DSM Reballing Ball Height Prediction Model

System in Package (SiP) is an outstanding assembly technology, which integrates active dies and passive components into a single tiny module. For further miniaturization, SiP module evolves from single side molding to double side molding (DSM) structure, which can enhance the space utilization. DSM involves backside molding and grinding to reduce the package thickness as well as solder ball exposure. After grinding, solder balls in backside become non-spherical and need further reballing process to form a protruded spherical shape for package mount. In this work, a reballing ball height prediction model was proposed. Through this model, a predictable ball height and process adjustment guideline could be obtained. DSM structure with 230$\mu$ m pad opening and 290$\mu m/ 250 \mu$ m ball size were utilized in this study. For 290$\mu$ m ball size, the predicted ball protrusion height is 68.31$\mu$ m, and the experimental result is 71.43$\mu$ m in average; for 250$\mu$ m ball size, a predicted ball protrusion height is 51.24$\mu$ m, and the experimental result is 52.28$\mu$ m in average. The deviations were quite low and only 3.12$\mu$ m and 1.04$\mu$ m in above two cases, respectively. In this work, a ball protrusion height simulation model was presented and precise prediction of ball protrusion height can be obtained with 1% dimension deviation by which effective and lower cost as product development was realized.