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Proceedings Paper

Fabrication method to create high-aspect ratio pillars for photonic coupling of board level interconnects
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Paper Abstract

An important challenge that remains to date in board level optical interconnects is the coupling between the optical waveguides on printed wiring boards and the packaged optoelectronics chips, which are preferably surface mountable on the boards. One possible solution is the use of Ball Grid Array (BGA) packages. This approach offers a reliable attachment despite the large CTE mismatch between the organic FR4 board and the semiconductor materials. Collimation via micro-lenses is here typically deployed to couple the light vertically from the waveguide substrate to the optoelectronics while allowing for a small misalignment between board and package. In this work, we explore the fabrication issues of an alternative approach in which the vertical photonic connection between board and package is governed by a micro-optical pillar which is attached both to the board substrate and to the optoelectronic chips. Such an approach allows for high density connections and small, high-speed detector footprints while maintaining an acceptable tolerance between board and package. The pillar should exhibit some flexibility and thus a high-aspect ratio is preferred. This work presents and compares different fabrication methods and applies different materials for such high-aspect ratio pillars. The different fabrication methods are: photolithography, direct laser writing and deep proton writing. The selection of optical materials that was investigated is: SU8, Ormocers, PU and a multifunctional acrylate polymer. The resulting optical pillars have diameters ranging from 20um up to 80um, with total heights ranging between 30um and 100um (symbol for micron). The aspect-ratio of the fabricated structures ranges from 1.5 to 5.

Paper Details

Date Published: 15 May 2008
PDF: 12 pages
Proc. SPIE 6992, Micro-Optics 2008, 69920T (15 May 2008); doi: 10.1117/12.782721
Show Author Affiliations
C. Debaes, Vrije Univ. Brussel (Belgium)
J. Van Erps, Vrije Univ. Brussel (Belgium)
M. Karppinen, VTT Technical Research Ctr. of Finland (Finland)
J. Hiltunen, VTT Technical Research Ctr. of Finland (Finland)
H. Suyal, Heriot-Watt Univ. (United Kingdom)
A. Last, Univ. Karlsruhe (Germany)
M. G. Lee, Fujitsu Labs. of America (United States)
P. Karioja, VTT Technical Research Ctr. of Finland (Finland)
M. Taghizadeh, Heriot-Watt Univ. (United Kingdom)
J. Mohr, Forschungszentrum Karlsruhe (Germany)
H. Thienpont, Vrije Univ. Brussel (Belgium)
A. L. Glebov, Fujitsu Labs. of America (United States)

Published in SPIE Proceedings Vol. 6992:
Micro-Optics 2008
Hugo Thienpont; Peter Van Daele; Jürgen Mohr; Mohammad R. Taghizadeh, Editor(s)

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