the increase in the NaCl concentration, the corrosion resistance of the Sn1.0Ag solder alloy decreases and the ECM reaction intensifies, but with a high concentration of the NaCl solution, a large amount of precipitation hinders the migration of Sn ions, resulting in the generation of no dendrites. The present study provides new insights into the ECM behavior of a low-silver-content Sn–Ag solder system. Full article

As semiconductor packaging technologies face limitations, through-silicon via (TSV) technology has emerged as a key solution to extending Moore’s law by achieving high-density, high-performance microelectronics. TSV technology enables enhanced wiring density, signal speed, and power efficiency, and offers significant advantages over traditional wire-bonding techniques. However, achieving fine-pitch and high-density interconnects remains a challenge. Solder flip-chip microbumps have demonstrated their potential to improve interconnect reliability and performance. However, the environmental impact of lead-based solders necessitates a shift to lead-free alternatives. This review highlights the transition from Sn-Pb solders to lead-free options, such as Sn-Ag, Sn-Cu, Sn-Ag-Cu, Sn-Zn, and Bi- or In-based alloys, driven by regulatory and environmental considerations. Although lead-free solders address environmental concerns, their higher melting points pose challenges such as thermal stress and chip warping, which affect device reliability. To overcome these challenges, the development of low-melting-point solder alloys has gained momentum. This study examines advancements in low-temperature solder technologies and evaluates their potential for enhancing device reliability by mitigating thermal stress and ensuring long-term stability. Full article

Resistance Element Soldering (RES) is one of the new methods of joining dissimilar materials by resistance heating using an element. Sn60Pb40 solder, which has been used for decades in tin smithing and the electrical industry, has already been tested for joining galvanized steel sheet with thermoplastic using RES. However, legal restrictions are currently moving towards prohibiting the use of lead in mass production. For this reason, the possibility of replacing Sn60Pb40 solder with Sn91Zn9 lead-free solder was verified. The results showed that with an appropriate choice of flux and resistance heating conditions, it is possible to replace Sn60Pb40 solder with Sn91Zn9 solder when joining galvanized steel sheet with thermoplastic using RES. With a suitable heat input during soldering, good conditions were achieved for wetting the base material with molten solder with a sufficient volume of remelted solder in the core of the Cu/Sn91Zn9 bimetallic element. The strength of the soldered joint made at a heat input of 901 J was measured at the level of 94% of the strength of Sn91Zn9 solder. Full article

Soldering with Sn alloys has always been the essential assembly step of microelectronics. The conductive Sn whiskers, which can spontaneously grow from soldering surfaces, mean a considerable reliability risk for microelectronics due to possible short circuit formation between the leads of the components. Since their discovery in 1951, thousands of research studies have been conducted to unravel their growth mechanisms and find effective prevention methods against them. Till 2006, the Sn whisker problem was solved and partially forgotten due to the very effective whisker suppression effect of Pb alloying into the solder materials. The lead-free change gave new impetus to the problem, which was further enhanced by the application of new material systems, growing reliability requirements, and accelerating miniaturization in the 21st century. Our review would like to give an overview of the Sn whisker’s history from the beginning till the latest results, focusing on the suppression solutions by the modification of the solder alloy compositions. Recently, promising results have been reached by alloying Bi and In, which are metals that are the focus of low-temperature soldering, and by composite solders. Full article

This study investigates the potential application of Zn5Al1.5Mg1.5Ti active solder in ultrasonic soldering of Al₂O₃ ceramics and Cu substrates. The research explores the microstructural characteristics, phase composition, and mechanical properties of the solder and the resulting joints. Particular attention is given to the formation mechanisms of the solder–substrate bond and the role of ultrasound activation in enhancing wettability and bond strength. The study aimed to provide a deeper understanding of active soldering processes and their suitability for high-temperature applications. The findings contribute to advancing lead-free soldering technologies for electronic and structural applications. Full article

This study proposes a Sn58Bi/SAC305 layered composite solder designed for low-temperature applications. By alternating high-melting SAC305 and low-melting Sn58Bi layers, the composite achieves a liquidus temperature of ~180 °C, comparable to traditional Sn-Pb solder. Synchrotron X-ray imaging reveals dynamic interfacial interactions, including partial dissolution of SAC305 into molten Sn58Bi and Bi diffusion, mitigating segregation and forming defect-free interfaces with cellular structures. The 7-layer composite exhibits a peak shear strength of 44.3 ± 0.8 MPa at 200 °C, surpassing single Sn58Bi (41.8 ± 1.1 MPa) and SAC305 (31.6 ± 1.4 MPa), attributed to the refined microstructure and uniform dispersion of Ag₃Sn phases. Fracture analysis indicates mixed ductile–brittle failure modes influenced by intermetallic compounds (IMCs). This work provides insights into the role of layered structures in controlling element diffusion and interfacial reactions, advancing the design of low-temperature lead-free solders. Full article

With the widespread application of lead-free solder, solder represented by the SAC series has been widely used. However, with the miniaturization and multifunctionalization of electronic devices, the distance between solder joints is becoming increasingly smaller, and the problem of electrochemical migration caused by Ag in the SAC series is gradually emerging. Therefore, it becomes imperative to develop a solder that has a melting point, mechanical properties, and other properties similar to those of the SAC series but does not contain silver. In this study, 1–3% of Bi and 1–3% of In were added to the Sn-0.7Cu solder to investigate the effects of these elements on the melting characteristics, microstructure, mechanical properties, wettability, and electrical conductivity of the Sn-0.7Cu solder. Due to the addition of Bi and In elements, the melting point of the Sn-0.7Cu solder was lowered, the shear strength was improved, and the solderability was enhanced, but the electrical conductivity was reduced. This article obtained the mechanism of the influence of Bi and In elements on the properties of the Sn-0.7Cu solder through experiments and theoretical analysis, providing a certain degree of theoretical support for the development of silver-free solder. Full article

In advanced microelectronic packaging, high thermo-mechanical loads arise on the solder interconnects. Accurate and efficient modeling of the mechanical behavior is crucial in the design of the package, and the simulation results can provide a basis for estimations of the reliability of the assembly. However, the accuracy of the simulation results depends on the accuracy of the modeled geometry and the modeling simplifications and assumptions employed to achieve computational cost-efficient calculations. In this work, finite element analysis (FEA) of a Fan Out—Wafer Level Packaging (FO-WLP) layout was carried out considering the following variations: modeling domain (2-D and pseudo-3-D) was defined for creating the efficient calculation framework, where soldering material (SAC 305 and SACQ), incorporation of intermetallic compound (IMC), bond pad edge geometry (sharp and blunt) were modeled for cycles of thermal load. Stress and strain analysis was carried out to evaluate the solder behavior for the parameter variations. Furthermore, fatigue indicators were evaluated. An efficient planar simulation framework with 2-D and pseudo-3-D meshed geometries provides a quick estimate for the lower and upper bound for the strain, stress and strain energy-related parameters, respectively. This calculation framework can be employed for extensive parameter studies solved rapidly at low computational costs. Full article

A Sn58Bi composite solder reinforced by Ni nanoparticles was prepared using a mechanical mixing technique, and the thermomigration microstructure and properties of the solder joints were studied. The findings indicate that incorporating an appropriate quantity of Ni nanoparticles can enhance the microstructure of the composite solder and mitigate the coarsening of Bi-phase segregation. At 0.75 weight percent Ni nanoparticle content, the composite solder’s tensile strength is 59.7 MPa and its elongation is 54.6%, both of which are noticeably greater than those of the base solder. When the thermal loading time is 576 h, the shear strength of the composite solder joint is 25.5 MPa, which is 30.1% higher than that of the base solder joint. This study reveals that the shear fracture path shifts from the boundary region between the solder seam and the IMC layer to the IMC layer itself. Concurrently, the fracture mode evolves from a mix of brittle–ductile fracture, characterized by quasi-cleavage, to a predominantly brittle fracture, marked by numerous “rock candy-like” cross-sectional features and secondary cracking. Adding Ni nanoparticles to the Sn58Bi composite solder/Cu solder junction can significantly extend its service life. Full article

With the development of electronic packaging technology toward miniaturization, integration, and high reliability, the diameter and pitch of solder joints continue to shrink. Adjacent solder joints are highly susceptible to electrochemical migration (ECM) due to the synergistic effects of high-density electric fields, water vapor, and contaminants. Dust has become one of the non-negligible causal factors in ECM studies due to air pollution. In this study, 0.2 mM/L NaCl and Na₂SO₄ solutions were used to simulate soluble salt in dust, and the failure mechanism of an Sn-58Bi solder ECM in the soluble salt in dust was analyzed by a water-droplet experimental method. It was shown that the mean failure time of the ECM of an Sn-58Bi solder in an NaCl solution (53 s) was longer than that in an Na₂SO₄ solution (32 s) due to the difference in the anodic dissolution characteristics in the two soluble salt solutions. XPS analysis revealed that the dendrites produced by the ECM process were mainly composed of Sn, SnO, and SnO₂, and there were precipitation products—Sn(OH)₂ and Na₂SO₄—attached to the dendrites. The corrosion potential in the NaCl solution (−0.351 V) was higher than that in the Na₂SO₄ solution (−0.360 V), as shown by a polarization test, indicating that the Sn-58Bi solder had better corrosion resistance in the NaCl solution. Therefore, an Sn-58Bi solder has better resistance to electrochemical migration in an NaCl solution compared to an Na₂SO₄ solution. Full article

As electronic packaging technology advances towards miniaturization and integration, the issue of electromigration (EM) in lead-free solder joints has become a significant factor affecting solder joint reliability. In this study, a Sn-3.0Ag-0.5Cu (SAC305) alloy was used as the base, and different Bi content alloys, SAC305-xBi (x = 0, 0.5, 0.75, 1.0 wt.%), were prepared for tensile strength, hardness, and wetting tests. Copper wire was used to prepare EM test samples, which were subjected to EM tests at a current density of approximately 0.6 × 10⁴ A/cm² for varying durations. The interface microstructure of the SAC305-xBi alloys after the EM test was observed using an optical microscope. The results showed that the 0.5 wt.% Bi alloy exhibited the highest ultimate tensile strength and microhardness, improving by 33.3% and 11.8% compared to SAC305, respectively, with similar fracture strain. This alloy also displayed enhanced wettability. EM tests revealed the formation of Cu₆Sn₅ and Cu₃Sn intermetallic compounds (IMCs) at both the cathode and anode interfaces of the solder alloy. The addition of Bi inhibited the diffusion rate of Sn in Cu₆Sn₅, resulting in similar total IMC thickness at the anode interface across different Bi contents under the same test conditions. However, the total IMC thickness at the cathode interface decreased and stabilized with increasing EM time, with the SAC305-0.75Bi alloy demonstrating the best resistance to EM. Full article

The restriction of lead content in alloys for the production of solder, based on the Directive of the European Parliament and of the Council of the European Union of 8 June 2011, which is also known as RoHS (Restriction of the use of certain Hazardous Substances in electrical and electronic equipment), had a very positive impact on research into lead-free solder alloys, as well as on the economic impact of the production of solders. It opened the door to issues relating to the mechanical properties of lead-free solders and the microhardness of formed joints, with the aim of increasing their quality and efforts to reduce production costs. In addition to the production efficiency increase, without the need for the manual removal of so-called slagging, the moderation of oxide formation on the melt surface, standing for an increase in the yield of the total amount of solder, represents one of the many factors influencing the production of lead-free alloys for tin-based soldering. This work deals with the issues of material selection for the production of lead-free solders. Temperature affects the formation of different phases when there is a change in the concentration of the elements involved because it can be a negative aspect for soldering. Therefore, it is necessary to have detailed knowledge on the entire process that takes place during temperature changes. Full article