Search results

This study aims to investigate the thermal fracture mechanism of moisture-preconditioned SAC305 ball grid array (BGA) solder joints subjected to multiple reflow and thermal cycling.

The BGA package samples are subjected to JEDEC Level 1 accelerated moisture treatment (85 °C/85%RH/168 h) with five times reflow at 270 °C. This is followed by multiple thermal cycling from 0 °C to 100 °C for 40 min per cycle, per IPC-7351B standards. For fracture investigation, the cross-sections of the samples are examined and analysed using the dye-and-pry technique and backscattered scanning electron microscopy. The packages' microstructures are characterized using an energy-dispersive X-ray spectroscopy approach. Also, the package assembly is investigated using the Darveaux numerical simulation method.

The study found that critical strain density is exhibited at the component pad/solder interface of the solder joint located at the most distant point from the axes of symmetry of the package assembly. The fracture mechanism is a crack fracture formed at the solder's exterior edges and grows across the joint's transverse section. It was established that Au content in the formed intermetallic compound greatly impacts fracture growth in the solder joint interface, with a composition above 5 Wt.% Au regarded as an unsafe level for reliability. The elongation of the crack is aided by the brittle nature of the Au-Sn interface through which the crack propagates. It is inferred that refining the solder matrix elemental compound can strengthen and improve the reliability of solder joints.

Inspection lead time and additional manufacturing expenses spent on investigating reliability issues in BGA solder joints can be reduced using the study's findings on understanding the solder joint fracture mechanism.

Limited studies exist on the thermal fracture mechanism of moisture-preconditioned BGA solder joints exposed to both multiple reflow and thermal cycling. This study applied both numerical and experimental techniques to examine the reliability issue.

This study aims to investigate the design configuration for an optimum solder height of reinforced SAC305 solder joint in an ultra-fine capacitor assembly.

A 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.

Good 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.

The 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.

Investigation 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.

This paper aims to investigate the effect of different beam distance by understanding laser beam influence on solder joint quality. The utilisation numerical-based simulations and experimental validation will help to minimise the formation of micro void in PTH that can lead to cracks and defects on passive devices.

The research uses a combination approach of numerical-based simulation using Finite Volume Method (FVM) and experimental validation to explore the impact of different laser beam distances on solder joint quality in PTH assemblies. The study visualises solder flow and identifies the optimal beam distance for placing a soldering workpiece and a suitable tolerance distance for inserting the solder wire.

The simulation results show the formation of micro void that occurs in PTH region with low volume fraction and unbalance heat concentration profile observed. The experimental results indicate that the focus point of the laser beam at a 99.0 mm distance yields the smallest beam size. Simulation visualisation demonstrates that the laser beam’s converging area at +4.6 mm from the focus point which provides optimal tolerance distances for placing the solder wire. The high-power laser diode exhibits maximum tolerance distance at 103.6 mm from the focus point where suitable beam distance for positioning of the soldering workpiece with 50% laser power. The simulation results align with the IPC-A-610 standard, ensuring optimal filling height, fillet shape with a 90° contact angle and defect-free.

This research provides implications for the industry by demonstrating the capability of the simulation approach to produce high-quality solder joints. The parameters, such as beam distance and power levels, offer practical guidelines for improving laser soldering processes in the manufacturing industry.

This study contributes to the field by combining high-power laser diode technology with numerical-based simulations to optimise the beam distance parameters for minimising micro void formation in the PTH region.

This study aims to investigate the influence of different solder alloy materials on passive devices during laser soldering process. Solder alloy material has been found to significantly influence the solder joint’s quality, such as void formation that can lead to cracks, filling time that affects productivity and fillet shape that determines the solder joint’s reliability.

Finite volume method (FVM)-based simulation that was validated using real laser soldering experiment is used to evaluate the effect of various solder alloy materials, including SAC305, SAC387, SAC396 and SAC405 in laser soldering. These solders are commonly used to assemble the pin-through hole (PTH) capacitor onto the printed circuit board.

The simulation results show how the void ratio, filling time and flow characteristics of different solder alloy materials affect the quality of the solder joint. The optimal solder alloy is SAC396 due to its low void ratio of 1.95%, fastest filling time (1.3 s) to fill a 98% PTH barrel and excellent flow characteristics. The results give the ideal setting for the parameters that can increase the effectiveness of the laser soldering process, which include reducing filling time from 2.2 s to less than 1.5 s while maintaining a high-quality solder joint with a void ratio of less than 2%. Industries that emphasize reliable soldering and effective joint formation gain the advantage of minimal occurrence of void formation, quick filling time and exceptional flowability offered by this solution.

This research is expected not only to improve solder joint reliability but also to drive advancements in laser soldering technology, supporting the development of efficient and reliable microelectronics assembly processes for future electronic devices. The optimized laser soldering material will enable the production of superior passive devices, meeting the growing demands of the electronics market for smaller, high-performance electronic products.

The comparison of different solder alloy materials for PTH capacitor assembly during the laser soldering process has not been reported to date. Additionally, volume of fluid numerical analysis of the quality and reliability of different solder alloy joints has never been conducted on real PTH capacitor assemblies.

This study aims to investigate the possible defects and their root causes in a soft-termination multilayered ceramic capacitor (MLCC) when subjected to a thermal reflow process.

Specimens of the capacitor assembly were subjected to JEDEC level 1 preconditioning (85 °C/85%RH/168 h) with 5× reflow at 270°C peak temperature. Then, they were inspected using a 2 µm scanning electron microscope to investigate the evidence of defects. The reliability test was also numerically simulated and analyzed using the extended finite element method implemented in ABAQUS.

Excellent agreements were observed between the SEM inspections and the simulation results. The findings showed evidence of discontinuities along the Cu and the Cu-epoxy layers and interfacial delamination crack at the Cu/Cu-epoxy interface. The possible root causes are thermal mismatch between the Cu and Cu-epoxy layers, moisture contamination and weak Cu/Cu-epoxy interface. The maximum crack length observed in the experimentally reflowed capacitor was measured as 75 µm, a 2.59% difference compared to the numerical prediction of 77.2 µm.

This work's contribution is expected to reduce the additional manufacturing cost and lead time in investigating reliability issues in MLCCs.

Despite the significant number of works on the reliability assessment of surface mount capacitors, work on crack growth in soft-termination MLCC is limited. Also, the combined experimental and numerical investigation of reflow-induced reliability issues in soft-termination MLCC is limited. These cited gaps are the novelties of this study.

This study aims to investigate the reliability issues of microvoid cracks in solder joint packages exposed to thermal cycling fatigue.

The specimens are subjected to JEDEC preconditioning level 1 (85 °C/85%RH/168 h) with five times reflow at 270°C. This is followed by thermal cycling from 0°C to 100°C, per IPC-7351B standards. The specimens' cross-sections are inspected for crack growth and propagation under backscattered scanning electronic microscopy. The decoupled thermomechanical simulation technique is applied to investigate the thermal fatigue behavior. The impacts of crack length on the stress and fatigue behavior of the package are investigated.

Cracks are initiated from the ball grid array corner of the solder joint, propagating through the transverse section of the solder ball. The crack growth increases continuously up to 0.25-mm crack length, then slows down afterward. The J-integral and stress intensity factor (SIF) values at the crack tip decrease with increased crack length. Before 0.15-mm crack length, J-integral and SIF reduce slightly with crack length and are comparatively higher, resulting in a rapid increase in crack mouth opening displacement (CMOD). Beyond 0.25-mm crack length, the values significantly decline, that there is not much possibility of crack growth, resulting in a negligible change in CMOD value. This explains the crack growth arrest obtained after 0.25-mm crack length.

This work's contribution is expected to reduce the additional manufacturing cost and lead time incurred in investigating reliability issues in solder joints.

The work investigates crack propagation mechanisms of microvoid cracks in solder joints exposed to moisture and thermal fatigue, which is still limited in the literature. The parametric variation of the crack length on stress and fatigue characteristics of solder joints, which has never been conducted, is also studied.

This study aims to investigate crack propagation in a moisture-preconditioned soft-termination multi-layer ceramic capacitor (MLCC) during thermal reflow process.

Experimental and extended finite element method (X-FEM) numerical analyses were used to analyse the soft-termination MLCC during thermal reflow. A cross-sectional field emission scanning electron microscope image of an actual MLCC’s crack was used to validate the accuracy of the simulation results generated in the study.

At 270°C, micro-voids between the copper-electrode and copper-epoxy layers absorbed 284.2 mm/mg³ of moisture, which generated 6.29 MPa of vapour pressure and caused a crack to propagate. Moisture that rapidly vaporises during reflow can cause stresses that exceed the adhesive/substrate interface’s adhesion strength of 6 MPa. Higher vapour pressure reduces crack development resistance. Thus, the maximum crack propagation between the copper-electrode and copper-epoxy layers at high reflow temperature was 0.077 mm. The numerical model was well-validated, as the maximum crack propagation discrepancy was 2.6%.

This research holds significant implications for the industry by providing valuable insights into the moisture-induced crack propagation mechanisms in soft-termination MLCCs during the reflow process. The findings can be used to optimise the design, manufacturing and assembly processes, ultimately leading to enhanced product quality, improved performance and increased reliability in various electronic applications. Moreover, while the study focused on a specific type of soft-termination MLCC in the reflow process, the methodologies and principles used in this research can be extended to other types of MLCC packages. The fundamental understanding gained from this study can be extrapolated to similar structures, enabling manufacturers to implement effective strategies for crack reduction across a wider range of MLCC applications.

The moisture-induced crack propagation in the soft-termination MLCC during thermal reflow process has not been reported to date. X-FEM numerical analysis on crack propagation have never been researched on the soft-termination MLCC.

This paper aims to investigate the effect of physical vapor deposition (PVD)-coated stencil wall aperture on the life span of fine-pitch stencil printing.

The fine-pitch stencil used in this work is fabricated by electroform process and subsequently nano-coated using the PVD process. Stencil printing process was then performed to print the solder paste onto the printed circuit board (PCB) pad. The solder paste release was observed by solder paste inspection (SPI) and analyzed qualitatively and quantitatively. The printing cycle of up to 80,000 cycles was used to investigate the life span of stencil printing.

The finding shows that the performance of stencil printing in terms of solder printing quality is highly dependent on the surface roughness of the stencil aperture. PVD-coated stencil aperture can prolong the life span of stencil printing with an acceptable performance rate of about 60%.

Stencil printing is one of the important processes in surface mount technology to apply solder paste on the PCB. The stencil’s life span greatly depends on the type of solder paste, stencil printing cycles involved and stencil conditions such as the shape of the aperture, size and thickness of the stencil. This study will provide valuable insight into the relationship between the coated stencil wall aperture via PVD process on the life span of fine-pitch stencil printing.

This paper aims to study the interfacial delamination found in the boundary of the copper/copper-epoxy layers of a multi-layer ceramic capacitor.

The thermal reflow process of the capacitor assembly and the crack propagation from the initial micro voids presented in the boundary, and later manifested into delamination, were numerically simulated. Besides, the cross section of the capacitor assembly was inspected for delamination cracks and voids using a scanning electronic microscope.

Interfacial delamination in the boundary of copper/copper-epoxy layers was caused by the thermal mismatch and growth of micro voids during the thermal reflow process. The maximum deformation on the capacitor during reflow was 2.370 µm. It was found that a larger void would induce higher vicinity stress, mode I stress intensity factor, and crack elongation rate. Moreover, the crack extension increased with the exerted deformation until 0.3 µm, before saturating at the peak crack extension of around 0.078 µm.

The root cause of interfacial delamination issues in capacitors due to thermal reflow has been identified, and viable solutions proposed. These can eliminate the additional manufacturing cost and lead time incurred in identifying and tackling the issues; as well as benefit end-users, by promoting the electronic device reliability and performance.

To the best of the authors’ knowledge, the mechanism of delamination occurrence in a capacitor during has not been reported to date. The parametric variation analysis of the void size and deformation on the crack growth has never been conducted.

Reflow solder joint quality is significantly affected by the ability of the solder to perfectly fill pad space and retain good solder joint shape. This study aims to investigate solder joint quality by quantitatively analyzing the stencil printing-deposited solder volume, solder height and solder coverage area.

The dispensability of different solder paste types on printed circuit board (PCB) pads using different stencil aperture shapes was evaluated. Lead-free Type 4 (20–38 µm particle size) and Type 5 (15–25 µm particle size) solder pastes were used to create solder joints according to standard reflow soldering.

The results show that the stencil aperture shape greatly affects the solder joint quality as compared with the type of solder paste. These investigations allow the development of new strategies for solving solder paste stencil printing issues and evaluating the quality of solder joints.

The reflow soldering process requires the appropriate selection of the stencil aperture shape according to the PCB and the solder paste according to the particle-size distribution of the solder alloy powder. However, there are scarce studies on the effects of stencil aperture shape and the solder alloy particle size on the solder paste space-filling ability.