Optimization of IC encapsulation considering fluid/structure interaction using response surface methodology

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.

Fluid/Structure Interaction Investigation in PBGA Packaging

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 ...

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

This paper presents a 3-D fluid-structure interaction (FSI) technique using mesh-based parallel code coupling interface (MpCCI) for the visualization of wire sweep during encapsulation of the plastic ball grid array packaging, considering the polymer rheology effect. In the molding process, the encapsulant flow behavior is modeled by the Castro-Macosko viscosity model including the curing effect and volume of fluid technique for melt-front tracking. The viscosity model is written in C language and compiled using user-defined functions into the FLUENT analysis. Wire sweep behavior is analyzed by ABAQUS and integrated with FLUENT software by MpCCI as an interface of fluid and solid interaction. Three types of epoxy molding compound (EMC), namely, Cases 1-3, were utilized for the study of fluid flow inside the mold cavity. The melt-front profiles and viscosity versus shear rate for all cases are analyzed and presented. The degree of conversion of the molding compound during the encapsulation process at the top view of the package for different EMCs is also studied. Pressure distribution around the wire region and wire sweep profiles within the mold are presented. The numerical results of the melt-front behavior and wire sweep are compared with the previous experimental results and found in good conformity. In the present case, Case 2 with a lower viscosity shows lower air trap, lower pressure distributions, and lower wire deformation. Therefore, the strength of MpCCI in handling FSI problems is proven to be excellent. The work presented in this paper is expected to be a reference and guide for the microelectronics industry.

FSI Simulation of Wire Sweep PBGA Encapsulation Process Considering Rheology Effect

Recent fluid–structure interaction modeling challenges in IC encapsulation – A review

More wires in a package and smaller wire gaps are the trend in the integrated circuit (IC) packaging industry. The effect of wire density is becoming increasingly apparent, especially on the flow pattern of the epoxy molding compound during the molding process and, hence, on the amount of wire sweep. In most mold flow simulations, the wire density effect is ignored. In order to consider the wire density effect on the predicted amount of wire sweep in the analysis, several indirect approaches were used by researchers before. But those approaches were not general enough to be applied to all cases. This paper presents a more direct and convenient approach to consider wire density effect by including wires in the mesh model for three-dimensional (3D) mold-filling analysis. A thin small outline package (TSOP) with 53 wires is used as the demonstration example, and all the wires are modeled in the 3D mesh. By comparison with experimental results, it is shown that this approach can accurately describe the wire density effect. When the wires are included in the mesh model, the predicted wire sweep results are better than those without considering the wire density effect.

Chien-Chang Pei

Papers

Prediction of Wire Sweep During the Encapsulation of IC Packaging With Wire Density Effect