MPS-C2 and Post Encapsulation Grinding technology for ultra fine pitch and thin die flip chip applications

Flip chip technology is now being introduced in PoP(Package on Package) packages for the digital consumer electronics such as digital still cameras and mobile phones. PoP reduces the component height and improves the electrical performance. A MPS-C2(Metal Post Solder Chip Connection) method was developed for ultrafine pitch flip chip interconnections in mobile applications. A bare die with Sn/Ag-solder-capped Cu post bumps is directly connected on an organic substrate by using a reflow process without flux cleaning. This technology supports the SMT/Flip Chip-hybrid assembly required for SoP (System on Package) manufacturing, and it is the least expensive method among current ultrafine pitch flip chip interconnetion methods. We ran reliability tests with 50-um-pitch MPS-C2 interconnections. In addition to fine pitch interconnections, each die must be less than 70 um thick to insure that the final stack will be thin enough. Such thin die were not unsuitable for the original MPS-C2 process, because the dies tended to move during the reflow process. We developed a Post Encapsulation Grinding (PEG) method to resolve this problem. In this method the die is ground down to be less than 70 um thick after joining and underfilling.