The increasing demand for flexible, lightweight, compact, and cost-effective electronic products has led to a growing preference for Flexible Printed Circuit Boards over Rigid Printed Circuit Boards. However, thermal challenges during the reflow soldering process can significantly impact FPCBs. When exposed to elevated temperatures, Flexible Printed Circuit Boards are highly susceptible to deflection and thermal stress. This study examines the impact of temperature profile on FPCBs during the reflow soldering. Deformation measurements for both FPCBs and Rigid Printed Circuit Boards were obtained using a KEYENCE ­LK-G152 laser sensor installed at a reflow oven’s entry and exit points. The experiment evaluated two temperature profiles, soaking and ramp profile, as variables. Findings revealed that FPCBs experienced greater deformation under the ramp profile, whereas RPCBs exhibited more deformation under the soaking profile. This research provides valuable insights for engineers and Printed Circuit Board designers, offering practical guidelines for optimizing mass production in the microelectronics industry.

Abstract The Active Disturbance Rejection Control (ADRC) framework offers a practical approach for stabilization, regulation, and tracking tasks in dynamic systems without relying on an exact mathematical model, making it a promising alternative to conventional PID control in industrial applications. This paper investigates the implementation of an ADRC strategy to address the temperature-tracking problem in an infrared-based thermal system for electronic soldering. One of the main challenges of this system is the input delay introduced by the heating process. By analyzing this delay through a first-order Padé approximation, it is shown that its effect can be treated as an external disturbance, which the ADRC effectively estimates and compensates for in real time. 
The closed-loop performance was evaluated numerically and experimentally and compared with that of a standard PID controller. Results show that ADRC achieved a 12% improvement in the control efficiency index (ITAE_eff), demonstrating a better trade-off between tracking accuracy and control energy. Furthermore, the proposed control approach improves precision and reliability in industrial soldering processes, potentially reducing energy consumption and electronic waste.

This study evaluates the efficiency of various cleaning chemistries under controlled process conditions, including conveyor belt speed and concentration, for the removal of water-soluble flux residues using a test vehicle incorporating different chip resistors, MLF and BGA components. The influence of solder powder size on flux composition was examined, with smaller powder sizes exhibiting increased flux activator content, leading to higher residue accumulation and greater cleaning complexity. By systematically testing different solder powder sizes T5 (25-15 μm), T6 (15-5 μm), and T7 (11-2 μm) this research aims to elucidate their effects on defluxing efficiency and residue removal. Experimental procedures involved assembling test vehicles having MLF-68, BGA-208 and resistors of varying sizes, followed by controlled reflow and standardized defluxing using aqueous-based defluxing systems. Post-defluxing, analysis was conducted using visual inspection to quantify and characterize flux residues. The study specifically addresses the challenges of flux removal under low-standoff components, where restricted access exacerbates residue entrapment. Results indicate that different solder powder sizes require selection of defluxing chemistry and process parameters. Further studies will aim to refine cleaning methodologies and investigate interactions between solder powder size, flux chemistry, and process conditions to enhance cleanliness and reliability in advanced semiconductor packaging.

ABSTRACT High-reliability solders may contain multiple elements (up to 6 or 7 elements) for strength, including intermetallic compound (IMC) particles, precipitates, solid solutions, and fine grains. The complicated alloy composition and microstructure impact solder melting behavior and thus influences the joint voiding performance. Solder joint voids may present a significant reliability challenge in electronics manufacturing, as they can compromise the mechanical integrity of solder joints, inhibit thermal dissipation, and interfere with electrical signal transmission. These effects can downgrade the solder joint performance and lifespan of printed circuit board assemblies (PCBAs), particularly in high-reliability applications. To address these concerns, a novel mixed-alloy solder paste system has been developed to deliver both low voiding and enhanced thermal cycling reliability of the formed solder joints. This system incorporates low-voiding alloy powders that promote early wetting during reflow, while another alloy powder contributes to improving joint strength and durability through reflow. The resulting solder joints are homogeneous. The mixed solder powder paste is designed as a drop-in replacement, requiring no modification to existing SMT reflow profiles. This work builds on a previous study aimed at reducing voiding in mixed alloy solder systems[1]. By further optimizing the reflow thermal profile, the project evaluated soldering performance on both organic solderability preservative (OSP) and immersion tin (ImSn) surface finishes using updated reflow profiles. Voiding levels were benchmarked against a standard SAC305 solder paste. The improved mixed alloy system consistently achieved voiding rates below 15%, outperforming SAC305. These results suggest that the optimized solder paste and process can reduce voiding to levels low enough to potentially eliminate the need for vacuum reflow in certain applications.

Abstract Due to the regulations restricting the use of lead, the implementation of lead-free solders became a legal requirement more than 15 years ago. In addition to the well-known SAC305 solder, new alloys containing various concentrations of Bi, together with other additives improving the soldering process and reliability of joints, have appeared. The paper focuses on comparative study of wetting properties of SAC305 and commercially available third-generation lead-free solder alloys containing Bi: REL61, REL22, and HRL-1. The improved sessile drop method, was applied to measure the contact angle ( θ ) of the selected solders on a copper substrate. The highest contact angle value (36°) was observe for HRL-1 and the lowest (27°) for REL22. Initially the spreading phenomenon was very fast, below the resolution of the measurement method. In some cases of the wetting disturbance by the external factors, wetting has been inhibited and the intermetallic phases developed at the solder/substrate. The formation of a halo area at the substrate around the drop was also observed, most likely formed due to the surface diffusion of solder atoms. This phenomenon led to a further reduction of the contact angle, but the spreading of the drop was much slower. Comprehensive microstructure and chemical composition examination of the drop/substrate interfaces after wetting tests evidenced the presence of Cu 6 Sn 5 phase for all samples. Moreover, it was proved that the alloy additives (e.g., Ag and Bi) influenced the achieved contact angle and reduced unfavorable intermetallic phases formation such as Cu 3 Sn (e.g., Ni, Sb, and Ti).

The reflow soldering process is an important stage in the assembly of electronic components that requires high-precision temperature control to ensure the quality of the solder joints. This study aims to evaluate the performance of a K-type thermocouple temperature sensor integrated into the solder reflow control system. Evaluation was carried out through temperature measurements at 20 different points, ranging from 35°C to 220°C, with a focus on reading accuracy and error rate. The results of the experiment showed that the type K thermocouple sensor had an error range between 0.02°C to 0.97°C, with an average error value of 0.54°C. These findings indicate that the sensor is stable and reliable enough to be used in industrial applications that demand temperature precision. The advantages of these sensors lie in their cost efficiency, ease of integration, and responsiveness to temperature changes. Nonetheless, periodic calibration is still necessary to maintain long-term accuracy, especially in dynamic work environments. This research contributes to the development of temperature control systems in the electronic manufacturing process, especially in the selection of the right sensors to support production quality. The conclusion of this study confirms that the K-type thermocouple is a practical and economical solution in reflow soldering systems, with sufficient performance to meet industry standards.

Discussion on the influence law of Ni/Al2O3 particles on the growth of interfacial IMC in solder joints during soldering and aging processes

The growing complexity of production systems in the technology sector demands advanced tools to ensure efficiency, flexibility, and cost-effectiveness. This study presents the development of a simulation model for a selective soldering line at a technology manufacturing company in Poland, created during an engineering internship. Using FlexSim 24.2 software, the real production process was replicated, including input/output queues, manual insertion (MI) stations, soldering machines, and quality control points. Special emphasis was placed on implementing dynamic process logic via ProcessFlow, enabling detailed modeling of token flow and system behavior. Through experimentation, various configurations were tested to optimize process time and the number of soldering pallets in circulation. The results revealed that reducing pallets from 12 to 8 maintains process continuity while offering cost savings without impacting performance. An intuitive operator panel was also developed, allowing users to adjust parameters and monitor outcomes in real time. The project demonstrates that simulation not only supports operational decision-making and resource planning but also enhances interdisciplinary communication by visually conveying complex workflows. Ultimately, the study confirms that simulation modeling is a powerful and adaptable approach to production optimization, contributing to long-term strategic improvements and innovation in technologically advanced manufacturing environments.

The article describes a basic comparison of soldering materials (preforms) from several suppliers, focusing on the main differences in surface structure, internal structure, and contamination on the surface and in the interior of the solder. As a result, we are able to define how different preforms of the surface, preforms related to impurities, or preforms of the structures of the composition parts of the power modules, which are subjected to the soldering process, influence the formation of different void types. Simultaneously an investigation of the impact on the soldering process (heating, cleaning, soldering, cooling), which influences the formation of the solder joint and on the formation intermetallic structure (IMC) and voids, is performed as well. A comparison of the individual results between RTG or X-ray (Radioisotope Thermoelectric Generator) and SAM (Scanning Acoustic Microscopy) are given together with the highlighted differences. This application study was carried out under various settings to investigate the effects of temperature and exposure time on formic acid. The findings confirm that oxide reduction is a time-dependent process. The lowest average void area—0.2%—was observed at the highest tested temperature of 230 °C, and the longest formic acid exposure duration of 300 s.

Purpose This paper aims to investigate the microstructural and diffusion behavior of the bonding interface between AuSn20 thermal interface material and tungsten-copper (WCu) alloy. Design/methodology/approach This research uses thermo-compression bonding, with a Ni/Au coated WCu alloy surface to examine the diffusion behavior of AuSn20 at the interface. Characterization techniques including scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray spectroscopy were used to analyze the interfacial microstructure and diffusion paths. Additionally, first-principles calculations were conducted to determine the diffusion coefficients of Cu and Sn in Ni, further elucidating the interaction mechanisms among elements during the soldering process. Findings The electroless nickel plating on WCu alloy surface promotes fast diffusion of AuSn solder into the grain boundary in Ni layer. It is found the solution of Cu in Ni layer also accelerates AuSn diffusion. As AuSn passed Ni layer and reached the WCu side, it tended to accumulate within the NiW rich region, forming an Au-Sn-Ni-W solid solution. Ni provides extra diffusion drive force for Au and Sn, on the other hand the moderate solubility of Au and Sn in NiW alloy improve solid solution stability via high-entropy effect. Under varying temperature and compositional conditions, the interfacial region displays phase transitions from a single-phase solid solution to multiphase structures, with elemental distribution inconsistencies. By combining first-principles calculations and energy-dispersive X-ray analysis, this study examined the temperature dependence of Ni-Cu and Ni-Sn interdiffusion coefficients, highlighting that larger difference in diffusion coefficients may lead to the Kirkendall effect, potentially affecting the bonding strength and interface stability. Originality/value This research offers both theoretical insights and experimental evidence for controlling AuSn and WCu alloy interfaces, but also sheds lights to the reliability of high-temperature soldering materials.

ABSTRACTLow‐temperature soldered wire interconnection (LTSWI) is a technology utilizing many interconnect wires carried on a polymer foil to form electrical connections against cell gridlines without a separate soldering process. In this work, LTSWI module samples were characterized for material properties and assembly dimensions and subjected to accelerated aging experiments to induce degradation. A finite element analysis model was developed based on characterization results, to analyze internal stressors during environmental exposures. The polymer foil contains polyethylene terephthalate and low‐density polyethylene layers, and solder composition was tin bismuth, which notably was not metallurgically bonded to cell gridlines. High temperature accelerated exposures created power loss up to 9% in minimodule samples, with fill factor losses implicating contact degradation. Posttest characterization identified solder‐gridline cracking and wire‐cell separation as contributing mechanisms. Finite element modeling demonstrated that wire‐to‐cell contact is maintained by polymer contraction post lamination but is reversible, resulting in contact loss and wire separation during high temperature exposure. Simulations also detected in‐plane wire‐to‐cell displacements, driven by surrounding polymer motion in response to high temperatures and mechanical load. We hypothesize that the propensity for wire movement during environmental exposure damages the not‐metallurgically bonded wire‐gridline interface and contributes to LTSWI contact degradation. Because distinct from thermal expansion mismatches which damage traditionally soldered modules, current test protocols are likely not applying the intended acceleration factors to LTSWI modules. This work highlights how construction‐specific accelerated testing may be needed for nontraditional module designs and provides a starting point for accurate LTSWI life assessment.

The special shape of Cu/In layer and ultrasonic vibration are used to realize fast bonding at room temperature, thus solving the problems of high thermal stress and signal delay caused by high temperature in the traditional reflow soldering process. The indium film-modified copper crystal microlayer substrates are used as bonding couples, and ultrasonic vibration and pressure are applied to the bonding contact area to realize the rapid solid-phase bonding of two copper substrates. The microstructure, intermetallic compounds and average shear strength at the bonding interface are analyzed by scanning electron microscopy, transmission electron microscopy, X-ray diffraction (XRD) and bond strength tester. Under ultrasonic vibration and small pressure, the micro-cone structures of Cu/In layers are inserted into each other to form a stable physical barrier structure. The atoms of the thin indium layer at the bonding interface transform into the high-quality phase Cu2In by rapid diffusion driven by ultrasonic energy. When the thickness of the indium layer at the bonding interface is 250 nm, the bonding pressure is 7 MPa, and the bonding time is 1 s, the relatively optimal bonding quality is obtained, and the holes at the bonding interface disappear. The results of heat treatment experiments show that this solid-phase bonding technique can obtain good bond strength without additional heat treatment. The special morphology of the Cu/In layer and ultrasonic vibration allow the bonding to be completed quickly at room temperature. The bonding quality is good and small bond sizes can be obtained.

Under the increasingly fierce competition in the consumer electronics market, product quality has become a crucial element of enterprises' core competitiveness. This study takes "Company A," a small and medium-sized electronic manufacturing enterprise, as a case to address the high defect rate (initially 5.2%) in its smart wristband assembly process. By systematically applying the PDCA cycle for quality improvement, the research identifies core issues such as unstable soldering processes and insufficient standardization of employee operations during the planning phase. Implementation measures include enhanced operator training, equipment calibration, and optimized self-inspection procedures. Verification in the checking phase demonstrates a significant reduction in the defect rate to 2.3%. Effective countermeasures are subsequently standardized into management protocols. The findings reveal that the PDCA cycle enables continuous quality enhancement with low-cost investments, providing a replicable practical framework for quality management improvement in small and medium-sized enterprises.

Laser tissue soldering (LTS) offers an innovative, suture-free approach to wound closure. However, challenges such as limited tensile strength and prolonged soldering time need solutions. This work combines BSA with PEG to enhance mechanical properties and introduces silver and titanium dioxide nanoparticles to accelerate soldering via localized surface plasmon resonance (LSPR). Real-time SS-OCT monitoring ensures precise evaluation of the soldering process, advancing LTS applications for diverse tissue. Four solder compositions (C1-C4) are prepared using combinations of BSA, PEG, silver nanoparticles (AgNP) and titanium dioxide nanoparticles (TiNP). Ex-vivo samples of chicken breast, chicken skin, and goat skin were incised in 1 cm incision with 0.45 mm width and soldered using a 980 nm, 5 W laser. Tensile strength was measured using a tensiometer, while cytotoxicity was assessed using HEK293 cells. SS-OCT captured real-time scattering coefficient changes during soldering, providing insight into coagulation dynamics. Combining bovine serum albumin (BSA) with PEG and nanoparticles (silver and titanium dioxide), tensile strength in ex-vivo tissue samples increased significantly-by 27% in chicken breast (0.4980 to 0.6366 N/cm²), 28% in chicken skin (0.6080 to 0.7840 N/cm²), and 23% in goat skin (0.6220 to 0.7666 N/cm²). Nanoparticle incorporation reduced soldering time by 33%, achieving complete fusion within 3 min using a laser of optical power of 5 W, central wavelength 980 nm and duty cycle of 50%. Real-time monitoring with Swept-Source Optical Coherence Tomography (SS-OCT) quantified the scattering coefficient changes during soldering, validating efficient bonding. Results demonstrate PEG's contribution to tensile strength, nanoparticles' role in reducing soldering time, and SS-OCT's utility for precision monitoring, supporting LTS as a promising wound closure method. The study validates PEG's biomechanical reinforcement and nanoparticles' role in efficient LTS. The integration of SS-OCT enables precise, real-time assessment, confirming the clinical potential of this enhanced LTS method for rapid and robust tissue closure.

A nonlinear disturbance observer-based adaptive back-stepping sliding-mode temperature control method for laser soldering processes

Abstract In this paper, the factors affecting the reliability of small-size PBGA with low thermal expansion coefficient are determined by theoretical and simulation analysis. The simulation results are verified by reliability test, dye penetration, metallographic section, and electron microscope scanning analysis, revealing that the height and diameter of solder joints are reliable with low CTE small size PBGA. The high-reliability welding process method of this kind of device is obtained, which is of great significance for the quality assurance of aviation and aerospace electronic products.

Abstract The replacement of glass fibres by cellulose‐based fibres in printed circuit board (PCB) is motivated by environmental reasons since the use of biodegradable components from renewable sources will have a significative impact in the life‐cycle assessment and sustainability evaluation of these materials. To study the potential of replacement of glass fibres by natural fibres in printed circuit board manufacturing we have used a finite element method (FEM) computational simulation methodology to evaluate the influence of key structural parameters on their thermomechanical properties, with the goal of predicting and quantifying its warpage at soldering process temperatures. In our work some printed circuit board (PCB) configurations have been selected and modelled using different natural fibres and compared with conventional printed circuit board systems, designated by flame retardant epoxy (FR4), that are made from glass fibres, epoxide resin and copper foils. The simulation results indicate that the printed circuit board assembly process, namely the number of layers, has a major influence on the key thermomechanical properties that were studied. Some optimized printed circuit board configurations were selected, based on the simulation studies, and the natural fibres were classified according to their potential to be used in the development of sustainable printed circuit board materials.

Conventional soldering methods can expose components to too much heat, which may cause failures and reduce reliability. It is essential to control the soldering process precisely to ensure electronic devices perform well and last longer. Microwave soldering offers a potential solution by using microwave energy to heat solder joints selectively, reducing heat exposure to nearby components. This study examines the effect of different silver percentages in Sn-35Bi on solder joint microstructure during microwave soldering. The substrate was then subjected to an isothermal ageing process and exposed for various periods. Solder joint microstructures were characterised using optical microscopy (OM), scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) analysis. The results revealed that the intermetallic compound (IMC) observed at the interface are Cu6Sn5 and Cu3Sn after microwave soldering through MHH. The IMC morphology of Cu6Sn5 was prismatic-like and changed to a more rounded-like shape when continuously exposed to the ageing process. The grain size increased when the ageing duration increased. Meanwhile, the different percentages of silver in Sn-35Bi do not affect the type of IMC formation. However, the high percentage of silver content was proportional to IMC thickness.

Solder joints are crucial in modern electronics to ensure electrical connectivity and mechanical stability. The specific problem lies in determining how repeated reflow cycles (e.g., microwave soldering) influence intermetallic compounds (IMC) morphology and thickness, how these changes affect the electrical properties of solder joints, and how the solder joints perform under corrosive conditions. Thus, this study investigates the effects of four-cycle microwave soldering on the formation and growth of IMCs and their impact on solder joints' electrical and corrosion properties. Specifically, Sn-35Bi-0.3Ag and Sn-35Bi-1.0Ag solder alloys on ENImAg surface finishes were analysed. Key findings reveal that after four cycles of microwave soldering, IMC thickness increased from 2.85 μm to 7.11 μm for Sn-35Bi-0.3Ag and from 6.97 μm to 11.92 μm for Sn-35Bi-1.0Ag. Corrosion behaviour in a 6M KOH alkaline solution showed a rise in corrosion current for Sn-35Bi-0.3Ag from 0.2623 μA to 1.0993 μA and for Sn-35Bi-1.0Ag from 0.278 μA to 1.6627 μA, with corresponding corrosion rates of 0.6387 mm/yr and 0.9660 mm/yr, respectively. The results highlight a balance between IMC growth, electrical performance, and corrosion resistance, with Sn-35Bi-0.3Ag offering superior electrical performance despite thermal exposure. These findings provide critical insights for optimising soldering processes and enhancing the reliability of electronic assemblies with applications in advanced manufacturing and product lifecycle management.

This research was conducted in the ACG-S Department with the object of observation of Man Power in the Wire Connection Soldering Stator Line 4B Process. With the aim of obtaining the value of Man Power's work posture and providing recommendations for improving work posture in the Wire Connection Soldering Process. To find out the data, the researcher used the Nordic Body Map (NBM) Questionnaire to find out subjective complaints from Man Power, then a work posture assessment was carried out using the Rapid Upper Limb Assessment (RULA) Method. The results of the Nordic Body Map (NBM) Questionnaire showed that 4 out of 6 Man Power complained of pain in the neck, back, shoulders, and waist areas, then from the results of the work posture assessment using the RULA method, a final score of 6 was obtained, which means that the Man Power's work posture position is at a high level (High) meaning that there is a high risk of Man Power getting Musculoskeletal Disorders (MSDs) and requiring posture improvement. Improvement of work posture is carried out by adding work aids, namely magnifying glasses and Poka Yoke Camera Soldering. After improving posture by adding work aids, the results of the work posture assessment using the RULA method obtained a final score of 3, which means that the Man Power work posture position after adding work aids is at a moderate level, which means that there is a moderate risk of Man Power getting Musculoskeletal Disorders (MSDs) and does not require action to improve body posture.