Flow modeling and visualization of the transfer molding of plastic ball grid array packages

Abstract

Recent advances in computer-aided tool design have reduced the cost of expensive prototype tooling. CAD-based software has 'been promoted for the design of plastic IC encapsulation tooling, but until recently, no real-time data from the encapsulation process had been collected to verify its effectiveness. A novel approach was used to capture the plastic IC encapsulation process. A 24x24mm PBGA mold was equipped with a window and video camera to capture the encapsulation process. Computer simulations of the cavity were also performed, using a new reactive 3-D flow simulation software suite. Computer predicted results showed only partial agreement with the observed molding results due to simplifications of the model required for timely simulation runs. More detailed models would provide better predictions at the cost of lengthy computer CPU time. IntroductionMost integrated circuits (IC) are packaged using transfer molding of epoxy compounds. Design of the molds used in these processes is a costly and lengthy process. The prototypes are expensive, because each piece of tooling must be designed, machined, and tested in a very short amount of time. Prototypes often require numerous modifications and rework. To minimize the impact of these changes, new designs are typically created on CAD (Computer-Aided Design) systems, which allow rapid modification of drawings at any point in the design process. Although these systems have simplified the drawing process, they have not affected the fabrication process. Each iteration in the design process still requires rework of the existing mold or the fabrication of a new mold, often at a cost of tens of thousands of dollars. Large amounts of time and money are also spent testing each revision. Mold design and flow simulation have been proposed as a more efficient methodology for tool manufacturing [l].

FSI Analysis of the Effect of Aspect Ratio of Stacked Chip in Encapsulation Process of Moulded Underfill Packaging

“…In order to minimize the impact of these problems and for better mold design and optimization, numerical analysis of flow during the encapsulation process is needed [4]. Turng and Wang [5], Han and Wang [6], and Nguyen et al [7][8][9][10] are the pioneers in numerical simulation of the flow during encapsulation. Their numerical formulation was mostly based on finite element method (FEM) coupled with the volume of fluid (VOF) technique.…”

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

“…The chemical reactions determine the rate of the conversion and the corresponding viscosity. The success to-thepoint of the flow simulation is strongly dependent on the input information related to the cure kinetic and rheology of the molding compound [13][14][15]. The chemo-rheological characteristics of the EMC may pose problems such as incomplete mold, voids [16,17], unbalanced flow [18] and wire sweeping [19].…”

“…Due to the complex features of the epoxy molding compound (EMC) as stated above, it seems the conventional trial-and-error method for optimization of the process is extremely difficult. Therefore, computer-aided-engineering (CAE) is introduced and proved to be an effective tool for analyzing the complicated process [20][21][22][23]. The field variable distribution and animation of analysis of results obtained by CAE provide valuable information in engineering aspects especially know-how and design improvements [24].…”