The manufacturing of electro-optical circuit boards (EOCB) is based to a large extent on established technologies. First
products with embedded polymer waveguides are currently produced in series. The range of applications within the
sensor and data communication markets is growing with the increasing maturity level. EOCBs require design flows,
processes and techniques similar to existing printed circuit board (PCB) manufacturing and appropriate for optical signal
transmission. A key aspect is the precise and automated assembly of active and passive optical components to the optical
waveguides which has to be supported by the technology.
The design flow is described after a short introduction into the build-up of EOCBs and the motivation for the usage of
this technology within the different application fields. Basis for the design of EOCBs are the required optical signal
transmission properties. Thereafter, the devices for the electro-optical conversion are chosen and the optical coupling
approach is defined. Then, the planar optical elements (waveguides, splitters, couplers) are designed and simulated. This
phase already requires co-design of the optical and electrical domain using novel design flows.
The actual integration of an optical system into a PCB is shown in the last part. The optical layer is thereby laminated to
the purely electrical PCB using a conventional PCB-lamination process to form the EOCB. The precise alignment of the
various electrical and optical layers is thereby essential. Electrical vias are then generated, penetrating also the optical
layer, to connect the individual electrical layers. Finally, the board has to be tested electrically and optically.
The increasing demand for planar polymer optical waveguides integrated into electrical printed circuit boards (PCB)
calls for mass production capabilities: Hence, appropriate materials, systems, assembly concepts and production
technologies become vital, in order to guarantee a high reproducibility and quality of the waveguides. The manufacturing
and assembly costs have to be kept on a low level, while the integration of the highly sensible waveguides into the rough
environment of PCB's with their cheap and non-ideal substrates is a particular challenge.
The present paper describes an assembly and manufacturing technology for electro-optical circuit boards which meets
these requirements.
First, the manufacturing and characterization of multimode polymer waveguides is presented and the process for layer
deposition and structuring is described. Specific attention is given to the reproducibility of these processes ensuring the
high optical quality of the waveguides. Additionally, some problems arising from the integration of the waveguides into
the PCB's are discussed.
Second, various light coupling concepts are presented. In particular, a novel mirror element based on parabolic reflectors
is described. The optical design was calculated analytically and optimized using computer simulations. The mirror
element was fabricated using injection molding in a reproducible manner at high quantities and lowest cost.
To allow for a wider tolerance in the subsequent assembly steps our novel electro-optical transceivers concept facilitates
the use of conventional SMD- placement machines for mounting which makes the process very cost effective. This
concept was demonstrated successfully and is also described within the third section.
In the last part the practical use of this building set is illustrated with different successfully realized applications in the
field of ICT and optical sensor technology.
For the realization of a polymer waveguide based optical backplane link for computing applications, we developed a
method to passively align multiple layers of polymer waveguide flex sheets in a single MT compatible ferrule. The
minimal feature forming the backplane is a 192 channel link. This link is equipped with four MT connector at each end,
and is performing a shuffling of the channels.
We describe the passive alignment used to realize the connectors. The achieved accuracy demonstrated in a 48 channels
connector consisting of 4 polymer sheets carrying 12 waveguides each, is shown to be better than ±5μm. The connection
losses between a 48 channel MT fiber connector and the realized polymer waveguide connector were found to be about
2dB.
Compared to fiber connectors, the presented concept using polymer waveguides has several advantages. The most
relevant are that only few assembly steps are needed, it is based on a totally passive alignment scheme and it can easily
be executed by standard pick and place tools.
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