Enhanced package on package with coreless substrate optimal design evaluation

Abstract

Coreless substrate was popularized to develop for Enhanced Package on Package (ePoP) series package to effectively shrink package thickness and provide higher electrical performance. Therefore, in order to achieve those targets, Embedded Trace Substrate (ETS) coreless substrate was approached on bottom FCCSP package of ePoP structure. However, the warpage performance is the critical challenge for ePoP structure, especially on bottom package. This paper will aim to investigate Molding Level Package (MLP) and Bare Die Package (BDP) of ePoP bottom package characteristics with 3 layer and 4 layer ETS coreless substrate by using Finite Element Method (FEM) to find out the major key factors on material property and structure. For the material property, this study will come out the CTE, modulus and Tg material property trend chart of compound, underfill, prepreg (PP) and solder mask. For the structure, there are several parameter studies such as die thickness, prepreg thickness, solder mask thickness and the Cu coverage of 3/4L ETS substrate effect. According to lots simulation work, this study shows MLP structure with optimal material and structure design on 3/4L ETS substrate could pass the warpage criteria at 25C and 260C, but BDP structure may still have warpage risk easily due to no compound material to resist substrate deformation. Based on that, this study keeps studying on the Molded Interconnection System (MIS) substrate for BD structure to make the BDP structure to have no warpage risk. After the evaluation, MLP and BDP structure with ETS or MIS substrate would have no warpage risk under the optimal simulation suggestions and the simulation results show good correlation results with our internal experiment data. Finally, it is successful to apply coreless substrate into novel ePoP series and also can achieve shrinking package thickness and providing higher electrical performance advantages.