This study investigates epoxy filling rate in the capillary underfill process of flip-chip packaging when the air is not trapped. Various design features were considered, they include; the shape of soldering bump, inlet size, bump height and bump spacing. The geometric models were made by CATIA and the analysis was carried out using commercial CFD software (Moldex3D capillary underfill packaging). In order to improve the usability of the analysis, the spherical bump shape was authenticated by the means of believe as a rhombic shape, and the analysis results were verified. The inlet size did not in any way whatsoever affect the underfill process analysis. From the analysis, we concluded that the epoxy of center parts needs to fill 80% or more of the inside of the edge in order to keep away from the air trapping on the flip-chip. This result can be a guideline for the underfill process conditions that may not be a reason for the air trap in the flip-chip design and manufacturing.