To realize higher wiring density, both finer line/space resolution and a smoother resin-metal interface are needed. These requirements, however, conflict to each other: sufficiently fine lines are difficult to form on a rough surface, while a smooth surface generally results in poor peel strength. The feasibility of various metallization processes that promote adhesion on smooth resin surfaces is examined. Their practical applicability to manufacturing high wiring-density packages is also assessed and the related issues that need to be improved are discussed.
We have been developing a new type of interposer based on a copper-filled aluminum oxide (Cu-AAO) film and SOV (Sea Of Via) design concept for application to high-density 3-D packaging. The Cu-AAO contains numerous through-copper filaments regularly positioned on a submicron pitch. By using Cu-AAO as a core substrate, it is possible to form free-shape through-packaging vias (TPVs) in any position. In this study, we first evaluated the insulation properties of the Cu-AAO substrate. Then, we formed the interposer including the fine-pitch coaxial TPVs that were developed utilizing the unique features of Cu-AAO. Furthermore, we demonstrated 3-D shortest connection between the chips by attaching a TEG (Test Element Group) chip on both sides of the interposer.
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