FOPOP Warpage Analysis for Package Design Optimization

Compared with HBWPOP (High Bandwidth Package on Package), a FOPOP (Fan Out Package on Package) which adopts RDL structure to replace traditional substrate has the advantages of thin package profile, high electric al and thermal performance…etc. And it has been used as high-end AP for smartphone in recent years. But package warpage control for the FOPOP is becoming more challenges than general package due to thinner package thickness. Poor package warpage will impact quality results of SMT and stacking DRAM. Thus, a 15x15 mm package size without DRAM pre-stacking is studied in this paper. Various structural factors includes die thickness, Cu stud height, top and bottom RDL thickness that will impact package warpage performance were simulated and analyzed. Simulation and analysis results showed that top and bottom RDL thickness are significant factors affecting package warpage. Moreover, an optimized FOPOP structure was proposed and assembled actually. Then its package warpage was measured by shadow moiré and compared with simulation results. Both results includes warpage values and contours were simulation and meet warpage requirement.