Parametric Study on the Void Risk in FC-POP Molded Underfill Process Using a Novel Porous Media, Two-Phase, Compressible Flow Simulation Method

Molded underfill process provides many benefits for higher productivity and lower cost over the conventional capillary underfill process. However, the void defects in a molded underfill process could cause pop-corning effect and solder extrusion during the reflow process. This paper presents a highly efficient and accurate hybrid model that can be applied to diagnose the void risk in vacuum molded underfill processes of real flip-chip, package-on-package devices with complex ball arrays and large PCB strips. The model combines multi-zone porous media model, Hele-Shaw model and compressible two-phase computational fluid dynamics model. The model has been well validated in terms of the entrapped void size and its behavior with flow visualization experiments. Also, a set of parametric studies on a FC-POP molded underfill flow process were performed to pre-assess the future node's molded underfill process. Not only the model provides a better understanding of the physics of void entrapment but also it is proven to be an effective tool for assessing the potential void risk through its application to 10nm flip-chip, package-on-package device manufactured in mass production line.