Structure reliability and characterization for FC package w/Embedded Trace coreless Substrate

Abstract

In recent years mobile devices are getting more and more involved in to our daily life. With the requirement of IC packages inside mobile devices toward smaller form factor, low cost with high performance, a coreless substrate technology, naming Embedded Trace Substrate (ETS) is developed to meet market requirement and it has been studied in this paper. For an IC package with coreless substrate, warpage performance is a concern comparing to non-coreless substrate package of which has better substrate strength to balance Coefficients of Thermal Expansion (CTE) mismatch from molding compound. A Flip Chip Chip Scale Package (FCCSP) with body size 12×12mm is used as a test vehicle for this study and molding underfill (MUF) structure is selected to reduce package cost of additional underfill material. To evaluate the warpage performance of the ETS coreless substrate, finite element analysis simulation tool is used to compare package warpage for room temperature and high temperature. Also experimental validation of warpage is done by Shadow Moire test equipment. The study matrix includes different molding compound materials, molding compound thicknesses, substrate designs, substrate thicknesses, die thicknesses. By simulation and Shadow Moire measurement results can help the package structure and molding compound material selection that with thicker molding compound thickness, die thickness and substrate thickness have better warpage performance. In addition to warpage, the reliability performance is also evaluated for package under different test conditions such as assembly out time zero, uHAST, TCT and HTST. The evaluation index is Open/Short yield and failure analysis is also done for the O/S failed samples to evaluate failure rate, failure mode and failure locations. In the end, a package structure and bill of material (BOM) selection is finalized to have suitable warpage performance that meets requirement and can also pass reliability criteria.