Fabrication and Characterization of Epoxy Molding Films (EMFs) for Wafer-Level and Panel-Level Fan Out Packages

Abstract

Recently, the fan out semiconductor packaging technology has been developed due to the demand for miniaturization and high performance of package products. The Wafer or Panel-Level Fan-Out Packages (FOPs) without package substrates such as Printed Circuit Boards (PCBs) can significantly reduce the package size and thickness and enhance electrical performances compared with conventional CSP(Chip Size Package) packages. As the Wafer or Panel-Level FOPs have been receiving more attention, FOPs related materials and processing techniques are becoming important too. At present, the transfer molding method using liquid or granular Epoxy Molding Compounds (EMCs) has been widely used to passivate chips and act as substrates. However, as wafers become larger and panel level FOPs are introduced, passivation methods using current liquid, granule, or pellet type EMCs are reaching some materials non-uniformity and thickness control limitations. To overcome these limitations, new Epoxy Molding Films (EMFs) type materials and processes have been introduced to replace the current liquid, granule and pellet type EMCs. The main roles of EMFs are to passivate semiconductor devices and act as substrates at the same time. In order to protect the semiconductor device from impact, heat, and moisture from the outside, the EMFs should have higher modulus, Glass Transition Temperature (Tg), adhesion, and lower Coefficient of Thermal Expansion (CTE). In this study, mixture of solid and liquid epoxies was used. Solid epoxy was used to provide lower CTE and higher modulus, and liquid epoxy was also used to provide higher adhesion property. After optimizing solid and liquid epoxies, the modulus, Tg, and CTE properties were significantly improved by adding the 5 µm diameter size silica filler content up to 70 wt% using. And the viscosity of EMFs was also affected by silica content. In order to improve the flow characteristics of EMFs, lower viscosities at the minimum temperature was recommended. In addition, the viscosity of the EMFs can be also decreased by the solvent content. The 10 cm × 10 cm size and the 400 µm thick EMFs were prepared for molding 10 mm × 10 mm size and 200 µm thick chips for the FOPs testing. The molding processes of EMFs were performed at various temperatures using a hot press equipment. The voids inside the EMFs were investigated using the Scanning Acoustic Microscopy (SAM) equipment to obtain optimized process conditions with no voids. And the warpage characteristics of EMFs were also observed using the Shadow Moire equipment. Finally, thermal cycle (T/C) test and 85 °C / 85% RH were performed to evaluate the effects of void, delamination, and moisture of EMFs on FOPs reliability.