Solder Joint Degradation Research Articles

Comprehensive evaluation of solder joint integrity in power semiconductors: Exploring multiple failure mechanisms and cumulative impact

Investigating the impact of solder joint degradation in power semiconductors is crucial given their widespread use. Solder joints, being the weakest link, are prone to multiple failure mechanisms, exacerbating degradation under normal operation. This paper presents a novel approach for assessing solder joint degradation, particularly in electric vehicles, where severe thermal and vibration stresses are prevalent. Our method categorizes solder joint conditions into discrete states, from fully perfect to fully damaged, integrating both thermal and vibration-induced failures. By considering cumulative effects, our approach yields more precise reliability estimates. Moreover, it offers a versatile framework applicable across various failure scenarios and readily deployable in the design phase.

A Bayesian Neural Network-based approach for multistate reliability assessment of solder joints exposed to various failure mechanisms

The evaluation of the operational lifespan of solder joints in electronic devices, especially when subjected to intricate mission profiles, stands as a pivotal imperative in the domain of electronic material design. In response to this critical concern, this study introduces an innovative methodology designed to discern between gradual and sudden failures, offering a nuanced exploration of the distinct failure mechanisms at play. Distinguishing itself through a sophisticated treatment of failure mechanisms—specifically, the incorporation of thermomechanical fatigue and vibration-induced mechanisms—within the context of solder joint degradation, the proposed approach significantly elevates the precision and accuracy of reliability evaluations. This refined methodology emerges as a valuable contribution to the field, promising more insightful and reliable results in the assessment of electronic device durability under diverse and complex operational conditions.

Solder Joint Degradation and Electrochemical Metallic Ion Migration Property of Solder Joints with Surface Finish

To confirm the degradation property of solder joints by substrate surface finish, chip resistors are reflow soldered to organic solderability preservative (OSP) and electroless nickel immersion gold (ENIG) finish substrate in a nitrogen atmosphere using the type 6 Sn-3.0Ag-0.5Cu (SAC305) solder paste. To confirm the electrochemical metallic ion migration (ECM) sensitivity with and without photo solder resist (PSR) ink-coated printed circuit board (PCB), comb patterned test vehicles were prepared by the hot air reflow soldering process in nitrogen atmosphere, and the SAC305 solder paste was printed on the conductor of the ECM test PCB. The ECM test was conducted under high temperature and high humidity conditions of 85℃ and 85% RH, respectively. As a result of measuring the void content of the 2012 chip resistor, the average void content of the OSP substrate was higher than that of the ENIG substrate. The thermal shock test (TST) indicated that the degradation rate of the OSP substrate was higher than that of the ENIG substrate. Microstructure analysis showed that the OSP substrate had more crack propagation and thicker intermetallic compound (IMC) thickness than the ENIG substrate. The ECM test revealed that the substrate with PSR-coated PCB coupon generated more dendrites than that without PSR-coated coupon. Because the PSR coated substrate decreased the moisture absorption into the substrate, moredendritesweredeterminedtobe generated.

Mechanical properties degradation of Sn 37Pb solder joints caused by interfacial microstructure evolution under cryogenic temperature storage

The interfacial microstructure, shear property and fracture behaviors of Sn37Pb joints after cryogenic temperature storage for different durations were investigated in this study, storage test at room temperature (298 K) and thermal aging test at 423 K were also carried out as comparison. The morphology of interfacial Cu6Sn5 IMCs for the joints stored under 77 K and 173 K transformed from scallop-like to column-like, moreover, the IMC layer thickness slowly increased with prolonged storage time. The growth rate of Cu6Sn5 layer in Sn37Pb joint stored at 77 K was slightly faster as compared with that stored at 173 K. However, the morphology and thickness of Cu6Sn5 IMC layer still remained roughly unchanged after storage at 298 K for up to 40 days. The Cu6Sn5 IMC growth of Sn37Pb joint stored at 77 K and 173 K was expected to be caused by Cu atom diffusion from Cu pad towards Sn37Pb solder, which was induced by the stress gradient. Additionally, the shear force declined and fracture position changed from in Sn37Pb solder to primarily in Sn37Pb solder and partly along the interface with the prolonging of storage time at 77 K and 173 K, which were induced by IMC layer growth.

Reliability and failure modelling of microelectronic packages based on ultrasonic nondestructive evaluation data

Reliability testing and failure modelling is crucial and very challenging for modern electronics, especially safety critical electronics-based systems working under harsh environmental conditions. In this paper, an approach based on ultrasonic Non-Destructive Evaluation (NDE) is proposed to establish a failure model for solder joints which is urgently needed for prognostic and health management of electronics. Printed Circuit Boards (PCB) containing flip-chip and Area Array packages were designed and aged using Accelerated Thermal Cycling (ATC) testing. During ATC testing solder joint degradation was regularly monitored by taking out the test boards from the temperature chamber at four thermal cycle intervals for ultrasonic micro-imaging. Data pre-processing techniques including dynamic range-based intensity normalization, gain compensation, and calibration for random transducer defocusing errors were developed to enhance the data consistency, integrity and accuracy. Furthermore, solder joint image labelling and segmentation methods were developed by exploiting the geometrical features of the solder joints to extract individual solder joints and Region of Interests (ROIs) from the sequential ultrasound images collected throughout the testing. The mean intensity of the ROIs was used as the precursor to degradation to build the solder joint failure model, from which cycles to failure for individual solder joints are finally derived for life prediction.

Microscale fracture toughness degradation of notched solder microcantilevers under varied accelerated aging process

Experimental fracture mechanics at the microscale became an indispensable tool for understanding and analyzing the solder joint degradation in microelectronics packaging, which is facing severe temperature swings and is prone to failure due to the delamination induced by the microcracks. In this work, we studied the fracture behavior of the widely used Sn-based solder on microscale with the notched microcantilevers fabricated using the focused ion beam (FIB) milling. The microcantilever bending tests were performed to demonstrate the fracture process by the nanoindentation system. Besides, the continuous stiffness measurement (CSM) for the dynamic stiffness was applied to assess the crack behavior. Crack resistance was obtained from the J-Δa curves and the fracture toughness was calculated from the bending tests based on the elastic-plastic fracture mechanics. The results indicated that the fracture toughness decreased after the thermal cycling test. Compared to the specimen without aging, the resistance to rupture decreases rapidly and tends to a low variation against the increased aging cycles. Moreover, the grain orientations and dislocation densities were analyzed using electron back-scatter diffraction (EBSD). It was found that the dislocation density and misorientations of the aged specimens correlated closely to fracture toughness. Furthermore, the stress distribution of the crack tip and the deformation in the plastic zone were analyzed by the finite element simulations. This work provided new insight into the degradation of fracture and deformation behavior of solder material on microscale and revealed the relationship of crack resistance and thermal cycling aging.

A feasibility study on potential of stress sensors to detect solder joint defects toward prognostics of power modules

The superiority of stress sensors over temperature sensors for detecting defects in solder joints was investigated. The effects of joint defects on device stress and temperature in a single-sided cooling structure were obtained via thermal stress simulation. The peripheral, edge, and central defects were assumed as the defect distributions. The central defects did not result in a remarkable occurrence rate of the stress waveform change. In contrast, the periphery and edge defects caused a large occurrence rate of the stress waveform change compared to that of the temperature. In general, the thermal strain of solder joints in a power module causes its initial degradation from the joint edge or periphery. Thus, the stress waveform provides useful information for detecting initial degradation. The change pattern of the temperature waveform because of the solder joint defects only caused an amplitude increase. In contrast, stress waveform changes exhibited four different patterns: amplitude increase, amplitude decrease, waveform inversion, and waveform disappearance. These results confirm that stress sensors are better than temperature sensors for detecting waveform changes caused by slight joint defects at peripheral or edge, particularly with a small number of sensors. Application of the data acquired via stress sensors to machine learning will allow estimation of the joint defect distribution. Furthermore, time-series stress waveform data can provide prognostics of solder joint degradation.

Analysis of solder joint degradation and output power drop in silicon photovoltaic modules for reliability improvement

With the growing worldwide demand for clean, reliable, and economical energy supply, Photovoltaic (PV) modules have raised the bar for the field over the last years. However, PV modules have shown some shortcomings as environment temperature influences not only the maximum power generation but also the life expectancy of the module. PV reliability has become a topic of extreme importance driven by the extension of the warranty period over the years. This study investigates the degradation of solder joints. A 2-D Finite Element Model (FEM) has been computed to evaluate the lifetime of the solder joints and the cell power drop using accelerated thermal cycling tests in the range of −40 to 85 °C according to IEC 61215 standard. 2 models were used to predict the lifetime. In addition, 5 PV modules were conducted to thermal cycling tests to validate the model. The results reveal that during the thermal cycling test, the rear solder is damaged in a much earlier stage than the top solder. The deterioration of the rear solder area becomes steep after 1000 cycles and the power loss of the module reaches 2% between 600 and 750 thermal cycles depending upon the mathematical model. When compared to experimental results, the Coffin-Mason model is more accurate, with a maximum data disparity of 4.3%. A solder without any residual stress will eventually pass the 600TC test according to CSA/ANSI C450–18 and IEC TS 63209 ED1 standards. These findings inform on the solder joint durability which is an important parameter for the reliability analysis of a PV module.

Research on Wiener Degradation Model and Failure Mechanism of Interconnect Solder Joints Under Random Vibration Load

Electronic packaging solder joints are the key parts of mechanical fixation and electrical interconnection between electronic chips and printed circuit boards, which are prone to failure and lead to electronic device failures under the action of vibration environment stress. In regard to the failure characterization and degradation modeling of electronic packaging solder joints under vibration load, this paper adopts environmental stress tests, builds a vibration failure test platform, designs a vibration load excitation spectrum, and obtains solder joint degradation data under vibration stress; it uses the square root amplitude, form factors, and kurtosis factors to characterize the solder joint degradation process, which effectively identify the solder joint degradation node, and improve the data monotonicity of the solder joint degradation process; the Wiener process is used to build a solder joint multi-stage degradation model. Based on the EM algorithm, the hyperparameters of the degradation model have been optimized, and the universal test of the Wiener degradation model with multiple samples is carried out in accordance with the LB index. The analysis shows that the effectiveness of different samples is as high as 87.5%, which verifies the universality of the Wiener degradation model; Based on the crack morphology subject to the solder joint test and the features of the solder joint in the multi-stages, the paper analyzes the crack propagation behavior of the solder joint, and clarifies the failure mechanism of the solder joint.

An investigation on function of current type on solder joint degradation in electronic packages

PurposeAs in real applications several alternating current (AC) currents may be injected to the electronic devices, this study aims to analyze their effects on the lifetime of the solder joints and, consequently, shed the light on these effects at the design phase for other researchers to consider.Design/methodology/approachIn this paper, the authors investigated on current waveform shapes on the performance and reliability of the solder joints in electronic package. Three common and extensively used current shapes in several simulations and experiments were selected to study their effects on the solder joint performance.FindingsThe results demonstrate a sever thermal swing and stress fluctuation in the solder joint induced in the case of triangle current type because the critical states lack any relaxation time. In fact, the stress intensification in the solder under application of the triangle current type has been shown to contribute to increasing brittle intermetallic compounds. An accelerated increase of on-state voltage of power semiconductor was also observed in under application of the triangle current type.Originality/valueThe originality of this paper is confirmed.

Dark Lock-in Thermography Identifies Solder Bond Failure as the Root Cause of Series Resistance Increase in Fielded Solar Modules

Correlating the electrical performance of photovoltaic modules to the spatially resolved photoluminescence, electroluminescence, and dark lock-in thermography (DLIT) images is an important long-term goal for developing solar cell technology. These images offer highly sophisticated and detailed information about the spatial distribution and (if imaged at successive time intervals) temporal degradation of local series and shunt resistances. There have been extensive studies to correlate these imaging techniques to local characteristics at the cell level. However, it has been difficult to extract and quantify module-level information from the techniques. In this study, we interpret module current-voltage (I-V) measurements along with corresponding DLIT images within a module-scale simulation framework, demonstrating that series resistance degradation of the module I-V characteristics, in this case, can be attributed to solder bond failures. Our simulations highlight how current crowding associated with a failed solder joint (or a section of the solder pad) translates to the characteristic point-like (asymmetric doublet) heating pattern in neighboring solder joints (or the neighboring regions of the solder pad). The correlation between series resistance and solder joint degradation could inform expedited diagnosis of field degradation of solar modules.

Study on Establishing Degradation Model of Chip Solder Joint Material under Coupled Stress.

The chip is the core component of the integrated circuit. Degradation and failure of chip solder joints can directly lead to function loss of the integrated circuit. In order to establish the degradation model of chip solder joints under coupled stress, this paper takes quad flat package (QFP) chip solder joints as the study object. First, solder joint degradation data and failure samples were obtained through fatigue tests under coupled stress. Three types of micro failure modes of solder joints were obtained by scanning electron microscope (SEM) analysis and finite element model (FEM) simulation results. Second, the characterization of degradation data was obtained by the principal component of Mahalanobis distance (PCMD) algorithm. It is found that solder joint degradation is divided into three stages: strain accumulation stage, crack propagation stage, and failure stage. Later, Coffin–Manson model and Paris model were modified based on the PCMD health index and strain simulation. The function relationship between strain accumulation time, crack propagation time, and strain was determined, respectively. Solder joint degradation models at different degradation stage were established. Finally, through strain simulation, the models can predict the strain accumulation time and failure time effectively under each failure mode, and their prediction accuracy is above 85%.

A competition between stress triaxiality and joule heating on microstructure evolution and degradation of SnAgCu solder joints

In this study, the simultaneous role of thermal cycling and electric current on the microstructure and degradation behavior of solder joints was investigated. For this purpose, FEM simulations and experimental works were performed on IGBT modules with the diverse solder joint thicknesses of 50, 70 and 90 μm. The results showed that the thermal cycling effect is a dominant factor in degradation of solder joints in thin solder layer (50 μm) which is due to the intensified stress triaxiality and higher accumulated creep energy per volume of the solder layer. However, in thicker solder joints (90 μm), the joule heating effect of electric current comes into play and accompanies with the thermal cycling effect to degrade the solder joint. This event is due to the fact that the thicker layer has a higher resistance to the electric current and induces more accumulated energy. This phenomenon is inconsistent with the thermal cycling effect which has an inverse relation with the solder thickness. Finally, it was revealed that an optimum solder thickness (70 μm) includes the minimum accumulated energy from simultaneous effects of thermal cycling and joule heating.

Study on Chip Reliability Modeling Based on Mutually Dependent Competing Failure of Solder Joints in Different Failure Modes

The chip is a core functional component. Its reliability plays a vital role in electronic equipment normal operation. As the typical cause for chip malfunction, the solder joint degradation is selected to study chip reliability. The degradation models of solder joint in different failure modes are established through data-driven and failure physical model, and chip reliability model is constructed based on mutually competing failures of multiple solder joints. First, the chip reliability degradation test and finite element modeling(FEM) are carried out under coupled environment stress. The solder joint failure modes and degradation processes are studied through the analysis of test data, microstructure and mechanical simulation. Then, solder joint degradation models are established based on Coffin-Manson and Paris functions that have been modified by a data-driven method. Taking the solder joint failure time of degradation model as the characteristic parameter of Weibull distribution, the solder joint reliability function is obtained. Finally, mutually dependent competing failure theory is cited to describe the correlation about solder joint reliability of different failure modes, then the chip reliability model is established. The parameter estimation is realized by the inference function for margins (IFM) method. From verification tests, results show models are highly consistent with the actual reliability, indicting our reliability modeling method achieves the transition from underlying solder joint level to integrated component level. The joint application of different models can make up for the deficiencies of the single model and obtain more accurate results. In addition, we determined that intermetallic compounds (IMC) are main source of model error.

A mission profile-based reliability analysis framework for photovoltaic DC-DC converters

Reliability of DC-DC converters is important in photovoltaic (PV) applications like building integrated PV systems, where the module-level converter may be stressed significantly. Understanding and predicting the most life-limiting components with accurate degradation models in such systems enable the design for reliability. In this paper, a mission profile-based reliability analysis framework for PV DC-DC converters is proposed where the inputs and models of the framework can be adjusted according to the converter topology, the components and the failure mechanisms under investigation. The framework is demonstrated by comparing the influence of two yearly mission profiles on the solder joint degradation of a MOSFET in an interleaved boost converter. This is done by using an electro-thermal circuit simulation in PLECS and a finite element MOSFET model in COMSOL. This framework allows for exploring more accurate models or even simplifying parts with low sensitivity in order to obtain a thorough understanding of their accuracy and to determine the overall converter reliability.

Bonding Strengths and Thermal Degradation of Photovoltaic Module Ribbon Solder Joints

In this study, solar ribbon solder joints were investigated to ensure the reliability of photovoltaic (PV) modules. Ribbon joints comprising two different solder compositions (wt. %: 60Sn40Pb, 62Sn36Pb2Ag) were used to perform thermal aging tests at three different temperatures (150 °C, 120 °C, and 90 °C) during a 1000-h period to analyze the resultant thermal degradation; shear tests were also performed to measure bond strengths. Initial bond strengths were 271.3 MPa and 241.3 MPa for 62Sn36Pb2Ag and 60Sn40Pb solder joints, respectively. Bonding strength decreased as a result of thermal aging, but was maintained at a value of around 130 MPa regardless of solder composition. Fracture surfaces from the shear test were observed to analyze for the constant bond strength phenomenon. It was verified that the shear fracture surface changed from the solder/sintered Ag interface and the sintered silver (Ag)/silicon (Si) wafer interface during thermal aging. Thus, the bond strengths and bonding characteristics of PV ribbon solder joints decreased under a thermal load, which could be attributed to a weakening of the bonding characteristics for sintered Ag silicon interfaces as opposed to a degradation of solder metallurgy.

Investigation and analysis of thermo-mechanical degradation of fingers in a photovoltaic module under thermal cyclic stress conditions

The reliability of current carrying fingers in a photovoltaic (PV) cell is essential to the overall performance of a PV module. The close proximity of the fingers to the solder layer makes it compelling to investigate its reliability under the premise of solder joint degradation, which is susceptible to high temperature transient variations. For the investigation of this particular aspect of finger reliability, a 3-D finite element model (FEM) of a PV module has been simulated under accelerated thermal cycle (TC) and outdoor weather temperature cycles. The FEM has been optimised to reduce computational complexity for accommodation of the small size of fingers in comparison to other components. Experimental TC test has also been performed on PV module batches to support the simulated findings by characterisation of observed finger breakages using illuminated current-voltage (I-V) and electroluminescence (EL) imaging technique. The finger-solder interface was identified to be vulnerable under prevailing thermal loading conditions, from both the simulated and experimental findings. To illustrate a larger spectrum of finger reliability, the influence of variable geometrical design parameters of finger and solder layer have been investigated for its dependence on electrical power loss and thermo-mechanical damage accumulation. It was demonstrated that solder thickness and finger spacing are key to the performance of fingers in a PV module. Under the outdoor weather temperature cycle the finger-solder interface was found to be more vulnerable to damage accumulation during the sunshine hours on a hot day as compared to a cold day. Further, an acceleration factor was estimated to establish a quantitative comparison between the outdoor weather temperature cycle and accelerated TC. This paper highlights the different aspects of thermo-mechanical degradation of fingers in PV modules under transient thermal conditions and is instrumental for optimization of variable design and packaging parameters for its enhanced reliability.

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.

Effect of viscoelasticity of ethylene vinyl acetate encapsulants on photovoltaic module solder joint degradation due to thermomechanical fatigue

The solder joint degradation due to thermomechanical fatigue is investigated in this paper for photovoltaic (PV) mini-modules with ethylene vinyl acetate (EVA) of different viscoelastic properties. The mini-modules were laminated at different curing temperatures in order to obtain EVA encapsulation with different viscoelastic properties. The influence of viscoelasticity of EVA on the thermomechanical fatigue generated on solder joint is analyzed based on a two-dimensional (2D) finite-element model. Based on simulation of thermomechanical stresses accumulation, mini-modules with EVA cured at lower temperatures accumulated approximately 40% more stresses during the thermal cycle testing than mini-modules with optimal cured EVA. The tested mini-modules with EVA cured at lower temperature showed greater power degradation than the optimal cured mini-modules. An apparent increase in equivalent series resistance is the primary factor the power loss. A good correlation between the accumulated thermomechanical fatigue and the increase in equivalent series resistance is demonstrated with the tested samples.

Effect of operating temperature on degradation of solder joints in crystalline silicon photovoltaic modules for improved reliability in hot climates

Accelerated degradation of solder joint interconnections in crystalline silicon photovoltaic (c-Si PV) modules drives the high failure rate of the system operating in elevated temperatures. The phenomenon challenges the thermo-mechanical reliability of the system for hot climatic operations. This study investigates the degradation of solder interconnections in c-Si PV modules for cell temperature rise from 25 °C STC in steps of 1 °C to 120 °C. The degradation is measured using accumulated creep strain energy density (Wacc). Generated Wacc magnitudes are utilised to predict the fatigue life of the module for ambient temperatures ranging from European to hot climates. The ANSYS mechanical package coupled with the IEC 61,215 standard accelerated thermal cycle (ATC) profile is employed in the simulation. The Garofalo creep model is used to model the degradation response of solder while other module component materials are simulated with appropriate material models. Solder degradation is found to increase with every 1 °C cell temperature rise from the STC. Three distinct degradation rates in Pa/°C are observed. Region 1, 25 to 42 °C, is characterised by degradation rate increasing quadratically from 1.53 to 10.03 Pa/°C. The degradation rate in region 2 ,43 to 63 °C, is critical with highest constant magnitude of 12.06 Pa/°C. Region 3, 64 to 120 °C, demonstrates lowest degradation rate of logarithmic nature with magnitude 5.47 at the beginning of the region and 2.25 Pa/°C at the end of the region. The module fatigue life, L (in years) is found to decay according to the power function L=721.48T-1.343. The model predicts module life in London and hot climate to be 18.5 and 9 years, respectively. The findings inform on the degradation of c-Si PV module solder interconnections in different operating ambient temperatures and advise on its operational reliability for improved thermo-mechanical design for hot climatic operations.