MoldFlow simulation study on void risk prediction for FCCSP with molded underfill technology

Abstract

The microelectronics products of Flip Chip-Chip Scale Package (FCCSP) with more increasing challenges are faced to assure molding capability with rapid advances in flip chip technology such as decreasing stand-off height and bump pitch, especially when Molded Underfill (MUF) is used during transfer molding process. There is one important challenge that faced severe air void entrapment under the die (air void concentrate among bumps region). Generally, the experiments involving a lot of DOE matrixes which spend a lot of time and materials (dummy die, substrate, mold compound...etc.) to solve this air void issue. As above reasons, the moldflow simulation can be used to apply molding parameters to find out optimum solutions for air void risk free of MUF FCCSP with different bump structure or substrate structure design, which can reduce development cycle time before mass production. In this paper, 3D moldflow simulation software which can apply transfer molding process parameters is used. There are two molding flow factors will be presented in this paper. One is MUF FCCSP with different stand-off height construction (control different bump height dimension) which performs significant difference molding melt-front position. And another is substrate solder mask with different pattern design (solder mask w/ all open or finger like pattern design) which molding compound through over on solder mask pattern (solder mask with open region as 10um depth structure) and performs different melt-front pattern. From this study, we can conclude some results for improvement molding performance of MUF FCCSP during transfer molding process. The MUF FCCSP with the 50um stand-off height structure performs low air void risk due to mold compound could easily flow under die region with more flow space. In addition, mold compound also performs well melt-front flow that the substrate solder mask with all open structure design can get more 10um flow space under die region. Finally, the simulation results are aligned with experiments and it can be used to predict void risk.