High aspect ratio 'multiple wire' microvias in flexible PCBs

摘要

Purpose - The purpose of this paper is to present an update and the latest results from work on high aspect ratio "multiple wire" microvias in porousrnflexible Kapton foils for printed circuit boards (PCBs).rnDesign/methodology/approach - Kapton foils are made porous by ion track technology and dry resist patterning. In combination with thin filmrndeposition and electroplating the technology is used to define circuits and sensors with microvias made of many individual high aspect ratio wires. Thernprocesses are within the reach of many production environments and are suitable for flexible PCB fabrication.rnFindings - The use of these novel processes enables new types of microvias and multiple wire structures in the foils for millimeter wave circuitry ofrnsubstrate integrated waveguides and shielding, as well as for sensors with high thermal resistance.rnResearch limitations/implications - Today, through foil electroplating is fairly slow and more work should be made with copper electroplating. Ionrntrack technology works well on polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polyimide (PI) but should also be studied forrnnovel polymer foils such as liquid crystal polymers (LCPs).rnOriginality/value - The paper details how ion track and PCB technology can be combined to enable a new type of through the foil via interconnectrnthat consists of a multitude of wires. With these porous substrates, double-sided circuits with high aspect ratio microvias and other multiple wirernstructures can be created using only lithography, thin film deposition, and electroplating. A new type of electrothermal sensorfoil is presented withrnseveral advantages over its competing micro electro mechanical systems (MEMS) based Si sensors.