Assembly-based Through-X Via (TXV) Integration Technology by Advanced Fan-Out Wafer-Level Packaging

A new formation technology of long through-hole vias we call TXV (Through-X Via, where X is polydimethylsiloxane, epoxy, or hydrogel etc.) is demonstrated without electro-less or electroplating processes. In this study, tiny copper pillars with a diameter/height of 300/300 μm are assembled by a pick-and-place method and molded with a soft epoxy as a flexible substrate based on die-first fan-out wafer-level packaging (FOWLP). Double-sided metallization is performed on the epoxy to interconnect the copper pillars. Adhesion and oxidation issues are solved with an adhesion promotor and a cleaning technique to give desired double-sided wirings connected with the copper pillars. The resulting daisy chain using the copper pillars shows relatively low resistance and good mechanical stability against repeated bending.