Solder Joint Reliability Research Articles

Board Level Reliability of Flipchip Package

In the world of electronic materials, solder is a critical material that plays an important role in the first level (silicon to package substrate) and second level (package to printed circuit board) interconnection. As a joining material in electronic assemblies, solder provides electrical and mechanical connections. The increasing need for reliable electronic devices for harsh environment triggers the need for reliable solder joints. This study focuses on reliability of second level interconnections between package and printed circuit boards. Board level temperature cycling and mechanical drop performance of a 15 mm x 15 mm FCBGA test vehicle were evaluated with different package construction (lidded vs non-lidded), and BGA solder alloys (SA1, SA2, and SA3). Daisy chain packages were assembled on 1.0 mm thick PCB. Mounted units were thermally cycled between from -40C to 125C. Additional samples were evaluated in mechanical drop test conditions following JEDEC standards. Results showed that packages with SA2, and SA3 BGA had significantly higher board-level thermal cycling life compared to SA1. The best drop performance was achieved with SA1 solder. The performance trend among different solder alloys was found to be similar between lidded vs non lidded package. However, lidded package showed improved board-level reliability performance compared to a non-lidded package.

Study on the Solder Joint Reliability of New Diamond Chip Resistors for Power Devices

New diamond chip resistors have been used in high-power devices widely due to excellent heat dissipation and high-frequency performance. However, systematic research about their solder joint reliability is rare. In this paper, a related study was conducted by combining methods between numerical analysis and laboratory reliability tests. In detail, the shape simulation and thermal cycling finite element simulation for solder joints with different volumes were carried out. The optimized solder volume was 0.05 mm3, and the maximum thermal cycling stress under the optimized shape was 38.9 MPa. In addition, the thermal cycling tests with current and high temperature storage tests were carried out for the optimized solder joint, which showed good agreement with the simulation results, clarified the growth and evolution law of intermetallic compound at the interconnection interface, and proved the optimized solder joint had great anti-electromigration, temperature cycling and high temperature storage reliability. In this work, an optimized solder joint structure of a diamond chip resistor with high reliability was finally obtained, as well as providing considerable reliability data for the new type of diamond chip resistors, which would boost the development of power devices.

Reliability and prediction of Sn36Pb2Ag solder joints under thermal aging test

In this work, the capacitor solder joints were aged at 50 °C, 75 °C, 100 °C, 125, and 150 °C from 100 h to 1000 h. The intermetallic compounds (IMCs) layer growth of Sn36Pb2Ag on hot air solder leveled (HASL) pad and electroless nickel/immersion gold (ENIG) pad was measured. Based on the empirical power-law of the IMC growth and the Arrhenius relationship between diffusion coefficient and aging temperature, a method to predict the IMC growth at a selected temperature was developed. The mechanical property of capacitor solder joints after thermal aging was investigated through the shear test. Through analysis of the fracture surface, the mixed fracture mode of ductile and brittle was exhibited. The porous structure of the Cu coating on the capacitor electrode was determined to be the origin of the crack.

Microstructural Evolution and Deterioration of Shear Properties of Sn3.0Ag0.5Cu/Cu Solder Joints after Long-Term Storage at Cryogenic Temperatures

In deep space exploration the exploration equipment will inevitably experience the harsh environment of cryogenic temperature. Solder joints belong to the most vulnerable parts of electronic equipment, and the harsh environment of extreme cryogenic temperature will seriously threaten the reliability of solder joints. In this paper, Sn3.0Ag0.5Cu/Cu solder joints were prepared and stored at cryogenic temperatures (−50 °C, −100 °C, and −196 °C) for up to 960 h, whilst studying the microstructural evolution and deterioration of shear properties. The results showed that the influence of cryogenic temperature on microstructure deterioration was greater than that of storage time. With the decrease of storage temperature and the extension of storage time, the Ag3Sn intermetallic compounds (IMCs) were uniformly dispersed in the β-Sn matrix; the size decreased and the number increased. After being stored at −196 °C for 960 h, some microcracks appeared at the interface of the solder joints. Meanwhile, the shear force of the solder joints was reduced by 19.02%, and the fracture mode changed from ductile fracture to ductile–brittle mixed fracture. Therefore, it is of great scientific significance to reveal the microstructural evolution and deterioration of shear properties of the solder joints under long-term storage at cryogenic temperatures.

Nickel Nanoparticle/Carbon Films as an Interlayer To Improve the Stability of Solder Joints

The growth of brittle intermetallic compounds (IMCs) generated between a solder and a substrate is crucial for the reliability of solder joints. Therefore, it is necessary to control the growth of IMCs at the interface. Herein, we propose a strategy with the nickel nanoparticle/carbon (Ni&C) films as an interlayer to improve the stability of the solder joint. After adding the interface with the Ni&C film and reflowing for 450 s, the growth of IMCs decreased by 41.05%. After reflowing for 450 and 2100 s, the grain size in the 300 s-Ni&C/Cu substrate decreased by 14.34 and 20.50%, respectively, compared with the pure Cu substrate. Furthermore, the Ni&C film changes the microstructure of the interface and the diffusion pattern of elements, thus reducing the number of Kirkendall voids. As the reflow time increases, the scalloped IMCs are transformed to be prismatic, which can be well explained by the Gibbs–Thomson effect. The synergistic effect between Ni and carbon in Ni&C can jointly control the interface reaction and the growth of IMCs, with the Ni&C film acting as an inert barrier to inhibit the growth of IMCs.

Effect of 0D and 1D ZnO nano additive reinforced Sn-3.0Ag-0.5Cu solder paste on InGaN LED chip/ENIG joints

Nanocomposite solder has been recognized as an excellent strategy to improve the reliability of solder joints. This study attempts to find the effects of ZnO nanoparticles (NP) and nanowires (NW), on the LED/Sn3.0Ag0.5Cu joint reliability. Varying amounts of ZnO NP and NW are dispersed into solder using a high-speed centrifugal paste mixer and LED/solder joints were assembled via paste printing and reflow technique. Until 0.2 wt %, adding NP and NW improved the spreading ratio of SAC 305 paste by 8.7 % and 11.1 %. However, due to ceramic/metal surface instability, higher addition declined the spreading ratio. Both NP and NW suppressed the (Cu, Ni)6Sn5 intermetallic compound (IMC) formed at the LED/solder joint. Dispersion strengthening provided by NP and NW improved the joint shear strength by 28.2 % and 31.1 %, respectively. The Weibull modulus and 75 % survival probability improved consistently with increasing ZnO NW addition, displaying homogeneity in shear strength and reliable LED/solder joints.

Failure Analysis of Printed Circuit Board Solder Joint under Thermal Shock

Investigating the failure mechanism of solder joints under different temperature conditions is significant to ensure the service life of a printed circuit board (PCB). In this research, the stress and strain distribution of a PCB solder joint was evaluated by high- and low-temperature thermal shock tests. The cross-section of the solder joint after thermal shock testing was measured using a 3D stereoscopic microscope and SEM equipped with EDS. The microstructure of the lead-free solder joint and the phase of the intermetallic compound (IMC) layer were studied by XRD. The working state of the PCB solder joint under thermal shock was simulated and analyzed by the finite element method. The results show that thermal shock has a great effect on the reliability of solder joints. The location of the actual crack is consistent with the maximum stress–strain concentration area of the simulated solder joint. The brittle Cu6Sn5 and Cu3Sn phases at the interface accelerate the failure of solder joints. Limiting the growth of Cu6Sn5 and Cu3Sn phases can improve the reliability of solder joints to a certain extent.

Arrhenius Fatigue Life Modeling for Lead-Free Solder Joints in Accelerated Combined Fatigue and Creep Tests at Different Operating Temperatures

Frequent failures in interconnected materials in microelectronic packages play a vital role in determining the reliability of electronic devices. Differences in the thermal expansion coefficients of the solder joint, printed circuit board (PCB), and electronic package are a major source of applied stress on solder joints. Due to health concerns and governmental regulations associated with using leaded solder alloys, SAC solder alloys are commonly used as an alternative to Pb-alloys because of their outstanding solderability and reliability. The shear fatigue creep accelerated test at different load levels (16 MPa, 20 MPa, and 24 MPa) was implemented in this study by using a universal micro-testing machine to investigate solder joint reliability. The creep effects were demonstrated by employing 60 seconds of dwell time for each alternating stress value and comparing its impact on solder joint reliability with the fatigue test results. The accelerated test was applied to SAC305 (96.5% Sn, 3% Ag, 0.5% Cu) solder joints with OSP surface finish at different testing temperatures (25°C, 60°C, and 100°C). Seven replicates were considered as a sample size for the reliability analysis. A two-parameter Weibull distribution was employed as the dominant distribution to describe the fatigue behavior at each condition. The characteristic life and shape parameters at each condition were extracted from the obtained Weibull models. The stress–life equation was used to estimate the reliability performance of the solder joints against fluctuations in stress amplitude at differing testing temperatures. The inelastic work per cycle and plastic strain were calculated from the acquired hysteresis loop under each condition. Coffin–Manson and Morrow energy models illustrate the relationships between fatigue life versus plastic strain and inelastic work, respectively. The effects of the oscillated testing temperature on the stress–life model, Morrow energy model, and Coffin–Manson model were elaborated using the Arrhenius equation. The results indicated a severe degradation of fatigue life with increased testing temperature. Raising the stress amplitude had a less significant impact on fatigue life reduction than increasing the testing temperature. The reliability prediction models, as a function of the fatigue properties and testing temperature, were derived from the Arrhenius, Coffin–Manson, and Morrow energy models. The acquired prediction equations produced acceptable goodness-of-fit values. Finally, a general reliability model with a 99% adequacy value (R <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) was constructed as a function of testing temperature and stress amplitude.

Effects of Voids on Thermal Fatigue Reliability of Solder Joints on Inner Rings in Ball Grid Array Packaging by Finite Element Analysis

Under alternating temperatures, the fatigue failure of solder balls caused by the mismatch of the thermal expansion coefficient is a key problem in a Ball Grid Array (BGA). However, the combined effects of the solder ball location and the size of voids within it can seriously affect the thermal fatigue reliability of BGA solder balls, which can be easily ignored by researchers. Firstly, the thermal fatigue reliability of the board-level solder balls was evaluated by a temperature cycling test of the BGA package at -20 °C-+125 °C. The experimental results showed that the thermal fatigue reliability of the outer ring's solder joint was lower than that of the inner ring. Secondly, the reliability of the solder balls in the BGA package was studied under the same thermal cycling condition based on finite element analysis (FEA). The influences of voids on fatigue life were investigated. Generally, a linear correlation between the void content and the fatigue life of the inner rings' solder balls could be identified with a gradually smoothed relationship for solder balls closer to the center. In addition, when the size of the void exceeded a critical volume, the inner ring's solder ball with the void would fail before the outermost ring. The results of FEA showed that the critical void volume ratio from the second to fifth ring increased from 10.5% to 42.3%. This study provides a valuable reference for the influence of voids on the thermal fatigue reliability of BGA solder balls.

Effects of alloying elements on the interfacial segregation of bismuth in tin-based solders

Sn-Bi solders are potential candidates for replacing traditional lead-based solders in electronic packaging due to their low melting points, superior wettability, and mechanical properties. The grain coarsening due to the interfacial Bi segregation is a vital issue that affects the reliability of Sn-Bi solder joints. Through first-principles calculations, this study systematically revealed the effects of different alloying elements on the interfacial segregation of Bi towards Sn(100) surface. Bi tends to segregate to the top-surface of Sn due to the formation of vacancies on Sn surface. However, doping alloying elements into the Sn-Bi solders could effectively suppress the interfacial Bi segregation. The presence of elements such as Pd, Pt, and Au located at the adjacent surface layer of Bi could inhibit the Bi precipitation, by apparently increasing the segregation energies of Bi to the Sn surface. The results can be interpreted by the enhanced bond orders and charge transfer between Bi, alloying elements, and their neighboring Sn atoms. This study could provide valuable insights into the design of multi-component Sn-Bi solders with minor alloying elements doping in the future.

Reliability modeling of the fatigue life of lead-free solder joints at different testing temperatures and load levels using the Arrhenius model

Reliability of the microelectronic interconnection materials for electronic packages has a significant impact on the fatigue properties of the electronic assemblies. This is due to the correlation between solder joints reliability and the most frequent failure modes seen in electronic devices. Due to their superior mechanical and fatigue properties, SAC alloys have supplanted Pb-solder alloys as one of the most commonly used solder materials used as interconnection joints on electronic packages. The main aim of this study is to develop a prediction model of the fatigue life of the solder joints as a function of the experimental conditions. Using a customized experimental setup, an accelerated fatigue shear test is applied to examine the fatigue life of the individual SAC305 solder joints at actual setting conditions. OSP surface finish and solder mask defined are used in the studied test vehicle. The fatigue test includes three levels of stress amplitude and four levels of testing temperature. A two-parameter Weibull distribution is used for the reliability analysis for the fatigue life of the solder joints. A stress–strain curve is plotted for each cycle to construct the hysteresis loop at each cyclic load and testing temperature. The acquired hysteresis loop is used to estimate the inelastic work per cycle and plastic strain. The Morrow energy and Coffin Manson models are employed to describe the effects of the fatigue properties on the fatigue life of the solder joints. The Arrhenius model is implemented to illustrate the evolutions in the stress life, Morrow, and Coffin Manson equations at various testing temperatures. The fatigue life of SAC305 solder joints is then predicted using a general reliability model as a function of the stress amplitude and testing temperature.

Wafer-level packaging solder joint reliability lifecycle prediction using SVR-based machine learning algorithm

Abstract The development of new electronic packaging structures often involves a design-on-simulation approach. However, simulation results can be subjective, and there can be variances in outcomes depending on who is conducting the simulation. To address this issue, packaging designers are now turning to machine learning to increase the accuracy and efficiency of the design process. This research study focuses on using support vector regression (SVR) techniques, such as single kernel, multiple kernels and a new SVR technique, to predict the reliability of the wafer-level packaging (WLP). By doing so, the study aims to provide designers with a reliable way to assess the reliability life cycle of their packaging designs. This research includes three steps: validating the WLP's reliability using finite element analysis (FEA) and experiment results, using the validated FEA result as input to obtain a predictive model through the SVR technique and the evaluating predictive model's performance. The results show that the predictive models developed using the SVR technique have stable performance on different testing data, which is consistent with the FEA results.

Thermomigration suppression in Sn3.5Ag solder joints by hot-end FeCoNiMn alloy

Temperature gradient is inevitable in solder joints in advanced electronic packaging; it induces thermomigration (TM), critically affecting the reliability of micro solder joints. Although a FeCoNiMn alloy (FCNM) can resist thermal aging in solder joints, its TM resistance has seldom been examined. Thus, this study investigated the TM in Cu/Sn3.5Ag (SA3.5)/FCNM solder joints between a cold end (50 °C) and a hot end (200 °C) at different times. A multielement intermetallic compound (MEIMC), (Cu, Mn, Fe, Co, Ni)6Sn5, is formed at the SA3.5/FCNM interface in the reflowed and aged solder joints. A (Fe, Co, Ni, Mn)Sn2 MEIMC also formed, but it was very thin. The (Cu, Mn, Fe, Co, Ni)6Sn5 was completely decomposed by TM from the hot-end FCNM. In contrast, the (Cu, Mn, Fe, Co, Ni)6Sn5 MEIMC thickened as the rapid TM flux of Cu from the hot-end Cu cap; however, the low chemical flux from FCNM hindered its formation, which was replaced by Cu6Sn5 formation near the Cu/SA3.5 interface. The findings demonstrate that FCNM providing a very low chemical flux is a remarkably promising diffusion barrier for TM in micro solder joints.

Effects of Nanoparticle Addition on the Reliability of Sn-Based Pb-Free Solder Joints Under Various Conditions: A Review

In order to satisfy the needs of electronic industries for high-reliability joints, different kinds of nanoparticles were incorporated into conventional Pb-free solders to enhance the performance of solder joints by researchers for decades. It is reported that doping certain nanoparticles to the solder can promote the wettability and strength of the solder, refine the grain size of solder and intermetallic compounds, and inhibit IMC layer growth. In this paper, the effects and the corresponding mechanism of nanoparticle addition on the reliability of Sn-based Pb-free solder joints in various conditions are comprehensively analyzed and summarized such as under thermal aging, thermal cycling, thermal shock, electromigration and so on. In addition, directions for future study about the reliability of nanoparticles-doped solder joints were discussed, so as to provide theoretical support for developing high-reliability nanocomposite solder joints.

Board-Level Drop Impact Reliability Analysis of Dual-Side Molding System-in- Package (SiP) Modules

System-in-package (SiP) modules are widely used in portable electronics such as Internet of Things (IoT) devices and mobile consumer equipment since they integrate multiple components in a single package and thus facilitate device miniaturization. An advanced packaging technology referred to as dual-side molding (DSM) has recently been proposed as a means of achieving even smaller form factors and lower cost solutions. However, shrinking the package size reduces the solder joint connection area between the SiP module and the printed circuit board (PCB). Consequently, the board-level drop reliability may be severely impaired. Accordingly, the present study utilizes a numerical model to investigate the board-level solder joint reliability of a DSM SiP package in drop impact tests performed in accordance with the Joint Electron Device Engineering Council (JEDEC) standard. The validity of the numerical model combined with a full-factorial design method is then employed to examine the effects of the main design parameters of the DSM SiP package on the reliability of the solder joints in the drop impact test. Overall, the present results show that a higher EMC coverage of the solder ball joints yields a significant improvement in the solder joint reliability. In addition, a larger solder joint volume is beneficial in reducing the solder joint stress by absorbing a greater proportion of the impact load and energy produced in the drop impact event.

Solid-state interfacial reaction of Sn-Ag solders with polycrystalline Cu and (0 0 1) Cu substrate

• For sn-Ag solder, the growth of Cu 3 Sn on (0 0 1)Cu is faster than on polycrystalline Cu in aging. • Ag increases the difference in Cu 3 Sn thickness on (0 0 1)Cu and polycrystalline Cu in aging. • Ag is beneficial to maintain the preferred orientation of Cu 6 Sn 5 in aging. The growth of Cu 3 Sn is associated with the formation of Kirkendall voids and is important to the reliability of solder joints. In this paper, the effect of Ag on the growth behavior of Cu 3 Sn on (0 0 1) Cu and polycrystalline Cu during aging was compared. Besides, the orientation evolution of Cu 6 Sn 5 on (0 0 1) Cu during aging was also investigated. Results suggested the growth rate of Cu 3 Sn on (0 0 1) Cu is higher than that of polycrystalline Cu during solid-state aging and the difference in the Cu 3 Sn layer thickness increases with the increases of Ag content in the solder. Moreover, the addition of Ag is beneficial to maintaining the preferred orientation of Cu 6 Sn 5 on (0 0 1) Cu during solid-state aging. The results have great help to deepen the understanding of the difference in growth behavior of intermetallic compounds on (0 0 1) Cu and polycrystalline Cu during aging.

A review: effect of copper percentage solder alloy after laser soldering

PurposeThis study aims to review the effect of copper percentage in Sn-based solder alloys (Sn-xCu,x= 0–5 Wt.%) on intermetallic compound (IMC) formation and growth after laser soldering.Design/methodology/approachThis study reviews the interfacial reactions at the solder joint interface, solder joint morphology and the theory on characterizing the formation and growth of IMCs. In addition, the effects of alloying and strengthening mechanism, including wettability, melting and mechanical properties are discussed.FindingsThis paper presents a comprehensive overview of the composition of tin-copper (Sn-Cu) solders with a potential to enhance their microstructure, mechanical characteristics and wettability by varying the Cu percentage. The study found that the best Cu content in the Sn-xCu solder alloy was 0.6–0.7 Wt.%; this composition provided high shear strength, vibration fracture life value and ideal IMC thickness. A method of solder alloy preparation was also found through powder metallurgy and laser soldering to improve the solder joint reliability.Research limitations/implicationsThis study focuses on interfacial reactions at the solder joint interface, solder joint morphology, modelling simulation of joint strength and the theory on characterising the formation and growth of IMC.Originality/valueThe paper comprehensively summarises the useful findings of the Sn-Cu series. This information will be important for future trends in laser soldering on solder joint formation.

Reliability of laser soldering using low melting temperature eutectic Sn Bi solder and electroless Ni-electroless Pd-immersion Au-finished Cu pad

The demand for flexible wearable devices/substrates with miniaturization and improved integration in microelectronic devices has intensified the research interest in low-temperature laser soldering processes as an alternative to conventional reflow soldering processes owing to their advantages, such as local heating, non-contact heating, and short bonding time. In this study, we compared and evaluated the reliability of laser soldered and conventional reflow soldered joints using representative low melting temperature eutectic Sn Bi solder and thin electroless Ni-electroless Pd-immersion Au (ENEPIG)-finished Cu pads. Laser soldering was performed using various laser powers (130, 150, and 170 W) and times (2 and 4 s). Furthermore, an aging test was performed at 110 °C for 2000 h to evaluate the long-term reliability of the soldered joints. The mechanical properties, including the top and cross-sectional views and fracture surfaces, of the soldered joints were analyzed by conducting shear tests after aging. During laser soldering, various intermetallic compounds (IMCs) were formed at the joints depending on the applied energy. The metallization layer and Cu reacted with Sn in the solder after different aging durations, and additional IMCs were formed and grown. After aging for 2000 h, the shear strength decreased, and the interfacial IMC thickness increased. As the aging time increased, the fracture mode changed from an initial ductile fracture to brittle fracture (between the solder and IMCs and/or between IMCs and the Cu pad). The reflow soldered joints exhibited stable shear strength, resulting in ductile fracture until aging for 500 h. However, the shear strength decreased sharply after aging for 1000 and 2000 h, and Bi-segregation was observed after aging for 1000 h, resulting in inferior long-term reliability. After laser soldering at 150 and 170 W for 4 s, the strength of the samples decreased sharply after aging for 1000 and 250 h, respectively, and Bi-segregation was observed after aging for 2000 h. The shear strength of the sample laser soldered at 170 W for 2 s gradually decreased with increasing aging time and maintained a stable shear strength until aging for 2000 h. Therefore, laser soldering at 170 W for 2 s was considered as the optimal condition for long-term reliability. • Soldering properties of laser soldered Sn-58Bi/Au/Pd/Ni-finished Cu joints evaluated. • Laser soldering results were compared with conventional reflow soldered joints. • Various IMCs were formed depending on laser power and irradiation time. • Laser conditions with low applied energy displayed superior long-term reliability. • Selection of the optimal laser conditions is crucial to ensure reliable solder joints.

Multi-Physics Fields Simulations and Optimization of Solder Joints in Advanced Electronic Packaging

The endurability of solder joints in the ball-grid array (BGA) packaging is crucial to the functioning of the microelectronic system. To improve electronic packaging reliability, this paper is dedicated to numerically optimize solder joint array configuration and study the influence of multi-physical fields on solder joint reliability. The uniqueness of this study is that on the basis of temperature field and stress field, the electric field is added to realize the coupling simulation of three physical fields. In addition, the “Open Angle” is mathematically defined to describe the array configuration, and it was used to reveal the influence factors of solder joint fatigue, including stress, temperature, and current density. In the single solder joint model, the impacts of geometric shape and working conditions on the maximum value and distribution of these evaluation factors (stress, temperature, and current density) were investigated. Overall, the numerical investigation gives the optimal configuration, geometric shape, and working condition of solder joints, which benefits the design of endurable and efficient BGA packaging.

Solderability and Reliability of Sintered Nano-Ag Bond Pads of Printed Re-Distribution Layer

Abstract Redistribution layer (RDL) is one key enabling technology for advanced packaging. RDL is usually fabricated at wafer level by a photolithography process. An alternative approach for implementing RDL by additive manufacturing (AM) method is proposed in this study. This allows RDL to be fabricated on a singulated chip. Nanosilver (nano-Ag) ink is printed on the silicon chip to form routing traces and bond pads. However, the Ag pad may be consumed by the solder quickly if the reflow process is not properly controlled. The mechanical integrity of the solder joint was evaluated by both solder ball shear and die shear tests. A high temperature storage test and humidity test were carried out to evaluate the solder joint reliability. Experiment results showed that the Ag pad fabricated by AM is compatible with surface mount technology (SMT). Reliable solder joints on the Ag pad were achieved. There was no significant change in the Ag3Sn intermetallic compound (IMC) layer thickness and mechanical strength after aging at high temperature and high humidity conditions. There was no early solder joint failure observed. The finding of the present study will serve as a very useful reference for the future practice of forming solder joints on sintered nano-Ag pads.