M.Z. Abdullah

A Study on the Effect of Epoxy Molding Compound (EMC) Rheology During Encapsulation of Stacked-CHIP Scale Packages (S-CSP)

The numerical and experimental investigations of three-dimensional (3-D) mold filling during encapsulation process in stacked-chip scale package (S-CSP) are presented. The finite difference method (FDM) based on Navier—Stokes equations has been employed for the flow analysis in the mold cavity. The mold flow is assumed to be non-Newtonian and non-isothermal. The proposed models can take care of polymer rheology with cure effect (Castro—Macosko model) and without cure effect (Cross model). A package with five, six, and seven overhang stacking dies without wire bonds is considered for simulation. The epoxy molding compound (EMC) used is HITACHI CEL-9200. The effects of gap between die top and mold cap surface, and between adjacent dies on flow rheology are analyzed and presented. The flow retardation in the limitation region (gap region) and smooth flow in the free region of the package is being predicted. Higher initial conversion of EMC demonstrated higher viscosity and slower melt front advancement especially under the overhang area of same die stacking region and critical gap between the die and mold cap. The void mechanism occurred due to unbalanced mold flow and critical gap clearance. The simulation results are verified with those obtained from a typical electronic industry and found in good agreement. From the results; the Castro—Macosko model is found to be more stable and reliable on the flow rheology.

Fluid/Structure Interaction Investigation in PBGA Packaging

This paper presents experimental and simulation studies of 3-D fluid/structure interaction (FSI) of wire sweep during the encapsulation process of plastic ball grid array (PBGA) packaging in different dies (single and stacked dies). A scaled-up package is fabricated to emulate the encapsulation of PBGA packaging and to study the effects of the FSI phenomenon in the PBGA package. A 3-D model of the mold and wires is created using GAMBIT, and the FSI is simulated using FLUENT and ABAQUS software integrated with mesh-based parallel code coupling interface for the real-time calculations. The effects of the stacked die and inlet pressure of the mold cavity on the melt flow behavior and wire sweep are mainly studied. A constant viscosity of the test fluid is assumed for the experiment. The volume-of-fluid technique is applied for melt-front tracking in the analysis. The numerical results of melt-front patterns and wire sweep are compared with the experimental results and good conformity is found. It is observed that the stacked die significantly influences the melt-front profile and the eventual wire sweep; as the number of dies in the stack increases, the wire sweep also increases.

Effect of Solder Joint Arrangements on BGA Lead-Free Reliability During Cooling Stage of Reflow Soldering Process

The aim of this paper is to investigate temperature and thermal stress responses at various joint arrangements during the cooling stage of the reflow process using an effective numerical approach. In this approach, numerical techniques for computational fluid modeling of the internal flow in the reflow oven were coupled with the structural cooling modeling at the board and package levels using a multi-physics code coupling interface. A thermal profiling experiment was conducted using the forced convection reflow oven to validate the simulation model. The numerical results were found to be in agreement with the experimental results. Results showed that the full-grid ball grid array (BGA) package has greatest temperature deviations, indicating different time responses between the start of the solidification process at different locations of the soldering process. Moreover, the solder joints experienced phase change from liquid to solid during the cooling stage of the reflow process. The large time interval for mushy zone of the full-grid BGA package indicated that the latent heat in a solder joint was hardly released to the environment. Consequently, this breaks the balance of the wetting force and increases the chances of the full-grid BGA package to skew. Generation of thermal stress at the interfaces of different materials occurred due to the mismatch of a variant coefficient of thermal expansion. Analysis and visualization of simulation results also showed that the maximum von-Mises stress of critically affected joints is influenced by solder joint arrangement patterns and not by the number of solder joints. The recommendation was also made to place dummy joints at the center of a package if routing and solder cracking problems were critical for peripheral array BGA package. The maximum von-Mises stress was reduced by 25.78% through improvement of solder arrangements. On the whole, the newly developed approach greatly helps reduce soldering defects and enhances solutions to lead-free reliability issues.

Lattice Boltzmann method study of bga bump arrangements on void formation

Abstract 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.

Influence of solder bump arrangements on molded IC encapsulation

Abstract This paper presents a fluid–structure interaction (FSI) analysis of ball grid array (BGA) package encapsulation. Real-time and simultaneous FSI analysis is conducted by using finite volume code (FLUENT) and finite element code (ABAQUS), which are coupled with MpCCI. A BGA integrated circuit (IC) package with different solder bump arrangements is considered in this study. In the FSI analysis, effects of solder bump arrangements on pressure distribution, void, deformation, and stress imposed on the IC structures are investigated. The maximum deformation and maximum stress on the silicon chip and solder bumps are evaluated. The findings indicate that the full-array solder bump package encounters lower stress and deformation during encapsulation. The void formation of each solder bump arrangement is examined. Scaled-up encapsulation is performed and the predicted flow front advancements are substantiated by experimental results. Results demonstrate the excellent capability of the proposed modeling tools for predictive trends of IC encapsulation. Thus, better understanding of IC encapsulation is provided to engineers and package designers in the microelectronics industry.

Design of an Underwater Glider Platform for Shallow-Water Applications

Underwater gliders are a type of autonomous underwater vehicles that glide by controlling their buoyancy and attitude using internal actuators. By changing the vehicles buoyancy intermittently, vertical motion can be achieved. Characteristic of glider motions include upward and downward in a saw tooth pattern, turning and gliding in a vertical spiral motion glides without using thrusters or propellers. This paper presents the development of the USM underwater glider as the first prototype for shallow water applications. The prototype development involves vehicle concept design using Solidworks™, vehicle simulations by computational fluid dynamics (CFD) and MATLAB Simulink™ as stage of the design process. Once the prototype fabrication and system integration are completed, it will be tested for vehicles modelling and controller development using the system identification approach and will be compared with the proven gliders control model.

Thermal Fluid-Structure Interaction in the Effects of Pin-Through-Hole Diameter during Wave Soldering

An effective simulation approach is introduced in this paper to study the thermal fluid-structure interaction (thermal FSI) on the effect of pin-through-hole (PTH) diameter on the wave soldering zone. A 3D single PTH connector and a printed circuit board model were constructed to investigate the capillary flow behavior when passing through molten solder (63SnPb37). In the analysis, the fluid solver FLUENT was used to solve and track the molten solder advancement using the volume of fluid technique. The structural solver ABAQUS was used to examine the von Mises stress and displacement of the PTH connector in the wave soldering process. Both solvers were coupled by MpCCI software. The effects of six different diameter ratios (0.1 < d/D < 0.97) were studied through a simulation modeling. The use of ratio d/D = 0.2 yielded a balanced filling profile and low thermal stress. Results revealed that filling level, temperature, and displacement exhibited polynomial behavior to d/D. Stress of pin varied quadratically with the d/D. The predicted molten solder profile was validated by experimental results. The simulation results are expected to provide better visualization and understanding of the wave soldering process by considering the aspects of thermal FSI.

Fluid Structure Interaction of Unsteady Aerodynamics of Flapping Wing at Low Reynolds Number

Abstract Wing flexibility controls the aerodynamic-force generation of flapping-wing flyers. As the wing flaps through the air, it is subjected to both aerodynamic force acting on the surface of the wing and inertial force due to the acceleration or deceleration of the wing’s mass. The interaction between these inertial-elastic and aerodynamic forces resulted in wing deformation. To study the effects of skin flexibility and wing deformation on the aerodynamic performance of a flapping wing, fluid flow and structural analyses (two-way fluid structure interaction) are implemented in real-time application through the Multi-Physics Code Coupling Interface, using FLUENT and ABAQUS solvers. The different bending stiffness ratios are highlighted at 2,489; 159 and 1, which correspond to rigid, flexible, and highly flexible cases, respectively. In the present research, wing flexibility is investigated at low Reynolds number (Re^9,000) and reduced frequency (k=1.92). To validate the numerical model, an experimental study was conducted, and the result of the mean aerodynamic lift and drag coefficient showed good agreement. The time-averaged aerodynamic performances, such as mean lift coefficient, drag coefficient, and lift-to- drag ratio, revealed that the aerodynamic performance of flapping wings increases with the increase in flexibility.

Flow Induced Deflection and Stress on Flexible Printed Circuit Board in Fan-Cooled Electronic Systems: FSI Approach

Flexible printed circuit boards (FPCBs) are going to replace rigid boards (PCBs) in numerous electronic devices due to their reduced thickness and ability to bend and adapt to various shapes. Deflection and stress are key factors affecting the reliability of FPCBs. In this paper, the fluid flow solver FLUENT and structural solver ABAQUS, are used to study the deflection and stress induced by axial flow fan on FPCBs, in the fan sucking mode. The flow is assumed to be 3-D, laminar, compressible, and steady. The effect of air flow rate on the force acting on the components mounted on the FPCB is analyzed. In the structural simulation using ABAQUS, the deflection and stress are observed for nine cases of different mounting options of the FPCB, at a fixed air flow rate. The proper selections of air flow rate and mounting option are found to be crucial in minimizing the flow induced deflection and stress in FPCBs.

Influence of PTH offset angle in wave soldering with thermal-coupling method

Purpose – The aim of this study is to investigate the effects of offset angle in wave soldering by using thermal fluid structure interaction modeling with experimental validation. Design/methodology/approach – The authors used a thermal coupling approach that adopted mesh-based parallel code coupling interface between finite volume-and finite element-based software (ABAQUS). A 3D single pin-through-hole (PTH) connector with five offset angles (0 to 20°) on a printed circuit board (PCB) was built and meshed by using computational fluid dynamics preprocessing software called GAMBIT. An implicit volume of fluid technique with a second-order upwind scheme was also applied to track the flow front of solder material (Sn63Pb37) when passing through the solder pot during wave soldering. The structural solver and ABAQUS analyzed the temperature distribution, displacement and von Mises stress of the PTH connector. The predicted results were validated by the experimental solder profile. Findings – The simulation rev...