Term Reliability Research Articles

Copper Crystal Structures in Plated Microvias. Their Recrystallisation and a Means to Identify Joints at Risk of Premature Failure

Abstract Plated microvias are widely used within todays PCB industry as a means of achieving the high-density designs that are required in modern mobile devices, however, there has been growing concern regarding their long term reliability performance when stacked directly on top of each other. Blind microvias (BMV) have a potentially complex metallurgical structure, with several interfaces located around the target pad - electroless Copper - electrolytic Copper joint. While field experience as shown that there are typically two major types of crystal structures formed across the BMV base, there has been little reported work investigating how or why such structures develop. In this paper, we review these two commonly observed microstructures within filled BMVs and offer proposals on how such structures are created. We subsequently describe a novel means to indicate if the microstructure of a BMV is likely to have a tendency for an early onset of failure.

C-doped LaFeO3 Porous Nanostructures for Highly Selective Detection of Formaldehyde

LaFeO3 is a promising sensing material owing to its preferable stability and lower phase formation temperature, while the sensing detection limit, working temperature and selectivity are far from the requirement of practical application. Herein, porous LaFeO3/C nanocomposites were successfully synthesized for the first time through a facile foaming sol-gel technique. The amount of carbon and the microstructure of nanocomposites can be simply controlled by adjusting the content of PVP in precursors. The systematical sensing investigation demonstrates that LaFeO3 with 10 % PVP exhibits excellent sensing properties with sensitivity of 74.3–50 ppm formaldehyde at 125 °C, which is around 3 times higher than that of pristine LaFeO3. When the formaldehyde concentration is as low as 500 ppb, the sample still presents a high response value of 2. Moreover, the sample shows good long term reliability and high selectivity of 13.3 to formaldehyde. Further detailed analysis indicates the improving sensing performance of LaFeO3/C can be attributed to the large specific surface area, porous structure and increased electrical conductivity of the material. This work builds an efficient and simple example for the fabrication of high sensing performance formaldehyde sensors.

Short term reliability and robustness of ultra-thin barrier, 110 nm-gate AlN/GaN HEMTs

Short-term reliability and robustness of 110 nm AlN/GaN HEMTs has been evaluated by means of off-state, semi-on state and on-state step stress tests on devices having different gate-drain distance, LGD. While breakdown voltages and critical voltages scale almost linearly with LGD, failure mode remains almost unchanged in all tested devices, and consists in an increase of gate leakage, accompanied by a positive shift of threshold voltage. In off-state, electroluminescence images detect the presence of localized leakage paths which may act as preferential paths for electron trapping. Degradation does not depend on dissipated power and is preliminary attributed to hot-electron trapping, enhanced by electric fields.

Microstructural characterization of alloyed palladium coated copper wire under high temperature

Palladium coated copper (PCC) wire has been increasingly used in the semiconductor package in the last 10 years, especially in consumer products as a low-cost alternative to gold (Au) bonding wire. However, the PCC wire is still not widely used in the automotive industry due to the reliability limitations under a high temperature condition. In order to improve the long term reliability of PCC wire under a high temperature condition, new additive elements in the Cu core have been considered. In this paper, we investigate the role of additive elements in PCC wire and their effect on corrosion resistance under high temperature conditions. Pd and platinum (Pt) are examined as additive elements. Additive Pd and Pt in PCC wire become a cause of degradation for the stitch bond reliability under the high temperature condition due to the different degradation microstructure from conventional PCC wire.

A review of intermetallic compound growth and void formation in electrodeposited Cu–Sn Layers for microsystems packaging

In recent years, Cu–Sn solid–liquid interdiffusion (SLID) bonding has been used in semiconductor packaging, die-attach, fine-pitch interconnection, and through-silicon vias (TSV)-based 3D stacking applications. Due to its specific advantages such as lower cost, less stringent surface uniformity requirements, higher thermal bond stability, and relatively lower processing temperatures, electrodeposited Cu–Sn-based bonding is explored to achieve wafer-level hermetic encapsulation of miniaturized sensors; however, the overall reliability of Cu–Sn bonds remains a challenge. The voids formed in the electrodeposited Cu–Sn layers and the brittle nature of the formed intermetallic compounds (IMC) affects the long term reliability of the Cu–Sn SLID bonds. A significant concern is the sporadic interfacial void formation within the Cu–Sn layers during the bonding process and high-temperature applications. This review article summarizes the different mechanisms of the IMC formation and their growth and explores the reasons behind the interfacial voids formed in the electrodeposited Cu–Sn layers when these are annealed at different temperatures ranging from 150 to 300 °C. A detailed description of the IMC and void formation and their subsequent growth in the thick electrodeposited Cu–Sn layers is presented, along with the various design parameters affecting the IMC growth during the bonding process. Various remedies to minimize these interfacial voids are also suggested. Higher bonding pressure, lower processing temperature, and reduced surface roughness are the key factors affecting the void size and voids density. The chemical impurity in the copper electrolyte and the resultant surface roughness affect the interfacial void formation in the electrodeposited Cu–Sn layers. This review will help minimize the interfacial voids and, thus, obtain higher bond reliability.

A Highly Scalable, Modular Test Bench Architecture for Large-Scale DC Power Cycling of SiC MOSFETs: Towards Data Enabled Reliability

Silicon carbide (SiC) power MOSFETs have superior conduction, switching and thermal properties compared to silicon (Si) MOSFETs and IGBTs [1]. However, unlike Si devices, whose reliability is well understood from decades of research and field data, SiC device technology is relatively nascent and has only recently started witnessing wide scale deployment. This reliability challenge can possibly be addressed through two complementary solutions as shown in Figure 1: 1) developing a large accelerated aging dataset of SiC devices under various conditions to understand their long term reliability and guide future device development, 2) using on-board, in-system prognostics and device health monitoring techniques to predict imminent device failures well ahead of time, thus ensuring reliable system operation [2]. In both cases, the large-scale reliability testing of SiC MOSFETs is needed. Generally, remaining useful lifetime (RUL) estimation methods for power devices use an empirical model obtained from fitting accelerated aging data [3]-[7], [9], [10]. Consequently, the accuracy of RUL models is directly related to the size and variety of available accelerated aging dataset. Moreover, large datasets are crucial in enabling machine learning (ML) and artificial intelligence (AI) based reliability models.

Interfacial structures between aluminum nitride and Cu–P–Sn–Ni brazing alloy with Ti film

Control of Ag electro chemical migration is crucial for long–term reliability of electrical components in high–voltage applications. In this work, Cu was bonded onto an AlN substrate at temperatures between 650 °C and 950 °C for 1 h using a Ag free Cu–P–Sn–Ni brazing filler metal with Ti as an active metal addition. The interfacial structure between the Cu and the AlN and the mechanical properties of the bond were both investigated. Three different phases which contain Ti and O were observed during the growth process of the Cu/AlN interfacial reaction layer: an amorphous P–Ti–O phase, an amorphous Ti–O phase and rutile, TiO2. The most stable Cu/AlN interfacial structure occurred when rutile was present, and where a particular orientation relationship with AlN was observed: TiO2 (101)//AlN (0001), TiO2 [010]//AlN [ $$11\overline{2}0$$ ]. The probability of Cu/AlN interfacial fracture decreased as the bonding temperature was increased. Cu/AlN interfacial fracture was completely suppressed above 850 °C where rutile was the dominant phase at the Cu/AlN interface.

High Cycle Fatigue Behaviour of Cu/Sn Intermetallic Compounds Prepared by Transient Liquid Phase Bonding Process

Transient liquid phase (TLP) bonds using Cu-Sn system have been suggested as high strength and temperature resistant joints for power electronics applications. While the physical and mechanical properties of these joints has been investigated to some extent, studies on fatigue properties and long term reliability of TLP joints are scarce. In this work TLP bonding was performed to produce thin Cu-Sn intermetallic joints by using Cu and 97Sn3Cu solder alloy as interlayer. Different processing conditions resulted in three types of thin joints consisting of three phases (Cu3Sn/Cu6Sn5/solder remnants), two phases (Cu3Sn/Cu6Sn5) and a single phase (Cu3Sn) with an overall thickness of ≤ 20 μm. The shear strength of the TLP joint containing one or two high melting point IMC layers showed a significant temperature resistance up to 200°C. Fatigue studies of TLP joints were conducted by using a 3-point-cyclic bending test system operating at 20 kHz. The highest fatigue resistance was obtained for the single-phase Cu3Sn joints with superior shear and flexural resistance. The two phase joints (Cu3Sn/Cu6Sn5) showed a slightly lower lifetime than the three phase system containing IMCs and residual solder. Fracture surfaces analysis in correlation with static and cyclic mechanical properties, provided insight into the failure mechanism of the Cu-Sn TLP joints.

Accelerated mechanical low cycle fatigue in isothermal solder interconnects

Properly assessing the underlying physics of failure is critical in predicting the long term reliability of electronic packages in their intended field applications, yet traditional reliability demonstration methods are complicated by time and cost considerations as well as deterministic inadequacies when considering thermomechanical failures. In this work, an alternative reliability testing apparatus and associated protocol were utilized to provide clarity and insight to solder fatigue mechanisms at the device scale; targeting rapid testing times with minimal cost while preserving fatigue life prediction accuracy. A test stand was developed to allow for bi-directional application of shear stress at elevated steady-state temperatures. Utilizing the mechanical force of springs to apply shear loads to solder interconnects within the devices, the reliability of a given device to withstand repeated cycling was studied using in situ resistance monitoring techniques to detect the number of cycles-to-failure (CTF) based on a 30% resistance increase criterion. A mathematical method for quantifying the plastic work density (amount of damage) sustained by the solder interconnects prior to failure was developed relying on the relationship between Hooke's Law for springs and damage deflection to accurately assess the mechanical strength of tested devices.

WITHDRAWN: Critical review on software reliability models: Importance and application of reliability analysis in software development

Abstract Initially the term reliability was used in the development of critical systems (controller of the nuclear plant, navigational system of the spacecraft, customer accounting system in a bank and stock-trading system… etc…). Later, it had been used in the small scale system and application development, due to the impact of it in the quality measurement and enhancement the of software system. In the software development, the word reliability means the failure free operation of the software system in a pre-specified time and environment. Reliability is the important metric which reflect the degree of correctness of the program. Reliability prediction in the early phase of the development process offers many advances like quality enhancement, resource allocation for development and testing and confidence about the software quality. Many programming languages (C++, Java, .NET… etc…) had developed based on this feature. Nowadays the complexity of software design and its size is augmented as the need of the societies increased. For this reason, software development process also moved towards the component based development and other advanced process for the development, which enable the superior reuse and easy maintenance and quick development of the software system. There is a need for the new models which would be developed based on the new development process. Because, all the existing models having assumptions and limitation which can only be suitable for the specific project or process. The main objective of this paper is to give the idea and knowledge to the young researchers, about the software reliability models of different development processes and its importance to produce the failure free software product. And also stimulate them to develop the novel models which can be used in the new software development process and projects.

Reliability analysis of corroded beams with FRP laminates

The term reliability and structural performance means the probability of the structure performing its intended function during its expected life time under the environmental conditions to which it is exposed. Reliability- based techniques can be used to account for the randomness in important variables that affect the strength of FRP strengthened RC beams. The use of such methods in structural engineering has greatly increased as reliability based models have been better properly understood and more widely accepted. Various parameters in GFRP strengthened corrosion-damaged RC beams are validated through reliability index by using simulation techniques and goodness of fit tests. Simulation is the technique of virtual testing of the validity of a physical phenomenon/structural design/mathematical equation without actually performing the experiment to obtain the values of the variables involved but by generating them through a mathematically tractable process called random number generation.

Experimental investigation on performance degradation of a supercritical CO2 radial compressor by foreign object damage

As more supercritical CO2 (S-CO2) power systems are operating around the world, long term operability and reliability of the system will become salient issues in the near future. In this research, the performance degradation of an S-CO2 compressor is investigated experimentally, and degradation models are developed to explain the performance degradation of the S-CO2 compressor at first. The investigated degradation is damaged on the impeller caused by foreign object approximately 3 mm size. The damage caused the shape change of the impeller. From the comparison of the performances of the damaged impeller to the intact impeller, it is confirmed that the performance degradation does not affect the surge margin. The correction model for the degradation of gas compressor performances has a limitation when the pressure ratio was used for measuring the performance. However, it is also shown that the correction model works well if the enthalpy rise is utilized instead of the pressure ratio. This study experimentally shows the possibility that the performance degradation of the S-CO2 compressor can be modeled through a linear model based on enthalpy. Further research is needed to validate the model for wider operating conditions and more severe degraded conditions.

Antibiotic induced changes to mitochondria result in potential contributions to carcinogenesis, heart pathologies, other medical conditions and ecosystem risks

With the discovery by Calghatgi (2013) that three common antibiotics (Abs) increased mitochondrial reactive oxygen (ROS) and lipid peroxide (LP) and depleted their natural absorbant glutathione led me to investigate further the potential impacts of these genotoxic substances on carcinogenesis. The range of impacts on mitochondria and cellular DNA varied by antibiotic to those consistent with known prior contributions to carcinogenesis. Specific cancers probably increased by these changes were HCC, RCC (KCC), CRC, cancer of the esophagus. Tumor suppressor gene mutations resulting from LP were noteworthy in this regard and mutations induced in CRC were consistent with those found in carcinogenesis of CRC. In addition depression of short chain fatty acids in microbiomes were found which depress the immune system increasing risk of all cancers. Many cancers were increased according to epidemiological studies linking Abs with elevated odds ratios, with one concern in particular, fatal breast cancer. The impact of loss of functionality of the mitochondria was also linked to depression of the citric acid cycle and therefore ATP which deflected metabolism to glycolysis, the Warburg mechanism also increasing risk of all cancers, favoured by cancer cells. In conclusion, some portion of many cancer types are probably increased in likelihood by number, type and frequency of Abs treatment and chronic residue exposure which varies from individual to individual. This led me to propose a three pronged carcinogenesis mechanism for Abs. 1. Cancer critical mutations 2. Immune depression 3. loss of mitochondrial functionality leading to Warburg effects. Damage to mitochondria were also noted by common pesticides tested in China and cancer associations were also found for many pesticides supporting a similar contributory etiology. Heart health concerns were raised by these findings because of the myriad mitochondria in the heart and because of long term reliability needs. Studies suggesting hearts were affected by Abs and pesticide exposure were presented. Because of their geographical ubiquitousness and the huge range of diseases associated with mitochondrial dysfunction, antibiotics and pesticides and bacteriocidal biocides are of concern for biodiversity and life in general. I propose research steps to evaluate Abs safety and suggest directions for further research and make suggestions on ways to ameliorate Abs toxicity.

Lithium Battery Cell Level Fusing with Aluminum Heavy Wire Bonds

Abstract Aluminum heavy wire bonds interconnects are a potential alternative to laser or resistance welded bus bars due to its ease of manufacturability, long term reliability and low cost for battery banks. They can also be utilized as a fault protection solution in case of a surge current, dead short, etc, and to isolate a bad cell preventing synchronous failure. Typically, the current-carrying capability of a wire is estimated using standard data generated by testing in free air. However, a deviation in the capacity limits can occur due to the proximity of interconnect to larger thermal masses and different heat extraction techniques found in present day lithium battery packs; e.g., fluid channel cooling, encapsulated wires, etc. The cylindrical cell cathode, anode, and the busbar material constitute a large thermal mass to increase the fusing current in wire bonds above conventional levels. To better predict and design the interconnects advanced and system-specific models should be developed. This paper presents a new mathematical approach which includes the effect of convective cooling inside the battery pack to do an early step estimation of the current handling capacity and fusing time of different diameter wires. The paper also presents a finite element model that includes the impact of boundary conditions, wire length and wire diameter on steady-state current handling capacity of 99.99 % Al wire. Both steady-state and transient simulations were performed to estimate fusing times at different time rated conditions. The paper concludes by providing new curve-fit patterns to give future battery pack designers further insight aiding new designs.

Plasma Surface Engineering: An Enabling Technology Designed to Clean and Protect Printed Circuit Boards

Abstract Long term reliability and performance of printed circuit boards (PCBs) are strongly affected by the presence of surface contaminants from the manufacturing and assembly processes. Flux and solder residue, dust particles, oils and greases are often found on the assembled boards and can inhibit the successful application of conformal coatings that are used to protect the electronic components. Surface contaminants can cause coating delamination, dendritic growth, electromigration, corrosion and result in compromised coatings. In the first part of this paper, the fundamental mechanism of plasma-induced removal of organic contaminants from PCBs will be presented. While vacuum based plasmas are considered the traditional solvent-free technology for surface cleaning, a new approach involving air plasma operating under atmospheric pressure conditions is gaining interest due to its adaptability for industrial inline processing. The low concentration of oxygen that is available in the plasma gas is effective in vaporizing organic contaminants leaving behind a clean surface. Additionally, atmospheric plasma processes focusing on the development of functional nanocoatings on PCBs have been investigated. These plasma-enhanced chemical vapor deposition (PECVD) processes involve the delivery and vaporization of small volumes of solvent-free precursors that react with the plasma to form thin coatings on polymer substrates. Depending on the chemical structure of the precursor used, adhesion promoting, water repellant or electrical barrier coatings of 30–100nm thickness can be deposited. These protective functional coatings do not require any curing or special handling and no chemical waste is generated. The latest developments in atmospheric pressure PECVD for electronics protection will be presented in the second part of the paper. Besides the improvement of device performance and reliability, the application of PECVD has the potential to replace chemical substances such as primers known to have harmful impact on human health and the environment.

The effect of rate design on power distribution reliability considering adoption of distributed energy resources

Electricity rates are a main driver for adoption of Distributed Energy Resources (DERs) by private consumers. In turn, DERs are a major component of the reliability of energy access in the long run. Defining reliability indices in a paradigm where energy is generated both behind and in front of the meter is part of an ongoing discussion about the future role of utilities and system operators with many regulatory implications. This paper contributes to that discussion by analyzing the effect of rate design on the long term reliability indices of power distribution. A methodology to quantify this effect is proposed and a case study involving photovoltaic (PV) and storage technology adoption in California is presented. Several numerical simulations illustrate how electricity rates affect the grid reliability by altering dispatch and adoption of the DERs. We further document that the impact of rate design on reliability can be very different from the perspective of the utility versus that of the consumers. Our model affirms the positive connection between investments in DERs and the grid reliability and provides an additional tool to policy-makers for improving the reliability of the grid in the long term.

Injectable and moldable hydrogels for use in sensitive and wide range strain sensing applications

Recently, the use of hybrid double network (DN) hydrogels has become prominent due to their enhanced mechanical properties, which has opened the door for new applications of these soft materials. Only a few of these gels have demonstrated both injectable and moldable capabilities. In this work, we report the mechanical properties, gauge factor (GF) values and demonstrate both the injectability and moldability of a gelatin/polyacrylamide DN hydrogel. We optimized several parameters, such as, gelatin to polyacrylamide ratio, reactant concentrations and metal ion concentration, to produce a gelatin/polyacrylamide hydrogel with superior mechanical properties. The highest water content gel was capable of withstanding strains of 5000% before failure. These gels were facilely injected into molds where they effectively changed shape and maintained similar properties prior to remolding. When 20 mM calcium was doped into a similar gel, a tensile strength of 1.71 MPa was achieved. Aside from improving the mechanical properties of the gels, both Ca2+ and Mg2+ also improved their conductivity, so they were tested for use as strain sensors. The sensitivity of the hydrogel strain sensors were measured using the GF. For the 20 mM Ca2+ hydrogel, these GF values ranged from 1.63 to 6.85 for strains of 100% to 2100% respectively. Additionally, the sensors showed good stability over continuous cyclic stretching, demonstrating their long term reliability for strain sensing.

KM3NeT acquisition: the new version of the Central Logic Board and its related Power Board, with highlights and evolution of the Control Unit

The KM3NeT collaboration is currently building two deep sea neutrino telescopes at the bottom of the Mediterranean sea. The acquisition electronics for the first phase of the telescopes has been produced and several Detection Units have already been deployed. For subsequent phases, an improved version of the acquisition electronics has been designed with the goal of reducing the power consumption and improving the long term reliability of the boards. The control software suite, named Control Unit, is also being upgraded, in particular to overcome hardware failures. In this article, we present the last versions of the Central Logic Board and its associated Power Board, together with the evolution of the Control Unit.

Long Term Reliability and Predictive Validity of a Universal Screening Tool for Identifying Students at Risk for Reading Problem

본 연구의 주된 목적은 보편적 선별검사로 사용한 읽기 CBM의 신뢰도와 예측타당도를 분석하는 것이었다. 특별히 본 연구에서는 초등학교 1학년부터 3학년 학기말까지의 자료를 종단적으로 수집하여 장기 신뢰도와 예측타당도를 검증한 연구의 의의를 갖고 있었다. 본 연구에서는 상관계수, ROC 곡선 분석, 잠재성장모형 분석방법을 사용하여 신뢰도와 예측타당도를 검증하였다. 연구결과에 따르면 CBM 선별검사의 점수는 안정적인 장기 신뢰도와 예측타당도를 지닌 것으로 나타났다. 또한 본 연구에서는 CBM 선별검사의 기울기 예측 타당도를 추가적으로 검증하였는데, 분석결과에 따르면 CBM 기울기는 3학년 학기말의 읽기학업성취검사점수를 통계적으로 유의하게 예측할 수 있는 독립변인으로 나타났다. 끝으로 본 연구는 보편적 선별에 대한 시사점과 향후 연구주제를 제안하고 있다.The current study seeks to investigate the reliability and the predictive validity of Korea maze CBM as a universal screening tool in reading. Especially this study focused on the long term reliability and predictive validity over the 3-year period(Grade1-3). Pearson product-moment correlations, ROC curve analysis, and individual latent growth modeling were used to examine the reliability and the predictive of Korea maze CBM. Results of this study showed that Korea maze CBM significantly predicted performance on a reading achievement test at the end of Grade 3. In addition, slope of Korea maze CBM was predictive of student’s reading skills. The findings have implications for universal screening using Korea maze CBM.

Long Term Reliability and Predictive Validity of a Universal Screening Tool for Identifying Students at Risk for Reading Problem

Long Term Reliability and Predictive Validity of a Universal Screening Tool for Identifying Students at Risk for Reading Problem