Solder Joint Fatigue Research Articles

Effect of PCB cracks on thermal cycling reliability of passive microelectronic components with single-grained solder joints

Lead-free tin-based solder joints often have a single-grained structure with random orientation and highly anisotropic properties. These alloys are typically stiffer than lead-based solders, hence transfer more stress to printed circuit boards (PCBs) during thermal cycling. This may lead to cracking of the PCB laminate close to the solder joints, which could increase the PCB flexibility, alleviate strain on the solder joints, and thereby enhance the solder fatigue life. If this happens during accelerated thermal cycling it may result in overestimating the lifetime of solder joints in field conditions. In this study, the grain structure of SAC305 solder joints connecting ceramic resistors to PCBs was studied using polarized light microscopy and was found to be mostly single-grained. After thermal cycling, cracks were observed in the PCB under the solder joints. These cracks were likely formed at the early stages of thermal cycling prior to damage initiation in the solder. A finite element model incorporating temperature-dependant anisotropic thermal and mechanical properties of single-grained solder joints is developed to study these observations in detail. The model is able to predict the location of damage initiation in the PCB and the solder joints of ceramic resistors with reasonable accuracy. It also shows that the PCB cracks of even very small lengths may significantly reduce accumulated creep strain and creep work in the solder joints. The proposed model is also able to evaluate the influence of solder anisotropy on damage evolution in the neighbouring (opposite) solder joints of a ceramic resistor.

Condition Monitoring of IGBT Modules Based on Changes of Thermal Characteristics

Condition monitoring (CM) of insulated-gate bipolar transistor (IGBT) modules is significant for improving power converter reliability and reducing the loss caused by IGBT failure. In this paper, we present an advanced method to evaluate the aging condition of an IGBT based on the changes of thermal characteristics in the module, which can be described by the junction and case temperatures. The variation of the case temperature distribution is used to monitor the solder fatigue. The estimated level of solder fatigue is used to update the parameters in the electrical-thermal model. Then, the junction temperature can be accurately estimated by the updated electrical-thermal model. The difference between junction temperatures estimated from the updated model and temperature-sensitive electrical parameter (TSEP) is utilized to monitor the aging of bond wires. The proposed CM method permits both of health level evaluation and accurate junction temperature estimation of IGBT in real time to prevent catastrophic failure caused by defective modules. The experimental results on a commercialized IGBT product have validated the feasibility of the proposed method.

Probabilistic methodology for reliability assessment of electronic packages

In the mechatronic devices, the finite element analyses are the most used method to determine time-dependent solder joint fatigue response under accelerated temperature cycling conditions, the deterministic analyses are the most used methods. However, the design variables show variability and randomness which will affect the lifetime prediction quality. This paper focuses on solder joint reliability in tape-based chip-scale packages(CSP) with the consideration of uncertainties in material parameters.

Health Condition Assessment of Base-Plate Solder for Multi-Chip IGBT Module in Wind Power Converter

The base-plate solder fatigue of the IGBT module is one of the failures of the wind power converter; however, the existing health condition monitoring method based on infrared thermography is difficult to be applied to the actual applications. In this paper, a health condition assessment method of the base-plate solder fatigue for the IGBT module is introduced based on the case temperature difference. First, according to the structure of the IGBT module, a 3D finite element model is established, and the junction and case temperatures at different delamination degrees are investigated. Second, for defining the degradation degree, identifying the steady-state process, and acquiring the case temperature, an assessment method of the base-plate solder fatigue based on the case temperature difference is established. Finally, taking the experiment of a practical wind turbine converter IGBT module as an example, the assessment process of base-plate solder of the IGBT module is demonstrated, and the results show that the proposed assessment method is correct and effective.

Effect of Cycling Amplitude Variations on SnAgCu Solder Joint Fatigue Life

Reliability of conventional electronic assemblies in real service applications is typically limited by fatigue failure of a single solder joint in reversed cyclic loading. Fatigue damage accumulation in a lead-free solder joint is still not well understood, especially not for cycling with a varying amplitude; i.e., random vibration testing is not representative of realistic service conditions and the common reliability models fail to offer relatively accurate life predictions. Developing or modifying a fatigue life model should, of course, consider the interactive effect of stress amplitude variations, which is found to be substantial. Cycling real individual SnAgCu solder joints with systematically varying stress amplitudes allowed understanding of the fatigue damage accumulation through monitoring of the plastic work dissipation during cycling. The results show a significant amplification in the work dissipation compared to what was expected based on fixed stress amplitude cycling results. Cycling with combinations of 16- and 20-MPa stress amplitudes leads to amplification of the work (more fatigue damage) at the 16-MPa amplitude, but no significant change in damage accumulation at the 20-MPa amplitude. Cycling with combinations of three or more stress amplitudes leads to work amplification at the lowest amplitude, no change at the higher amplitude, and slight to moderate amplifications at the intermediate amplitudes. In addition, the value of the work amplification at any stress amplitude depends on the sequence of higher amplitudes applied immediately before it. It is also found that any high amplitude does not affect subsequent work at a lower amplitude if an even higher amplitude was applied just before it.

A Systematic Approach to the Reliability Characterization of System in Package (SiP)

Abstract System-in-Package (SiP) solutions are gaining popularity across multiple market segments, dually reducing product design complexity for Original Equipment Manufacturers (OEMs) while increasing system performance and functionality. For SiP customers, product design complexity is reduced with the integration of electrical sub-system functionality into a module that can be designed into a product with relative ease. Further, logistical complexity is reduced, with the supplier carrying responsibility for the sub-system's quality and reliability. In addition, OEMs benefit from the performance, functionality and form factor improvements enabled by advanced SiP packaging and substrate technologies. With the increased responsibility of SiP solutions in mind, the authors addressed a systematic approach and methodology to understand the complexity of thermo-mechanical risk and challenges in SiP solutions. A modeling and characterization methodology was used to systematically identify and mitigate reliability risks for system-in-package SiP modules. Specifically, a combination of Shadow-Moire technique, digital image correlation (DIC), reliability testing and finite element (FE) models were used to demonstrate this upstream thermo-mechanical evaluation for SiP Solutions. Empirical warpage trends for the SiP module and solder joint fatigue failure trends were in close agreement with the model output based upon design and material factor inputs to the FE models.

Prediction of Fatigue Resistance in Lead-Free Ni-Doped SAC 1205 Solder Alloys Using a Rate-Dependent Material Model and Subjected to Drop Tests

In this paper, a novel Ni-doped SAC 1205 (Sn–1.2Ag–0.5Cu) solder alloy is investigated to determine its mechanical behavior at a high strain rate. The Ni-doped SAC 1205 solder alloy has never been discussed in terms of high-strain-rate testing. The purpose of the SAC 1205 solder material doped with Ni is to enhance the mechanism of the solder alloy and delay the formation of the brittle intermetallic compound. In the drop test standard (Joint Electron Device Engineering Council condition B), the test vehicle was subjected to impact loading with a peak acceleration of 1500G and a time duration of 0.5 ms. Because the test board supported the impact loading for a very short time, the solder joint material was considered to have a rate-dependent elastic–plastic behavior. The quasi-static mechanical behavior and dynamic behavior were estimated for the simulation modeling by conducting a quasi-static tensile test and a split Hopkinson tensile bar test. A finite-element model was used to analyze the stress and strain of the solder joint during the drop test. The experimental results revealed that Young’s modulus and yielding strength of the Ni-doped SAC 1205 solder alloy increased during the high-strain-rate testing. Therefore, a rate-dependent elastic–plastic model of the Ni-doped SAC 1205 solder alloy was designed and implemented to describe the real mechanical behavior of a solder joint at a high strain rate during a drop test. The primary failure mode occurs at the top of the solder joint (package side) during the drop test. The predicted fatigue model we provided was focused on the primary failure mode. Eventually, the fatigue life curve of the rate-dependent elastic–plastic model offered the greatest accuracy in predicting the solder joint fatigue life.

Online condition monitoring of IGBT modules using voltage change rate identification

As insulated gate bipolar transistors (IGBTs) have gained an important status in a wide range of applications, reliability, and availability of these units are of paramount importance to meet stringent requirements spelled in aviation and industrial standards. Reliability of a power converter is mainly verbalized by the failure rate of power modules. Hence, monitoring IGBTs degradation is very crucial to give early sign of power-module-related failures in power converters. This paper proposes a new potential precursor parameter for IGBTs based on voltage change rate to detect early failure of power modules. The proposed method pays more attention to power modules with chip solder fatigue and bond-wire lift off as a major failure mechanism. An experimental setup using an accelerated power cycling machine is constructed to trigger degradations and failures on several IGBT modules. The experimental results indicate that voltage change rates of the IGBT modules decrease with ageing over time. It is found that the local damage induced by ageing over time changes the parasitic capacitances of an IGBT that leads to a decrease of the voltage change rate of the device.

Quantification of lead-free solder fatigue by EBSD analysis

Since lead-free solder was adopted for in-vehicle electronic components, a sufficient number of years have passed to allow examining the condition of lead-free solder joints in components used in the field. For this paper, using an EBSD analysis technique, solder joint degradation analysis was conducted on specimens subjected to accelerated testing and field-aged components. Degradation indicators of the level of grain refining and the amount of strain in the Sn phase in solder were obtained from specimens subjected to accelerated testing. The analysis results of field-aged components revealed increases in the degradation indicators commensurate with the age of components, thereby we were able to estimate field stress from the recovered components.

Accelerated Vibration Reliability Testing of Electronic Assemblies Using Sine Dwell With Resonance Tracking

In this work, a sinusoidal vibration test method with resonance tracking is employed for reliability testing of circuit assemblies. The system continuously monitors for changes in the resonant frequency of the circuit board and adjusts the excitation frequency to match the resonant frequency. The test setup includes an electrodynamic shaker with a real-time vibration control, resistance monitoring for identifying electrical failures of interconnects, and vibration logging for monitoring changes in the dynamic response of the assembly over time. Reliability tests were performed using the resonance tracking sinusoidal test method for assemblies, each consisting of a centrally mounted ball grid array (BGA) device assembled with 63Sn37Pb and SAC105 solder alloys. These tests show that the resonance tracking method gives more consistent failure times. Failure analysis for the tested devices shows the primary failure mode is “input” trace crack first, followed by fatigue through the solder for complete failure. A finite element (FE) model, correlated with experimental modal analysis, is shown to accurately estimate the circuit board deflection estimated from the harmonic vibration data. This provides a means of estimating the stresses in the electronic interconnections while accounting for the variability between test parts. These fine-tuned vibration measurement techniques and related FE models provide the building blocks for high cycle solder fatigue plots (i.e., S–N curves).

Flip-Chip (FC) and Fine-Pitch-Ball-Grid-Array (FPBGA) Underfills for Application in Aerospace Electronics—Brief Review

In this review, some major aspects of the current underfill technologies for flip-chip (FC) and fine-pitch-ball-grid-array (FPBGA), including chip-size packaging (CSP), are addressed, with an emphasis on applications, such as aerospace electronics, for which high reliability level is imperative. The following aspects of the FC and FPGGA technologies are considered: attributes of the FC and FPBGA structures and technologies; underfill-induced stresses; the roles of the glass transition temperature (Tg) of the underfill materials; some major attributes of the lead-free solder systems with underfill; reliability-related issues; thermal fatigue of the underfilled solder joints; warpage-related issues; attributes of accelerated life testing of solder joint interconnections with underfills; and predictive modeling, both finite-element-analysis (FEA)-based and analytical (“mathematical”). It is concluded particularly that the application of the quantitative assessments of the effect of the fabrication techniques on the reliability of solder materials, when high reliability is imperative, is critical and that all the three types of research tools that an aerospace reliability engineer has at his/her disposal, should be pursued, when appropriate and possible: experimental/testing, finite-element-analysis(FEA) simulations, and the “old-fashioned” analytical (“mathematical”) modeling. These two modeling techniques are based on different assumptions, and if the computed data obtained using these techniques result in the close output information, then there is a good reason to believe that this information is both accurate and trustworthy. This effort is particularly important for high-reliability FC and FPBGA applications, such as aerospace electronics, as the aerospace IC packages become more complex, and the requirements for their failure-free operations become more stringent.

Active Thermal Control of GaN-Based DC/DC Converter

The new packaging technologies used for gallium nitride (GaN) devices avoid wire bonds and leads in order to completely utilize their switching performance. This also means that thermomechanical fatigue that used to exist within the device may no longer be a reliability problem. And one of the main bottlenecks for reliability will be the solder joints between the device and the printed circuit board (PCB). To limit the thermal cycling induced failures in these points, an active thermal control scheme using a two step gate driver designed for GaN is presented in this paper. In contrast to the active thermal control techniques employing variable switching frequency control, this method does not alter the converter operation frequency; instead, it merely controls the GaN device slew rates. A simple temperature control algorithm that actively varies the device losses with the objective to minimize thermal cycling is proposed. The solder fatigue due to thermal cycling has been discussed. The effectiveness of this active thermal control scheme has been analyzed also in comparison with losses and validated with analysis, simulation, and experimental results.

Effect of Long-Term Room Temperature Aging on the Fatigue Properties of SnAgCu Solder Joint

Solder joints in electronic assemblies are subjected to mechanical and thermal cycling. These cyclic loadings lead to the fatigue failure of solder joints involving damage accumulation, crack initiation, crack propagation, and failure. Aging leads to significant changes on the microstructure and mechanical behavior of solder joints. While the effect of thermal aging on solder behavior has been examined, no prior studies have focused on the effect of long-term room temperature aging (25 °C) on the solder failure and fatigue behavior. In this paper, the effects of long-term room temperature aging on the fatigue behavior of five common lead-free solder alloys, i.e., SAC305, SAC105, SAC-Ni, SAC-X-Plus, and Innolot, have been investigated. Several individual lead-free solder joints on printed circuited boards with two aging conditions (no aging and 4 years of aging) have been prepared and subjected to shear cyclic stress–strain loadings until the complete failure. Fatigue life was recorded for each solder alloy. From the stress–strain hysteresis loop, inelastic work and plastic strain ranges were measured and empirically modeled with the fatigue life. The results indicated that 4 years of room temperature aging significantly decreases the fatigue life of the solder joints. Also, inelastic work per cycle and plastic strain range are increased after 4 years of room temperature aging. The fatigue life degradation for the solder alloys with doped elements (Ni, Bi, Sb) was relatively less compared to the traditional SAC105 and SAC305.

Vibration-Induced Failures in Automotive Electronics: Knowledge-Based Qualification Perspective

This paper intends to address an important gap between reliability standards and the physics of how components respond to real use conditions using a knowledge-based qualification (KBQ) process. Bridging the gap is essential to developing test methods that better reflect field performance. With the growth in importance of automotive market and the wide usage of electronics in this market, vibration-induced failures was chosen for this study. MIL-STD-810G and ISTA4AB are couple of industry standards that address the risk of shipping finished goods to a customer. For automotive electronic products that are exposed to vibration conditions all through their life, USCAR-2 and GMW3172 are more relevant. Even though the usage models and transportation duration for shipping fully packaged systems is different from automotive electronics, the source of energy (road conditions), driving the risks, are similar. The industry standards-based damage models appear to be generic, covering a wide variety of products and failure modes. Whereas, the KBQ framework, used in this paper, maps use conditions to accelerated test requirements for only two failure modes: solder joint fatigue and socket contact fretting. The mechanisms were chosen to be distinct with different damage metric and drivers. The process is intended to explain how industry standards reflect field risks for two of the risks relevant for automotive electronics.

Prognostic Health Monitoring Method for Fatigue Failure of Solder Joints on Printed Circuit Boards Based on a Canary Circuit

Devices mounted on printed circuit boards (PCBs) are subject to temperature variations resulting from power switching and ambient temperature changes, and may be subject to random dynamic load histories from sources such as vibration. Since solder material is mechanically the most ductile part, fatigue failure may occur in solder joints. Health monitoring for fatigue life under field conditions is a key issue for improving availability and serviceability for maintenance. We have developed a failure precursor detection technology and a fatigue life estimation method for ball grid array (BGA) solder joints, based on a canary circuit. This method estimates fatigue failure life of an actual circuit by detecting failure connections in a canary circuit (a dummy circuit of daisy-chained solder joints). The canary circuit is designed to fail before the actual circuit under the same failure mode by using accelerated reliability testing and inelastic stress simulation. A feasibility study of the failure probability estimation method is conducted by applying the method to a PCB on which a BGA component is mounted. It is confirmed that the fatigue life under a thermal cyclic load can be estimated from a canary circuit, that estimation of fatigue life under a random dynamic load is feasible, and that the estimation results are consistent with results from actual random vibration tests. The proposed method is found to be useful for prognostic health monitoring of solder joint fatigue failure.

Microstructural evolutions of Sn-3.0Ag-0.5Cu solder joints during thermal cycling

Temperature-induced solder joint fatigue is a main reliability concern for aerospace and military industries whose electronic equipment used in the field is required to remain functional under harsh loadings. Due to the RoHS directive which eventually will prevent lead from being utilized in electronic systems, there is a need for a better understanding of lead-free thermomechanical behavior when subjected to temperature variations. As solder joints mechanical properties are dependent of their microstructural characteristics, developing accurate solder joint fatigue models means to correctly capture the microstructural changes that undergo the solder alloy during thermal cycling. This study reports the Sn3.0Ag0.5Cu (SAC305) solder joints microstructural evolution during damaging temperature cycles. Electron BackScatter Diffraction (EBSD) analysis was conducted to assess the SAC305 microstructure corresponding to a specific damage level. Investigated microstructural features included the β-Sn grain size and crystallographic orientation, as well as the grain boundary misorientation and Ag3Sn intermetallic compound (IMC) size. As-reflowed and damaged components were also mechanically characterized using nanoindentation technique. The microstructural analysis of SAC305 solder joints prior to thermal cycling showed a highly textured microstructure characteristic of hexa-cyclic twinning with two β-Sn morphologies consisting of preferentially orientated macrograins known as Kara's beach ball, along with smaller interlaced grains. The main observation is that recrystallization systematically occurred in SAC305 solder joints during thermal cycling, creating a high population of misoriented grain boundaries leading to intergranular crack initiation and propagation in the high strain regions. The recrystallization process is accompanied with a progressive loss of crystallographic texture and twinning structure. Ag3Sn IMCs coalescence is another strong indicator of SAC305 solder damage since the bigger and more spaced the IMCs are the less dislocation pinning can prevent recrystallization from occurring.

Combined simulation and optical measurement technique for investigation of system effects on components solder fatigue

Among others, physics of failure related concepts are being developed to address the thermo-mechanical reliability challenges in automotive electronics. Limitations in particular applied for finite element (FE-) analyses are models of limited size, which rarely address the system character of failure. Also in testing a system view on fully mounted electronic control units (ECU) and loaded by environmental and active loading cannot be taken performing end-of-life tests for time limitations. Accelerated testing is done instead, however, mostly on board level.To overcome some of these limitations, a combined measuring-simulation technique is being developed, which is described in the paper. System level view on boards mounted in automotive ECUs is taken by a newly developed high-precision optical deformation measuring system. The multi-sensor measuring method combines a chromatic sensor for topography and warping analysis with an optical sensor for in-plane deformation and strain field analysis. By this combination, a high resolution can be reached for all three components of displacement vectors. Additionally, software tools allow the determination of derived quantities like strains, local curvatures and local warpage radius. The latter can be taken as input for FE-simulations. It is shown that some components, in particular QFNs, are sensitive to thermally induced cyclic warpage even if the corresponding bending deflections are in the micrometers range. Worst case in-plane stretching and cyclic warpage of a board mounted in an ECU have been measured. By corresponding simulations on QFN solder fatigue, mounted on a special test board, the critical fatigue life can be determined dependent on the interaction to the case, which differs by several hundred percent from a free-standing assembly.

Impact of underfill and other physical dimensions on Silicon Lateral IGBT package reliability using computer model with discrete and continuous design variables

An effort to design and build a prototype LED driver system which is energy efficient, highly compact and with few component count was initiated by a consortium UK universities. The prototype system will be based on Silicon Lateral IGBT (LIGBT) device combined with chip on board technology. Part of this effort, finite element modelling and analysis were undertaken in order to mitigate the underfill dielectric breakdown failure and solder interconnect fatigue failure of the LIGBT package structure. Electro-static analysis was undertaken to predict the extreme electric field distribution in the underfill. Based on electro-static analysis, five commercial underfill were selected for thermo-mechanical finite element analysis on solder joint fatigue failure prediction under cyclic loading. A design optimisation analysis was endeavoured to maximise the solder interconnect reliability by utilising a computer model with continuous variable (physical dimensions) and discrete variables (underfill type) and a stochastic optimiser such as multi-objective mixed discrete particle swarm optimisation. From the optimisation analysis best trade off solution are obtained.

Role of Plastic Behaviors of Ni3Sn4 Intermetallic Compound on Solder Joint Reliability

The study aims at investigating the influences of the elastoplastic behaviors of the micrometer-thick Ni3Sn4 intermetallic compound (IMC) observed in the Cu/Ni/Sn3.5Ag solder joints of 3-D chip stacking package on the solder joint reliability under accelerated thermal cycling (ATC). The IMC’s elastoplastic properties are characterized through the developed forward-reverse analysis algorithm, which integrates parametric finite element analysis (FEA) of instrumented indentation, dimensional analysis, and an experimental instrumented indentation test. The algorithm is first applied to characterize the elastoplastic behaviors of an electrodeposited Cu thin film, the results of which are compared with the known data, followed by a test on the thin Ni3Sn4IMC. The predicted elastoplastic properties are input to the ATC FEA model of the package to simulate the solder joint mechanical response, by which the corresponding fatigue life is assessed using a Coffin–Manson model. The simulation is validated against the experimental data. Besides, the prediction is compared with that without the plastic effect. Results show that despite bulk IMCs being normally elastic, brittle, and hard, the thin Ni3Sn4 IMC possesses a highly ductile (plastic) and strain-hardening behavior. Moreover, taking the plastic behavior of the thin Ni3Sn4 IMC into account helps improve the prediction of the solder joint fatigue life of the package.

Parameter driven monitoring for a flip-chip LED module under power cycling condition

In this paper, a parameter driven monitoring model is introduced, in which a flip-chip LED module was investigated during a power cycling test. This approach was investigated to develop a monitoring model to describe thermally induced solder fatigue as root cause of flip-chip failure in a power cycling test. As monitoring parameter the thermal resistance of the LED module was used, which was determined by thermal impedance measurements of the whole LED module, as well as for each LED chip itself. Further analyses of the occurring temperature at the LED junction recorded of each chip during the power cycling test were used to generate a prediction model. The evaluation of the temperature change allowed to forecast the number of cycles until failure.