Solder Research Articles

Cu Pillar Electroplating Using a Synthetic Polyquaterntum Leveler and Its Coupling Effect on SAC305/Cu Solder Joint Voiding

With the advancement of high-integration and high-density interconnection in chip manufacturing and packaging, Cu bumping technology in wafer- and panel- level packaging is developed to micrometer-sized structures and pitches to accommodate increased I/O numbers on high-end integrated circuits. Driven by this industrial demand, significant efforts have been dedicated to Cu electroplating techniques for improved pillar shape control and solder joint reliability, which substantially depend on additive formulations and electroplating parameters that regulate the growth morphology, crystal structure, and impurity incorporation in the process of electrodeposition. It is necessary to investigate the effect of an additive on Cu pillar electrodeposition, and to explore the Kirkendall voids formed during the reflowing process, which may result from the additive-induced impurity in the electrodeposited Cu pillars. In this work, a self-synthesized polyquaterntum (PQ) was made out with dual suppressor and leveler effects, and was combined with prototypical accelerator bis- (sodium sulfopropyl)-disulfide (SPS) for patterned Cu pillar electroplating. Then, Sn96.5/Ag3.0/Cu0.5 (SAC305) solder paste were screen printed on electroplated Cu pillars and undergo reflow soldering. Kirkendall voids formed at the joint interfaces were observed and quantified by SEM. Finally, XRD, and EBSD were employed to characterize the microstructure under varying conditions. The results indicate that PQ exhibits significant suppressive and levelled properties with the new structure of both leveler and suppressor. However, its effectiveness is dependent on liquid convection. PQ and SPS work synergistically, influencing the polarization effect in various convective environments. Consequently, uneven adsorption occurs on the surface of the Cu pillars, which results in more Kirkendall voids at the corners than at the center along the Cu pillar surface.

IMC growth mechanism of Sn58Bi/Cu solder joints and its effect on the coarsening of the Bi phase

IMC growth mechanism of Sn58Bi/Cu solder joints and its effect on the coarsening of the Bi phase

Solder joint lifetime model using AI framework operating on FEA data

Solder joint lifetime model using AI framework operating on FEA data

Fatigue life prediction of BGA solder joint of several alloy compositions under an isothermal harmonic vibration

To ensure durable performance and optimal function of electronic components, it is crucial to guarantee their reliability, robustness and goodness of fit. The solder joints used in the BGA (Ball Grid Array) component play an intrinsic role in the reliability of the system. The vibration present in BGA triggers fatigue in solder joints, which raises a major reliability problem in various sectors such as aerospace, automotive and military industries. This study handles the response to a harmonic vibration at three specific temperatures (−40°C, 25°C, and 125°C) for four types of solder alloys in BGA Soldering. Within this framework, predicting the fatigue life of BGA solder joints with various alloy compositions under the influence of an isothermal harmonic vibration emerges as a crucial challenge in the design as well as reliability of modern electronic devices. The investigated solder compositions are SAC105, SAC305, SAC405, and InnoLot. To simulate and analyze the behavior of solder joints, we used the Ansys APDL finite element analysis (FEA). At both 125°C and −40°C, the Von Mises values proved to exceed those observed at 25°C. Likewise, an S-N curve for InnoLot and the different SACs, under a harmonic vibration at 25°C, was fitted using the Basquin power law relationship. As far as the current research work is concerned, an initial comparison was enacted between InnoLot and SAC alloys under an isothermal harmonic vibration, aiming to ascertain the most reliable alloy. The fatigue life under a harmonic vibration loading at 25°C was estimated. The results revealed that under a harmonic vibration at 25°C, the InnoLot solder displayed the longest lifespan, while the SAC105 solder exhibited the shortest fatigue life.

Electromigration in Cu–Cu joints: Measurement of activation energy and polarity effect

Electromigration (EM) has been a pivotal reliability challenge for interconnects, but there are only few studies on EM in Cu–Cu joints. In this work, accelerated EM tests for the Cu–Cu joints were conducted at three temperatures (150 °C, 179 °C, and 208 °C) and the temperature-dependent failures were discussed. The polarity effect of the grain growth behaviors at the bonding interfaces was observed at the opposite electron flows, which may be attributed to the difference in EM-build-up stress conditions and the divergence in atomic fluxes. Moreover, the activation energy (Ea) extrapolated from the three EM temperatures was derived as 0.9 eV. As compared to the solder joints with same dimensions, the Cu–Cu joints possess more than ten times of time-to-failures (TTFs) under the same EM condition.

Influence of Al2O3 Nanoparticles on the Morphology and Growth Kinetics of Cu-Sn Intermetallic Compounds in Sn-Ag-Zn/Cu Solder Joints

Intermetallic compounds (IMCs) growth can simultaneously bring about low-resistance electrical pathways and drastically reduce joint lifetime. Recently, incorporated trace nanoparticles into the free-Pb solder were found to promote the performance of the solder joints. Sn3Ag0.9Zn (SAZ) nano-composite solders were developed by doping 0.5 wt.% Al2O3 nanoparticles into the SAZ solder. The IMCs formation and growth behavior at the interfacial reactions between the SAZ-0.5Al2O3 nano-composite solder and the Cu substrate during soldering at temperatures ranging from 250 to 325 °C for 30 min were investigated. The results showed that after the addition of Al2O3 nanoparticles into the SAZ solder, the elongated-type IMCs layer changed into a prism-type IMCs layer, and Ag3Sn nanoparticles were absorbed on the grain surface of the interfacial Cu6Sn5 phase, effectively suppressing the growth of the IMCs layers. The activation energies (Q) for the IMCs layers (Cu6Sn5 + Cu3Sn) were determined to be 36.4 and 39.1 kJ/mol for the SAZ/Cu and SAZ-Al2O3/Cu solders, respectively.

Cu–Cu joint with great strength using In/Sn–58Bi hybrid soldering at low temperature (90 °C)

This study investigates Cu single-sided solder joints using hybrid soldering (In + Sn58Bi) at reflow temperatures ranging from 80 to 130 °C. The wetting angles of 27° at 90 °C and 22° at 130 °C demonstrated good wettability. The hybrid solders were composed of γ-In(Sn, Bi) and Bi(In, Sn)2 phases, forming Cu6(In, Sn)5 interfacial intermetallic compounds (IMCs). Thermodynamic calculations proved that the hybrid soldering possessed a low liquid temperature of 86.8 ° C, making it suitable for low-temperature applications. The hybrid solders demonstrated notable mechanical performance, with microhardness values exceeding 10 HV—higher than Sn–52In solder (6 HV). Sandwich hybrid-solder joints, reflowed at 90 and 130 ° C, outperformed Sn–52In soldering strength (30.1 and 35.5 MPa) by over 135% and 175%. Additionally, the hybrid solder contains only 41.9 wt% In, lower than Sn–52In, reducing material costs. This study reveals the hybrid solder system offers a promising low-cost and good-strength solution for low-temperature soldering applications.

Effects of ZrO2 Nano-Particles' Incorporation into SnAgCu Solder Alloys: An Experimental and Theoretical Study.

This study investigates the mechanism and effects of incorporating different ZrO2 nano-particles into SAC0307 solder alloys. ZrO2 nano-powder and nano-fibers in 0.25-0.5 wt% were added to the SAC0307 alloy to prepare composite solder joints by surface mount technology. The solder joints were shear tested before and after a 4000 h long 85 °C/85% RH corrosive reliability test. The incorporation of ZrO2 nano-particles enhanced the initial shear force of the solder joint, but they decreased the corrosion resistance in the case of 0.5 wt%. SEM, EDS, and FIB analysis revealed intensive growth of SnO2 on the solder joint surfaces, leading to the formation of Sn whiskers. Density functional theory (DFT) simulations showed that, despite Sn being able to bond to the surface of ZrO2, the binding energy was weak, and the whole system was therefore unstable. It was also found that ZrO2 nano-particles refined the microstructure of the solder joints. Decreased β-Sn grain size and more dispersed intermetallic compounds were observed. The microstructural refinement caused mechanical improvement of the ZrO2 composite solder joints by dispersion strengthening but could also decrease their corrosion resistance. While ZrO2 nano-particles improved the solder joint mechanical properties, their use is recommended only in non-corrosive environments, such as microelectronics for space applications.

The Effect of Bi Addition on the Electromigration Properties of Sn-3.0Ag-0.5Cu Lead-Free Solder

As electronic packaging technology advances towards miniaturization and integration, the issue of electromigration (EM) in lead-free solder joints has become a significant factor affecting solder joint reliability. In this study, a Sn-3.0Ag-0.5Cu (SAC305) alloy was used as the base, and different Bi content alloys, SAC305-xBi (x = 0, 0.5, 0.75, 1.0 wt.%), were prepared for tensile strength, hardness, and wetting tests. Copper wire was used to prepare EM test samples, which were subjected to EM tests at a current density of approximately 0.6 × 104 A/cm2 for varying durations. The interface microstructure of the SAC305-xBi alloys after the EM test was observed using an optical microscope. The results showed that the 0.5 wt.% Bi alloy exhibited the highest ultimate tensile strength and microhardness, improving by 33.3% and 11.8% compared to SAC305, respectively, with similar fracture strain. This alloy also displayed enhanced wettability. EM tests revealed the formation of Cu6Sn5 and Cu3Sn intermetallic compounds (IMCs) at both the cathode and anode interfaces of the solder alloy. The addition of Bi inhibited the diffusion rate of Sn in Cu6Sn5, resulting in similar total IMC thickness at the anode interface across different Bi contents under the same test conditions. However, the total IMC thickness at the cathode interface decreased and stabilized with increasing EM time, with the SAC305-0.75Bi alloy demonstrating the best resistance to EM.

Microstructural Evolution of Intermetallic Compound Between SN100C Solder and ENIMAG Substrate During Isothermal Ageing

SN100C alloy emerges as a promising candidate when introducing lead-free solder alternativesdue to its mechanical properties and solderability. The study aims to explore interfacial reactions between SN100C solder and ENIMAG surface finish. Methods involve preparingENIMAG substrates, solder paste application, and reflow processes following JEDEC standards. Isothermal ageing treatments were conducted, and interfacial reactions were characterized using top surface and cross-section analyses via Optical Microscope (OM), Scanning Electron Microscope (SEM), and Energy Dispersive X-ray (EDX). Post-reflow, distinct IMC layers formed at the SN100C/ENIMAG solder joint's interface, evolving with ageing. Further analysis via cross-section confirms the initial formation of (Ni, Cu)3Sn4 layer followed by (Cu, Ni)6Sn5, each exhibiting varying appearance and thicknesses. Isothermal ageing increases IMC thickness, which is particularly influenced by Cu diffusion and exposure to high temperatures, and itfacilitates the growth rate of IMCs.

Estimation of solder joint reliability in electronic packaging: Insights from finite element analysis on intermetallic compounds and voids

Estimation of solder joint reliability in electronic packaging: Insights from finite element analysis on intermetallic compounds and voids

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.