Enhance Solder Ball Shear Value in SiP Embedded Packages

The trend of integrating more functions into portable devices has demanded IC packages to put more dies, more components into a small footprint. To meet this demand, SiP (System in Package) technology has been one of the alternative solutions to system integration. Compare to SoC (System on Chip), SiP has the advantages of integration of dies made from different technology, e.g. GaAs and Silicon; and also can integrate active and passive components together. Hence it gets lots attention lately. In ACET’s SiP embedded process, the bare dies and other components are embedded in a filler material to form a wafer-like panel. Later; the dielectric and RDL are processed on top of this panel in a process similar to the RDL of WLP. After making the RDL, the UBM process is followed. Later, the solder balls are placed on top of the UBM and solder balls are reflowed. The packages are then been tested, inspected and ready for shipping. We have successfully used this process in mass production of SiP embedded packages using 8¨ panels. The technology has also been demonstrated by using both 12¨ circular and square panels. The filler material and dielectric material used have a low Young’ s modules. During ball shear test, the solder ball shear force for solder balls on top of the filler is less than that of on top of the die. For some customers, it is desirable to improve the shear force of the solder ball on top of the filler. For the package in this study, the shear force of solder ball on top of the die is averaged 235 gf, however, the same size solder ball on top of the filler materials is averaged only 136 gf. In order to enhance the solder shear force on top of the filler, two methods have been proposed. The first one is using dielectric materials with a higher Young’s modules. The high Young’s modules material is used only on the very top layer of package. The second method is using stiffer materials underneath the filler area. Both methods are successful to enhance solder ball shear values in the final packages.