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Purpose The purpose of this paper is to present the experimental and simulation studies on the influence of copper pillar bump structure on flip chip packaging during reflow soldering. Design/methodology/approach In this work, solidification/melting modelling and volume of fluid modelling were used. Reflow soldering process of Cu pillar type FC was modelled using computational fluid dynamic software (FLUENT). The experimental results have been validated with the simulation results to prove the accuracy of the numerical method. Findings The findings of this study reveal that solder volume is the most important element influencing reflow soldering. The solder cap volume reduces as the Cu pillar bump diameter lowers, making the reflow process more difficult to establish a good solder union, as less solder is allowed to flow. Last but not least, the solder cap height for the reflow process must be optimized to enable proper solder joint formation. Practical implications This study provides a basis and insights into the impact of copper pillar bump structure on flip chip packaging during reflow soldering that will be advancing the future design of 3D stack package. This study also provides a superior visualization and knowledge of the melting and solidification phenomenon during the reflow soldering process. Originality/value The computational fluid dynamics analysis of copper pillar bump structure on flip chip packaging during reflow soldering is scant. To the authors’ best knowledge, no research has been concentrated on copper pillar bump size configurations in a thorough manner. Without the in-depth study, copper pillar bump size might have the impact of copper pillar bump structure on flip chip packaging during reflow soldering. Five design of parameter of flip chip IC package model was proposed for the investigation of copper pillar bump structure on flip chip packaging during reflow soldering.

To achieve high fuel efficiency, vehicles designs are inclined to choose lightweight materials and structures. However, these structures are generally weak, and structural integrity is a common concern. The purpose of this paper is to carry out fluid-structure interaction (FSI) study in one-way coupling analysis on a Shell Eco Marathon (SEM) prototype car which travels in a low-speed range to analyse its structural response. A new set of economical materials is proposed and analysed with the concern on self-fabrication process. The Flax fibre composite is introduced as a part of the proposed material set due to its environmental and economic advantages. The study herein is purely a numerical simulation work as a first approach to design a sustainable SEM prototype car. The fully assembled SEM prototype car was analysed with the proposed materials with ANSYS Workbench in the coupling of the fluid (ANSYS Fluent) and structural solver (ANSYS Mechanical) in a one-way FSI. Even with a thin shell design, the proposed material only experiences minimum deformations. The simulations also reveal that the maximum von-Mises stress experienced, after considered the safety factor, is still several order lower than the yield strength. This study has confirmed that the car design has fulfilled its structural requirements to operate at the design speed.

The first step in the surface mount technology is the printing of the solder paste. The amount of solder placed on the cooper pad is important in guaranteeing an acceptable quality of soldering. Experimental works and studies for this process consume time and cost. There is a need for a cost-effective method to study this process. The simulation method has shown as a good alternative method for the solder paste printing process. Thus, this study presents a 3D computer simulation of stencil printing for the deposited volume prediction of solder paste. The volume of fluid (VOF) method integrated with the cross viscosity model was used for the numerical simulation. A widely used industry lead-free solder paste Sn/Ag/Cu (SAC305) of type 3 was utilized. The experimental and simulation results for filling volume of solder paste at different aperture sizes were compared. Results for different aperture sizes show a similar trend and agree well with the experimental results. This study was extended to investigate stencil printing at different squeegee speeds and aperture sizes. The squeegee speed of 35 mm/s provided the highest solder paste volume in the aperture with acceptable printing time.

Purpose The purpose of this study is to investigate the effect of the adhesive force and density ratio using lattice Boltzmann method (LBM) during underfill process. Design/methodology/approach To deal with complex flow in underfill process, a framework is proposed to improve the lattice Boltzmann equation. The fluid flows with different density ratio and bump arrangement in underfill are simulated by the incorporated Carnahan–Starling (CS) equation of state (EOS). The numerical study conducted by finite volume method (FVM) and experimental results are also presented in each case at the different filling percentage for verification and validation purpose. Findings The numerical result is compared well with those acquired experimentally. Small discrepancy is detected in their flow profile. It was found that the adhesive force between fluid and solid was affected by the density ratio of the fluids and solder bump configuration. LBM has shown better adhesive force effect phenomenon on underfill process compared to FVM. LBM also demonstrated as a better tool to study the fluid flow in the underfill process. Practical implications This study provides a basis and insights into the impact of adhesive force and density ratio to the underfill process that will be advancing the future design of flip chip package. This study also provides superior guidelines, and the knowledge of how adhesive force is affected by flip chip package structure. Originality/value This study proposes the method to predict the adhesive force and density ratio effect for underfill flow in flip chip package. In addition, the proposed method has a good performance in representing the adhesive force during the underfill simulation for its natural physical basic. This study develops understanding of flow problems to attain high reliability for electronic assemblies.

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.

This study discusses the use of different spindle type for the testing of lead-free solder paste by using Computational Fluid Dynamics (CFD) simulation. The study focuses on measuring the volume of solder paste deposition on the solder pad. Parallel-plate (PP) and Cone-plate (CP) spindle were used with five different tests consist of different spindle type and setting. The Volume of Fluid (VOF) method was used for the simulation while Cross model was applied as viscosity model for the solder paste. SAC305 type 3 lead-free solder paste was used in this study as it is mostly popular used by the industries nowadays. The solder paste filled the volume under different squeegee speeds and aperture size was compared between experiments and simulations. For different squeegee speed, PP 0.5 mm gap obtained the lowest average discrepancy value between simulation and experimental results. At different aperture size, all test show similar trend line and about the same value of average discrepancy with CP1° while PP 0.5 mm gap showed the lowest average discrepancy. At small aperture volume, all tests performed shows similar value of filled volume except PP 0.5 mm which exhibit the lowest percentage difference when compared with the experimental values at a bigger aperture volume.

This paper studies the three-dimensional simulation of pressurized underfill process for I-type dispensing method on a ten-by-ten, middle empty ball grid array (BGA) using lattice Boltzmann method. Pressurized underfill process is introduced to overcome the drawbacks of capillary underfill process that includes incomplete filling, void formation and extended filling time. The effects of capillary and pressurized underfill methods of BGA encapsulation process on the flow front, filling time and pressure of the fluid are investigated. Four different pressure values are used as the input pressure in the lattice Boltzmann simulation. Experiments are carried out as well to validate the simulation results. In general, pressurized underfill method results in a dramatically shorter filling time compared to capillary underfill. The flow front obtained from both simulation and experimental results is quite similar for the BGA model studied. The pressure inside the flow domain is significantly higher than its inlet pressure and thus, caution needs to be taken by the design engineer such that the printed circuit board (PCB) and flip chip are capable to withstand this pressure to prevent from the occurrence of breakage.

Binary biofuel has a relatively higher viscosity compared to conventional diesel, which affects the spray injection and restricts the maximum evaporation. In this paper, the discrete phase model (D...

The stress concentration and deformation of the 3D stacked IC structures can be minimized with an optimal design of the integrated circuit (IC) using a response surface methodology. The geometrical and process parameters (i.e., A = inlet pressure, B = solder bump standoff height, C = chip thickness, and D = aspect ratio) were optimized via a central composite design (CCD) for the molded encapsulation process. The fluid/structure interaction (FSI) aspects were considered in the optimization of the molded encapsulation process. The separate effects of the independent variables and their interactions were studied. The calculated empirical models were carried out and well validated with the simulation results. The optimum geometrical and process parameters of the 3D stacked IC package with perimeter solder bump arrangement were characterized as follows: inlet condition of 3.65 MPa, 150 μm of solder bump standoff height, 250 μm of chip thickness, and 2.1 of aspect ratio. The outcomes herein may significantly contribute to the advancement of microelectronic industries.

This paper presents the study of infrared (IR) reflow oven characteristics for suitable operating conditions of the flexible printed circuit board (FPCB) in the reflow soldering process. A computer-based model that imitates a real-time oven was developed with practical boundary conditions. Since the radiation effect is dominant in the reflow process, a discrete ordinate (DO) model was selected to simulate the effect. The experimental work acts as a benchmark and the reflow profile was set to follow the standards of JSTD-020E. The simulation of the model has a great consensus between the experimental data. It was found that the temperature distribution was inhomogeneous along with the phases. The FPCB surface also has a higher surface temperature than oven air during the operating reflow profile. An in-depth study using the simulation approach reveals that the temperature distribution of the desktop reflow oven is dependent on several factors, namely fan speed, FPCB position, and FPCB thickness. The rotational fan generates an unsteady flow that induces inhomogeneous temperature at different positions in the reflow oven cavity. The results are useful for studying further improvements to achieve temperature uniformity within the oven chamber.

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.

This study investigates fluid–structure interaction (FSI) analysis of stacked chip in the encapsulation of molded underfill packaging using ANSYS Coupling Work bench with fluid and structural solvers. During encapsulation, FSI analysis is applied to a molded package with different layouts, namely cases 1–4 of stacked chip. An even ratio of inlet and outlet gate pressures is used to produce a regular melt front advancement. An experimental setup is fabricated to validate the simulation results in the FSI study. A digital camera is used to capture the melt front advancement and structural deformation. The interaction between structures (silicon chip) and epoxy molding compound (EMC) is displayed in the displacement profile. Maximum deformation is evaluated during the final stage of filling. The silicon die experiences von Mises stresses, which are monitored to observe the risk of die cracking. The results of this study showed that, the EMC flow front advancement was the fastest in case 4. The pressure distribution of each case was nearly identical, and the maximum von Mises stress was distributed unevenly at the middle of the stacked chip. The proposed analysis can serve as a reference and guide in designing and improving 3D integration packages in industry.

The substrate of the flexible printed circuit board (FPCB) introduced a new segment in surface mount technology (SMT) microelectronic industry to replace the conventional rigid printed circuit board (RPCB). Superior in flexibility and thin physical accommodate the necessity of present electronic devices. However, a far more critical issue would lie in the soldering connection between components and FPCB in the thermal reflow soldering atmosphere. These works investigate the factor of Reynold numbers (Re) and a conveyor speed of FPCB surface with the incorporation of single BGA. For this simulation purpose, the model was performed using finite volume (FV) based and finite element (FE) based, coupled simultaneously in FLUENT system coupling. Findings indicate both effects have major respond on FPCB surface and soldering connection at maximum deflection and von Mises stress, respectively. Moreover, the Re showed dominant influence towards soldering connection over conveyor speed.

The encapsulation process is crucial since its act as first layer protection for the LED. The encapsulation process also influences the quality of the product. The structure of the encapsulate will affect the quality of emitting light in term of brightness and color. Thus, the process of encapsulation is one of the factors that can improve the quality of the product. This study aimed to observe the encapsulation process of LED and the interaction between gold wire bonding and EMC. By considering the computational method using Fluid-Structure Interaction (FSI), the VOF was used to simulate the dispense of EMC during the encapsulation process. Besides, an experiment was conducted to validate the simulation result. Thus, the FSI was utilized to predict the amount of stress on to the gold wire bonding during the encapsulation process. The broken gold wire bonding that connects these two elements indirectly will cost the failure of the product to work as intended.

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 work has been conducted to predict the real time observation of solder paste Sn96.5Ag3.0Cu0.5 (SAC305) filling process into stencil apertures as well as print quality in stencil printing by using Computational Fluid Dynamics (CFD) approach. A 3-Dimensional stencil printing model was developed and simulated in FLUENT by using different squeegee parameters which are the angle and printing speed. An experimental work was performed to be compared with part of the simulation results in term of print quality for validation purpose. It is found that squeegee angle 60° to 80° has potential to obtain good print quality of solder paste. In addition, print speed range between 35 mm/s to 95 mm/s also can be the good print speed option to achieve good print quality in stencil printing process. Finally, the maximum pressure distribution of solder paste also changes substantially as the squeegee travel further with respect to different values of tested parameters.

The present work studied on the volume reduction and cold slump effect for lead-free solder. The solder paste SAC305 type 3 was used to study the effect of waiting time on the solder volume and height at room temperature. DEK 265 was used for the printing purpose and KOH YOUNG Aspire 2 was fully utilized for the measurement of solder volume and solder height. The experiment was conducted for 120 minutes with 15 minutes gap between the measurements. Three types of components size (0603, SOT and Tantalum-D) was compared to see the effect on different components sizes. Solder paste volume and height shows a reduction from its initial values after 120 minutes for all three components size. For solder volume, biggest size component, Tantalum-D give lowest volume reduction at 3.55% compared to 0603 (3.68%) and SOT (3.76%). Meanwhile, solder height gives different results where Tantalum-D have the highest height reduction at 2.8% while SOT and 0603 have lower height reduction at 2.17% and 1.84% respectively.

This work describes the aerodynamic characteristics of an aircraft wing model with a Rüppell’s griffon vulture (RGV)-type winglet. A computational fluid dynamics (CFD) study using ANSYS 15.0 was conducted to study the effect of the RGV winglet on a rectangular wing. The NACA 65(3)-218 wing consists of 660 mm span and 121 mm chord length where the aspect ratio is 5.45. Eight different winglet configurations have been studied. Furthermore, the study is extended to study effect of cant angle and different angles of attack (AOA) to the winglet. A comparative study is done on aerodynamic features such as lift coefficient (CL), drag coefficient (CD), lift/drag ratio (CL/CD) and tip vortices to get the best RGV winglet design. The RGV winglet achieved highest CL compared to other types of winglets configuration. Based on contour plot analysis, the RGV winglet shows lower vortex formation compared to without winglet. The results show about 15 to 30% reduction in drag coefficient and 5 to 25% increase in lift coefficient by using an RGV winglet.

Prediction of void occurrence during capillary underfill encapsulation process is vital to avoid package failure due to incomplete filling during the encapsulation process. Two design variables, namely the gap height and package orientations, together with different types of industrial standard design of dispensing methods were identified as possible influences to the void formation in encapsulated package. In this paper, all these factors have been closely related to the void formation and subsequently the best chip design has been formulated to improve package reliability. From the study, air entrapment is clearly visualized in the experiment, which can be detrimental as it contains trapped oxygen, which can combust at high temperature. A series of experiments eventually showed higher possibility of air void formation by U-type dispensing method compared with the L-type dispensing method. In addition, it is found that the chip design parameters that include the scaling size and ball grid array orientation have an effect on the size of void formed. Our experimental findings were validated using lattice-Boltzmann method simulation and great consensus is found between both approaches. These findings provide additional insights to the electronic packaging developer to effectively reduce the formation of void during encapsulation process.

Finite volume method (FVM) based simulation of 3D fluid-structure interaction (FSI) of stacked chip package during the encapsulation process of moulded underfill (MUF) in different aspect ratio is presented in this paper. The 3D model of flip chip package is built and meshed using ANSYS ICEM, and simulated by FLUENT software. Castro–Macosko viscosity model and volume of fluid (VOF) technique are applied for flow front tracking of the encapsulant. Curing kinetics is taken into consideration in the simulation using Kamal’s equation. To solve the Castro–Macosko and Kamal models, suitable user defined functions (UDFs) are developed using MS VISUAL STUDIO.NET software and incorporated into the FLUENT. The parameter such as different aspect ratio of stacked die of mold cavity on the flow front behaviour is mainly studied. Mechanical stresses experienced by the silicon die will also be monitored for risk of die cracking. The visualisation of the 3D stacking-chip package encapsulation process was presented at different filling times. The encapsulation model aided a clear visualisation and improved fundamental understanding of the design of a 3D integrated circuit encapsulation. The proposed analysis is expected to be a reference and guide in the design and improvement of 3D integration packages.

In this paper, the discrete phase model (DPM) was introduced to study the fuel injector cavitations process and the macro spray characteristic of three different types of nozzle spray shape with diesel and hybrid biofuel blend for several injection pressures and backpressures. The three types of nozzle spray shapes used were circle, elliptical A type, and elliptical B type. The cavitations&rsquo, flows inside the injector nozzles were simulated with Computer Fluid Dynamics (CFD) simulations using the cavitations mixture approach. The effect of nozzle spray shape towards the spray characteristic of hybrid biofuel blends is analyzed and compared with the standard diesel. Furthermore, a verification and validation from both the experimental results and numerical results are also presented. The nozzle flow simulation results indicated that the fuel type did not affect the cavitation area vastly, but were more dependent on the nozzle spray shape. In addition, the spray width of the elliptical nozzle shape was higher as compared to the circular spray. Moreover, as the backpressure increased, the spray width downstream increased as well. The spray tip penetration for the elliptical nozzle shape was shorter than the circular nozzle shape due to circular nozzles having smaller nozzle widths and lesser spray cone angles. Thus, this resulted in smaller aerodynamic drag.

This paper studies the three-dimensional simulation of pressurized underfill process for I-type dispensing method on a 10 by 10, middle empty ball-grid-array (BGA) using lattice-Boltzmann method. Underfill encapsulations plays an important role in increasing the reliability of a flip chip package. Pressurized underfill process is introduced to overcome the drawbacks of the usual capillary underfill process which include extended filling time, incomplete filling and the high chances of void formation. Four different pressure values are used as the input pressure in the lattice-Boltzmann simulation of the pressurized underfill process. It was shown that the high pressure region concentrates at the inlet region, while the peak pressure in the flow domain is around four times the initial input pressure.

This paper simulates and predicts the laminar flow inside the 3D aneurysm geometry, since the hemodynamic situation in the blood vessels is difficult to determine and visualize using standard imaging techniques, for example, magnetic resonance imaging (MRI). Three different types of Lattice Boltzmann (LB) models are computed, namely, single relaxation time (SRT), multiple relaxation time (MRT), and regularized BGK models. The results obtained using these different versions of the LB-based code will then be validated with ANSYS FLUENT, a commercially available finite volume- (FV-) based CFD solver. The simulated flow profiles that include velocity, pressure, and wall shear stress (WSS) are then compared between the two solvers. The predicted outcomes show that all the LB models are comparable and in good agreement with the FVM solver for complex blood flow simulation. The findings also show minor differences in their WSS profiles. The performance of the parallel implementation for each solver is also included and discussed in this paper. In terms of parallelization, it was shown that LBM-based code performed better in terms of the computation time required.

In the conventional underfill (CUF) encapsulation process, there are few drawbacks encountered such as extended filling time, incomplete filling and voids formation. Finite volume method (FVM) simulations have been conducted to study different CUF dispensing method for different types of ball grid array (BGA) orientations in a single-layered PCB. It is investigated that the most ideal combination of orientations and dispensing type is middle empty orientation with L-type flow achieving relatively fast filling time. The findings show that the arrangement of BGA sizes with the small solder balls placed at the bottom layer, followed by the medium size solder balls in the middle stack and the largest solder balls at the top layer has been shown to enhance the flow rate of the encapsulant. This study also reveals the potential of air gaps in improving velocity and pressure distribution near inlet and outlet to achieve faster total filling time in all layers of BGA.

This paper studies the three dimensional (3D) simulation of fluid flows through the ball grid array (BGA) to replicate the real underfill encapsulation process. The effect of different solder bump arrangements of BGA on the flow front, pressure and velocity of the fluid is investigated. The flow front, pressure and velocity for different time intervals are determined and analyzed for potential problems relating to solder bump damage. The simulation results from Lattice Boltzmann Method (LBM) code will be validated with experimental findings as well as the conventional Finite Volume Method (FVM) code to ensure highly accurate simulation setup. Based on the findings, good agreement can be seen between LBM and FVM simulations as well as the experimental observations. It was shown that only LBM is capable of capturing the micro-voids formation. This study also shows an increasing trend in fluid filling time for BGA with perimeter, middle empty and full orientations. The perimeter orientation has a higher pressure fluid at the middle region of BGA surface compared to middle empty and full orientation. This research would shed new light for a highly accurate simulation of encapsulation process using LBM and help to further increase the reliability of the package produced.