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Ion Track Enabled Multiple Wire Microvia Interconnects in Printed Circuit Boards
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Micro Structural Technology.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Micro Structural Technology.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Micro Structural Technology.
2008 (English)In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 266, no 8, 1659-1665 p.Article in journal (Refereed) Published
Abstract [en]

As the call for higher wiring density in packaging and vertical microvia interconnections (microvias) rapidly evolves, the need for smaller lateral dimensions in printed circuit boards (PCB) microvias must be met. The ion track lithography described in this paper allows for high throughput micromachining of small, deep, vertical microvias in flexible PCB and all-polymer laminates.

Ion track lithography makes use of swift heavy ion irradiation to enhance the selectivity and directionality of chemical etching. Within the areas exposed to the ion irradiation, small sub-micron pores (capillaries) are created, one for every ion. If etching is prolonged, the pores become merged. Electrodeposition from a metallic seed layer is used to fill these structures with metal. The lithography masks define either the areas where the ion tracks are developed or where the tracks are metallized. The smallest achievable size of the microvias is only limited by the resolution of the mask; microvias below 10 μm in diameter can also be achieved also in thick polyimide foils.

Since each impinging ion forms one track, the foil’s porosity can be controlled by adjusting the irradiation dose, as well as by etching the pores to a suitable size. Depending on the porosity and material, the resultant metallized microvia consists of either individual or interlaced wires (like strands in a bundle wire), or is a solid. As an individual sub-micron wire may have an aspect ratio of several hundreds, this allows for the fabrication of truly vertical microvia structures, allowing ultra-high density microvia batch production.

Demonstrator microstructures with highly vertical microvias have been fabricated in foils up to 125 μm thickness. Several components integrated in flexible PCB have been presented by us, e.g. magnetoresistive sensors, thermopile IR-sensors and microwave components like inductor elements.

Place, publisher, year, edition, pages
2008. Vol. 266, no 8, 1659-1665 p.
Keyword [en]
Printed circuit board, Polyimide, Foil, Lithography, Ion track, Template
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-96876DOI: 10.1016/j.nimb.2007.11.014ISI: 000256677600105OAI: oai:DiVA.org:uu-96876DiVA: diva2:171604
Projects
wisenet
Available from: 2008-03-19 Created: 2008-03-19 Last updated: 2016-04-13Bibliographically 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, HannaLindeberg, MikaelHjort, Klas

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Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
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