The flow characteristics of a number of underfills were evaluated with quartz dies of different patterns and pitches bonded on different substrate surfaces. Perimeter, mixed array, and full array patterns were tested. Observations on the flow front uniformity, streaking, voiding, and filler segregation were collected. The information was compared with the results predicted by a new simulation code, plastic integrated circuit encapsulationcomputer aided design (PLICE-CAD) under DARPA-funded development. The two-phase model of the combined resin and air takes into account geometrical factors such as bumps and die edges, together with boundary conditions in order to track accurately the propagation of the flow fronts. The two-phase flow field is based on the volume-of-fluid (VOF) methodology embedded in a general-purpose three-dimensional (3-D) flow solver. Index Terms-Capillary flow, filler settling, flip chip, flow simulation, flow streaking, full array pattern, mixed array pattern, organic laminates, peripheral pattern, quartz dies, underfill flow.

This paper presents, discusses, and compares results from experimental and computational studies of the plastic encapsulation process for a 144-lead TQFP package. The experimental results were obtained using an instrumented molding press, while the computational predictions were obtained using a newly-developed software for modeling transfer molding processes. Validation of the software is emphasized, and this was done mainly by comparing the computational results with the corresponding experimental measurements for pressure, temperature, and flow front advancement in the cavities and runners. The experimental and computational results were found to be in good agreement, especially for the flow-front shapes and locations. [S1043-7398(00)00502-8]

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In the last few years, flip chip technology has been increasingly employed in a variety of applications in the microelectronics industry. Comparing to conventional wirebonding technology, flip chip provides lower profile, faster signal transfer, and higher VO

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].