FOStrip Technique for Low-Cost Fan-Out Package

This paper presents a novel method for the low-cost fan-out package named FOStrip (R) and successfully builds up the test vehicle with a package size of 17mm x 17mm. The FOStrip is a chip-last strip level fan-out package technique and is not only compatible with both wafer level and panel level processes in the front-end assembly process but also retains the benefit of the strip level process in the back-end assembly process. Due to the warpage control being the main issue in the process for fan-out wafer level package (FOWLP) or fan-out panel level package (FOPLP), the material selection is extremely important, and it also affects the cost. The superior FOStrip technique shows better warpage control in the process because the strip size is smaller than the wafer or panel size. In other words, it has more space in material selection and could get better cost control. Furthermore, the FOStrip is compatible with the general substrate electronic package process flow and doesn't need to invest additional equipment in the back-end assembly process. The demand for organic substrates has also increased with the continuous increase in applications such as servers, high-performance computing (HPC), Networks, and automotive applications. Meanwhile, the increasing application of chiplet design and the adoption rate of 2.5/3D packaging technology have made organic substrates usher in a structural increase in demand. A feature of the fan-out package is a substrate-less package that it uses RDL for interconnection. Compared with organic substrates, RDL has a finer line width and line spacing, so a more compact routing configuration can be designed, which in turn shortens the transmission line path and excellent high-speed signal transmission, and the package size can be further miniature. The fan-out package is a substrate-less package and could shrink the package size, Using the FOStrip technique not only has the benefit of the fan-out package but also has the low-cost benefit in the process, in the roughly estimate the fan-out package could reduce the cost equal or less than 50% by comparing with the general substrate-type packages. As a result, a test vehicle with a package size of 17mm x 17mm has been successfully built by the FOStrip (R) technique, and the package warpage was measured less than 20um by shadow moire.