High aspect ratio “multiple wire” microvias in flexible PCBs

Abstract

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 porous flexible Kapton foils for printed circuit boards (PCBs).

Design/methodology/approach

Kapton foils are made porous by ion track technology and dry resist patterning. In combination with thin film deposition and electroplating the technology is used to define circuits and sensors with microvias made of many individual high aspect ratio wires. The processes are within the reach of many production environments and are suitable for flexible PCB fabrication.

Findings

The use of these novel processes enables new types of microvias and multiple wire structures in the foils for millimeter wave circuitry of substrate integrated waveguides and shielding, as well as for sensors with high thermal resistance.

Research limitations/implications

Today, through foil electroplating is fairly slow and more work should be made with copper electroplating. Ion track technology works well on polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polyimide (PI) but should also be studied for novel polymer foils such as liquid crystal polymers (LCPs).

Originality/value

The paper details how ion track and PCB technology can be combined to enable a new type of through the foil via interconnect that consists of a multitude of wires. With these porous substrates, double‐sided circuits with high aspect ratio microvias and other multiple wire structures can be created using only lithography, thin film deposition, and electroplating. A new type of electrothermal sensorfoil is presented with several advantages over its competing micro electro mechanical systems (MEMS) based Si sensors.

Citation

Lindeberg, M. and Hjort, K. (2009), "High aspect ratio “multiple wire” microvias in flexible PCBs", Circuit World, Vol. 35 No. 4, pp. 18-21. https://doi.org/10.1108/03056120911002370