Challenge to zero CTE and small cure shrinkage organic substrate core material for thin CSP package

To reduce warpage of thinner package application such as POP (package on package), the ultra-low CTE (coefficient of thermal expansion) core materials has been developed. The resin system was originally designed by the concept of the combination of the hard and the soft segments. The hard segments composed of a stack structure of aromatic rings and the strong intermolecular force between them, which are the origin of the ultra-low CTE. The soft segments can follow the thermal motion of the glass fabric well due to the low elastic modulus. The CTE of the newly developed core material was as low as 0.7 ppm/°C. Then, it showed the ability to reduce warpage of PoP before/after assembly process. Our fundamental study revealed that the amount of the warpage is affected by not only the CTE but also the shrinkage of resin component in the core.