C.Y. Khor

Fluid/Structure Interaction Analysis of the Effects of Solder Bump Shapes and Input/Output Counts on Moulded Packaging

This paper presents a fluid/structure interaction (FSI) analysis of the effects of solder bump shapes and input/output (I/O) counts on moulded packaging. The FSI events during the encapsulation process are investigated using a virtual modeling technique, whose mesh-based parallel code-coupling interface couples both finite volume and finite element codes. In this paper, the effects of five different solder bump shapes, denoted Cases 1-5, are considered in the perimeter and full array of solder bump arrangements with different I/O counts. The FSI between the epoxy moulding compound and structures (silicon chip and solder bumps) is presented in the displacement profile. The effects of the bump shape and I/O count are considered in the flow front advancement, structure displacement, stress, and void formation. The maximum displacements, von Mises stresses, and voids are minimized by implementing the bump shape in Case 3. The applications of Cases 3 and 5 with higher I/O counts (full array type) reduced the stress concentration in the solder bump by nearly 40% and 60%, respectively, compared to the cases with lower I/O counts (perimeter type).

Optimization of the reflow soldering process with multiple quality characteristics in ball grid array packaging by using the grey‐based Taguchi method

Purpose – Reflow soldering is one of the most significant factors in determining solder joint defect rate. This study aims to introduce an innovative approach for optimizing the multiple performances of the reflow soldering process.Design/methodology/approach – This study aims to minimize the solder joint defect rate of a ball grid array (BGA) package by using the grey‐based Taguchi method. The entropy measurement method was employed together with the grey‐based Taguchi method to compute for the weights of each quality characteristic. The Taguchi L18 orthogonal array was performed, and the optimal parameter settings were determined. Various factors, such as slope, temperature, and reflow profile time, as well as two extreme noise factors, were considered. The thermal stress, peak temperature, reflow time, board‐ and package‐level temperature uniformity were selected as the quality characteristics. These quality characteristics were determined using the numerical method. The numerical method comprises the ...

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.

Study on the Fluid–Structure Interaction of Flexible Printed Circuit Board Electronics in the Flow Environment

Flexible printed circuit board (FPCB) can be an alternative to the rigid printed circuit board (PCB) because of its excellent flexibility, twistability, reduced thickness, and light weight. In a flow environment, although the deflection and stress induced are often ignored by PCBs, these are key factors that affect the reliability of FPCBs. Thus, this paper aims to examine the effect of flow velocity, component thickness, types of component arrangement, misalignment, and inclination on a typical FPCB electronics under flow condition. These factors are found to significantly affect the deflection and stress levels of FPCBs. On the basis of the results, a few design strategies are suggested to FPCB designers to develop more reliable products. In this paper, a fluid-structure interaction (FSI) study was performed using the fluid solver FLUENT and the structural solver ABAQUS, coupled online by the mesh-based parallel code coupling interface. A simple experiment was also performed to validate the FSI numerical technique used. The research findings in this paper are believed to be valuable and important to the FPCB industries.

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...

Influence of Gap Height in Flip Chip Underfill Process With Non-Newtonian Flow Between Two Parallel Plates

In this paper, the finite volume method (FVM) is used for the simulation of flip chip underfill process by considering non-Newtonian flow between two parallel plates that emulate the silicon die and the substrate. 3D model of two parallel plates of size 12.75 mm � 9.5 mm with gap heights of 5 lm, 15 lm, 25 lm, 35 lm, 45 lm, and 85 lm are developed and simulated by computational fluid dynamic (CFD) code, FLUENT 6.3.26. The flow is modeled by using power law model and volume of fluid (VOF) technique is applied for flow front tracking. The effect of change in height of the gap between the plates on the underfill process is mainly studied in the present work. It is observed that the gap height has significant influence on the melt filling time and pressure drop, as the gap height decreases filling time and pressure drop increase. The simulation results are compared with previous experimental results and found in good conformity. [DOI: 10.1115/1.4005914]

Study on the fluid‐structure interaction of flexible printed circuit board motherboard in personal computer casings

Purpose – The flexible printed circuit board (FPCB) can be an alternative to the rigid printed circuit board because of its excellent flexibility, twistability, and light weight. Using FPCB to construct personal computer (PC) motherboard is still rare. Therefore, the present study aims to investigate the fluid‐structure interaction (FSI) behaviors of the newly proposed FPCB motherboard under fan‐flow condition in the PC casings.Design/methodology/approach – The deflection and stress induced, which are usually ignored in the traditional rigid motherboard, are the main concern in the current FPCB motherboard studies. Only a few studies have been conducted on the effect of inlet locations, effect of inlet sizes, effect of multi‐inlets, and effect of a two‐fan system. These numerical analyses are performed using the fluid flow solver FLUENT and the structural solver ABAQUS; they are real‐time online coupled by Mesh‐based Parallel Code Coupling Interface (MpCCI).Findings – A smaller inlet size can cause higher...

Effect of piezoelectric fan height on flow and heat transfer for electronics cooling applications

Piezoelectric fan is used to remove the heat from the microelectronic devices, owing to their low power consumption, minimal noise emission and small in size. In the present study, a piezoelectric fan has been investigated to analyze the performance. The paper also discusses the capability of piezoelectric fan to cool the microelectronic device and its performance. The simulation and experimental investigations have been made for two different positions of piezoelectric fan i.e. vertical and horizontal positions. The Fluent 6.2.3 software which is a computational fluid dynamics (CFD) code has been used in the simulation to predict the heat transfer coefficient and the flow fields. In the experimental set-up, two heaters in line arrangement have been used in the set-up. The flow measurements have been carried out by using the particle image velocimetry (PIV) system at different piezoelectric fan height. The heat transfer coefficients have been plotted and compared with the experimental values. The simulation results obtained are found in satisfactory agreement with the experimental results.

Effects of Solder Temperature on Pin Through-Hole during Wave Soldering: Thermal-Fluid Structure Interaction Analysis

An efficient simulation technique was proposed to examine the thermal-fluid structure interaction in the effects of solder temperature on pin through-hole during wave soldering. This study investigated the capillary flow behavior as well as the displacement, temperature distribution, and von Mises stress of a pin passed through a solder material. A single pin through-hole connector mounted on a printed circuit board (PCB) was simulated using a 3D model solved by FLUENT. The ABAQUS solver was employed to analyze the pin structure at solder temperatures of 456.15 K (183°C) < T < 643.15 K (370°C). Both solvers were coupled by the real time coupling software and mesh-based parallel code coupling interface during analysis. In addition, an experiment was conducted to measure the temperature difference (ΔT) between the top and the bottom of the pin. Analysis results showed that an increase in temperature increased the structural displacement and the von Mises stress. Filling time exhibited a quadratic relationship to the increment of temperature. The deformation of pin showed a linear correlation to the temperature. The ΔT obtained from the simulation and the experimental method were validated. This study elucidates and clearly illustrates wave soldering for engineers in the PCB assembly industry.

Visualization of Fluid/Structure Interaction in IC Encapsulation

This paper presents the visualization of the fluid/structure interaction (FSI) in molded integrated-circuit (IC) packaging. The complexity and high cost of the experimental setup in the molded packaging make the FSI visualization difficult during the encapsulation process, particularly for tiny and thinned chips in IC packages. To address this problem, we fabricated a scaled-up transparent molded package, and the encapsulation process was experimentally performed to visualize the FSI phenomenon. Two scaled-up (single- and stacked-chip) IC packages were considered in the experiment to investigate the FSI, flow front advancement, and void formation. The void formation mechanisms for both imitated IC packages were also studied. Moreover, finite-volume and finite-element codes, via the mesh-based parallel code coupling interface method, were used to describe the physics of FSI during the encapsulation. The predicted flow front advancement, flow profiles, and chip deformation were validated with the experimental results. Hence, this paper is expected to provide a better understanding of the FSI phenomenon during the IC encapsulation.