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Purpose This paper aims to study the interfacial delamination found in the boundary of the copper/copper-epoxy layers of a multi-layer ceramic capacitor. Design/methodology/approach 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. Findings 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. Practical implications 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. Originality/value 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.

Purpose This paper aims to study the filling progression of underfill flow and void formation during the flip-chip encapsulation process. Design/methodology/approach A new parameter of filling progression that relates volume fraction filled to filling displacement was formulated analytically. Another indicative parameter of filling efficiency was also introduced to quantify the voiding fraction in filling progression. Additionally, the underfill process on different flip-chips based on the past experiments was numerically simulated. Findings All findings were well-validated with reference to the past experimental results, in terms of quantitative filling progression and qualitative flow profiles. The volume fraction filled increases monotonically with the filling displacement and thus the filling time. As the underfill fluid advances, the size of the void decreases while the filling efficiency increases. Furthermore, the void formed during the underfilling flow stage was caused by the accelerated contact line jump at the bump entrance. Practical implications The filling progression enabled manufacturers to forecast the underfill flow front, as it advances through the flip-chip. Moreover, filling progression and filling efficiency could provide quantitative insights for the determination of void formations at any filling stages. The voiding formation mechanism enables the prompt formulation of countermeasures. Originality/value Both the filling progression and filling efficiency are new indicative parameters in quantifying the performance of the filling process while considering the reliability defects such as incomplete filling and voiding.

Purpose This paper aims to present new analytical model for the filling times prediction in flip-chip underfill encapsulation process that is based on the surface energetic for post-bump flow. Design/methodology/approach The current model was formulated based on the modified regional segregation approach that consists of bump and post-bump regions. Both the expansion flow and the subsequent bumpless flow as integrated in the post-bump region were modelled considering the surface energy–work balance. Findings Upon validated with the past underfill experiment, the current model has the lowest root mean square deviation of 4.94 s and maximum individual deviation of 26.07%, upon compared to the six other past analytical models. Additionally, the current analytically predicted flow isolines at post-bump region are in line with the experimental observation. Furthermore, the current analytical filling times in post-bump region are in better consensus with the experimental times as compared to the previous model. Therefore, this model is regarded as an improvised version of the past filling time models. Practical implications The proposed analytical model enables the filling time determination for flip-chip underfill process at higher accuracy, while providing more precise and realistic post-bump flow visualization. This model could benefit the future underfill process enhancement and package design optimization works, to resolve the productivity issue of prolonged filling process. Originality/value The analytical underfill studies are scarce, with only seven independent analytical filling time models being developed to date. In particular, the expansion flow of detachment jump was being considered in only two previous works. Nonetheless, to the best of the authors’ knowledge, there is no analytical model that considered the surface energies during the underfill flow or based on its energy–work balance. Instead, the previous modelling on post-bump flow was based on either kinematic or geometrical that is coupled with major assumptions.

Purpose This paper aims to determine the optimum set of temperatures through correlation study to attain the most effective capillary flow of underfill in a multi-stack ball grid array (BGA) chip device. Design/methodology/approach Finite volume method is implemented in the simulation. A three-layer multi-stack BGA is modeled to simulate the underfill flow. The simulated models were well validated with the previous experimental work on underfill process. Findings The completion filling time shows high regression R-squared value of up to 0.9918, which indicates a substantial acceleration on the underfill process because of incorporation of thermal delta. An introduction of 11 °C thermal delta to the multi-stacks BGA managed to reduce the filling time by up to 16.4%. Practical implications Temperature-induced capillary flow is a relatively new type of driven underfill designed specifically for package on package BGA components. Its simple implementation can further improve the productivity of existing underfill process in the industry that is desirable in reducing the process lead time. Originality/value The effect of temperature-induced capillary flow in underfill encapsulation on multi-stacks BGA by means of statistical correlation study is a relatively new topic, which has never been reported in any other research according to the authors’ knowledge.

Laser soldering is becoming more popular for soldering pin through-hole (PTH) components onto printed circuit boards (PCBs). Solder volume influences soldering joint reliability. However, it is difficult to accurately measure the effect of solder volume during the laser soldering process. The finite volume method (FVM) is used to simulate the molten solder flow in laser soldering to connect the through-hole capacitor onto the PCB in ansysfluent software. The simulation results reveal the effects of different SAC305 solder volumes on joining quality in terms of fillet shape formation, pressure, and velocity. The preferred solder volume is 1.517 mm3 with a filling time of 1.7 s, a temperature of 642 K, a hole diameter of 1.0 mm, a lead diameter of 0.5 mm and a PCB thickness of 1.20 mm, produces a fillet shape similar to a real sample of PTH laser soldering joint from the industry. This ideal volume was chosen with a suitable pressure and velocity to create a nice concave fillet shape and minimize voids during soldering. The pressure and velocity increase when the solder volume increases causing solidified solder to melt. The discrepancy between numerical and experimental values of fillet height is comparable, which inferred that the numerical model was well-validated. The good consistency between both results proves that the finite volume model will effectively predict the optimum solder volume. This opens up new opportunities for the optimization of the laser soldering parameters in the application of electronic manufacturing.

Purpose The purpose of the study is to investigate the spatial aspects of underfill flow during the flip-chip encapsulation process, for instance, meniscus evolution and contact line jump (CLJ). Furthermore, a spatial-based void formation mechanism during the underfill flow was formulated. Design/methodology/approach The meniscus evolution of underfill fluid subtended between the bump array and the CLJ phenomenon were visualized numerically using the micro-mesh unit cell approach. Additionally, the meniscus evolution and CLJ phenomenon were modelled analytically based on the formulation of capillary physics. Meanwhile, the mechanism of void formation was explained numerically and analytically. Findings Both the proposed analytical and current numerical findings achieved great consensus and were well-validated experimentally. The variation effects of bump pitch on the spatial aspects were analyzed and found that the meniscus arc radius and filling distance increase with the pitch, while the subtended angle of meniscus arc is invariant with the pitch size. For larger pitch, the jump occurs further away from the bump entrance and takes longer time to attain the equilibrium meniscus. This inferred that the concavity of meniscus arc was influenced by the bump pitch. On the voiding mechanism, air void was formed from the air entrapment because of the fluid-bump interaction. Smaller voids tend to merge into a bigger void through necking and, subsequently, propagate along the underfill flow. Practical implications The microscopic spatial analysis of underfill flow would explain fundamentally how the bump design will affect the macroscopic filling time. This not only provides alternative visualization tool to analyze flow pattern in the industry but also enables the development of accurate analytical filling time model. Moreover, the void formation mechanism gave substantial insights to understand the root causes of void defects and allow possible solutions to be formulated to tackle this issue. Additionally, the microfluidics sector could also benefit from these spatial analysis insights. Originality/value Spatial analysis on underfill flow is scarcely conducted, as the past research studies mainly emphasized on the temporal aspects. Additionally, this work presented a new mechanism on the void formation based on the fluid-bump interaction, in which the formation and propagation of micro-voids were numerically visualized for the first time. The findings from current work provided fundamental information on the flow interaction between underfill fluid and solder bump to the package designers for optimization work and process enhancement.

Purpose In line with the recent development of flip-chip reliability and underfill process, this paper aims to comprehensively investigate the effect of different hourglass shape solder joint on underfill encapsulation process by mean of experimental and numerical method. Design/methodology/approach Lattice Boltzmann method (LBM) numerical was used for the three-dimensional simulation of underfill process. The effects of ball grid arrays (BGA) encapsulation process in terms of filling time of the fluid were investigated. Experiments were then carried out to validate the simulation results. Findings Hourglass shape solder joint has shown the shortest filling time for underfill process compared to truncated sphere. The underfill flow obtained from both simulation and experimental results are found to be in good agreement for the BGA model studied. The findings have also shown that the filling time of Hourglass 2 with parabolic shape gives faster filling time compared to the Hourglass 1 with hemisphere angle due to bigger cross-sectional area of void between the solder joints. Practical implications This paper provides reliable insights to the effect of hourglass shape BGA on the encapsulation process that will benefit future development of BGA packages. Originality/value LBM numerical method was implemented in this research to study the flow behaviour of an encapsulation process in term of filling time of hourglass shape BGA. To date, no research has been found to simulate the hourglass shape BGA using LBM.

Recent advances in the micro-electronics industry have increased the demand for smaller and more compact package devices with higher performance. This paper presents an analytical multiparametric design optimization approach for the miniaturization of flip-chip package, while considering the filling time of the subsequent underfill encapsulation process. The design optimization approach was based on the latest regional segregation-based analytical filling time model. Numerical simulation was conducted to verify the governed analytical model. The discrepancies in the filling times are less than 9.9%, and the predicted critical bump pitch has a low deviation of 4.1%, affirming that both the analytical and numerical models were in great consensus. The variation effects of bump pitch, gap height, and contact angle on the filling time were analyzed and discussed thoroughly. Both the critical bump pitch and the critical gap height were computed and fitted into respective empirical equations. Subsequently, a new multiparametric design optimization approach based on the thresholding and criticality of underfill parameters was proposed to determine the optimum parameters that yield to the most compact flip-chip package with acceptable low filling time during the encapsulation process. Lastly, this proposed optimization technique was tested on the four flip-chips used in a previously published underfill experiment.

The conventional method of selective soldering has been practiced using wave soldering, convection reflow, and hand soldering. However, due to industry automation and high demand for quality, repeatability and flexibility, laser soldering process has been developed to meet these demands. This article investigates the effect of different temperature of laser soldering process on lead-free solder (SAC305) by means of numerical method that is validated by experiment. Finite volume method (FVM) was used for the three-dimensional simulation to simulate the filling flow of the lead-free solder. Experiments were carried out to complement simulation validity and the results of both methods show good agreement. The findings show that a better result can be achieved when the angle of component lead (θle) approaches 90 deg. Using optimized lead angle, five different temperature simulations were set in the range of 550 K

The scope of review of this paper focused on the precuring underfilling flow stage of encapsulation process. A total of 80 related works has been reviewed and being classified into process type, method employed, and objective attained. Statistically showed that the conventional capillary is the most studied underfill process, while the numerical simulation was mainly adopted. Generally, the analyses on the flow dynamic and distribution of underfill fluids in the bump array aimed for the filling time determination as well as the predictions of void occurrence. Parametric design optimization was subsequently conducted to resolve the productivity issue of long filling time and reliability issue of void occurrence. The bump pitch was found to the most investigated parameter, consistent to the miniaturization demand. To enrich the design versatility and flow visualization aspects, experimental test vehicle was innovated using imitated chip and replacement fluid, or even being scaled-up. Nonetheless, the analytical filling time models became more accurate and sophiscasted over the years, despite still being scarce in number. With the technological advancement on analysis tools and further development of analytic skills, it was believed that the future researches on underfill flow will become more comprehensive, thereby leading to the production of better packages in terms of manufacturing feasibility, performances, and reliability. Finally, few potential future works were recommended, for instance, microscopic analysis on the bump–fluid interaction, consideration of filler particles, and incorporation of artificial intelligence.

Purpose This paper aims to introduce a new indicative parameter of filling efficiency to quantify the performance and productivity of the flip-chip underfill encapsulation process. Additionally, the variation effect of the bump pitch of flip-chip on the filling efficiency was demonstrated to provide insight for flip-chip design optimization. Design/methodology/approach The filling efficiency was formulated analytically based on the conceptual spatial and temporal perspectives. Subsequently, the effect of bump pitch on filling efficiency was studied based on the past actual-scaled and current scaled-up underfill experiments. The latter scaled-up experiment was validated with both the finite volume method-based numerical simulation and analytical filling time model. Moreover, the scaling validity of scaled-up experiment was justified based on the similarity analysis of dimensionless number. Findings Through the scaling analysis, the current scaled-up experimental system is justified to be valid since the adopted scaling factor 40 is less than the theoretical scaling limit of 270. Furthermore, the current experiment was qualitatively well validated with the numerical simulation and analytical filling time model. It is found that the filling efficiency increases with the bump pitch, such that doubling the bump pitch would triple the efficiency. Practical implications The new performance indicative index of filling efficiency enables the package designers to justify the variation effect of underfill parameter on the overall underfill process. Moreover, the upper limit of scaling factor for scaled-up package was derived to serve as the guideline for future scaled-up underfill experiments. Originality/value The performance of underfill process as highlighted in this paper was never being quantified before in the past literatures. Similarly, the scaling limit that is associated to the scaled-up underfill experiment was never being reported elsewhere too.

Purpose This study aims to investigate the NiO nano-reinforced solder joint characteristics of ultra-fine electronic package. Design/methodology/approach Lead-free Sn-Ag-Cu (SAC) solder paste was mixed with various percentages of NiO nanoparticles to prepare the new form of nano-reinforced solder paste. The solder paste was applied to assemble the ultra-fine capacitor using the reflow soldering process. A focussed ion beam, high resolution transmission electron microscopy system equipped with energy dispersive X-ray spectroscopy (EDS) was used in this study. In addition, X-ray inspection system, field emission scanning electron microscopy coupled with EDS, X-ray photoelectron spectroscopy (XPS) and nanoindenter were used to analyse the solder void, microstructure, hardness and fillet height of the solder joint. Findings The experimental results revealed that the highest fillet height was obtained with the content of 0.01 Wt.% of nano-reinforced NiO, which fulfilled the reliability requirements of the international IPC standard. However, the presence of the NiO in the lead-free solder paste only slightly influenced the changes of the intermetallic layer with the increment of weighted percentage. Moreover, the simulation method was applied to observe the distribution of NiO nanoparticles in the solder joint. Originality/value The findings are expected to provide a profound understanding of nano-reinforced solder joint’s characteristics of the ultra-fine package.

The conventional capillary underfill process has been a common practice in the industry, somehow the process is costly and time-consuming. Thus, no-flow underfill process is developed to increase the effective lead time production since it integrates the simultaneous reflow and cure of the solder interconnect and underfill. This paper investigates the effect of different dispense patterns of no-flow underfill process by mean of numerical and experimental method. Finite volume method (FVM) was used for the three-dimensional (3D) simulation to simulate the compression flow of the no-flow underfill. Experiments were carried out to complement the simulation validity and the results from both studies have reached a good agreement. The findings show that of all three types of dispense patterns, the combined shape dispense pattern shows better chip filling capability. The dot pattern has the highest velocity and pressure distribution with values of 0.0172 m/s and 813 Pa, respectively. The high-pressure region is concentrated at the center of the chip and decreases out toward the edge. Low in pressure and velocity flow factor somehow lead to issue associated with possibility of incomplete filling or void formation. Dot dispense pattern shows less void formation since it produces high-pressure underfill flow within the ball grid array (BGA). This paper provides reliable insight into the industry to choose the best dispense pattern of recently favorable no-flow underfill process.

Purpose This paper aims to investigate the characteristics of ultra-fine lead-free solder joints reinforced with TiO2 nanoparticles in an electronic assembly. Design/methodology/approach This study focused on the microstructure and quality of solder joints. Various percentages of TiO2 nanoparticles were mixed with a lead-free Sn-3.5Ag-0.7Cu solder paste. This new form of nano-reinforced lead-free solder paste was used to assemble a miniature package consisting of an ultra-fine capacitor on a printed circuit board by means of a reflow soldering process. The microstructure and the fillet height were investigated using a focused ion beam, a high-resolution transmission electron microscope system equipped with an energy dispersive X-ray spectrometer (EDS), and a field emission scanning electron microscope coupled with an EDS and X-ray diffraction machine. Findings The experimental results revealed that the intermetallic compound with the lowest thickness was produced by the nano-reinforced solder with a TiO2 content of 0.05 Wt.%. Increasing the TiO2 content to 0.15 Wt.% led to an improvement in the fillet height. The characteristics of the solder joint fulfilled the reliability requirements of the IPC standards. Practical implications This study provides engineers with a profound understanding of the characteristics of ultra-fine nano-reinforced solder joint packages in the microelectronics industry. Originality/value The findings are expected to provide proper guidelines and references with regard to the manufacture of miniaturized electronic packages. This study also explored the effects of TiO2 on the microstructure and the fillet height of ultra-fine capacitors.

Consistent with the recent trends in which the flip-chip reliability and performance being prominently prioritized, this paper is devoted to study the effects of solder bump shapes on the capillary underfill flows during the flip-chip encapsulation. A new experimental approach based on the particle image velocimetry (PIV) is set-up to visualize the underfill flow in the flip-chip. A more generalized analytical model for predicting the underfill filling time was developed to be applied for the triple-inlets dispensing (U-shape) underfill process with its application extended to a more generic bump shape. The theoretical analysis based on averaging method has been found viable for prediction of the underfill pressure, velocity and permeability. Findings from both finite volume method (FVM) simulation and PIV experiment achieved great consensus and are in line with the new theoretical estimates. These three distinct methodologies independently concluded the direct impact of different bump shapes design on the underfill flow. Altering the truncated spherical-shaped bump into a narrow-neck bump, for instance hourglass and concave shapes, would respectively reduce the filling times by 8.86% and 11.4% respectively; apart from having the increase in flow pressure and velocity. The mean permeability of the bump array computed is observed to be in an increasing order starting from spherical, cylindrical, hourglass and concave shapes. Generally, this comprehensive study had identified the geometrical parameters of solder bump that necessitated for faster underfill flow, being low sphericity and high pad-to-neck ratio.

This paper presents a 3D numerical simulation of nano-reinforced lead (Pb)-free solder at the ultra-fine joint component for 01005 capacitor with dimension of 0.2 × 0.2 × 0.4 mm 3 . The nano-reinforced particles introduced in the Sn-3.0Ag-0.5Cu (SAC305) solder is titanium oxide (TiO 2 ) nanoparticles with approximate diameter of ≈ 20 nm at different weight percentages of 0.01, 0.05 and 0.15 wt% respectively. The 3D model developed is based on the reflow thermal profile of nano-reinforced Pb-free solder in the wetting zone temperature of 217 °C–239 °C. A two way interactions utilizing both volume of fluid method (VOF) and discrete phase method (DPM) are introduced in the current study. The study effectively shows the distribution of the nanoparticles as it is being doped in the molten solder after undergoing soldering process. Based on the findings, it was shown that good agreement can be seen between experimental data obtained using High Resolution Transmission Electron Microscope (HRTEM) system as compared to multiphase DPM based simulation. At weight percentage of SAC305 + 0.05% TiO 2 nanoparticles, the nanoparticles are well distributed. The fillet height of nano-reinforced solder also meets the minimum requirement for 01005 capacitor. Additionally, as the weight percentage of the doped nanoparticles increases, the time required for the formation of wetted solder also increases. In terms of the velocity and pressure distribution of the nano-reinforced lead (Pb)-free solder, higher weight percentage of doped nanoparticles have higher velocity distribution and lower pressure distributions.

Purpose This paper aims to present experimental and finite volume method (FVM)-based simulation studies on the scaling effect on the capillary contact angle and entrant pressure for a three-dimensional encapsulation process of ball-grid array (BGA). Design/methodology/approach With the development of various sizes of BGA packages, the scaling effect of BGA model on capillary underfill (CUF) process is investigated together with the influences of different industrial standard solder bump arrangements and dispensing methods used as case study. Findings The experimental results agree well to the simulation findings with minimal deviation in filling time and similar flow front profiles for all setups. The results revealed that the capillary contact angle of flow front decreases in scale-up model with larger gap height observed and lengthens the encapsulation process. Statistical correlation studies are conducted and accurate regression equations are obtained to relate the gap height to the completion filling time and contact angle. CUF threshold capillary pressures were computed based on Leverett-J function and found to be increasing with the scale size of the package. Practical implications These statistical data provide accurate insights into the impact of BGA’s scale sizes to the CUF process that will be benefiting the future design of BGA package. This study provided electronic designers with profound understanding on the scaling effect in CUF process of BGA, which may be extended to the future development of miniature-sized BGA and multi-stack device. Originality/value This study relates the flow behaviour of encapsulant to its capillary contact angle and Leverett-J pressure threshold, in the CUF process of different BGA and dispensing conditions. To date, no research has been found to predict the threshold pressure on the gap between the chip and substrate.

Advanced composite-encapsulant with reinforced solid inorganic fillers dispersed in the epoxy resin is regarded as a revolutionary effort in promoting the reliability of electronic device. While various researches have been conducted to study the preparation, chemical and thermomechanical properties of composite-encapsulant using filler-reinforcement, there is however no work found on the visualization aspect of the encapsulant flow progression and filler distribution in the encapsulant. In this paper, the underfilling rheology for encapsulation process of ball grid array (BGA) will be investigated using mono-dispersed nano-silica (SiO2) composite-encapsulant. The filler loadings will be varied in the range of 2–25 wt% (weight percent) for optimization purpose. Eventually this work is aimed to provide an in-depth understanding on the impact of the amount of nano-silica fillers being added in the epoxy resin. Finite volume method (FVM) based numerical simulation using discrete phase model (DPM) will be used in this paper. The simulation works reported that the increase in filler loadings of composite-encapsulant effectively lengthen the underfilling process by up to 22% together with a decrease in average encapsulant's pressure. Furthermore, the flow profiles revealed an asymmetry flow front that is prone to form at high filler loadings. This subsequently leads to issues associated to filler's accumulation and swirling. Given these issues, the optimization of filler loadings in composite-encapsulant is of prime importance. Accordingly, this study recommended the usage of 15 wt% of nano-silica composite-encapsulant that balances between the relatively lower filling time and with reduced issues relating to filler accumulation and swirling while preserve the improvement in reliability upon the fillers additive. Additionally, the simulation of dispersed particle in continuous fluid phase using DPM had decisively proven its mettle and is hopefully will pioneer a new viable numerical tool in the nano-filler composite polymer study of electronic packaging in near future.

The applications of porous media burners are of massive interest to researchers from decades, and still trending in the modern world because of their tremendous advantages, such as high thermal efficiency and low emissions. In this work, a microburner was made to achieve surface and submerged flame region for different thicknesses of preheat layers. A reaction layer of alumina foam with a predefined thickness was used, whereas the preheat layer of porcelain foam was replaced with three different thicknesses namely 5, 10, and 15 mm. By using 5 mm preheat layer, only surface flame was visible with absolutely no trace of submerged flame region, while 10 and 15 mm can undergo both surface and submerged flame region. Equivalence ratio of 0.7 was observed to give best performance with regards to surface flame, while 0.5 for submerged flame region. Only 10 mm can able to give highest thermal efficiencies reaching 90% and 38% for the surface and submerged flame region respectively. Finally, low emission rate for NOx and CO was seen for all the possible individual cases.

This paper presents a new analytical filling time model to predict the flow of non-Newtonian underfill fluid during flip-chip encapsulation process. The current model is formulated based on the regional segregation approach, instead of the conventional porous media approximation. In this approach, the filling times were computed separately at different filling stages, before being summed up till the required filling distance. The non-Newtonian property of underfill fluid is modeled using the conventional power-law constitutive equation. Additionally, the spatial aspects of the underfill flow were incorporated into the present analysis. For instance, the evolution of underfill menisci from convex to concave was analytically developed and the contact line jump (CLJ) criterion was improved using minimal flow assumption. Upon validated with three distinct past underfill experiments, the current analytical model is found to have the best performance as it predicted the filling times with the least discrepancy among other existing filling time models. Quantitatively, the discrepancies were averagely reduced by an absolute value of at least 8.68% and 4.90%, respectively, for the first two set of validation studies. Generally, this model is particularly useful in manufacturing lines to estimate the process time of flip-chip underfill, as well as for the optimizations of process and package design.

Recent trend in electronic industries are demanding smaller chip packaging process along with increase in performance and reliability of the package. The introduction of Multi-stack Ball Grid Array (BGA) to enhance the performance of the conventional BGA flip chip has frequently encountered several hitches such as extended filling time and incomplete filling at the upper layer of the multi-stacks BGA. It has been found that the encapsulant lacks energy to flow at the upper layer due to lower hydrostatics pressure. In this paper, a straightforward solution by incorporating additional thermal energy in the encapsulant to increases its flow ability is introduced. This additional thermal energy at the upper layer produces a distinct temperature difference between the upper and lower layers, or simply thermal delta. This research attempts to demonstrate the effectiveness of thermal delta in solving the aforementioned flow problem during encapsulation process of multi-stacks BGA, by means of experiment and numerical simulation. The findings have shown that the experimental data compares well with the simulation results. It was also found that the implementation of thermal delta substantially reduces the filling time across the multi-stack packages. This study reveals the potential of thermocapillary-driven underfill encapsulation being widely adopted in future industrial encapsulation of multi-stacks BGA packaging.

The current study applied the lattice Boltzmann method to examine the effects of stacking chips layout to the micro-void formation in three-dimensional (3D) packaging. Three-dimensional 19-velocities commonly known as D3Q19 scheme is utilized in this study. Three different cases, which are different in layout design, are examined. For code verification purpose, an experimental work is also presented to compare the flow front results between numerical and experimental at different filling percentage. The numerical predictions compared well with the experimental results. Minor differences are observed in their flow front profile. The numerical findings identified the predicted locations of micro-void formation during the encapsulation process. The entrapment of micro-void was visualized clearly in the simulation because of the unbalanced molecular force at the interface during encapsulation. Knit lines were also identified at the interface between the flows that occurred in the encapsulation. Different layout of stacking flip-chips package have influence the micro-void in the package, which tended to form at the stacking chips region. The results show that the lattice Boltzmann method has a good performance in the IC encapsulation simulation.

Underfill encapsulation play an important role to improve the reliability of flip chip package, yet the conventional underfill (CUF) encapsulation process is subjected to several drawbacks such as extended filling time, incomplete filling and voids formation. Therefore, the focal point of this project is on the study of different CUF dispensing method for different types of ball grid array (BGA) orientations. The experimental works and numerical simulations were performed to predict the interaction of fluid on the structure and the results from both studies have reached a good agreement. This paper explores the effect of BGA orientations and dispensing types namely I, L and U on the behavior of underfill flow and the filling time. This study reveals the potential of both aspects in improving the efficiency of CUF encapsulation. The findings show that of all 9 different combinations of orientations and dispensing type, the fastest filling time is achieved by combining perimeter orientations with U-type flow. However, it suffers from racing effect that might lead to possible voids formation. The findings are then applied on real size 16×16 BGA and it was found that the flow front propagation changed from concave to convex shape for small size BGA and the filling time is also highly dependent on the BGA size and the solder ball count. Display Omitted This paper study the effect of I, L and U dispensing types on three common BGA orientations in terms of its flow attributes.3D multiphase setup of ILU dispensing encapsulation process based on scale up and real size BGA models for 6×6 and 16×16 BGA.Combination of U-type perimeter orientation has the fastest filling time and the slowest is given by I-type full orientation.Flow front propagation changed from concave to convex shape for small size BGA.The overall filling time and flow characteristics are highly dependent on the BGA size and the solder ball count.

This paper studies effects of different bump orientations on the void formation using Lattice Boltzmann method (LBM) based software. Prediction of air void is vital typically at the onset of reflow soldering which could reduce the reliability of the mold cavity. The effect of variations in pressure and velocity of the mold during flow on the formation of air voids are investigated for three different ball grid array (BGA) orientations namely perimeter, middle empty and full. The findings identified the predicted locations of void formation during the underfill encapsulation process. It was shown that middle empty orientation has the highest potential of void formation typically towards the end of mold flow as a result of low pressure and high velocity flow. In addition, using high bond number and high viscosity material could further reduce the air void formation.

This paper presents a study on structural assessment of ultra-fine package assembly with nano-composites lead free solder joint after reflow soldering process. In this work, various nanoparticles (i.e. TiO2, Fe2O3 and NiO) with different weightage percentage (i.e., 0.01, 0.05 and 0.15 wt.%) were successfully incorporated into SAC305 solder paste using the mechanical solder paste mixer to synthesize novel lead-free composite solders. Effects of the nanoparticles addition on the quality of joining and fillet height between various weightage (wt.%) for the ultra-fine package assembly in the reflow soldering process have been investigated after the reflow soldering process by using the scanning electron microscope (SEM) system equipped with an energy dispersive X-ray spectroscopy (EDS) and XTV 160 x-ray inspection system. The experimental results show the increment of TiO2, Fe2O3 and NiO nanoparticles addition to 0.15wt.%, 0.05wt.% and 0.01wt.%, respectively, produce highest fillet height of each composition of nanoparticles solder paste. Among all these new composition of nanoparticles solder paste, NiO nanoparticles reinforced solder paste with 0.01wt.% yielded highest fillet height The miniaturized solder joints do not cause any problem in terms of solder voids. The findings show the capability of the reflow soldering process in assembling miniaturized electronics assembly and expected to provide a reference in electronic package industry.