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This work investigates the endurance and performance of aluminum-doped zinc oxide (AZO) thin films fabricated on flexible polyethylene terephthalate (PET) substrates, providing new insights into their degradation linked to mechanical flexing and accelerated thermal cycling (ATC). The current study uniquely combines cyclic bending fatigue at 23 °C and 70 °C with ATC between 0 °C and 100 °C, simulating operational stresses in real-world environments, in contrast to previous research that has focused primarily on either isolated mechanical or thermal effects. The 425 nm thick films showed high transparency and conductivity, making them suitable materials for flexible electronics and optoelectronic devices. In this work, electrical resistivity, one of the most important performance parameters, was investigated after each mechanical or thermal cycle. The results indicate that mechanical cycling at high temperatures can drastically enhance the crack formation and electrical degradation, with an over 250% change in the electrical resistance (PCER) after 12,000 cycles at 70 °C and more than 300% after 500 thermal cycles. The highly deleterious effects of combined stressors on the structural integrity and electrical properties of AZO films are underlined by these observations. This study further suggests that the design of more robust AZO-based materials/coatings would contribute toward achieving better durability in flexible electronic applications. These findings also go hand in glove with the ninth goal of the United Nations' Sustainable Development Goals, specifically Target 9.5: Enhance Research and Upgrade Industrial Technologies. [ABSTRACT FROM AUTHOR]

This study examines copper thin films under tensile stress and their shape and percentage change in electrical resistance (PCER) as a function of applied strain. Copper films of 100 and 200 nm thickness were sputtered onto polyethylene terephthalate (PET) substrates and were then sequentially stretched to examine how film thickness affects strain-induced morphological changes and electrical resistance. A scanning electron microscope (SEM) was used to track crack patterns, and electrical resistance was monitored throughout tensile testing. Thinner films (100 nm) had quick crack initiation and propagation, leading to an increase in PCER under strain, while thicker films (200 nm) had more gradual morphological and electrical resistance changes. This differential reaction demonstrates the importance of film thickness in mechanical deformation and strain sensitivity, which could affect the design of flexible electronic devices that require mechanical durability and reliable electrical performance. These findings will help to optimize film thickness for stretchable sensors and wearable electronics to balance strain sensitivity and morphological degradation. This study will help designers and users of sensors, stretchable electronics, and other devices that require mechanical durability and electrical performance to understand the relationship between mechanical deformation and electrical properties in thin films. This paper aligns with the ninth goal of the United Nations Sustainable Development Goals, specifically Target 9.5: Enhance Research and Upgrade Industrial Technologies. [ABSTRACT FROM AUTHOR]

The mechanical and electrical deterioration of chromium (Cr) thin films sputtered onto polyethylene terephthalate (PET) substrates under tensile strain was studied. Understanding mechanical and electrical stability due to imposed strain is particularly important for device reliability, as the demand for flexible electronic devices increases. Cr thin films, widely spread across the field of electronic and sensor applications, face crack propagation with electrical degradation with tensile stress that can seriously compromise the performance. Accordingly, this study offers new findings on how Cr film thickness might influence crack formation and electrical resistance differently and also the general guidelines for flexible electronic component design with respect to long-term durability. Electrical resistances were measured while mechanically stretching 100- and 200 nm thin sheets. The study focused on crack development and propagation mechanisms in both film thicknesses and their effects on percentage change in electrical resistance (PCER). Scanning electronic microscopy (SEM) was used to characterize surface morphology and observe cracks as the strain rose. Early crack formation in 100 nm Cr films led to rapid PCER increases due to quick crack propagation and fast electrical degradation. Thicker 200 nm films, however, showed a more gradual PCER rise with fewer but deeper cracks, indicating a regulated strain response. Unlike the sharp PCER spike in 100 nm films, 200 nm samples were more variable, with three out of four showing a slight PCER decrease at the end, hinting at partial crack repair or conductive realignment before full failure. These results underscore the role of layer thickness in managing crack propagation and electrical stability, relevant for flexible electronics and strain sensors. This paper is aligned with the ninth goal of the United Nations Sustainable Development Goals, specifically Target 9.5: Enhance Research and Upgrade Industrial Technologies. [ABSTRACT FROM AUTHOR]

The paper presents a methodology that integrates Quality-Function Deployment (QFD) and the Theory of Inventive Problem Solving (TRIZ) used for generating innovative solutions to design problems. It proposes a modified analytical House of Quality (HoQ) to reveal and prioritize contradictions between design parameters and between customer requirements. The proposed methodology extends the traditional HoQ and eliminates the need for the TRIZ's Function Analysis (FA) procedure. Function Analysis involves identifying the functions of a product or process elements and trying to find contradictions between the system elements. The usability of the proposed method is illustrated through the redesign of an assembly workshop to overcome major problems addressed by the various stakeholders of the process. The new design of the assembly workshop helps reduce the number of work stages from 3 to 1, reduce the number of workers from 4 to 2, decrease rework, decrease the percentage of damaged products, enhance workplace ergonomics and improve the overall system efficiency. [ABSTRACT FROM AUTHOR]

During operation, electronic components are exposed to high temperatures that may last for long periods, depending on the operating duration. Solder joints are one of the components most affected by thermal aging while in service. In this research, the effect of thermal aging duration and temperature on the mechanical properties of 92.8%Sn-3%Ag-0.5%Cu-3.3%Bi (Cyclomax) was investigated. The novelty of this work lies in the study of the important properties of a new generation of Sn-Ag-Cu (SAC) materials (i.e., Cyclomax). Cyclomax is rare in industry and immature in research. To understand the effect of thermal aging, the microstructure was investigated, and changes in it and its mechanical properties were observed. To simulate solder joints in electronic devices, samples of solder balls were prepared and attached to copper pads on electronic boards. Most samples were then treated at 150 °C or 100 °C for up to 1000 h and some samples were left untreated for comparison. A scanning electron microscope (SEM) was used to obtain images of the microstructure. The shear stress–shear strain relationships, including the ultimate shear strength (USS), the modulus of elasticity and the ultimate energy (UE), were investigated. The microstructure images indicated the presence of a layer of Cu6Sn5 on top of the copper pad before thermal aging was applied. The thickness of this layer increased with the application of thermal aging over time. The results for the shear stress–shear strain relationship indicate that all of the USS, the total energy (TE) to shear off the solder balls and the UE decreased at the beginning of the thermal aging and then reversed to increase later. In general, isothermal aging reduces the performance of Cyclomax solder joints in terms of the minimum force and energy required to separate and subsequently damage electronic components. [ABSTRACT FROM AUTHOR]

Solder joints are subjected to varied stress cycle circumstances in the electronic packaging service life but are also influenced by aging. There has been limited investigation into the influence of aging and varying cycles on SnAgCu-Bi (SAC-Bi) solder joint fatigue. Cyclic fatigue tests were performed on solder joints of several alloys, including SnAgCu (SAC305), SnAgCu-Bi (SAC-Q), and SnCu-Bi (SAC-R). Individual solder joints were cycled under varying stress levels, alternating between mild and harsh stress levels. At least seven samples were prepared for each alloy by alternating between 25 mild stress (MS) cycles and three harsh stress (HS) cycles until the solder joint broke off. The impact of aging on Bi-doped solder joints fatigue under varied amplitude stress was examined and predicted for 10 and 1000 h under 125 °C. Because of the "Step-up" phenomenon of inelastic work, a new fatigue model was developed based on the common damage accumulation (CDA) model. The experimental results revealed that aging reduced the fatigue life of the tested solder alloys, particularly that of SAC305. According to the CDA model, all solder alloys failed earlier than expected after aging. The proposed model uses the amplification factor to assess inelastic work amplification after switching between the MS and HS cycles under varying stress amplitude conditions. The amplification factor for the SAC-Bi solder alloys increased linearly with fracture initiation and substantially followed crack propagation until the final failure. Compared with existing damage accumulation models, the proposed fatigue model provides a more accurate estimation of damage accumulation. For each case, the cut-off positions were examined. The SAC-Q amplification factor increased linearly to 83% of its overall life, which was much higher than that of SAC305 and SAC-R. This study identified three distinct failure modes: ductile, brittle, and near intermetallic compound (IMC) failure. It was also observed that SAC-Q with an organic solderability preservatives (OSP) surface finish was more susceptible to brittle failure owing to the excessive brittleness of the alloy material. [ABSTRACT FROM AUTHOR]

The surface finish (SF) becomes a part of the solder joint during assembly and improves the component's reliability. Furthermore, the SF influences the solder joint's reliability by affecting the thickness of the intermetallic compound (IMC) layer at the solder interface and copper pads. In this experiment, five different alloys are used and compared with the SAC305 alloy, two of which, Innolot and SAC-Bi, are bi-based solder alloys. This study includes three common SFs: electroless nickel immersion gold (ENIG), immersion silver (ImAg), and organic solderability preserve (OSP). The performance of three surface finishes is examined in terms of component characteristic life. All of the boards were isothermally aged for twelve months at 125 °C. The boards were then exposed to 5000 cycles of thermal cycling at temperatures ranging from −40–+125 °C. Most of the current research considers only one or two factors affecting the reliability of the electronic package. This study combines the effect of multiple factors, including solder paste content, SF, isothermal aging, and thermal cycling, to ensure that the test conditions represent real-world applications. In addition, the electronics packages are assembled using commercialized alloys. The current study focuses on a high-performance alloy already present in the electronic market. The failure data were analyzed statistically using the Weibull distribution and design of experiments (DOE) analysis of variance (ANOVA) techniques. The findings reveal that the micro and uniformly distributed precipitates in solder microstructures are critical for high-reliability solder joints. Re-crystallization of the thermally cycled solder joints promotes the local formation of numerous new grains in stress-concentrated zones. As the fracture spreads along these grain boundaries and eventually fails, these new grains participate in crack propagation. Aging significantly worsens this situation. Finally, although the ENIG surface finish with its Ni layer outperforms other SFs, this does not imply that ENIG is more reliable in all solder paste/sphere/finish combinations. [ABSTRACT FROM AUTHOR]

The failure of one solder joint out of the hundreds of joints in a system compromises the reliability of the electronics assembly. Thermal cycling is a result of both creep–fatigue mechanisms working together. To better understand the failure process in thermal cycling, it is crucial to analyze both the effects of creep and fatigue mechanisms in a methodical manner. In this work, individual solder junctions are subjected to accelerated shear fatigue testing to investigate the effects of creep and fatigue on joint dependability at room temperature. A modified fixture is used to conduct fatigue tests on an Instron 5948 micromechanical tester. SAC305 joints with an OSP surface finish were cycled under stress control at first, and then the strain was maintained for a set amount of time. In this investigation, three stress amplitudes of 16, 20, and 24 MPa are used, together with varying residence periods of 0, 10, 60, and 180 s. The fatigue life of solder junctions is described for each testing condition using the two-parameter Weibull distribution. Additionally, as a function of stress amplitude and residence time, a dependability model is created. For each testing scenario, the progression of the stress–strain loops was studied. By quantifying relevant damage metrics, such as plastic work per cycle and plastic strain at various testing circumstances, the damage due to fatigue is distinguished from creep. To investigate the relationships between plastic work and plastic strain with fatigue life, the Coffin–Manson and Morrow Energy model is used. The results indicate that using greater stress magnitudes or longer dwell periods significantly shortens fatigue life and dramatically increases plastic work and plastic strain. The housing impact is significant; in some circumstances, testing with a longer dwelling period and lower stress amplitude resulted in more damage than testing with a shorter dwelling period and higher stress levels. When illustrating the fatigue behavior of solder junctions under various stress amplitudes or dwellings, the Coffin–Manson and Morrow Energy model were both useful. In the end, general reliability models are developed as functions of plastic work and plastic strain. [ABSTRACT FROM AUTHOR]

The mechanical and fatigue properties of microelectronic interconnection materials are important issues in critical applications in the life of electronic assemblies. Due to the growth in the applications of electronic components in new technological products used in tough conditions, evaluating the reliability of solder alloys has become crucial to the prediction of product life. SAC (Sn-Ag-Cu) solder alloys are common lead-free alloys used to form solder joints. In the current study, the reliability of individual SAC305 solder joints in actual setting conditions with an organic solderability preservative (OSP) surface finish was examined using an accelerated shear fatigue test at different load levels (16 MPa, 20 MPa, and 24 MPa). Four operating temperature levels (−10, 25, 60, and 100 °C) were also used. Seven samples were utilized at each experimental condition. An orthogonal array (L12) was employed for this experiment. The fatigue behavior of the SAC305 solder joints in actual setting conditions was described by a two-parameter Weibull distribution. The characteristic life and the shape parameter were extrapolated from the Weibull distribution for each experimental condition. Characteristic life was employed to represent the fatigue resistance of the solder joints. For each sample, the inelastic work per cycle and plastic deformation were determined. The results indicated a notable increase in the inelastic work per cycle and the plastic strain as a result of increasing either the stress load or the working temperature. Combinations of stress amplitude, working temperature, inelastic work, and plastic deformation were applied as inputs to the fuzzy system for computing a comprehensive output measure (COM-Value) using the Mamdani method. A negative relationship was observed between the solder life and the four fuzzy inputs. To fuzzify the inputs of the fuzzy system, two membership functions, "MFs", were formed for each input, and five MFs were set for the output. The center-of-gravity (COG) theorem was utilized as a defuzzification method in the fuzzy inference system. The characteristic life of the solder joints was predicted by the COM-Value, which was used as an independent variable. Finally, The COM-Value was used to generate a general predicted reliability model for SAC305 solder joints with an acceptable model adequacy index. [ABSTRACT FROM AUTHOR]

Many electronic products are subjected to heat for long periods, depending on their operations. Thus, it is expected that the physical and mechanical properties of electronic elements, including the soldering joints, will be affected. In this study, the impact of thermal aging time and temperature on the microstructure and mechanical properties of 96.5Sn–3.0Ag–0.5Cu (SAC305) was investigated. The samples used were SAC305 solder balls attached to copper pads. The research began by examining the microstructure of the aged samples at 150 °C for 100 and 1000 h. Then, this was compared to the microstructure of the same samples without thermal aging. Then, five groups of 10 samples were prepared from a shear stress–shear stain experiment. The first group was as produced, the second group was aged for 2 h, the third group was aged for 10 h, the fourth group was aged for 100 h, and the fifth group was aged for 1000 h. All groups were aged at a temperature of 150 °C. An Instron testing machine was used to plot a shear stress–shear stain curve until the ball was completely sheared off the pad. The mechanical properties, including the ultimate shear strength, the ultimate energy used to shear the ball, and the total energy used to shear the ball at all thermal aging times were then estimated. The results of this study indicated the formation of a layer of Cu6Sn5 over the copper pad, which thickened with thermal aging time. Furthermore, the ultimate and total shear strengths decreased with thermal aging time. The same procedure was repeated to assess the ultimate shear strength at 100 °C. The decrease in ultimate shear strength was more severe with increasing thermal aging temperature. [ABSTRACT FROM AUTHOR]