Solder Joint Failure Research Articles

Design guideline on board-level thermomechanical reliability of 2.5D package

A vast range of electronics products have utilized 2.5D packages for better performance and miniaturization. As multi-level assembly technologies are getting mature, 2.5D packaging technology becomes affordable. In this work, design guideline for board-level reliability of a 2.5D package was provided with respect to accelerated thermal cycling (ATC) and power cycling (PC). Finite element models were built and validated step-by-step by warpage measurement. Solder fatigue life in power cycling was investigated with temperature mapping technique merged into the process of scripting, which conducts load transfers from computational fluid dynamics (CFD) simulation to finite element analysis (FEA). ATC test was conducted with solder joint failure analysis. Fatigue life projection model was determined by correlation between tested life data and simulation results. Parametric studies regarding geometry factors and material properties were performed including PCB, substrate, thermal interface material (TIM) and lid adhesive, to give design suggestions to improve board-level thermal reliability. It is found that CTE mismatch between the substrate and the PCB is the major factor affecting board-level reliability in accelerated thermal cycling. Maximum junction temperature of a 2.5D FPGA package is dependent on application scenarios and working environment. Designed maximum junction temperature and applied heatsink clamping force have considerable influences on board-level reliability.

Effects of isothermal aging on interfacial microstructure evolution and shear behavior of Au-12Ge/Ni(P)/Kovar Solder Joints

Au-12Ge(wt.%) eutectic solder is widely used in electronic packaging thanks to its good electrical conductivity, solderability, and chemical stability. To investigate the stability of Au-12Ge solder during high-temperature service, the effects of different isothermal aging conditions on the microstructure and performance of Au/Ni(P)/Kovar substrate after soldering were investigated. Solder joints produced at 400 °C for 1 min showed excellent wetting behavior with NiGe/Ni5Ge3/Ni3(P,Ge) intermetallic layers formed at the interface. The thickness of generated interfacial intermetallic compounds was estimated to only 1.56 μm due to the amorphous nature of Ni-P coating that hindered the diffusion of Ni atoms. As aging increased with time and temperature, the interfacial intermetallic compounds grow further, leading to deterioration and failure of solder joints. The growth mechanism of interfacial intermetallic compounds was then examined, and activation energy was estimated to 95.4 kJ/mol. In turn, shear strength of solder joints declined and fracture mode became brittle as aging time and temperature increased. Meanwhile, fracture position evolved from IMC layer to Ni-P layer. At aging temperatures above 290 °C, Ni-P layer showed crystallization transition to porous Ni3P, leading to formation of holes and cracks, and resulting in exfoliation of coating with Kovar substrate.

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%.

Microstructural Characterization and Unified Reliability Assessment of Aged Solder Joints in a PV Module

In this article, the finite-element method (FEM) along with experimental analysis was used to establish a mission profile-based reliability assessment of solder joints of the photovoltaic module under thermal cycling conditions. While considering the uncertainties of the solder joint lifetime model that leads to more realistic results, this method is able to estimate the time if the probability of solder joint failure reaches 10%. Several conditions, including standard and nonstandard cases, were simulated and performed to obtain the fatigue lifetime models. The experimental results, that is, scanning electron microscopy (SEM) along with X-ray tomography, showed that more intermetallic compounds and microvoids are formed in the nonstandard conditions (STCs). As a result, the non-STC leads to the accelerated failure in the solder interconnection, which is consistent with the FEM outcomes. In the end, a real case study was considered to investigate the efficiency of thermomechanical fatigue reliability model.

Modeling and Simulation of Multi-Material Soldering Performance for Spacecraft

In recent years, there have been several on-orbit failure cases of spacecraft thermistor circuit. Through the analysis of failure mode, it is confirmed that the failures are mostly caused by the failure of wire solder joint. In this paper, the finite element method (FEM) is used to simulate the effects of different soldering parameters on the stress-strain characteristics of spacecraft solder joints in cold-hot alternating environment.

Evaluation of the relationship between stress and lifetime of Pb-free solder joints subjected to vibration load using a generalized local stress approach

The article proposes a generalized high cycle fatigue evaluation methodology for solder joints based on a local stress finite element method (FEM) and compares with experimental results. A method to predict the damage initiation of surface mount technology (SMT) solder joints is accomplished in this article by making use of generic coupon level SAC387 solder specimens. High cycle fatigue (HCF) experiments conducted on generic solder specimens are followed by means of FKM guidelines, which are translated to microelectronic elements for the first time. The FEM predicted lifetime values of solder joints agree with the experimental results performed on SMT components. In addition, the overall results show that the predicted values act as a threshold damage line from which the solder joint failure regimes can be differentiated. The results also show the differences in the predicted damage line and failure line for SMT solder joints.

Understanding the impact response of lead-free solder at high strain rates

As resistance to drop impact is a standardized evaluation for consumer electronics, the dynamic behaviour of solder material is critical to ensure the prediction accuracy about damage and failure in solder joints using finite element analysis. In this paper, the dynamic constitutive behaviour of Sn–3.0Ag–0.5Cu (SAC305) lead-free solder is investigated at different strain rates from 733.8/s to 1758.1/s by using the split-Hopkinson pressure bar (SHPB) with the applied gas gun pressure increasing from 0.1 MPa to 0.5 MPa at room temperature. It is shown that the flow stress increases but the strain rate decreases with the increasing strain of a visco-plastic solder alloy. More importantly, it is found that the strain rate effect is pronounced and the peak strength is thus enhanced until the strain rate is up to 1172.9/s. Nevertheless, if the strain rate increases further, the peak strength deteriorates. Under such high strain rates, this interesting transition is speculated due to the temperature rise and the induced softening effect on material strength of the SAC305 solder with a relatively low melting point. This speculation is supported by the fact that compared with the solder samples under different strain rates, the microstructures of post-impact solder samples with degraded strengths are observed to be apparently different by using a scanning electron microscopy. A finer morphology of solder material results from the rapid cooling process after the transient temperature rise due to a high impact velocity. Lastly, the dynamic constitutive behaviour is further described in the framework of the strain rate dependent Johnson–Cook model and validated using finite element simulations.

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.

Random Voids Generation and Effect of Thermal Shock Load on Mechanical Reliability of Light-Emitting Diode Flip Chip Solder Joints.

To make the light-emitting diode (LED) more compact and effective, the flip chip solder joint is recommended in LED chip-scale packaging (CSP) with critical functions in mechanical support, heat dissipation, and electrical conductivity. However, the generation of voids always challenges the mechanical strength, thermal stability, and reliability of solder joints. This paper models the 3D random voids generation in the LED flip chip Sn96.5–Ag3.0–Cu0.5 (SAC305) solder joint, and investigates the effect of thermal shock load on its mechanical reliability with both simulations and experiments referring to the JEDEC thermal shock test standard (JESD22-A106B). The results reveal the following: (1) the void rate of the solder joint increases after thermal shock ageing, and its shear strength exponentially degrades; (2) the first principal stress of the solder joint is not obviously increased, however, if the through-hole voids emerged in the corner of solder joints, it will dramatically increase; (3) modelling of the fatigue failure of solder joint with randomly distributed voids utilizes the approximate model to estimate the lifetime, and the experimental results confirm that the absolute prediction error can be controlled around 2.84%.

Improving the Solder Joint Reliability of a Power Leadframe Package Using Thermomechanical Simulation

Leadframe-based packages are commonly used for semiconductor power devices. With these packages, heat dissipation is much better compared with laminate substrated-based packages. However, the solder joint reliability requirement under thermal cycling condition is also higher and this is what makes the development of a power package challenging. One of the usual requirements from customers is that there should be no solder joint failure up to 2,000 thermal cycles. This paper presents the thermomechanical simulation of a power leadframe package that was conducted to improve its solder joint reliability. Board level solder joint cycle life was predicted using finite element analysis and the result was validated with actual solder life result from board level reliability evaluation. Since available solder prediction equation was for the characteristic life (63.2% accumulative failure), using the normalized characteristic life was implemented for predicting the number of cycles to first failure of the solder joint connection and the approach showed good agreement with the actual result. Results also indicated that the choice of epoxy mold material and the type of PCB (printed circuit board) have a significant contribution to the solder joint reliability performance.

Interaction of thermal cycling and electric current on reliability of solder joints in different solder balls

This paper deals with the effects of electric current on the thermomechanical lifetime of solder joint as the most vulnerable part in electronic packages. The main focus of this paper is located on the Sn3.8Ag-0.5Cu based solder. Different current densities from 1 A mm−2 to 10 A mm−2 are under considered in two well-known solder ball joints, namely barrel- and hourglass-type, in the temperature cycling conditions. Electrical properties of the interested solder joints are experimentally extracted and applied to the finite element analysis in order to reveal the thermomechanical coupling effects of thermal cycling and electric current. Two most important phenomena including joule heating effects and induced triaxility play major roles in determination of solder joint types in the electronic packages. The results reveal that at the lower current density in which the joule heating effects are insignificant, the sharp triaxiality in the barrel-type solder joint is evident due to sharp tilting angle of solder joint. However, in the higher current densities in which the joule heating effects come into play, the number of cycle to failure of hourglass-type solder joint is lower in comparison with barrel-type solder joint. This event may be due to the lower diameter of hourglass-type solder joint in its neck so that more losses in the neck of hourglass-type solder joint, the more effective joule heating is occurred.

Machine learning framework for predicting reliability of solder joints

Purpose This paper aims to present a machine learning framework for using big data analytics to predict the reliability of solder joints. The purpose of this study is to accurately predict the reliability of solder joints by using big data analytics. Design/methodology/approach A machine learning framework for using big data analytics is proposed to predict the reliability of solder joints accurately. Findings A machine learning framework for predicting the life of solder joints accurately has been developed in this study. To validate its accuracy and efficiency, it is applied to predict the long-term reliability of lead-free Sn96.5Ag3.0Cu0.5 (SAC305) for three commonly used surface finishes such OSP, ENIG and IAg. The obtained results show that the predicted failure based on the machine learning method is much more accurate than the Weibull method. In addition, solder ball/bump joint failure modes are identified based on various solder joint failures reported in the literature. Originality/value The ability to predict thermal fatigue life accurately is extremely valuable to the industry because it saves time and cost for product development and optimization.

Microstructural evolution and failure mechanism of 62Sn36Pb2Ag/Cu solder joint during thermal cycling

To clarify the mechanism leading to solder joint failure easily in multi-field conditions in electronics system, the microstructural evolution of 62Sn36Pb2Ag/Cu solder joint during thermal cycling was investigated precisely using scanning electron microscopy and transmission electron microscopy. It was found that the as-reflowed microstructure of the solder joint was compact and uniform, being consist of Sn, Pb and Ag3Sn phases within original solder and Cu6Sn5 compound at the interface to Cu substrate. Addition of 2 wt% Ag resulted in isolated Ag3Sn particles (0.2–0.5 μm in diameter) distributed in Sn matrix of the solder joint. During thermal cycling process, the microstructure of solder became more and more coarsening, especially the average diameter of Pb particles increased to more than 3.5 times larger after 2500 thermal cycles. Moreover, Cu3Sn was generated at Cu6Sn5/Cu interface, and the total thickness of IMC layer increases almost linearly with the number of cycles. Due to the difference in coefficients of thermal expansion (CTE) among PCB board, Cu substrate and solder alloy, thermal mismatch occurred and contributed to the microstructural coarsening of solder alloy. Furthermore, due to the difference of expansion and contraction between Pb phase and Sn phase in the solder, cracks were formed and propagated along the interface between these two phases, which can accumulate and result in final failure of the solder joint thoroughly.

A State-of-the-Art Review of Fatigue Life Prediction Models for Solder Joint

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

RETRACTED ARTICLE: High-G drop effect on the creep-fatigue failure of SAC solder joints in BGA packages

The purpose of this work is to show the effects of drop impact on the creep-fatigue evolution of solder balls in an electronic device. Finite element method analysis was carried out for evaluation of stress and strain distribution in the solder joints. According to the simulation outcomes, the thermal cycling made an accumulated creep strain in the solder balls. The concentration of creep strain considerably increased with the coupling of drop impact into the thermal cycling. This event was owing to the excessive stress exerted on the samples by drop impacts. The stress analysis also indicated that with the addition of drop impacts into the thermal cycling intensified the stress triaxiality at the interfaces. Moreover, the experimental works were done and determined the elemental heterogeneity phenomenon in the solder joints and crack propagation along the interface.

Comprehensive comparative analysis of microstructure of Sn–Ag–Cu (SAC) solder joints by traditional reflow and thermo-compression bonding (TCB) processes

Thermo-compression bonding (TCB) process has been considered an emerging alternative to the conventional reflow process because of its significantly fast bonding time due to rapid ramping and its ability to fabricate ultra-fine pitch 3D stacked interconnections to achieve package miniaturization, as is necessary in high bandwidth memory (HBM) modules. Since the TCB-process bonded joints are usually followed by additional solder reflow processes for bonding of other components, no attention has been solely dedicated to the reliability of TCB-only bonded joints. In addition, there has not been any fundamental and comparative studies between the conventional reflow bonding and the TCB process. A recent study showed that the TCB joints could be vulnerable to thermal cycling and electro-migration (EM), and therefore risk exhibiting early failures. A significant difference in bonding processes between the two processes may affect solder grain and crystallographic characteristics, thus affecting the reliability performance. Here, we show that the Cu6Sn5 intermetallic compound (IMC) morphology at Sn–Ag–Cu (SAC-305) solder joint interfaces and the β-Sn crystallographic orientation of the solder joint could explain for the premature EM failure in TCB-utilized solder joints. The effect of the IMC layer of TCB-processed solder joints on the diffusion of Cu and Ni atoms at the solder/bond pad interfaces is presented. Furthermore, the thermomigration (TM) caused by Joule heating for TCB-utilized solder joints is discussed. Lastly, statistical studies using electron backscatter diffraction (EBSD) results reveal the higher lattice coherency of β-Sn crystallographic texture for TCB-processed solder joints.

Failure Mechanism of Die-Attach Solder Joints in IGBT Modules Under Pulse High-Current Power Cycling

Applications under extreme conditions, such as solid circuit breakers and electromagnetic launching systems, are great challenges to semiconductor power devices. The die-attach solder joint is as one of the most vulnerable structures and critical to the reliability of insulated-gate bipolar transistor (IGBT) modules. In this paper, IGBT modules were cross sectioned and tested under pulse high-current power cycling. The failure mechanism of the die-attach solder in IGBTs at pulse high-current modes was investigated. Evolution of microdefects in the die-attach solder during power cycling was characterized and factors for the failure of die-attach solder joints was discussed. The results revealed that voids, cracks, and detachment of interface were the major microdefects in the die-attach solder layer. A detachment of the Si/Sn–Ag–Cu (SAC) interface is verified as the major failure mode under pulse high-current power cycling. Interface cracks between the Si-chip and die-attach solder layer were found to initiate first at the solder layer edges and then extended to the center of the solder layer with the increase of power cycles. The detachment of Si/SAC interface was more similar to the brittle fracture. The junction temperature swing and heating rate were the key factors for detachment of the Si/SAC interface.

Laser impact welding: Investigation on microstructure and mechanical properties of molybdenum-copper welding joint

Due to their excellent properties, molybdenum and copper are widely used in the electronics industry. However, the welding of molybdenum and copper is difficult, which limits their application prospects in the field of microelectronics devices. This paper describes a novel method for Mo/Cu welding in micro devices: laser impact welding (LIW). The experimental results found that welding improved with the increase of laser energy. The springback and interface wave in the welding area were observed by optical microscope and scanning electron microscope (SEM)and the results showed that the shapes of the interface wave were flat and zigzag. Energy dispersive spectroscopy (EDS) showed little or no diffusion of elements at the welding interface. Tensile shear test results of the welded specimens showed that there were two kinds of failure forms: solder joint failure and solder joint edge failure. The nano-hardness of the materials in the welding area increased compared with the raw materials.

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.

Failure study of Sn37Pb PBGA solder joints using temperature cycling, random vibration and combined temperature cycling and random vibration tests

In this paper, the tin-lead (Sn-37wt%Pb) eutectic solder joints of plastic ball grid array (PBGA) assemblies are tested using temperature cycling, random vibrations, and combined temperature cycling and vibration loading conditions. The fatigue lives, failure modes for the solder joints and the typical locations of the failed solder joints for single-variable loading and combined loading conditions are compared and analyzed. The results show much earlier solder joint failure for combined loading than that for either temperature cycling or pure vibration loading at room temperature. The primary failure mode is cracking within the bulk solder under temperature cycling, whereas the crack propagation path is along the intermetallic compound (IMC) layer for vibration loading. The solder joints subjected to combined loading exhibit both types of failure modes observed for temperature cycling and vibration loading; in addition, cracking through the IMC and the bulk solder is observed in the combined test. For temperature cycling and vibration loading, the components in the central region of the printed circuit board (PCB) have more failed solder joints than other components, whereas for combined loading, the number of failed solder joints in the components in different locations of the PCB is approximately the same.