We report on the co-packaging of electrical CMOS transceiver and VCSEL chip arrays on a flexible electrical substrate
with optical polymer waveguides. The electro-optical components are attached to the substrate edge and butt-coupled to
the waveguides. Electrically conductive silver-ink connects them to the substrate at an angle of 90°. The final assembly
contacts the surface of a package laminate with an integrated compressible connector. The module can be folded to save
space, requires only a small footprint on the package laminate and provides short electrical high-speed signal paths.
With our approach, the electro-optical package becomes a compact electro-optical module with integrated polymer
waveguides terminated with either optical connectors (e.g., at the card edge) or with an identical assembly for a second
processor on the board. Consequently, no costly subassemblies and connectors are needed, and a very high integration
density and scalability to virtually arbitrary channel counts and towards very high data rates (20+ Gbps) become
possible. Future cost targets of much less than US$1 per Gbps will be reached by employing standard PCB materials and
technologies that are well established in the industry. Moreover, our technology platform has both electrical and optical
connectivity and functionality.
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.
Optical link technology will play an increasingly important role for board-level interconnects in servers and supercomputers as a means to keep pace with the increasing intra-system bandwidth requirements. Low-cost and high density optical packaging concepts are required. We describe the development of board-level interconnects based on polymer waveguide technology. In this paper, we focus on flexible optical waveguide sheets and the passive alignment of optical connectors.
We present a novel approach for packaging high-speed opto-electronic 12x-array devices in a compact, low-cost package
for waveguide-based intra-system links. In order to avoid optical signal loss and crosstalk, the mutual alignment between
PCB-embedded multimode waveguides and the opto-electronic components needs to be in the order of 5-10 micrometer,
which is an order of magnitude tighter than standard PCB manufacturing tolerances. Our packaging concept uses a
combination of passive alignment steps, tolerance stackup reduction and a misalignment-tolerant coupling scheme in
order to bridge this gap in a cost competitive way.
Using flip-chip technology, the opto-electronic components are placed onto a very thin substrate with holes for the light
path. The top side of the 25 μm liquid crystal polymer (LCP) substrate not only provides fast and low-loss electrical
connections, but also serves as alignment reference plane for the entire module, avoiding alignment tolerance
accumulation over different assembly steps. Openings for the laser beams, passive lens alignment features, centering
holes for mechanical alignment pins between module and board and optional MT-guide receptacles are all laser-cut
within one single process step, with a precision better than 5 μm. A similar approach is used for the PCB-side optics, and
a lens-pair coupling scheme provides for a sufficiently large misalignment tolerance between the package and the PCB.
Mechanical rigidity of the package and thermal protection are provided by an epoxy filled aluminum frame.
We will present our design considerations, the basic package concept, the actual experimental implementation and
characterization results of our first prototype package.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.