Package-on-Package or PoP technology was developed to provide more functionality in a smaller footprint for the fast paced consumer electronics market. Electronics design and assembly has traditionally been a two-dimensional process, with each component being placed on the same horizontal plane in different X and Y locations. With PoP technology, components can be placed or stacked on successively higher layers. Using PoP devices allows designers more flexibility and decreases the development time and cost. From the assembly system point of view, PoP requires new techniques when compared to standard SMT assembly.
Since components are stacked on top of each other, traditional solder paste printing cannot be used. The typical SMT method to print solder paste can only be used to print paste on a single horizontal plane. For PoP, the components that are placed on top of existing components need to have flux or solder paste applied at the time of assembly. This paper will explore the challenges and solutions of PoP assembly for the SMT assembly system.