PurposeThis paper aims to systematically summarize recent advances in low-temperature interconnection using Cu nanoparticles, nanoporous Cu and one-dimensional (1D) nanocopper arrays, clarify their advantages and bottlenecks and provide theoretical support and technical references for industrial applications to sectors including new energy vehicles and 5G/6G communications. Design/methodology/approachThis study reviews synthesis, anti-oxidation and sintering mechanisms of Cu nanoparticles, nanoporous Cu and 1D arrays for low-temperature interconnection. It analyzes how sintering parameters (temperature, pressure, time, atmosphere) impact joint reliability (mechanical, electrical, thermal). By evaluating and comparing these three systems based on current research, this work provides a comprehensive framework for understanding interfacial behaviors and performance in advanced packaging. FindingsNanocopper materials (nanoparticles, nanoporous Cu and 1D arrays) enable high-performance, low-temperature sintering for robust interconnections with excellent conductivity and heat resistance. While nanoparticles offer high strength, they face oxidation and densification issues. Nanoporous Cu provides superior bonding efficiency without organic residues, and 1D arrays offer directional conductivity for complex packaging. Ultimately, optimizing sintering parameters is essential to regulating microstructure and ensuring the mechanical, electrical and thermal reliability of the resulting joints. Originality/valueThis review summarizes nanocopper-based low-temperature interconnection progress, compares Cu nanoparticles, nanoporous Cu and 1D nanocopper arrays and highlights their respective advantages and bottlenecks. By clarifying the mechanisms of sintering parameters and outlining future research directions – focusing on stability, compatibility and reliability – this work provides a framework for addressing the packaging challenges of high-power devices.
Purpose As an emerging interconnection technology, microspring array pins exhibit superior resistance to mechanical shock compared to traditional ball grid array or column array. However, high-impact dynamic loads in aerospace environments are prone to inducing microspring fracture, thereby compromising the operational safety of electronic systems. This study aims to post-printed circuit board-assembly reinforcement schemes for large-scale integrated circuits to enhance the anti-vibration performance of microspring array interconnections under extreme service conditions.Design/methodology/approach Three configurations (unreinforced, corner epoxy bonding and corner L-shaped epoxy bonding) were compared. Finite element simulation - incorporating modal, random and sinusoidal vibration analyses - was used to screen the optimal reinforcement scheme. Daisy-chain circuits facilitated in-situ monitoring, while vibration tests conducted in accordance with aerospace standards validated the reliability of the optimized method.Findings The corner L-shaped reinforcement scheme demonstrated superior performance. Modal analysis revealed that the first-order natural frequency increased from 419.33 Hz to 589.07 Hz. Under random vibration, simulation results showed the maximum stress of microsprings was reduced to 37.047 MP. Sinusoidal vibration tests minimized peak stress to 6.034 MPa. Post-vibration measurements indicated the resistance change of daisy-chain circuits was = 6%, confirming the scheme's suitability for aerospace applications.Originality/value The authors present results with advanced simulation method, the results of the simulation is verifired with independently experiment.
Purpose This study aims to investigate the effect of microwave hybrid heating (MHH) reflow on the corrosion immersion and mechanical reliability of SAC305/Cu solder. SAC305/Cu solder joints were reflowed by MHH using controlled processing durations.Design/methodology/approach Corrosion behavior was evaluated through 3.5 Wt.% NaCl immersion for up to 28 days. Structural phase evolution, interfacial morphology and elemental distribution were analyzed. Metallic ion dissolution was quantified to evaluate corrosion-induced ion release behavior, and Vickers hardness measurements were conducted to assess mechanical integrity.Findings Uniform scalloped Cu6Sn5 intermetallic layers with stable ss-Sn matrix were formed by MHH reflow method. Immersion exposure induced progressive pitting corrosion dominated by Cl--assisted ss-Sn dissolution. Oxide phases (SnO, SnO2) and complex Sn3O(OH)2Cl2 formed, contributing to partial passivation. Immersion corrosion was more severe at solder edges, whereas pitting dominated at peak regions. High initial dissolution of the Cu element was observed, followed by stabilization attributed to the formation of a protective oxide layer. A noticeable reduction in hardness (9.43%) was observed after 28 days, reflecting corrosion-induced degradation of the ss-Sn matrix.Originality/value This work provides a comprehensive correlation between MHH-induced microstructure, electrochemical degradation mechanisms and mechanical reliability of SAC305/Cu solder joints in saline environments.
Purpose SiC MOSFETs are widely used in aerospace and power electronics owing to their superior electrical properties, yet they suffer from combined threats of space radiation and thermo-electrical stress fatigue. This study aims to explore the influence of electron irradiation on the power cycling lifetime of SiC MOSFETs and reveal the corresponding failure mechanisms, offering a theoretical basis for the reliability evaluation of SiC MOSFETs in space radiation environments. Design/methodology/approach Experiments were conducted using 10 MeV electron irradiation at doses of 3 Mrad, 5 Mrad and 10 Mrad(Si), followed by forward-mode power cycling tests. Electrical parameters including threshold voltage and on-resistance were monitored periodically. Optical microscopy was adopted to characterize bond wire and solder layer damage. Electro-thermal-mechanical coupling simulation and Geant4 simulation were applied to analyze the internal stress distribution and energy deposition, clarifying the failure evolution process. Findings Electron irradiation induces negative drift of threshold voltage and reduction of on-resistance via gate oxide charge trapping. During power cycling, threshold voltage shifts positively and on-resistance rises significantly with cycling count, and higher irradiation dose aggravates the drift amplitude. Electron irradiation drastically shortens the power cycling lifetime, which is reduced by 60% at 10 Mrad compared with unirradiated devices. Irradiation creates lattice defects in the solder layer, forming voids under cyclic thermal stress, which intensifies stress concentration at bond wire-chip joints and accelerates bond wire lift-off as the final failure mode. Originality/value This study systematically reveals the synergistic degradation mechanism of electron irradiation and power cycling on SiC MOSFETs, distinguishing chip-level electrical parameter degradation and package-level mechanical failure. It provides key data and mechanistic support for the lifetime prediction and reliability optimization of SiC power devices in space applications.
Purpose This paper aims to conduct a finite element simulation to study the method of changing the shape of array micro solder joints at dangerous positions in electronic packaging design, to reduce overall stress and strain during service and thereby enhance the fatigue life. Design/methodology/approach Based on the stress-strain response and fatigue life of individual micro solder joints under alternating temperature loads, hybrid micro solder joints were designed with a drum-shaped middle part and an hourglass-shaped/laminated drum-shaped part on both sides. Through finite element analysis, the mechanical responses of the three different-shaped hybrid micro solder joints under temperature cycling were studied and analyzed. Findings The finite element analysis result illuminates that the stress of laminated drum-shaped micro solder joints is the smallest, and the fatigue life is the largest. According to the calculated results of the single solder joints, hourglass-drum-shaped, laminated drum-drum-shaped and all drum-shaped micro solder joint arrays are designed. The results show that the maximum stress produced by the laminated drum-drum-shaped and hourglass-drum-shaped micro solder joint is small, which is 46.17 MPa and 46.64 MPa, respectively. While all drum-shaped micro solder joints are the largest (47.02 MPa). The fatigue life of hourglass-drum-shaped micro solder joints is the longest. Originality/value According to the calculated results of individual solder joints, an innovative three-dimensional hybrid micro solder joint array model is proposed to characterize the influence of micro solder joint shape on temperature-dependent behavior.
yPurpose This study aims to investigate the mechanical behavior and complex coupling effects of key components in transmitter-receiver (TR) modules with quasi-coaxial structures under high-impact loads, identifying stress distribution characteristics to facilitate high-reliability anti-impact design. Design/methodology/approach An integrated finite element mechanical model comprising the module housing, 0.6-mm inner-conductor quasi-coaxial structures, alumina substrates, chips and 25-mu m gold bonding wires was established via ANSYS. A half-sine impact load (20,000 g acceleration, 10 ms pulse width) was applied. A rigorous mesh convergence analysis was performed to validate the numerical reliability in the absence of physical experimental data. Findings Results reveal a hierarchical stress gradient, diminishing from the top layer down to the interior components. The top solder ball section bore the maximum stress of 57 MPa. Quantitative analysis reveals that edge proximity significantly affects reliability: reducing the distance between the quasi-coaxial structure and the frame from 0.5 to 0.3 mm intensified local stress concentration, raising the peak frame stress from 16.53 to 19.23 MPa. Furthermore, low-arc-height bonding wires with platforms were identified as the optimal configuration for minimizing deformation. Practical implications The proposed optimization principles for key structures (via holes, bonding wires, quasi-coaxial structures, etc.) provide direct technical guidance for the anti-impact design of TR modules. They can be applied to radar, communication and other high-mobility electronic systems, effectively reducing failure risks (e.g. via cracking, chip detachment) under extreme conditions like missile launches, improving module reliability and engineering application efficiency. Social implications Reliable TR modules are critical for high-performance electronic systems in national defense, aerospace and other fields. This study's findings enhance the stability of equipment operating in harsh environments, support the development of high-mobility and anti-interference electronic technologies and indirectly contribute to national security, technological progress and the reliability of critical infrastructure. Originality/value This work fills a gap in the quantitative analysis of "deformation-stress" coupling mechanisms for quasi-coaxial TR modules under high-g environments. It provides critical, data-driven design guidelines, specifically advocating for optimized edge spacing and wire geometries to mitigate stiffness mismatch failures in severe mechanical shock applications.
Purpose This study aims to investigate the fracture behavior and reliability of large-area sintered Cu for power electronic packaging, with a specific focus on the influence of the "edge effect" on interfacial performance and structural deformation.Design/methodology/approach By fabricating sintered Cu joints with different dimensions (8 & times; 8 mm2, 16 & times; 16 mm2 and 32 & times; 32 mm2) and evaluating their microstructures, mechanical properties and warpage behavior, the mechanism of nonuniform performance degradation induced by the "edge effect" is revealed.Findings As bonding area increases from 8 & times; 8 mm2 to 32 & times; 32 mm2, shear strength drops from 105.18 MPa to 61.36 MPa, while edge porosity rises from 13.92% to 28.87%. High-temperature storage and thermal cycling (TC) exacerbate void expansion, with edge porosity reaching 37.73% after TC. Simulation reveals that stress induced by coefficient of thermal expansion mismatch increases nonlinearly with area, correlating with strength degradation zones. Experimental warpage matches simulation results within 6% error.Originality/value This study provides a crucial experimental basis and theoretical support for the process optimization and reliability design of large-area sintered Cu.
PurposeThis study aims to investigate the issue of nodule formation during wafer-level copper electroplating and explore corresponding mitigation strategies. Through experiments involving wafers with different opening areas and modified electroplating process parameters, the underlying causes of nodule formation were revealed, and engineering solutions were proposed. This research holds significant importance for enhancing the stability of the wafer-level copper electroplating process and the reliability of the packaging structure. Design/methodology/approachA multi-dimensional validation experimental scheme was designed: systematic and comprehensive research into the causes of wafer-level electroplating nodules and process optimization methods was conducted from three perspectives – root cause investigation, reproduction of copper nodule defects and process optimization approaches. Furthermore, the overall reliability of the electroplated layer structure and the solder ball structure of the improved process samples was verified through a solder ball placement and reflow process on the plated samples. FindingsThe study indicates that the severity of copper nodule defects in wafer-level electroplating is inversely proportional to the electroplating area. The nodule issue can be effectively mitigated through three methods: increasing the electroplating area on the wafer by adding dummy pads; applying a small cathode current as the wafer enters the electroplating bath; and shortening the immersion delay time while using a low current density in the initial stage to address seed layer damage. Originality/valueThis research provides an important reference for achieving smooth copper deposition in wafer-level electroplating. Through uniformity testing and comparative experiments before and after wafer immersion in the electroplating solution, it was identified that the primary cause of copper nodules is the corrosion damage of the seed layer metal induced by the “galvanic effect.” An easily implementable process improvement method is proposed by reducing the delay time and adopting a low-current-density initial plating step, the number of nodule defects on test samples can be reduced by 80%.
Purpose The thermo-mechanical properties of System-in-Package (SiP) products play a crucial role in manufacturability and reliability. The multi-material and cross-scale properties of SiP pose challenges for thermo-mechanical modeling and simulation. The industry primarily uses homogenization-based material equivalence methods to avoid dense meshing of microstructures, thereby significantly reducing the scale of Finite Element Analysis (FEA).Design/methodology/approach To address the issues of insufficient accuracy, high computational resource consumption and poor engineering usability in existing homogenization methods, this study proposes a modeling method based on a convolutional neural network (CNN) for predicting monoclinic homogenized constitutive parameters. This method can accurately characterize the tension-shear coupling and thermal expansion-shear coupling effects caused by the asymmetry of the package's microstructure. The surrogate model for equivalent mechanical parameter representation, constructed using a CNN based on a multi-channel encoding method of pixel gray values, exhibits strong adaptability to multi-material systems.Findings This study achieves cross-scale reduced-order modeling of multi-material advanced packaging and complex substrate circuit patterns and it has been preliminarily validated through application in thermal warpage optimization simulations for a product-level SiP. The number of mesh elements constructed is merely 1/3136 of that in traditional direct modeling methods, significantly shortening simulation time while maintaining accuracy.Originality/value This study introduces a unified CNN framework for the precise characterization of multiple material systems to predict monoclinic homogenized constitutive parameters. The method accurately captures the tension-shear coupling and thermal expansion-shear coupling effects arising from the asymmetry of the package microstructure, significantly reducing simulation time while maintaining accuracy.
PurposeWith the rapid evolution of semiconductor technology, the demand for high bonding reliability in electronic devices has become increasingly stringent. This study aims to overcome the limited mechanical strength of conventional Sn-based solders. Design/methodology/approachThis study introduced a Cu-10Ni (Wt. %) alloy layer coated on a pure Ni mesh, forming a Ni@Cu10Ni composite reinforcement. This hybrid mesh was incorporated into a SAC305 alloy to fabricate a composite solder, which was subsequently applied in low-temperature soldering of Cu substrates. The influence of mesh composition and soldering time on the microstructure and mechanical performance of the joints was systematically examined. FindingsIt was found that the reaction kinetics between the Ni@Cu10Ni mesh and the SAC305 matrix were markedly accelerated compared to those of pure Ni mesh-reinforced solders. After 1 min of soldering, the joint microstructure comprised predominantly (Cu,Ni)6Sn5 intermetallic compounds (IMCs), residual Ni skeletons and trace amounts of unreacted ß-Sn; prolonging the soldering time to 5 min resulted in IMC grain refinement; further extension of the soldering time induced IMC coarsening. Correspondingly, the shear strength initially increases and then decreases, reaching a maximum of 79.0 MPa at 5 min, representing a 50.5% improvement compared to joints using pure Ni mesh/SAC305 composite solder. Originality/valueThis research offers a promising strategy for producing high-strength solder joints under low-pressure, short-duration soldering conditions.
PurposeThe purpose of this study is to implement a hybrid finite element analysis (FEA) and machine learning framework. A deep neural network (DNN) surrogate model was trained on parametric FEA data for rapid multiobjective optimization. The Anand viscoplastic model captured SAC305 solder behavior, while the Darveaux fatigue model predicted joint lifetime using a submodeling approach. Experimental validation included thermal warpage measurements (25-150 degrees C) and microscopic analysis of fabricated prototypes using X-ray and scanning electron microscopy to correlate simulation predictions with actual manufacturing quality.Design/methodology/approachTo address thermo-mechanical reliability challenges in heterogeneous millimeter-wave radio frequency (RF) front-end packages for 5G/6G systems, this study develops an efficient co-design methodology. The work aims to predict SAC305 solder joint fatigue life while optimizing geometric parameters (chip thickness, high-density interconnect (HDI) thickness and solder spacing) to balance thermal performance and mechanical stress, bridging the gap between theoretical modeling and manufacturing realities in multimaterial high-density interconnect substrates.FindingsThe DNN achieved high accuracy (temperature MAE 1.77 K, displacement MAE 0.0001 mm). Optimization yielded chip thickness 0.07 mm, HDI thickness 0.7 mm and solder spacing 0.6 mm. Fatigue analysis predicted 476 cycles for critical corner joints. Warpage measurements confirmed simulation trends (21.2 & micro;m concave to 34.3 & micro;m convex). However, manufacturing defects - including via misalignment and incomplete filling - were identified, suggesting actual reliability may be lower than predicted and highlighting critical process control requirements.Originality/valueProposing a validated hybrid FEA-ML framework for heterogeneous RF packaging, correlating fatigue predictions with manufacturing defects to provide process control guidelines for solder joint reliability.
PurposeThis work is an investigation of the tensile creep behavior of the conventional tin-lead (Sn−40Pb) solder and three Pb-free solders, tin−copper (Sn−0.7Cu), tin−zinc (Sn−9Zn) and tin−zinc−copper (Sn−49Zn−1Cu), to find an appropriate green substitute for industry use. Design/methodology/approachTensile creep tests were conducted on Sn–40Pb, Sn–0.7Cu, Sn–9Zn and Sn–49Zn–1Cu alloys under uniaxial stresses of 10, 13 and 17 MPa. The study primarily focuses on the creep behavior of these solders, including the evolution of creep stages, steady-state creep rates and resistance to tertiary creep, also the abrasive wear surface of the alloys studied under scanning electron microscope (SEM). FindingsThe Sn–49Zn–1Cu had the best creep resistance and smallest steady-state creep rate among the studied solders, while Sn–0.7Cu was most prone to creep and Sn–9Zn exhibited medium property. At high stress levels, Sn–49Zn–1Cu did not exhibit tertiary creep as the other alloys did. A power-law relationship between minimum creep rate and applied stress was established for all materials. SEM observations on the worn surfaces showed that Sn–49Zn–1Cu had a more homogeneous structure with shallower grooves and less defects, which was interpreted as better wear resistance and microstructural stability. Originality/valueThis study presents a comparative assessment of the tensile creep behavior of Pb-free solder alloys relative to conventional Sn–40Pb solder. The findings indicate that the Sn–49Zn–1Cu alloy demonstrates superior creep resistance, highlighting its potential as a reliable and environmentally friendly alternative for applications that require improved long-term mechanical stability.
PurposeThis paper aims to systematically investigate the effect of the sintering pressure on the microstructure and tensile behavior of sintered silver at both room and elevated temperatures. In contrast to earlier studies, this research uniquely explores the combined influence of sintering pressure, strain rate, on the high-temperature mechanical response of the porous sintered silver material.Design/methodology/approachSpecimens were manufactured from a microscale silver paste using sintering pressures of 7 and 15 MPa at sintering temperatures of 230 degrees C for three minutes, to forcibly induce distinct porosity levels. Subsequently, tensile tests were carried out at strain rates of 10-4 and 10-5 s-1, and at room temperature and at 200 degrees C.FindingsThe porosity level, as extracted from optical microscopy image analysis, were computed as 24.1% and 14.7% for sintering pressures of 7 and 15 MPa, respectively. In addition, the results indicated that higher sintering pressure, that is, lower porosity, consistently improves mechanical performance across all test configurations. Statistical analysis further reveals that porosity, strain rate and loading temperature collectively govern the mechanical response, with porosity acting as a key microstructural link between processing conditions and material behavior. Notably, thermal effects were found to be more dominant than rate effects. The combined influence of porosity, strain rate, on the high-temperature mechanical properties has been unified in a bilinear isotropic hardening material model and validated with finite element simulations.Originality/valueSintered silver has become a preferred bonding solution for high-performance power electronics due to its outstanding mechanical and thermal properties. Among the various sintering parameters, applied pressure plays a critical role in determining the porosity and, consequently, the mechanical performance of the resulting bond. Although the influence of sintering pressure has been widely studied, its effects remain not fully understood, especially under elevated temperature conditions. Unlike earlier studies, this research has exclusively explored the high-temperature behavior of the sintered silver with various porosity levels. The findings of the present study highlight the importance of explicitly incorporating porosity into constitutive models to enhance the accuracy of finite element simulations for sintered silver joints in power electronic applications.
Purpose This study aims to investigate the effect of particle size on the microstructure and mechanical behavior of sintered Cu, focusing on the differences in mechanical properties between sintered submicron Cu and sintered micron Cu for potential applications. Design/methodology/approach Crystallographic analysis was performed to assess the recrystallization degree and grain boundary characteristics. Nanoindentation testing was conducted to measure the Young’s modulus, work done and contact stiffness of sintered submicron Cu, sintered micron Cu and bulk Cu. Stress–strain constitutive equations for the three samples were derived from dimensionless equations, and the fracture toughness of two types of sintered Cu was evaluated based on the energy analysis method. Findings Sintered submicron Cu exhibits a higher degree of recrystallization and greater dislocation annihilation compared to sintered micron Cu, resulting in a higher proportion of high-angle grain boundaries and a lower dislocation density. The Young’s modulus of sintered submicron Cu is higher than that of sintered micron Cu, and bulk Cu exhibits the highest modulus, thus reflecting the negative relationship between porosity and Young’s modulus. The fracture toughness of sintered submicron Cu is greater than that of sintered micron Cu, which is attributed to its smaller grain size and porosity, as well as its higher Young’s modulus and degree of recrystallization. Originality/value This study provides theoretical foundations and mechanical performance data to support the design of high-reliability sintered Cu joints.
PurposeThe purpose of this study is to reveal the electromigration-induced failure mechanisms in Cu-Cu hybrid bonding structures and to identify the key factors governing failure location and lifetime under multiphysics coupling conditions.Design/methodology/approachA multiphysics coupled simulation model based on the atomic flux divergence method is developed to analyze electromigration behavior in Cu-Cu hybrid bonding structures. The effects of current density, temperature, equivalent stress and alignment offset on failure evolution are systematically investigated. Simulation results are further validated through comparison with reported experimental observations.FindingsThe results indicate that although electromigration, thermomigration and stress migration influence the failure process, electromigration dominates failure in Cu-Cu hybrid bonding structures due to limited temperature and stress gradients from small feature sizes and high thermal conductivity. Alignment offset is a critical factor determining device lifetime and failure location, with a transition in failure mode when the offset exceeds 90 nm. The extrema of the current density gradient accurately predict failure locations and reflect failure severity. An optimized bonding structure with a modified Cu pad etch angle is proposed, effectively reducing current density gradient extrema and improving reliability.Research limitations/implicationsThis study is primarily based on numerical simulations and relies on previously reported experimental data for validation. Future work investigation via in situ experimental characterization would further strengthen the generality of the conclusions.Practical implicationsThe findings provide practical design guidelines for improving the reliability of Cu-Cu hybrid bonding structures by controlling geometric parameters to mitigate current density gradients. The proposed structural optimization offers a feasible approach for extending device lifetime in advanced interconnect technologies.Originality/valueThis work establishes a comprehensive multiphysics framework for analyzing electromigration in Cu-Cu hybrid bonding structures and identifies the current density gradient as a key indicator of failure location and severity. The study further demonstrates a geometry-based optimization strategy to suppress electromigration-driven failure, offering valuable insights for the design of reliable hybrid bonding interconnects.
PurposeGaN HEMT devices are often exposed to harsh environments (such as irradiation and temperature fluctuations) in practical applications, which can significantly degrade their reliability. The purpose of this study is to investigate the degradation of electrical performance and failure mechanisms of GaN HEMT devices under the combined effects of electron irradiation and thermal cycling, providing valuable reference information for the reliability assessment of GaN HEMT devices.Design/methodology/approachBy comparing with the individual thermal cycling experiments, this study investigates the effects of the combined electron irradiation and thermal cycling on device failure. An optical microscope was used to observe the liftoff phenomenon of the bond pads, and finite element analysis was used to simulate the device's behavior. In addition, G4 simulation software was used to analyze the accumulation of residual stress in the bond pad region after irradiation. These findings provide crucial insights into the failure mechanisms of the device under the combined effects of electron irradiation and thermal cycling.FindingsStudies have shown that the electron irradiation on the device surface generated localized heat after the introduction of irradiation, which further led to residual stresses in the metal pad region. Under the combined effect of electron irradiation and thermal cycle, the device showed chip-level degradation in the first 750 thermal cycles, and the on-resistance increased by 20%. With the further extension of the aging time, the device entered the package-level degradation stage, and the on-resistance increases significantly, reaching 106 %.Originality/valueThis study provides valuable insights into the long-term reliability of P-GaN gate HEMTs for simulated space applications. By considering electron irradiation and thermal cycling as combined stress factors, the degradation process of the chip was examined, with initial degradation occurring at the chip level, followed by packaging-level degradation.
Purpose-This study aims to evaluate the curing, thermo-mechanical and interfacial behavior of two commercial reworkable epoxy underfills for surface mount technology (SMT) applications. The work focuses on understanding the relationship between curing characteristics, viscosity and wettability, and how these parameters influence underfill flow, fillet formation, voiding and rework performance. By integrating Fourier Transform Infrared (FTIR), Differential Scanning Calorimetry (DSC), thermomechanical analysis (TMA), rheology, contact angle and microstructural analyses, the study seeks to identify an optimal underfill formulation that balances processability, reliability and reworkability which are critical factors for improving manufacturing yield, repair efficiency and sustainability in advanced electronic packaging. Design/methodology/approach-The increasing complexity of SMT assemblies has intensified the need for reliable yet reworkable underfill materials. This study evaluates two commercial reworkable epoxy underfills (samples A and N) with respect to their curing, thermo-mechanical, flow and rework performance. FTIR and DSC analyses confirmed complete curing for both materials, with sample N showing higher reactivity while sample A exhibited controlled curing behavior favorable for reworkability. TMA and rheological measurements highlighted significant differences in thermal expansion and viscosity response at processing temperatures, with sample A maintaining more stable flow and wettability at 60 degrees C. Contact angle, cross-sectional and lapping analyses revealed that sample A achieved superior wetting, fillet formation and coverage, reducing void formation compared to sample N. Rework tests demonstrated that sample A could be removed cleanly with minimal Printed Circuit Board and component damage, while sample N left residues and caused surface scratches. Overall, sample A provided a more balanced trade-off between reliability, processability and reworkability, underscoring its suitability for advanced SMT applications and its potential contribution to cost-effective and sustainable electronics manufacturing. Findings-Both underfills achieved complete curing, but Sample A exhibited controlled curing, balanced viscosity and stable wettability at dispensing temperature, enabling superior flow and coverage. Sample N showed higher crosslink density and adhesion, improving stability but hindering reworkability. Cross-sectional and lapping analyses confirmed that Sample A produced fewer voids and better fillet uniformity, while rework trials demonstrated cleaner removal and minimal substrate damage. Overall, Sample A offered an improved trade-off between reliability and reworkability, making it more suitable for high-density SMT assemblies where efficient repair and process stability are essential. Originality/value-This work provides an integrated, process-focused evaluation of commercially available reworkable underfills, linking fundamental material behavior to actual SMT assembly and rework performance. Unlike prior studies that focus mainly on resin formulation or curing kinetics in isolation, this study correlates curing conversion (FTIR/DSC), thermo-mechanical response (TMA), flow behavior (viscosity/ wettability), fillet formation, void distribution and rework cleanliness under realistic dispensing and rework conditions. The results highlight the trade-off between reliability and reworkability and identify an underfill formulation that supports both high assembly yield and clean component recovery, directly addressing manufacturability and sustainability requirements in advanced electronic packaging.
Purpose This study aims to optimize the electrohydrodynamic (EHD) inkjet printing process for silver nanoparticle ink on alumina (Al2O3) ceramic substrates, focusing on improving print quality and reducing the electrical resistance of silver circuits. Design/methodology/approach This study systematically examines the influence of key process parameters (amplitude voltage, bias voltage, pulse frequency and duty cycle) on silver circuit printing quality, establishes a coupled electric field-hydrodynamics model via COMSOL Multiphysics to analyze the correlation between electric field distribution and droplet ejection, explores the effect of 160-200 degrees C sintering temperature on silver layer densification and controls the number of printed layers to test electrical performance. Findings The optimal process parameter combination for the EHD inkjet printing process is determined as bias voltage 800V, amplitude voltage 1200V, pulse frequency 100 Hz and duty cycle 30%; the coupled electric field-hydrodynamics model established by COMSOL Multiphysics reveals the correlation mechanism between electric field distribution and droplet ejection behavior, thereby theoretically validating the rationality of the parameter optimization; eight-layer unsintered nanosilver printed lines sintered at 200 degrees C exhibit a low resistance of 2.7O across a 20 mm length. Originality/value This study provides a parameter optimization scheme for the EHD inkjet printing of silver nanoparticle ink on alumina ceramic substrates; it establishes a coupled electric field-hydrodynamics model to support the optimization of the EHD inkjet printing process theoretically; it clarifies the effects of sintering temperature and the number of printed layers on the electrical performance of the silver circuit.
PurposeThis study aims to investigate the effects of die-attaching temperature, force and time on the paste overflow behavior, microstructure and shear strength of Cu-Cu sintered joints.Design/methodology/approachThe dried Cu substrate was transferred to the die bonder for die-attaching operation. In the experiment, three parameters - die-attaching temperature, die-attaching force and die-attaching time - were adjusted separately. After die-attaching, the samples were sintered at 230 degrees C and 20 MPa for 7 min. Finally, the shear strength and microstructure of the sintered joints were characterized and analyzed.FindingsThe experiment shows that the optimal die-attaching temperature is 70 degrees C, a shear strength of 91.6 MPa is achieved through die-attaching at 30 kg (18.8 MPa) for 10 s, and it can reach 88.9 MPa at 10 kg (6.3 MPa) for 15 s. The die-attaching temperature effectively prevents paste overflow of post-sintering joints, an increase in die-attaching force can not only cause slight plastic deformation of Cu particles and change their initial packing state but also damage the oxide film on the surface of Cu particles, prolonging the die-attaching time enhances the effect of the die-attaching force.Originality/valueThe die-attaching process is a crucial link in the sintering workflow. Adjustments to its key parameters - die-attaching temperature, force and time - exert a significant impact on the performance of sintered joints. Therefore, the results of this study provide important reference value for the practical application of nano-Cu sintering technology.
Purpose - The purpose of this study is to investigate the failure mechanisms of thermal migration in microbump joints with limited Sn grains under temperature gradients and to assess the effectiveness of hourglass structures in suppressing intermetallic compound (IMC) growth and improving thermal reliability. Design/methodology/approach - A thermal migration test platform was used to expose barrel- and hourglass-shaped Cu/Ni/Sn-3.5Ag microbump joints to a temperature gradient of 16,029 degrees C/cm. Through the integration of FE-SEM, electron backscatter diffraction and finite element simulations, the correlation between IMC growth behavior and Sn grain orientation was systematically analyzed. Findings - When subjected to temperature gradients, IMC grows asymmetrically along high-misorientation-angle boundaries (ss > 15 degrees) and medium-to-low a-angle (< 55 degrees) Sn grains, with the IMC/Sn interface at the hot end being particularly susceptible to cracking. While hourglass structures increase diffusion distance, they are unable to regulate grain orientation and, thus, demonstrate limited effectiveness in suppressing thermal migration. Originality/value - This study identifies three distinct mechanisms by which Sn grain orientation and grain boundaries govern preferential IMC growth. It clarifies the limitations of hourglass structures in suppressing thermal migration, offering new insights for microbump reliability design.
