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Photonics Assembly in an EMS Environment, Series in Optoelectronics, Part II:
December 31, 1969 |Estimated reading time: 3 minutes
This second part of a two-part series discusses rules that must be followed for successful optoelectronic manufacturing.
By Glenn Woodhouse
There is considerable effort in module miniaturization taking place to facilitate the on-board incorporation of modules into optoelectronic board designs and as a means to lower costs for what traditionally has been a high-cost device. Optical/photonic modules integrate supporting digital and power circuitry with active photonic components to produce standard and application-specific functional photonic receivers, transmitters and transceivers. Typically ranging from 0.50 x 1.0" to 6 x 6", photonic modules are far from simple, using the latest in SMT advances. These substrate-based assemblies incorporate SMT devices including passives down to 0201s, microBGA, TSOPs, TQFPs, fine-pitch SOICs to 0.4 mm and high-density area-array SMT connectors.
For the state of the electronics manufacturing services (EMS) industry today, with regard to manufacturing capability, this synthesis of SMT and photonic components is where the most logical opportunity for market entry lies. The EMS provider can augment SMT core competencies with new capabilities in the areas of photonic device handling, assembly and test for photonic module manufacture. Both the photonic component and optical network system OEM would be potential customers to an EMS provider offering photonic module assembly and test services.
This augmentation of the EMS provider's core competencies cannot be taken lightly. To support these activities, the EMS provider must acquire new tools. In some cases, these tools may not be readily available and must be developed by the provider. Photonics assembly is an entry into a strange new territory that affords the EMS provider little luxury in drawing upon existing process technology knowledge. A process engineer who has mastered the art of convection reflow profiling will be at a loss if asked to develop or troubleshoot an optical fiber fusion splicing profile. None of the rules of soldering apply to fiber splicing. A new mindset is required that comes with training, practice and experience. Prior to any photonic component integration, the photonic module will go through SMT assembly and in-circuit test (ICT). Active and passive optical components then are mounted and interconnected via fusion splicing and optical fiber connectors are installed. Any remaining optical fiber pigtails for interface with the optoelectronic datacom board are terminated at this time as well.
Without special training, an SMT or test operator, technician, or engineer is unprepared to handle optical fiber, fiber terminations/connectors and photonic modules, which incorporate optical fiber pigtails and terminated cables.
There are new rules for optoelectronic manufacturing, including:
- Safety — Disconnected optical connectors may emit radiation if the far end is coupled with a working laser or light-emitting diode (LED). Do not view the fiber end of a cable or plug with an optical instrument until absolute verification is established that the fiber is disconnected from any laser or LED source. Short segments or "shards" of raw optical fiber can enter the skin, eyes and mouth. Workers must wear protective equipment such as gloves and safety glasses.
- Handling — Fiber should be handled carefully without pulling, twisting or bending.
- Bend Radius — The recommended minimum bend radius for SMT fiber routing and handling is 1".
- Cleaning — Fiber connector performance is degraded by the presence of contaminants. Compressed air and isopropyl alcohol cleaning of fiber connectors should be performed as a final step in the assembly operation. Dust caps should remain on all unused connections
As simple as these rules sound, it is easy to violate the minimum bend radius rule. For example, fiber can be overstressed during transportation of a photonic component or module from its bubble pack to a workstation by not paying attention to how the fiber coil is supported. Additionally, it generally is not possible to detect if the fiber has been damaged until the photonic device is mounted to the optoelectronic board later in the process and a downstream functional test is performed. Module fiber pigtail replacement or repair generally is not an option. Also, an order of magnitude in manufacturing process cleanliness and awareness is required.
Glenn Woodhouse, formerly of Plexus, may be reached at Schweitzer Engineering Laboratories; (509) 334-8726; E-mail: glenn_woodhouse@selinc.com.