Once the main printed circuit board (PCB) has been designed, the assembly guidelines for the 0.5mm package-on-package (PoP) applications processor and companion memory device must be considered. PoP applications processors have an enormous number of variables associated with assembly. The following factors have a major effect on the quality and reliability of PCB assembly: PoP applications processor solder paste requirements, solder paste deposition and reflow profile, and the fluxing or solder paste deposition onto the memory prior to assembly.
There are two common techniques used for PoP assembly – one-pass and two-pass. Although both will be discussed, Texas Instruments (TI) recommends the one-pass process, as it is the most economical and produces approximately the same assembly yield. This paper provides a starting point for establishing a set of assembly guidelines; however, it can not cover all of the possible variations. It is strongly recommended that you perform actual studies in conjunction with your assembly vendors to optimize the PoP assembly process.