Fatigue failure of solder joints is one of the major causes of failure in electronic devices. Fatigue life prediction models of solder joints were first put forward in the early 1960s, and since then, numbers of methods were used to model the fatigue mechanism of solder joints. In this article, the majority fatigue life models are summarized, with emphasis on the latest developments in the fatigue life prediction methods. All the models reviewed are grouped into four categories based on the factors affecting the fatigue life of solder joints, which are: plastic strain-based fatigue models, creep damage-based fatigue models, energy-based fatigue models, and damage accumulation-based fatigue models. The models that do not fit any of the above categories are grouped into “other models.” Applications and potential limitations for those models are also discussed.

The reliability of solder joints plays a critical role in electronic assemblies. SnAgCu solder alloys with doped elements such as Bi and Sb is one of the candidates for high reliability applications. However, the mechanical and fatigue properties of the actual solder joint structure have not been studied for these new alloys. In this paper, a cyclic fatigue test was conducted on individual real solder joints of different alloys, including SnAgCu, SnCu–Bi, SnAgCu–Bi, and SnAgCu–BiSb. The fatigue property of those solder joints was analyzed based on the characteristic fatigue life and stress–strain, hysteresis, loops. The results show that solder joints with both Ag and Bi content have a better fatigue resistance than the solder joints with Ag or Bi content only. The results of SnAgCu and SnCu–Bi solder alloys show similar fatigue performance. Also, the fatigue performance of SnAgCu–Bi is close to SnAgCu–BiSb in the accelerated test. But the SnAgCu–Bi alloy is estimated to have a longer characteristic life under low-stress amplitude cycling. The microstructure analysis shows a bismuth-rich phase formed around the Ag3Sn precipitates. Adding bismuth in the solder alloy can significantly improve the fatigue properties through solid solution hardenings. On another hand, the plastic strain range and work dissipation were measured from the hysteresis loops for all tests. The Morrow Energy and the Coffin–Manson models were developed from the fitted data to predict the fatigue life as a function of work dissipation and plastic strain range.

Molybdenum chips are vital in manufacturing photovoltaic cells and electronics because they offer a combination of high reliability, corrosion resistance, and exceptional electrical conductivity. These qualities make them suitable for applications demanding these characteristics. This study delves into the behavior of thin molybdenum films deposited on plastic substrates under increasing stress. Films of 100 nm and 200 nm thicknesses were stretched, revealing intricate relationships between crack formation, film thickness, and electrical conductivity. Scanning electron microscopy captured the evolution of cracks, initially forming perpendicular to stress and later branching at roughly 30 degrees, hinting at anisotropic material behavior. Thicker films displayed lower crack density and less branching, highlighting their enhanced stress resistance. Further, secondary cracks short between the original cracks was developed. Percentage change of electrical resistance mirrored this trend, gradually increasing with strain before a sharp spike and eventual disconnection due to crack-induced conductivity loss. Thinner films succumbed to failure at lower strains. These findings offer valuable insights into the design and optimization of molybdenum-based microelectronic devices and sensors, paving the way for further quantitative analysis to fully elucidate the intricate mechanisms at play.

Aluminum-doped zinc oxide (AZO) presents an attractive option for cost-effective utilization as a transparent conductive oxide (TCO). Possessing favorable electrical and optical characteristics, AZO thin films hold potential, yet their dependability necessitates meticulous attention in both the manufacturing process and the practical deployment of flexible electronic devices. This paper presents a comprehensive investigation into the influence of cyclic bending fatigue on AZO thin films deposited on polyimide Kapton substrates. The AZO thin films were meticulously prepared using Radio Frequency (RF) magnetron sputtering, with precise attention to factors such as substrate cleanliness, target purity, and deposition parameters. The experimental setup involved cyclic bending fatigue experiments on carefully prepared specimens, with a focus on electrical resistance and optical transmittance measurements. The Analysis of Variance (ANOVA) was performed to ascertain the impact of various factors on the percentage change in electrical resistance (PCER). The results revealed that the number of cycles and bending diameter significantly affect the PCER. Notably, a detailed examination of the relationship between significant factors and PCER was facilitated through main effect plots. The study elucidates the interplay between factors such as bending cycles, bending diameter, bending frequency, and sample width, shedding light on the development of cracks due to fatigue. These findings contribute to the understanding of thin film behavior under cyclic bending conditions, with implications for applications such as flexible electronic packaging and solar cell technology.

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.

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.