Reliability Test Conditions Research Articles

Integrated design and real-world application of a tuned mass damper (TMD) with displacement constraints for large offshore monopile wind turbines

Passive tuned mass dampers (TMDs) have been increasingly investigated for vibration control of wind turbines. However, TMD designs based on individual or a few operating conditions may result in insufficient consideration of the TMD's impact on wind turbines. For instance, the influence of end-stop collision forces on the main structural damage may be significantly underestimated, thereby affecting the overall lifecycle evaluation. In this study, focusing on large offshore fixed-bottom monopile wind turbines, we propose an integrated TMD design methodology taking the damper displacement constraints into full account. A comprehensive optimization of the passive omnidirectional pendulum-type TMD is conducted considering large number of operating conditions in the offshore environment. Next, a real-world application of the optimally designed TMD is performed for a 6450 kW monopile offshore wind on the Yellow Sea, China. We develop an on-site testing methodology and evaluation criteria for assessing the effectiveness of the TMD offshore. The results of resonance, emergency stop, operatingand reliability test conditions demonstrate the following: under the optimized TMD design taking into account all operating conditions, the TMD with a mass ratio of 1.56% can offer added damping in the fore-aft and side-side directions of the turbine, and provides the desired damping ratio of 1%; within a 4% frequency range around the design frequency, the TMD achieves effective vibration control; at rated power, the TMD achieves a reduction of more than 50% in the amplitude of the tower base side-side bending moment (Mx). The integrated TMD design with displacement constraints allows for the optimal TMD design across all operating conditions, thereby achieving superior overall vibration control and reduction in fatigue loads. The successful real-world application of the TMD based on integrated design methodology is of high value to the research community.

Effects of alloying elements in high reliability copper wire bond material for high temperature applications

Recently, a shift from Au bonding wire to Cu bonding wire is expected for automotive application. Palladium coated copper (PCC) wire is strong candidate since it is widely used in LSI packages owing to its high performance and low cost. In order to apply PCC wire to automotive devices, long-term reliability specific to automobiles including stable operation under harsh environment with high temperature and humidity is required. However, pitting corrosion at the wedge bond portion was reported with PCC wire under high temperature storage life (HTSL) test. Depending on the surrounding environment such as mold compound, it is difficult for conventional PCC wire to achieve the target of automotive application. A newly developed PCC wire (EX1R) has thus developed. By using additive element in Cu core, halide induced interface corrosion and also pitting corrosion can be prevented successfully. In this paper, effect of additive element on the corrosion resistance will be discussed. The result shows that additive element forms protective passivation layer on the intermetallic compound (IMC) and Cu surface. Thereby, EX1R improves bond reliability even under severe reliability test condition.

30μm Thick Cu RDL in WLCSP

In situations where a device may have an interconnect pad arrangement in wafer level packaging, an additional layer of lateral connections may be employed to rearrange the connections in a manner suitable for wafer level processing. This additional layer is known as a redistribution layer, or RDL, and fabricated from a thin layer of metal with dielectrics in between. An RDL is used for higher electrical performance and complex routing to meet electrical requirements. As the importance of high power and power management in electronics products continue to rise, so also will the demands for power ICs to handle ever higher voltages without appreciably adding size and heat to the end product. Using thicker Cu metallization in an RDL is an ideal choice that accommodates high current density and lower resistance for high power applications. Assembling multiple chips in multiple layers requires more electrical connections, which in turn requires both thinner lines within the RDL and an increase in the number of RDL layers. The RDL line width of WLCSP started at over 20μm, but has already been reduced to 10~15μm in HVM. Industry players are now working in R&D to develop 2μm wide and even smaller line/space (L/S) capability to meet the requirements of today's high-end applications. In this study, we present the development of 20–30 μm thick plated Cu RDL for high power and high current density applications. Using a plated Cu process and photo-sensitive spin-on-dielectrics materials, thick Cu RDL was achieved with the AR 1:1 design rule and the reliability assessment was carried out with JEDEC reliability test conditions. A 2-layer Cu RDL (total 6-mask process with UBM) was developed and characterized for its component and board level reliability for 5×5/7×7mm, 0.35/0.4mm ball pitch WLCSP test vehicles.

<inline-formula> <tex-math notation="LaTeX">$In\ Situ$ </tex-math> </inline-formula> Failure Detection of Electronic Control Units Using Piezoresistive Stress Sensor

Recent advancements in automotive technologies, most notably autonomous driving, demand electronic systems much more complex than those realized in the past. The automotive industry has been forced to adopt advanced consumer electronics to satisfy the demand, and thus it becomes more challenging to assess system reliability while adopting the new technologies. The system-level reliability can be enforced by implementing a process called condition monitoring. In this paper, a piezoresistive silicon-based stress sensor is implemented to recognize in situ failure in outer molded electronic control units subjected to reliability testing conditions. The test vehicle consists of six double decawatt package power packages and three stress sensors mounted on a printed circuit board. A unique algorithm is proposed and implemented to handle the data obtained from the piezoresistive stress-sensing cells. The accuracy of measured data is examined by finite-element method, and the physical changes are validated with scanning acoustic microscope. One-class support vector machines are used to autonomously classify data based on a training set of measurements from healthy state, and the reported results confirm that robust classification is possible based on data from the silicon stress sensor.

Effect of texture and grain size on the residual stress of nanocrystalline thin films

Residual stresses develop in thin film interconnects mainly as a result of deposition conditions and multiple thermal loading cycles during the manufacturing flow. Understanding the relation between the distribution of residual stress and the interconnect microstructure is of key importance to manage the nucleation and growth of defects that can lead to failure under reliability testing and use conditions. Dislocation dynamics simulations are performed in nanocrystalline copper subjected to cyclic loading to quantify the distribution of residual stresses as a function of grain misorientation and grain size distribution. The outcomes of this work help to evaluate the effect of microstructure in thin films failure by identifying potential voiding sites. Furthermore, the simulations show how dislocation structures are influenced by texture and grain size distribution that affect the residual stress. For example, when dislocation loops reach the opposite grain boundary during loading, these dislocations remain locked during unloading.

Reliability of Heavy Gage Aluminum Wire-bonds under High Temperature Aging

Abstract Thick aluminum (Al) wedge bonds have been widely used in analog microelectronic packages due their lower cost, ease of use and excellent thermal and electrical performance. Reliability of thick Al wedge bonds on bare copper (Cu) leadframes under high temperature aging conditions has not been studied at a fundamental level in the past. This study investigates the reliability performance of Al wedge bonds on bare Cu surfaces under isothermal aging conditions specified by the automotive grade product qualification requirements. Results obtained show that Al/Cu intermetallic formed at the interface is detrimental to the mechanical and electrical package reliability. Plating on the leadframe has been evaluated as a potential mitigation to prevent intermetallic growth and hence improve the overall wedge bond and package reliability under high temperature reliability testing conditions. Significant improvement in the wedge bond and package reliability was achieved by using nickel plating under the wedge bonds. The results presented in this study can be used to design a more robust package capable of meeting stringent automotive grade requirements.

Stress and stress relaxation behaviors of multi-layered polarizer structures under a reliability test condition characterized by use of a bending beam technique

The bending curvature, stresses, and stress relaxation of various multi-layered structures with different adhesive layers pertaining to the polarizer in a thin-film transistor liquid-crystal display (TFT-LCD) have been successfully characterized by using bending beam technique under reliability test. To be more specific, three different types of pressure-sensitive adhesive (hard-, middle-, and soft-type) and various poly(vinyl alcohol) (PVA) stretched directions are devised to examine to key stress contributors and correlations with light leakage. The shrinkage stress in stretched PVA film and stress relaxation ability of pressure-sensitive adhesives (PSA) layers are found to be the key factors determining the stress distribution and out-of-plane displacement of a polarizer stack. For hard-type PSA, its polarizer stack generates the highest bending curvature with maximum out-of-plane displacement but minimum in-plane displacement, leading to anisotropic stress distribution with high stress around the edges. On the other hand, polarizer stack with soft-type PSA yields the maximum in-plane displacement but the minimum out-of-plane displacement, resulting in isotropic stress distribution.

Thermoelectrical Generator for a MEMS-Fuze

The structure of modern fuzes includes micro-electromechanical systems (MEMS), which have such advanced devices as micro-accelerometers and micro-switches, being triggered at a specified level of setback. Independent power source (PS), as an inherent part of the MEMSfuze, charges an energy storage unit during the shot and triggers the fuze firing circuit when the shell encounters the target. Operating level of the control signal should be achieved within the time of remote arming, determined by the type of ammunition. The paper considers a possibility to develop PS as a thermoelectric generator (TEG) with aerodynamic heating of hot junctions due to friction of the projectile body on the incoming airflow. The initial temperature is determined by the driving band cutting into the rifling and friction during the movement of projectile through the tube bore. The paper presents a technique for calculating the temperature field along the body of the projectile from the critical point, located at the top of the shell head. The solution of the equation of heat balance reveals the temporal development of the projectile body temperature. The proposed mathematical model of the TEG describes the process of converting heat into electrical output signal (thermo-EMF). An example of calculation for a specific artillery system – 57-mm anti-aircraft gun S-60 is given. Calculation of the TEG output signal was limited by the time, which is necessary to reach the top of the projectile trajectory. It is shown that at high altitude the temperature difference may drop to zero, thus cutting off the TEG output signal. Selection of capacitive storage parameters can be based on the reliability test conditions of the fuze firing circuit actuators, taking into account the partial storage discharge on the trajectory before the projectile encounters the target.

Lead-Free Solders: Focus on Fundamentals, Reliability, and Applications

Although lead-free solders have been adopted by much of the commercial electronics industry, the implementation of lead-free processes still faces some challenges. The performance of lead-free solder joints in high-reliability aerospace, military, and medical applications is still a concern. There is a clear shortcoming in the ability to predict the lifetime of lead-free assemblies in service. Thus, a common objective of current researchers is to develop a fundamental understanding of the initial solder microstructure, its evolution under various reliability test conditions, and the failure mechanism of lead-free solder joints. Their research focus often includes control of the solidification microstructure by understanding the nucleation of Sn, investigating the role of precipitates and intermetallic compounds at the interface during the deformation of solders, and examining the effect of Sn grain morphology and orientation on the thermomechanical response of solder joints. Researchers are trying to better understand strain-enhanced coarsening, recrystallization, and crack initiation and propagation to develop models that can explain the failure mechanism in different reliability experiments. One goal of this research is to provide a microstructurally adaptive model that can accurately predict the life of soldered electronic devices. Concurrent with the transition to lead-free manufacturing, the electronics industry is experiencing a major revolution associated with the introduction of 2.5D and 3D packaging technologies. There, the lead-free challenges faced by materials scientists become even more complex as the size of electronic packages and solder interconnects shrink to enable deployment of thinner, faster devices. New challenges will be introduced as the entire solder joint may be transformed into intermetallic compounds during assembly or operation. Reducing the size of the solder bumps additionally results in higher current density and increased power dissipation, making electromigration reliability more of a concern. More efficient thermal interface materials are needed to increase the heat flux from die to thermal solution. Moreover, the electronic industry is seeking new solder alloys that are low cost but have acceptable reliability performance in both high-strain applications such as drop/shock and vibration and low-strain applications such as thermal and power cycling. The addition of various fourth and fifth alloying elements to SnAgCu solder alloys is being investigated. The effects of these additional elements on mechanical properties, failure mechanisms, and other reliability phenomena such as Sn whisker formation are not fully understood. In addition, there is a desire among the industrial electronics community to develop new solder alloys for high-temperature applications such as aviation engine controls and downhole drilling electronics as these industries anticipate a future transition to lead-free electronic assembly. Several of these topics were discussed during the Pb-Free Solders and Emerging Interconnect and Packaging Materials Symposium at the TMS 2014 Annual Meeting in San Diego, California. Researchers from industry and academia from different parts of the globe shared their latest research findings in this leading symposium on electronic packaging. More than 60 works were presented in 8 different sessions. A poster session was also organized to include the numerous additional contributions. Three of those technical presentations are presented in this issue of JOM, while others will be published in a special issue of the Journal of Electronic Materials as well as other journals published by TMS. The first article, by E. J. Cotts et al., discusses the effect of impurities on the solidification behavior Babak Arfaei is the guest editor for the Electronic Packaging & Interconnection Materials Committee of the TMS Functional Materials Division, and coordinator of the topic Progress with Lead-Free Solders in this issue. JOM, Vol. 66, No. 11, 2014

Stepped‐isothermal fatigue analysis of engine piston

ABSTRACTStepped‐isothermal fatigue failure is the main failure mechanism of modern engine pistons under bench reliability test condition. This paper presents a methodology for stepped‐isothermal fatigue analysis of engine pistons, which consists of a fatigue criterion, evaluation of temperature and stress distribution by finite element analysis and the final life prediction. The major character of the methodology is the fatigue definition of engine pistons with respect to engine load change cycle and a damage‐based fatigue criterion accounting for the nonlinear creep–fatigue damage. Taking as an example, the fatigue life of an engine piston was predicted by the proposed analysis procedures. The analysis results showed that the most critical area was located in the throat edge. Moreover, the proposed methodology can give a relatively accurate and reasonable life prediction for an engine piston under the loading condition of bench reliability test, with a benefit of decreasing the needed component's reliability tests and design time.

SCADA System of CNC System Reliability Testing and Implement Loading Conditions

This paper puts forward the overall scheme of CNC System Reliability Testing base on the SCADA(Supervisory Control And Data Acquisition) system,introduces to the principle and sets up the physical system According to the selected hardware and software of data acquisition system and data storage system.It selects the mechanical load set load simulation method according to the characteristics of the test sample size is bigger. Using UG software to design and install to loading plate ,and tested.At present,The system of test has run with the safe operation of the normal,and obtain actual measured data about the reliability of CNC system.

Fluid–solid coupling thermo-mechanical analysis of high power LED package during thermal shock testing

The virtual design by numerical simulation to model various accelerated reliability testing conditions is adopted to validate and improve the reliability of the high power LED package. In this study, the reliability of the high power LED package during thermal shock testing is investigated by fluid–solid coupling thermo-mechanical modeling by considering nonlinear time and temperature dependent material properties. Through fluid–solid coupling transient thermal transfer analysis, it is found that the maximum thermal gradient exceeds 75K during the rapid cooling process and 91K during the rapid heating process of the thermal shock testing which is ignored in the traditional isothermal assumption. The calculation results indicate that the equivalent plastic strain range of the bonding wire within the LED package with consideration of the temperature gradient is much higher than that with the isothermal assumption. The assumption of the isothermal condition is not appropriate which will lead to overestimation of the predicted lifetime. The viscoelastic behaviors of the silicone have significant influences on the lifetime prediction of the bonding wire and silicone with low elastic modulus and coefficient of thermal expansion (CTE) can significantly enhance the reliability of the bonding wire under the thermal shock loading. The results in this study could provide a guideline on design for reliability in the high power LED packaging.

Review of Statistical Induction Analysis Methods on Aircraft Vibration Test Data

The development of reliability and environment vibration test conditions depends on the processing of vibration test data. Because of randomness of vibration sources and different purposes of reliability testing and environmental testing, testing data should be dealt with different methods. This paper summarizes various statistical induction analysis methods for aircraft vibration test data, and indicates their advantages, disadvantages and applicability scope. Statistical analysis method on small sample, time-varying structures, non-stationary data processing and vibration environment prediction are the further research directions.

Detection of sigma phase in 22% Cr duplex stainless steel by electrochemical methods

Duplex stainless steels (DSS) may undergo various structural transformations as a function of temperature, leading to formation of secondary phases when exposed to temperatures in the range 600–1000°C for prolonged periods of time. Among these phases, apart from carbides and nitrides, sigma is the most prominent intermetallic compound, since it is known to adversely affect mechanical properties and corrosion resistance of DSS as a consequence of Cr and Mo depletion in the boundary zones of ferrite grains. As a result of sigma precipitation, DSS become susceptible to localized corrosion via a mechanism resembling sensitization in austenitic stainless steels. Electrochemical methods, known to successfully detect sensitization in austenitic SS, have been used to identify reliable test conditions with appropriate sensitivity also for DSS. A modified electrochemical potentiokinetic reactivation method was developed to investigate 22% Cr DSS sensitivity under different thermal cycles. Modifications were designed by closely analysing DSS anodic behaviour changes with respect to the operating testing conditions. All findings were confirmed by SEM, optical microscopy and XRD.

Thermo-mechanical analysis and interfacial energy release rate estimation for metal–insulator–metal capacitor device

The metal–insulator–metal (MIM) capacitor device is the most popular structure that has been massively used in system circuit designs in IC and PCB processes. The characteristics of system will be changed and electrical performances will be impaired if large deformations are resulted in MIM capacitor device. Therefore, the concerns of reliability for MIM capacitor devices are very important issues. For the purpose of realizing the probability of delamination of GaAs/Si 3N 4 interface in MIM capacitor device, the four-point bend experiment is employed to evaluate the critical energy release rate, which is an important index to determine the possibility of inducing interfacial delamination. Moreover, to validate the phenomenon of delamination in MIM capacitor device, the finite element analysis (FEA) and modified virtual crack closure technique (MVCCT) are adopted. Thermo-mechanical stress distributions in MIM capacitor device that under reliability test conditions can be illustrated. The results show that the maximum stress occurs at the layer of Si 3N 4 or its corresponding interfaces. These stress concentration areas are critical places to be fractured. Furthermore, the designs of experiments (DOE) analysis is also employed to have better geometric parameters in MIM capacitor device to reduce stresses. It is believed that this study will be useful design guideline to prevent the phenomenon of interfacial delamination and enhance the reliability.

Effect of PCB Surface Modifications on the EMC-to-PCB Adhesion in Electronic Packages

The characteristics of interfacial adhesion between epoxy molding compound (EMC) and printed circuit board (PCB) were investigated. The surface conditions of solder resist (SR) layers, which were used as an outer skin of PCB, were varied within the range that would be encountered in the manufacturing process and reliability test conditions. First, the number of times of plasma treatment on the SR surfaces and the delay time prior to EMC molding on them were considered to examine the surface cleaning process and the aging effect, respectively, on adhesion. Second, moisture on the surfaces of PCB prior to EMC molding and moisture absorption and desorption at the interface were considered to investigate the environmental effect on adhesion. An unsymmetric double cantilever beam test method was devised by modifying the conventional symmetrical double cantilever beam. As a result, the phase angle of fracture could be controlled to achieve stable crack propagation along the desired interface, which enabled valid adhesion energy to be measured. The adhesion energy increased with plasma treatment by over 50%, from 55 to 86 J/m2. The improved adhesion was attributed to the increased the polar groups on the SR surface due to plasma treatment, which helped enhanced chemical bonding between the EMC resin and the SR resin. However, excessive plasma was counterproductive as it weakened the SR surface and caused cohesive crack propagation to occur within the SR layer. Adhesion remained nearly constant for delay time up to several hours between plasma treatment and EMC molding. However, small degradation of adhesion was observed when the delay time was extended to 12 h. Moisture on and in the SR material before EMC molding had a significant effect on adhesion. Absorbed moisture at the interface decreased the adhesion. However, when the moisture was baked out, adhesion was recovered almost to the original reference.

Reliability analysis of a novel fan‐out type WLP

PurposeThe wafer level package (WLP) is a cost‐effective solution for electronic packaging and has been increasingly applied in recent years. The purpose of this paper is to propose a newly developed packaging technology, based on the concepts of the WLP, the panel base package (PBP) technology, in order to further obtain the capability of signal fan‐out for fine‐pitched integrated circuits (ICc).Design/methodology/approachIn the PBP, the filler material is selected to fill the trench around the chip and provide a smooth surface for the redistribution lines. Therefore, the solder bumps could be located on both the filler and the chip surface and the pitch of the chip side is fanned‐out. The design concept and the manufacturing process of the PBP would first be described in this study. The three‐dimensional finite element model is established based on the real testing sample and the thermo‐mechanical behavior of the PBP is simulated.FindingsIt is found that the solder joint reliability of the PBP can be highly improved because of the applied stress buffer layer. However, the accumulated stress/strain from the coefficient of thermal expansion mismatch may transfer to the metal lines in package. In order to enhance the robustness of the redistribution lines, the bypassed type interconnect is suggested. Moreover, the trace/pad connecting junction and the conductive via which have smooth outline are preferred to avoid stress concentration effects.Originality/valueIn this paper, a low‐cost and short time‐to‐market packaging technology is proposed which is especially suitable for high density IC devices. The PBP technology has the ability to meet the requirements of major reliability testing conditions and it will have a high potential for application in the near future.

Foreword

The seven papers in this special section focus on delamination and cracking in electronic devices during assembly, packaging and reliability testing conditions. The papers are selected from the presentations of conferences organized under the auspices of the IEEE Components, Packaging, and Manufacturing Technology (CPMT) Society.

Development and reliability of non-conductive adhesive flip-chip packages

Driven by miniaturization, cost and environmental friendliness, non-conductive adhesive (NCA) is emerging as one of the potential alternatives for solder-less flip-chip interconnections. It offers inherent characteristics such as finer pitch interconnect, green process, good electrical performance, lower cost and low processing temperature compatible with organic substrates. A reliability evaluation of NCA for flip chip application was carried out to investigate the degradation of the NCA joint in environmental tests. Finite element analysis was also performed to understand the observed phenomenon. In order to obtain accurate material properties for precise finite element simulation, NCA pastes are characterized, as close as possible to reliability test condition, in terms of their thermo-mechanical, moisture diffusion, and viscoelastic properties. The results showed that failures occurring in NCA joints are caused by moisture induced hygroscopic swelling and stress relaxation. All these factors affect the degradation of the compressive force that maintains the mechanical contact in NCA flip chip. The common failure modes observed were interfacial delamination, bump/pad opening as well as cracking.

電子デバイスはんだ接合部の熱サイクル加速信頼性試験方法

Thermal cycle tests for solder joints of electronic devices are generally performed to investigate their reliability under field service (design) conditions. It is important to clear a relationship between an accelerated test condition and a service condition and to determine a practical accelerated test condition. The relationship between an accelerated test condition and a service condition is explained by use of the solder joint fatigue curve. An accelerated reliability test condition is shown taking account of several factors such as a number of test samples, strain ranges of solder joints under accelerated test temperatures conditions, standard variations of fatigue life of solder joints, reliability and confidence level of devices under service conditions. Moreover, the cases that the standard deviation of fatigue life is known or unknown are investigated. A specific analytical and experimental result for single outline packages is shown.