Benson Chan

Terabit/s-Class Optical PCB Links Incorporating 360-Gb/s Bidirectional 850 nm Parallel Optical Transceivers

We report here on the design, fabrication, and characterization of highly integrated parallel optical transceivers designed for Tb/s-class module-to-module data transfer through polymer waveguides integrated into optical printed circuit boards (o-PCBs). The parallel optical transceiver is based on a through-silicon-via silicon carrier as the platform for integration of 24-channel vertical cavity surface-emitting laser and photodiode arrays with CMOS ICs. The Si carrier also includes optical vias (holes) for optical access to conventional surface-emitting 850 nm optoelectronic devices. The 48-channel 3-D transceiver optochips are flip-chip soldered to organic carriers to form transceiver optomodules. Fully functional optomodules with 24 transmitter + 24 receiver channels were assembled and characterized with transmitters operating up to 20 Gb/s/ch and receivers up to 15 Gb/s/ch. At 15 Gb/s, the 48-channel optomodules provide a bidirectional aggregate bandwidth of 360 Gb/s. In addition, o-PCBs have been developed using a 48-channel flex waveguide assembly attached to FR4 electronic boards. Incorporation of waveguide turning mirrors and lens arrays facilitates optical coupling to/from the o-PCB. Assembly of optomodules to the o-PCB using a ball grid array process provides both electrical and optical interconnections. An initial demonstration of the full module-to-module optical link achieved >; 20 bidirectional links at 10 Gb/s. At 15 Gb/s, operation at a bit error ratio of <; 10- 12 was demonstrated for 15 channels in each direction, realizing a record o-PCB link with a 225 Gb/s bidirectional aggregate data rate.

Terabit/sec-class board-level optical interconnects through polymer waveguides using 24-channel bidirectional transceiver modules

We report here on the design, fabrication and characterization of an integrated optical data bus designed for terabit/sec-class module-to-module on-board data transfer using integrated optical transceivers. The parallel optical transceiver is based on a through-silicon-via (TSV) silicon carrier as the platform for integration of 24-channel VCSEL and photodiode arrays with CMOS ICs. The Si carrier also includes optical vias (holes) for optical access to conventional surface-emitting 850-nm optoelectronic (OE) devices. The 48-channel transceiver is flip-chip soldered to an organic carrier forming the transceiver Optomodule. The optical printed circuit board (o-PCB) is a typical FR4 board with a polymer waveguide layer added on top. A 48-channel flex-waveguide is fabricated separately and attached to the FR4 board. Turning mirrors are fabricated into the waveguides and a lens array is attached to facilitate optical coupling. An assembly procedure has been developed to surface mount the Optomodule to the o-PCB using a ball grid array (BGA) process which provides both electrical and optical interconnections. Efficient optical coupling is achieved using a dual-lens optical system, with one lens array incorporated into the Optomodule and a second on the o-PCB. Fully functional Optomodules with 24 transmitter + 24 receiver channels were characterized with transmitters operating up to 20 Gb/s and receivers up to 15 Gb/s. Finally, two Optomodules were assembled onto an o-PCB and a full optical link demonstrated, achieving > 20 bidirectional links at 10 Gb/s. At 15 Gb/s, error-free operation was demonstrated for 15 channels in each direction, realizing a record o-PCB link with a 225 Gb/s bidirectional aggregate data rate.

BGA sockets-a dendritic solution

Todays high density technology requires a large number of I/O pins in CPU packages. The direct soldering of these devices can lead to solder joint reliability concerns. The sockets can provide a cost-effective solution in such applications when it comes to equipment upgrades and reducing the rework cost of CPU replacements. The sockets allow the mother boards to be assembled off shore and imported with low tariffs. The CPUs can then be inserted on the planar according to the demands of US market. This paper compares the current BGA socket technology and describes a low profile BGA/LGA socket based on dendrite technology developed by IBM Microelectronics Division.

225 Gb/s bi-directional integrated optical PCB link

We report a bidirectional optical link through polymer waveguides integrated on PCB. With 15 channels at 15 Gb/s (BER &#60;10−12 and &#60;10 pJ/bit), the channel and aggregate bandwidths are the highest reported for waveguide interconnects.

AC coupled interconnect using buried bumps for laminated organic packages

Various techniques for providing non-contacting, interchip signaling have been demonstrated, such as: ACCI presented in S. Mick et al. (2002) and L. Luo et al. (2005), proximity communication based in R. Drost et al. (2004), and wireless superconnect (WSC) reported in K. Kanda et al. (2004). ACCI using buried bumps is the only technology that provides a manufacturable solution for non-contacting I/O signaling by integrating high-density, low inductance power and ground distribution with high-density, high-speed I/O. This completely integrated solution has been demonstrated at 2.5Gb/s/channel across 5.6cm of micro-strip transmission line using 0.35mum CMOS ICs that were flip-chip attached onto a silicon MCM-D as presented in J. Wilson et al. (2005)

Packaging aspects of the Litebus/sup TM/ parallel optoelectronic module

The Litebus module is an optoelectronic transceiver and the key component in a parallel fiber optic data link. The module is designed to extend computer-to-computer communications to data rates and link distances beyond those achievable in copper at comparable cost. A transceiver configuration was selected to keep the modules size compact (45 mm/spl times/32 mm/spl times/ 9.8 mm) and to facilitate the integration of an IEC Class 1 laser safety strategy. The Litebus module consists of various packaging components and both CMOS and optoelectronic dies. It is designed to accept a single connector, having one receive and one transmit section, that is mounted on the end of a dual 12 channel fiber optic ribbon cable. Channel-to-channel spacing is 250 /spl mu/m throughout and standard multimode fiber is used. The transmitter consists of a VCSEL (Vertical Cavity Surface Emitting Laser) source having a wavelength of 850 nm. The receiver consists of a transimpedance amplifier with integrated Metal-Semiconductor-Metal (MSM) detector. The modules transmit and receive sections were designed to operate at data rates greater than 1.25 Gb/s (gigabits per second) per channel, yielding a maximum aggregate data rate in excess of 15 Gb/s. In one mode of operation, byte-wide data is simultaneously transmitted from and received by the module at 1.25 GB/s (gigabytes per second), with the four remaining channels on each side being assigned to user-defined overhead functions. The maximum cable length is 400 m in asynchronous mode and 200 m in synchronous mode.

Organic optical waveguide fabrication in a manufacturing environment

Optical waveguides based on organic materials have been fabricated in a laboratory environment but the scaling and manufacturing processes needed to produce these waveguides have been scant. The volume production of low loss organic waveguides in a conventional state of the art Printed Circuit Board (PCB) manufacturing plant has proven to be challenging both from processing and equipment set perspectives. In collaboration with IBM and Dow Chemicals, Endicott Interconnect (EI) has developed scalable processes that can be implemented in a manufacturing environment. Our contribution is to refine and adapt the processes developed by our collaborators to provide the basic frame work required for the volume manufacturing of organic optical waveguides. The resulting organic optical waveguide yields and cost are the most important consideration in this development work. In this paper, we will show various organic optical waveguide samples using the fabrication methods developed in this work. A detailed discussion of: all the processes, materials and equipment sets that are employed in the fabrication of the organic optical waveguides will be presented. The preparation of substrates to be used as the base for waveguide build up layers is described. The need for clean room processing steps for the subsequent fabrication of optical layers will be explained. Rational of fabrication tool set and process selection will be discussed. Loss measurement test equipments and test strategy of organic optical waveguides will also be described. Finally, waveguide reliability and loss measurement results will be presented.