Contract manufacturers make strides in active components

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The sourcing and manufacture of the transmitter and receiver optical subassemblies (TOSAs and ROSAs) are the most costly and precisely manufactured parts of a transceiver. Contract optoelectronic-component manufacturers with materials management supply-chain and precision manufacturing competencies are realizing high-volume cost-effective manufacturing of these complex components. As optical components have migrated from the long-haul (LH) network to metro and access applications, which require higher volumes, automation companies and manufacturing service providers are working together to develop manufacturing processes. The expertise that these partnerships bring to equipment companies will make fiber to the home (FTTH) an affordable option for consumers.Th 159447

Photo 1. Disciplined cleanroom protocol is essential for the manufacture of complex precision optomechanical and electromechanical devices as shown in this facility operated by Fabrinet in Thailand.

A contract manufacturer specializes in precision manufacturing of complex optomechanical and electromechanical devices (see Photo 1). They perform contract assembly on a range of passive and active optical components, including optical switches, integrated power monitoring modules, wavelength lockers, fused fiber couplers, three-port filters, variable optical attenuators, laser modules, TOSAs, ROSAs, and transceivers as well as optical modules such as EDFAs, cable TV transmitters, triplexers, DWDM multiplexers, and tunable optical detectors.

Since the optoelectronic package is a hybrid processor of both electronic and photonic signals, a plethora of unique materials are used in device fabrication. This variety of materials is one of the factors that distinguish optoelectronic-device assembly from conventional microelectronic manufacturing. Devices may be manufactured from a variety of materials, including silicon, quartz, doped silica, lithium niobate, gallium arsenide (GaAs), and indium phosphide (InP). Vertical integration of manufacturing links material procurement with production and shortens the supply chain, resulting in savings in procurement, packing, and shipping costs.

Modules that incorporate active laser diodes (LDs) and photodiodes (PDs) represent 80%-90% of optical-component value today. Over the next several years, growth will primarily be focused on data communications applications and shorter-reach access/metro telecommunications applications. LH backbone networks have sufficient capacity today, and growth in this area will be very limited in the near-term.

Overall, unit shipments of transceivers were only 4% lower in 2003 than in 2000, according to electronics industry consultant Prismark Partners (Cold Spring Harbor, NY). But in value terms, the overall market decline between these years was 55% (see Table). Continued price erosion can be expected over the next five years and cost reduction will be an important differentiator going forward as the industry focus will be on cost-sensitive markets (e.g., metro and access).Th 159450

Total transceiver units are expected to increase by an average rate of about 19% per year through 2009 to 37 million units (compared to 12.9 million last year). Most telecom optical-component growth over the next several years is anticipated for low-speed telecom products (<2.5 Gbits/sec), including FTTH. In the context of component manufacturing, the majority of these components will be produced in transistor-outline (TO) packages.

LDs and PDs are commonly packaged in TO-cans for lower-data-rate and shorter-distance communications applications. The LD or PD is first mounted onto a submount, which is in turn mounted onto a TO-can header. At lower data rates (e.g., 100 Mbits/sec), silver-filled epoxy die attach is commonly used as the die attach medium. But at higher data rates (e.g., 1 Gbit/sec), gold-tin solder is predominantly used for optimal thermal management. The LD bonding process requires a placement accuracy of between 5 and 20 µm (true position radial), depending on the application (transmission distance and data rate). The PD die bonding accuracy requirement is about 20 µm.

TO-cans are the most common LD and PD package today for applications below 2.5 Gbits/sec, and they will continue to be the highest-volume package configuration in the future. In addition, TO-cans are often used for low- to mid-end telecom LDs as well, incorporating a silicon microbench with lenses and mirrors.

Precision eutectic component attach, which is shown in Photo 2, includes pick and place of silicon, GaAs, or InP chips; in-situ reflow of preform or pre-tinned devices in concert with programmable x-, y-, or z-axis agitation; and programmable pulse heating or steady-state temperature.Th 159448

Photo 2. Automated precision eutectic component attach in transistor-outline (TO)-packaged transceivers is facilitated by quick-change tooling that secures the devices during assembly and eliminates the need for an operator to handle individual components.

The reflow profile during an in-situ eutectic die-attach process is engineered to provide consistent melting and a void-free attach interface. That results in consistent heat transfer from the LD and contributes significantly to temperature stabilization during laser operation.

Physical, thermal, electrical, mechanical, assembly, and manufacturability considerations, in addition to price and time-to-market, challenge the package designer. These same issues face the equipment designer who must not only satisfy current requirements, but also anticipate the capabilities that will be required in equipment platforms five years ahead. Machine architecture and functional advances have been enabled by large-area air bearings, accurate linear motors and encoders, voice coil drives, powerful machine software, and rich graphical user interfaces. Equipment capable of placing p-side-down LDs with an accuracy of 1.5 µm, 3 sigma at production rates in an equipment footprint less than one square meter is currently available. With these tools, it is important for equipment suppliers in the optoelectronics market segment to endeavor to understand their customer’s processes to an even greater degree than the companies themselves. That is especially true in the case of complex process automation such as the exercise of automating complex dispense and die attach processes, high I/O wire bonding, and active optical alignment.

Augmenting production capabilities with automated high-precision assembly systems enables high yield at high-volume production levels, revenue growth, and improved margins for both OEMs and electronic manufacturing services (EMS) companies. New higher-volume optoelectronic components requiring scalable manufacturing capacity dictate a cost-effective manufacturing strategy tailored to meet the unique demands of precision optical-component assembly.

A new model for EMS emerged after the telecom bubble burst. A highly educated and available workforce of trained operators, technicians, and engineers, even in many low-cost geographies, now provide OEMs the option to outsource complex assemblies and reduce their manufacturing costs. Today, a growing number of EMS companies specialize in the assembly of complex electronic and, in a limited number of cases, mechanical and optical devices. A select number of these EMS companies possess an existing base of engineering expertise and manufacturing technology, guard-banded IP protections, and traceability of materials, manufacturing, and engineering from procurement through shipment of finished goods.

OEMs are outsourcing the manufacture of TOSAs and ROSAs for a variety of reasons. One of the essential core competencies that an OEM requires of an EMS provider is engineering strength, specifically the ability to develop and customize the manufacturing process to fit the manufacturing requirements in terms of cost, yield, and lead-time, while at the same time protecting the intellectual property (IP) of their client.

One of the tools that an EMS company has at its disposal to enable cost reduction of active optical components is production volume. By sharing the cost of capital, infrastructure, and supporting team, the EMS company manages fixed costs. In addition to fixed-cost sharing, other tools are commonly used in cost reduction programs, including 6 sigma strategies to maximize yield and minimize defects, turnkey material procurement, and capacity planning to maximize the facility utilization.

From the EMS company’s viewpoint, each customer has its own specific design, all of which require somewhat different manufacturing approaches. The machines used in manufacturing must be set up specifically for each product. But when the machines are used for multiple products, the changeover time becomes significant to the utilization rate of the machine (see Photo 3). Therefore, engineers, technicians, and operators involved in optoelectronics package manufacturing are required to understand the manufacturing process/machine more thoroughly and have higher assembly skills than is required in typical microelectronic package assembly.Th 159449

Photo 3. Different manufacturing approaches, often driven by specific product designs, are facilitated by flexible tooling such as the gold-tin pulse-heat reflow stage (shown here) that can handle a range of package sizes and formats with relatively quick changeover.

Several EMS companies now provide full vertical integration for optical-device manufacturing with turnkey material services. The result is an EMS component manufacturer with ISO 9001:2000-, 14001-, and TS 16949-certified facilities; a materials management supply chain; Oracle-based information technology; and a Web-based manufacturing tracking system.

A major concern of OEMs in making the decision to outsource complex processes is the ability of the potential EMS partner to securely protect the OEM’s IP from competitors. OEMs today are defining their core competencies and more willing to outsource all other operations. However, a company’s IP is its main asset, thus the reluctance to pass more complex processes onto an EMS company. In addition, with the trend for EMS companies to specialize in a particular market sector or technology, how does that company handle multiple customers that are direct competitors of each other?

Most EMS companies realize that their ability to conduct business depends on their credibility, honesty, and ability to safeguard customer IP, so many have put processes in place to ensure that the OEM is comfortable with the EMS it has selected. One method of addressing the IP issue is the factory-in-a-factory concept. In this model, the EMS company provides dedicated personnel and floorspace to a specific OEM. When requested, some EMS companies have guard-gated or keycoded areas for specific customers. It is important that all IP concerns and expectations be addressed at the time the contract is negotiated. The OEM should conduct due diligence in researching the history of IP protection before selecting an EMS company and manufacturing geography.

Manufacture of low-cost active components is beginning to hit its stride. The equipment and process expertise that contract manufacturers are developing today will not only facilitate the efficient manufacture of optical components, but will also enable component designers to continue to push the envelope of communications technology into the foreseeable future.

Bruce W. Hueners is vice president of marketing at Palomar Technologies (Vista, CA) and Paleerat Lakawathana is senior engineering manager at Fabrinet (Bangkok, Thailand). Dr. Nutchai Sroymadee, a senior engineer in Fabrinet’s optical engineering department, contributed to this article.

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