New ideas for package designs using plastic core solder balls

A variety of packaging technologies are widely used in mobile phone applications. One of the major concerns is reduction of the assembly space, and to this end, wafer-level chip-size package (WLCSP) and package-on-package (PoP) methods have been adopted. On the other hand, as the market transitions to LTE smartphones, larger dies and packages are needed to meet the demand for higher performance and functionality. However, for larger packages, due to the difference in the coefficient of thermal expansion (CTE) between the silicon die and substrate, more thermal stress is generated at the solder joint. Therefore, thermal reliability is of great concern. Moreover, in large-size PoP, since the solder connection can be deformed by the package weight, causing a solder bridge to be produced, there is a need to regulate the lower ball-pitch limit. Thus, the ability to control the standoff height is also a key factor in PoP design.