An alternative 3D packaging route through wafer reconstruction

Abstract

With the continuous development of 3D technology, il enables different variety in advanced 3D packaging. One oi the 3D package type which is currently being explored is the die-to-wafer (D2W) configuration. The 3D D2W assembly can be packaged using a standard flip chip with a laminate or BGA substrate but it has certain limitation in terms oi deformation induced during processing due to temperature changes as it is composed of different materials mainly substrates, silicon-die and mold compound with different coefficient of thermal expansions (CTE). Hypothetically. removing one of its main material component could simplify the complexity of CTE mismatch and provide better deformation control. Wafer reconstruction technique was then applied to reduce the deformation caused by the presence of BGA substrates. Meaning, the packaging main components are silicon- and mold compound only in which classify as Fan-out Wafer Level packaging (FOWLP). It provides the same functions as wafer level packaging without the use of BGA substrates. However, there are certain trade-offs particularly in molding process especially on fully stacked D2W 300 mm wafer size. Molding with large area as 300mm diameter and narrow gap around 300μm down to 50μm are part of the major challenges. One of the major concern in wafer reconstruction is the warpage problem. Warpage is commonly due to CTE mismatch between two or more different bonded materials. In this paper, the feasibility of Wafer Level Packaging wil demonstrated using the compression molding method with single and balancing wafer. The balancing wafer will be explored in terms of warpage reduction and can also act as a heat spreader. The single and balancing molded wafei warpage assessment will be then explored. Theoretically, molding compound plays a significant role in warpage aspect. The thickness of the mold compound or moldcap has significant effect in the degree of bowing of the package. The thicker the moldcap, the more severe in warpage behavior in the field of wafer molding. This paper will also demonstrate the effect of single and balancing wafer in compression molding process.