Mold-flow study for different bump height, bump pitch and die size in FCCSP with molded underfill technology

Abstract

Currently electrical products such as smart phone and tablet, light weight and thin feature of them are definitely required. To achieve several requirements, size of IC package assembled in limiting space become more crucial and development orientated. Microelectronics products of FCCSP (Flip Chip-Chip Scale Package) with more increasing challenges are countered to assure molding capability with rapidly advancing encapsulation process in flip chip technology such as decreasing bump height and bump pitch, especially when Molded Underfill (MUF) is used and in particular during transfer molding process. Moldflow simulation is valid method to predict and resolve in air void entrapment severely occurred under the die (air void concentrated within bump region). Optimum solutions would be found out for air void risk free of MUF FCCSP with different bump structure or die size design, which can reduce development cycle time before mass production. In this paper, two molding flow factors for void prediction will be performed by moldflow simulation software. One of the two is about characteristics of bump structure including bump height and bump pitch. By varying different bump dimensions, melt-front position of molding frontier is affected in relevantly significant. In addition, the other factor is package with different die size design. Die size also presents obvious influence on melt-front pattern while molding compound flow through region under die. From this study, some results can be concluded for getting improvement on mold flow performance of MUF FCCSP package during molding process. The first of all is MUF FCCSP with the 58um bump height and 100um bump pitch will perform low air void risk since there is more space under die letting compound flow though more easily. Based on the same concept mention previously, the second one is smaller die arrangement that also can be benefit to compound flowing and get better pattern of melt-front. Finally, the simulation results provide a prediction guideline that MUF FCCSP with suitable bump height/pitch and die size structure condition to prevent void issue occur under die region during molding process.