Study on Dynamic Void Evolution During Transfer Molding Process of Flip Chip Package

Transfer molding is a widely adopted process in electronic packaging. Due to the presence of chips, flow-front merging frequently occurs during molding, potentially trapping air that may lead to void formation. Such voids can compromise the stability and reliability of electronic components, making their prevention a key concern for process engineers. However, in practice, trapped air does not always result in voids, and the mechanisms behind this phenomenon merit further investigation. This study presents an innovative approach by designing a visualization mold to observe the dynamic evolution of trapped air during the transfer molding process. Moldex3D, a three-dimensional mold flow analysis software, was employed for simulation and comparison. The experiments successfully captured the sequential behavior of trapped air—including formation, compression, movement, and eventual escape from beneath the chip—thereby elucidating why voids do not always form despite air entrapment. Furthermore, by incorporating air compressibility into the simulation model, the dynamic motion of trapped air—previously difficult to replicate—was effectively reproduced. These findings provide valuable insights for industry practitioners, enabling them to use mold flow analysis to evaluate different product geometries and process parameters in advance, thus improving defect prediction and enhancing the quality and reliability of packaging products.