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Reliable small via interconnects made of multiple sub-micron wires in flexible PCB boards
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
2007 (English)In: Journal of Micromechanics and Microengineering, ISSN 0960-1317, E-ISSN 1361-6439, Vol. 17, no 4, 700-708 p.Article in journal (Refereed) Published
Abstract [en]

A fabrication process for small through-hole vias consisting of multiple sub-micron electrodeposited wires has been developed for flexible printed circuit boards (PCB). The resistance of the vias is controlled by adjusting the number of wires per via, as well as the dimensions of the wires. The process steps include modification of the foils by irradiation with energetic ions, wet etching and metallization of the through-hole vias, double-sided surface metallization of the dielectric layer and interconnection lithography. Series of up to 360 interconnected vias of electrodeposited nickel are demonstrated in a flexible PCB foil (75 µm Kapton HN polyimide). The vias have a lateral size of 26 µm. The metal content of the demonstrated vias is 0.12% and 10% of their total volume, corresponding to a metal cross-section of 3.2 µm2 and 270 µm2, respectively. The electrical resistance per interconnected via is 2.6 Ω and 0.07 Ω, respectively. The vias can carry a current density of at least 4 × 106 A cm−2.

Place, publisher, year, edition, pages
2007. Vol. 17, no 4, 700-708 p.
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-96874DOI: 10.1088/0960-1317/17/4/005ISI: 000245434200011OAI: oai:DiVA.org:uu-96874DiVA: diva2:171602
Available from: 2008-03-19 Created: 2008-03-19 Last updated: 2016-04-11Bibliographically approved
In thesis
1. High Aspect Ratio Microstructures in Flexible Printed Circuit Boards: Process and Applications
Open this publication in new window or tab >>High Aspect Ratio Microstructures in Flexible Printed Circuit Boards: Process and Applications
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Flexible printed circuit boards (flex PCBs) are used in a wide range of electronic devices today due to their light weight, bendability, extensive wiring possibilities, and low-cost manufacturing techniques. The general trend in the flex PCB industry is further miniaturization alongside increasing functionality per device and reduced costs. To meet these demands, a new generation of low cost manufacturing technologies is being developed to enable structures with smaller lateral dimensions and higher packing densities.

Wet etching is today the most cost-efficient method for producing a large number of through-foil structures in flex PCBs. However, conventional wet etch techniques do not allow for through-foil structures with aspect ratios over 1 – a fact that either necessitates thin and mechanically weak foils or puts severe limitations on the packing density. The fabrication techniques presented in this thesis allow for through-foil structures with higher aspect ratios and packing densities using wet etching. To achieve high aspect ratios with wet etching, the flex PCB foils are pre-treated with irradiation by swift heavy ions. Each ion that passes through the foil leaves a track of damaged material which can be subsequently etched to form highly vertical pores. By using conventional flex PCB process techniques on the porous foils, high aspect ratio metallized through-foil structures are demonstrated.

The resulting structures consist of multiple sub-micrometer sized wires. These structures are superior to their conventional counterparts when it comes to their higher aspect ratios, higher possible packing densities and low metallic cross-section. Furthermore, metallized through-foil structures with larger areas and more complicated geometries are possible without losing the mechanical stability of the foil. This in turn enables applications that are not possible using conventional techniques and structures. In this thesis, two such applications are demonstrated: flex PCB vertical thermopile sensors and substrate integrated waveguides for use in millimeter wave applications.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2008. 58 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 407
Keyword
Engineering physics, flexible printed circuit boards, polyimide, through-hole vias, ion track technology, thermoelectricity, thermopiles, substrate integrated waveguides, millimeter wave devices, Teknisk fysik
National Category
Other Engineering and Technologies
Identifiers
urn:nbn:se:uu:diva-8565 (URN)978-91-554-7127-9 (ISBN)
Public defence
2008-04-11, SiegbahnSalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:30
Opponent
Supervisors
Projects
wisenet
Available from: 2008-03-19 Created: 2008-03-19 Last updated: 2011-01-17Bibliographically approved

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Yousef, HannaHjort, KlasLindeberg, Mikael

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