Abstract
A fabrication process for high aspect ratio plated through-hole vias is presented for flexible printed circuit boards. A 75 µm thick porous Kapton foil that allows direct definition of high aspect ratio through-hole vias by dry photoresist film lithography and electrodeposition is presented. Pretreatment with swift heavy ion irradiation and wet etching define the pore density and porosity of the foil, similar to ion-track-etched filter membranes. Thin film metallization of a seed layer and lithography of a laminated dry photoresist film define the via sizes and positions. Subsequent through-hole electrodeposition produces vias consisting of multiple wires, where each open pore defines one wire. The via geometries are characterized by scanning electron microscopy. The electrical properties of the vias are characterized by resistance measurements. Vias with an aspect ratio over 2 and a side length of 33 µm show high yield with low resistance and low variation in resistance.
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