Solder Research Articles

On-Chip Sensor for Monitoring Crack Propagation in Solder Joints Using RF Signals: Electrical Modeling and Circuit Design

On-Chip Sensor for Monitoring Crack Propagation in Solder Joints Using RF Signals: Electrical Modeling and Circuit Design

Understanding the deformation creep and role of intermetallic compound-microstructure in Sn-Ag-Cu solders

Tin-based alloys are commonly used in lead-free solder joints in electronic interconnection applications, where creep can limit joint reliability. In this work, directionally solidified bulk solder alloys of different compositions (pure tin, SAC105 and SAC305) are mechanically tested under a constant load for each composition at room temperature to understand mechanical creep performance and quantify the role of different content of Ag3Sn and Cu6Sn5 intermetallic compounds (IMCs) in terms of secondary creep strain rate, microstructural evolution, and total amount of accumulated strain. In this work, microstructures are fabricated using directional solidification to promote a systematic variation in IMC sizes, shapes, and distributions within similar crystal orientations of the primary β-Sn matrix. Analysis of creep data indicates that secondary creep is dominated by obstacle-controlled dislocation motion. This is further confirmed by electron backscatter diffraction (EBSD) analysis, which reveals that the formation of subgrains and internal structure, correlating to the initial microstructure of the sample, i.e. changes in secondary dendrite arm spacing (λ2) and eutectic intermetallic spacing (λe). The experimental observations are supported further by crystal plasticity simulations that explicitly model the presence of IMCs within the Sn-based samples and show the dependence of the secondary creep rate upon the IMC content, and therefore be beneficial for the possible future composition design in solders.

Numerical modeling and optimization of fillet height of reinforced SAC305 solder joint in an ultra-fine capacitor assembly

PurposeThis study aims to investigate the design configuration for an optimum solder height of reinforced SAC305 solder joint in an ultra-fine capacitor assembly.Design/methodology/approachA multiphase finite volume model is developed for reflow soldering simulations to determine the fillet height of reinforced SAC305 solder joint in an ultra-fine capacitor assembly. Different solders, namely SAC305-x, SAC305-xNiO and SAC305-xTi, with varying percentage weight compositions of nanoparticles (x = 0 Wt.%, 0.01 Wt.%, 0.05 Wt.%, 0.10 Wt.%, 0.15 Wt.%) are investigated. A reflow soldering experiment is also conducted, and the cross-sections of the reflowed packages are examined using a High-Resolution Transmission Electron Microscope (HRTEM). The optimum design configurations (nanoparticle composition and material) for the solder fillet height are investigated using the Taguchi orthogonal array method.FindingsGood correlations were recorded between the HRTEM micrographs and the numerical predictions of the nanoparticles' distribution in the molten solder. The numerical prediction of the fillet height also agrees with the experiment, with a maximum disparity of 5.43%. It was found that Ti nanoparticles, having the smallest density compared to NiO and, exhibit the highest buoyancy effect in the molten solder. The Taguchi analysis revealed that the nanoparticles' material factor is more significant than the Wt.% factor for an optimum fillet height. An optimum design configuration for fillet height was established as SAC 305–0.15 Wt.% Ti, corresponding to a 41.13% improvement of the plain SAC 305 solder.Practical implicationsThe fillet height of solder joints greatly influences the solder joint reliability of miniaturized electronic packages. Solder joint reliability of ultra-fine capacitors can be improved using this study's findings on the optimum design configuration for the capacitor's solder fillet. The study’s findings can be practically implemented in industries such as electronics manufacturing, where enhanced solder joint reliability is critical.Originality/valueInvestigation of the optimum design configuration for reinforced SAC305 solder fillet is almost nonexistent in the literature. This study explored the optimization of fillet height of reinforced SAC305 solder joints in miniaturized capacitor assembly.

SnAgCu Solder Joint Microstructure Evolution During Thermal Aging: Influence of Flux

An intermetallic layer (IML) between the solder alloy and the soldered surface affects the mechanical and electrical performance of the resulting joints. Numerous studies have explored the possibilities of influencing the IML to achieve more reliable interconnections. However, the type and composition of the used flux, crucial for the proper creation of solder joints, is rarely included as a possible influencing factor. In this article, a comprehensive study on the interfacial microstructure evolution of lead‐free SnAgCu solder joints, accounting for the flux type and the temperature of the preheating phase of reflow soldering, where the flux contained in the solder paste becomes active, is presented. In the results, it is shown that the IML of as‐reflowed and thermally aged solder joints depends significantly on the flux. The IML activation energy is 57% higher for rosin‐based low‐activity (ROL)0 flux compared to ROL1 flux. The ROL0 flux, containing fewer active components, also outperforms the ROL1 flux in both the mechanical and electrical properties of the joints. Furthermore, the temperature profiles also show slight differences in measured properties, with the fluxes responding differently to changes in preheating temperature. In the presented results, importance of the used flux on solder joint microstructure is demonstrated.

Microstructural Coarsening Kinetics and Mechanical Property Changes in Long-Term Aged Sn–Pb–Sb Solder Joints

Microstructural Coarsening Kinetics and Mechanical Property Changes in Long-Term Aged Sn–Pb–Sb Solder Joints

The influences of microstructural length scale on the tensile properties and deformation mechanisms of Sn-3.0Ag-0.5Cu solder alloys

Optimizing microstructures remains critical for improving the reliability of Pb-free solder joints, especially in applications with high failure risks. The mechanical properties of Sn-3.0Ag-0.5Cu (SAC305) solder alloys is intricately linked to the length scale of the initial microstructure. This paper investigates the effects of microstructure refinement on uniaxial tensile properties, nanomechanical response, plastic deformation, and fracture using directional solidification techniques. The findings demonstrate that controlling the microstructure can effectively enhance mechanical properties, dynamic recrystallization, and intragranular deformation in SAC305 alloys. Furthermore, the study explores heterogeneous plastic deformation and the interaction between eutectic intermetallics and β-Sn. These results offer valuable insights for optimizing microstructures to achieve superior solder joint performance.

Dendrite Growth in Single-Grain and Cyclic-Twinned Sn–3Ag–0.5Cu Solder Joints

The microstructure of electronic solder joints is generated by the solidification of a small volume of bulk undercooled liquid. Here, we study β-Sn dendrite growth in Sn–3Ag–0.5Cu in the specific geometry and nucleation conditions of ball grid array (BGA) solder joints by combining electron backscatter diffraction and imaging of microstructures. It is shown that, while ⟨110⟩\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\langle 110\\rangle$$\\end{document} is the preferred dendrite growth direction, out-of-plane branching and growth with ⟨11W⟩\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\langle 11W\\rangle$$\\end{document} directions are important for allowing dendrites to fan out into the spheroidal volume of BGA joints due to the low symmetry of β-Sn. We find that the crystallographic orientation of β-Sn at the nucleation point plays a strong role in subsequent dendrite growth. In single-grain joints, dendrites are often unfavorably oriented for growth, resulting in different types of zig-zag dendrite growth. In cyclic-twinned joints, it is shown how competitive out-of-plane trunk growth between three dendrite orientations produces {101} boundaries and the characteristic beachball microstructure.

Study on Thermal Cycling Reliability of Epoxy-Enhanced SAC305 Solder Joint.

In this work, epoxy was added into commercial Sn-3.0Ag-0.5Cu (SAC305) solder paste to enhance the thermal cycling reliability of the joint. The microstructure and fracture surface were observed using a scanning electron microscope/energy dispersive spectrometer (SEM/EDS), and a shear test was performed on the thermally cycled joint samples. The results indicated that during the thermal cycling test, the epoxy protective layer on the surface of the epoxy-enhanced SAC305 solder joint could significantly alleviate the thermal stress caused by coefficients of thermal expansion (CTE) mismatch, resulting in fewer structural defects. The interfacial compound of the original SAC305 solder joints gradually coarsened due to the accelerated atomic diffusion, but epoxy-enhanced SAC305 solder joints demonstrated a thinner interfacial layer and a smaller IMC grain size. Due to the reduced stress concentration and the additional mechanical support provided by the cured epoxy layer, epoxy-enhanced SAC305 solder joints displayed superior shear performance compared to the original joint during the thermal cycling test. After 1000 thermal cycles, Cu-Sn IMC regions were observed on the fracture surfaces of the original SAC305 solder joint, exhibiting brittle fracture characteristics. However, the fracture of the SAC305 solder joint with 8 wt.% epoxy remained within the solder bulk and exhibited a ductile fracture mode. This work indicates that epoxy-enhanced SAC305 solder pastes display high thermal cycling reliability and could meet the design needs of advanced packaging technology for high-performance electronic packaging materials.

Investigation on electromigration failure behavior of SAC305/SnPb micro-hybrid solder joints for package-on-package techniques: Experiment and simulation

The failure mechanism of electromigration (EM) for electronic packaging technology has garnered interest. Electromigration-caused voids reduce electronic device dependability. Two-step reflow at 250℃ and 210℃ was employed to create SAC305/SnPb micro-hybrid solder connections. Finite element analysis confirmed electromigration failure. After 768 h at 10A, the anode interface IMC thickness increased by 149.8 %, while the cathode IMC increased less. Polarity accelerates anode IMC growth. Electromigration of Cu from cathode to anode causes structural flaws and 44.6 % shear strength loss to 35.1 MPa. Fractures shift from inside the solder joint to the IMC layer becoming brittle. COMSOL simulation demonstrates greatest current density, temperature, and stress at the current inlet and Cu pad-solder joint junction.

Tin Multilayer‐Aided SAC305‐Based Lead‐Free Solder Joint Interface with Cu: An Investigation of the Stress Distribution by Finite Element Analysis and Nanoindentation Studies

Two different types of lead‐free solder joints Cu/(Sn3.0Ag0.5Cu)/Cu and Cu/Sn/(Sn3.0Ag0.5Cu)/Sn/Cu have been investigated. Joints are produced following the transient liquid phase like soldering process. The microstructure of different intermetallic compounds (IMCs) present at the joint interfaces, as well as their indentation hardness and elastic modulus, have been investigated and analyzed using scanning electron microscopy (SEM), X‐ray diffraction (XRD) spectroscopy, and nanoindentation. The exact position of different microcracks inside the interfaces has been identified by analyzing the elastic–plastic properties and interfacial toughness of these solder joints. The modulus and hardness of the Sn multilayer‐assisted solder joint interface are found to be 60.08%, and 90.18% higher than those of its non‐layered counterpart, respectively. The finite element analysis (FEA) has been done to estimate and compute stress distributions over the interfacial region. The dislocation mechanics involved in strengthening the joint strength are related to the nature of stress flow; as observed in FEA. It is reconfirmed that the high susceptibility to brittle failure of the non‐layered Cu‐SAC305 solder joints could be avoided by using a Sn interlayer in between the Cu substrates and the SAC305 solder paste.

Effects of Minor Zn Dopants in Sn-10Bi Solder on Interfacial Reaction and Shear Properties of Solder on Ni/Au Surface Finish.

Sn-10Bi low-bismuth-content solder alloy provides a potential alternative to the currently used Sn-Ag-Cu series due to its lower cost, excellent ductility, and strengthening resulting from the Bi solid solution and precipitation. This study primarily investigates the interfacial evolution and shear strength characteristics of Sn-10Bi joints on a Ni/Au surface finish during the as-soldered and subsequent isothermal aging processes. To improve the joint performance, a 0.2 or 0.5 wt.% dopant of Zn was incorporated into Sn-10Bi solder. The findings demonstrated that a 0.2 or 0.5 wt.% Zn dopant altered the composition of the intermetallic compound (IMC) formed at the interface between the solder and Ni/Au surface finish from Ni3Sn4 to Ni3(Sn, Zn)4. The occurrence of this transformation is attributed to the diffusion of Zn atoms into the Ni3Sn4 lattice, resulting in the substitution of a portion of the Sn atoms by Zn atoms, thereby forming the Ni3(Sn, Zn)4 IMC during the soldering process, which was also verified by calculations based on first principles. Furthermore, a 0.2 or 0.5 wt.% Zn dopant in Sn-10Bi significantly inhibited the Ni3(Sn, Zn)4 growth after both the soldering and thermal aging processes. Zn addition can enhance the shear strength of solder joints irrespective of the as-soldered or aging condition. The fracture mode was determined by the aging durations-with the brittle mode occurring for as-soldered joints, the ductile mode occurring for aged joints after 10 days, and again the brittle mode for joints after 40 days of aging.

Lifetime prediction of copper pillar bumps based on fatigue crack propagation

2.5D package realizes the interconnection of multiple dies through Si interposers, which can greatly improve the data transmission rate between dies. However, its multi-layer structure and high package density also place higher reliability requirements on the interconnection structure. As a key structure for interconnection, copper pillar bump (CPB) has small size, high heat generation, and thermal mismatch with silicon chips. The thermal fatigue failure of CPB has gradually become the main failure mode in 2.5D package. Due to the small size of CPB and the large proportion of intermetallic compound (IMC) layers, the lifetime prediction method of spherical solder joints is no longer suitable for CPB. Therefore, it is necessary to establish a fatigue lifetime prediction method for CPB. This paper establishes a method for obtaining the lifetime of CPB based on the basic theory of fatigue crack propagation. Using the extended finite element simulation method, the crack propagation lifetime of CPB under thermal cycling was obtained, and the influence of different IMC layer thickness on the fatigue lifetime of CPB was analyzed. The results indicated that the fatigue lifetime of cracks propagating in the IMC layer is lower than that of cracks propagating in the solder layer, and an increase in the thickness of the IMC layer leads to a significant decrease in the fatigue lifetime of CPB. The lifetime prediction method for CPB proposed in this paper can be used for reliability evaluation of 2.5D package, and has certain reference value for the study of the lifetime of CPB.

The Evolution of Interfacial Intermetallic Compound Growth and Solder Joint Strength of Sn-40Pb/Cu under Thermal Aging

The Evolution of Interfacial Intermetallic Compound Growth and Solder Joint Strength of Sn-40Pb/Cu under Thermal Aging

Optimizing of Microbump Design for Stable Solder Joints in Thermocompression Bonding: A Simulation-Based Approach

Optimizing of Microbump Design for Stable Solder Joints in Thermocompression Bonding: A Simulation-Based Approach

High-reliability Sn37Pb/Sn58Bi composite solder joints by solid-liquid low-temperature soldering

As the feature sizes of integrated circuits approach their physical limits, 3D packaging has emerged as a crucial technology for enhancing integration and extending Moore's Law. To meet the future requirements for low-temperature solder and interconnect processes in aerospace 3D packaging, this study combined Sn37Pb solder balls with Sn58Bi solder paste to prepare uniform composite solder joints under reflow conditions of 180°C for 10 minutes (CS-180–10) and 190°C for 1 minute (CS-190–1). The Bi atoms dissolved in the Pb phase strengthened the composite solder and made the crystal structure more ordered and predictable. The composite solder joints formed under both process conditions exhibited shear strengths higher than those of Sn37Pb solder joints prepared at 220°C for 1 minute, both before and after aging at 100°C. The fracture mode of the composite solder joints transitioned from ductile to mixed ductile-brittle with aging. Additionally, the composite solder demonstrated better creep resistance than SnPb solder at all tested strain rates in nanoindentation tests. Compared to CS-180–10, the lower heat input CS-190–1 featured finer Pb phases and Pb grains, better wettability, and better thermal stability. CS-190–1 showed only a 5.9 % decrease in shear strength after 42 days of aging at 100°C. This study offers a new solution for low-temperature, high-reliability interconnections in future aerospace integrated circuit 3D packaging.

Recent Advences in Laser and Laser-Assisted Bonding (LAB) Technologies for Micro-Soldering and Applications to Mini-LED

Advancements in laser soldering and laser-assisted bonding (LAB) have revolutionized electronic manufacturing by enhancing solder joint formation with precise control, reduced thermal impact, and improved reliability. These technologies are crucial for high-density assemblies in advanced electronics, supporting miniaturization and increasing functionality. This paper introduces recent advancements in laser and LAB technologies for micro-soldering. The paper describes Nd:YAG and diode lasers, their micro-soldering results, the microstructure of the solder joint, and the author's LAB application to mini-LEDs using type-8 SAC305 solder paste. Future advancements in laser technology will further improve soldering and bonding techniques to ensure the reliability and performance of smaller, more complex electronic devices.

Strong grain size effect on the liquid/solid reactions between molten solder and electroplated Cu

Electrodeposition of Cu metallization and its soldering reaction with solder alloy are of technological significance in microelectronic packaging industry. This study aims to investigate the effect of Cu grain size on the liquid/solid reactions between molten Sn-3 wt% Ag-0.5 wt% Cu (SAC305) solder alloy and electroplated Cu. Two Cu electroplated films, denominated as fine-grained Cu (FG-Cu) and coarse-grained Cu (CG-Cu), are prepared and reacted with SAC305 at 260 °C for 5–20 min. Microstructural characterization shows that the Cu6Sn5 intermetallic compound (IMC) is formed in these two solder joints, while that in the FG-Cu solder joint grows at a faster rate than that in the CG-Cu solder joints. The Cu6Sn5 IMC in the FG-Cu solder joint exhibits a slender column-like grain morphology, unlike the common scallop-like grain morphology in the CG-Cu solder joints. The strong grain size effect is rationalized by comparing the contribution of two fluxes of ripening and interfacial reaction to the growth of Cu6Sn5.

The Effect of Multiple Solder Reflows on the Formation of Cu6Sn5 Intermetallics and the Decomposition of SnAg3.0Cu0.5 Solder Joints in the Framework of Rework and Reuse of MLCC Components

The Effect of Multiple Solder Reflows on the Formation of Cu6Sn5 Intermetallics and the Decomposition of SnAg3.0Cu0.5 Solder Joints in the Framework of Rework and Reuse of MLCC Components

Formation and growth mechanism of thin Cu6Sn5 films in Sn/Cu and Sn-0.1AlN/Cu structures using laser heating

PurposeThe purpose of this study is the formation and growth of nanoscale intermetallic compounds (IMCs) when laser is used as a heat source to form solder joints.Design/methodology/approachThis study investigates the Sn/Cu and Sn-0.1AlN/Cu structure using laser soldering under different laser power: (200, 225 and 250 W) and heating time: (2, 3 and 4 s).FindingsThe results show clearly that the formation of nano-Cu6Sn5 films is feasible in the laser heating (200 W and 2 s) with Sn/Cu and Sn-0.1AlN/Cu system. The nano-Cu6Sn5 films with thickness of 500 nm and grains with 700 nm are generally parallel to the Cu surface with Sn-0.1AlN. Both IMC films thickness of Sn/Cu and Sn-0.1AlN/Cu solder joints gradually increased from 524.2 to 2025.8 nm as the laser heating time and the laser power extended. Nevertheless, doping AlN nanoparticles can slow down the growth rate of Cu6Sn5 films in Sn solder joints due to its adsorption.Originality/valueThe formation of nano-Cu6Sn5 films using laser heating can provide a new method for nanofilm development to realize the metallurgical interconnection in electronic packaging.

PCB plug-in solder joint defect detection method based on coordinated attention-guided information fusion

Printed Circuit Boards (PCBs) are the foundational component of electronic devices, and the detection of PCB defects is essential for ensuring the quality control of electronic products. Aiming at the problem that the existing PCB plug-in solder defect detection algorithms cannot meet the requirements of high precision, low false alarm rate, and high speed at the same time, this paper proposes a method based on spatial convolution pooling and information fusion. Firstly, on the basis of YOLOv3, an attention-guided pyramid structure is used to fuse context information, and multiple convolutions of different size are used to explore richer high-level semantic information; Secondly, a coordinated attention network structure is introduced to calibrate the fused pyramidal feature information, highlighting the important feature channels, and reducing the adverse impact of redundant parameters generated by feature fusion; Finally, the ASPP (Atrous Spatial Pyramid Pooling) structure is implemented in the original Darknet53 backbone feature extraction network to acquire multi-scale feature information of the detection targets. With these improvements, the average detection accuracy of the enhanced network has been elevated from 94.45 to 96.43%. This experiments shows that the improved network is more suitable for PCB plug-in solder defect detection applications.