Fiber cable assembly reaches new levels
By RANDY REAGAN, FONS Corp. -- Improvements in the fiber-optic cable assembly process allow a new level of performance while reducing costs.
Improvements in the fiber-optic cable assembly process allow a new level of performance while reducing costs.
The slump in the fiber-optic industry has put customers in the driver's seat with respect to setting expectations for fiber-optic cable assemblies. Today customers expect to buy cable assemblies that have higher quality and performance than ever before, yet wish to pay significantly reduced prices versus those of just a few years ago. Cable assembly suppliers are faced with seemingly impossible demands -- improve product quality and performance while reducing costs. How can suppliers respond?
Current standards provide a backdrop -- and a blue print -- for success. Customers today select cable assemblies based on insertion loss, back reflection, and end-face geometry using the Telcordia standards as a basis for performance criteria. Thus, to ensure fiber-optic cable assemblies meet customer performance requirements, manufactures design their products and processes to conform to these Telcordia requirements. For instance, singlemode cable assemblies must conform to criteria found in Telcordia GR326-CORE, Issue 3, "Generic Requirements for Singlemode Optical Connectors and Jumper Assemblies." This standard is widely recognized as the most rigorous baseline for fiber-optic cable assembly performance and reliability.
In this context, leading suppliers have focused on overall process and quality improvement. Process changes may include improvements in the areas of materials, calibration, assembly, testing, facilities, training, quality control, and certification. As a result of quality and process improvement efforts, manufacturers can now provide a new level of performance while achieving significant cost efficiencies.
Materials used in fiber-optic cable assemblies must be carefully specified to achieve performance and reliability over a range of applications and environmental conditions. Manufacturers today carefully specify design dimensions and material properties for components including cords, connector bodies, ferrules, strain relief, and boots to optimize the cost-performance equation.
Often, changes to materials and components are required to achieve enhanced performance and improvements in cable assembly yields. Changes are implemented only after thorough qualification testing to ensure that performance and reliability can be maintained while achieving low costs. Materials and components are qualified using a complete analysis and testing regime so that changes can be introduced without degrading the quality of the assembly process or the product.
Equipment used in the manufacture of fiber-optic cable assemblies is subject to repeated use and wear. For instance, stripping tools and polishing pucks wear over time. Polishing paper can wear throughout the day. Test instruments need periodic adjustments and recalibration.
If any one piece of equipment is out of calibration it can result in reduced throughput and cost inefficiencies. Therefore, it is imperative to institute a program for calibration and periodic recalibration for each piece of equipment used in the cable assembly process. Assembly equipment in the manufacturing cell -- including stripping machines, crimping machines, epoxy application machines, polishing machines, and test equipment -- are periodically calibrated.
A carefully designed program of calibration at optimal intervals is required to maximize the up time of the assembly line and avoid rework. Samples are reviewed several times during each shift to ensure the overall process is in calibration and that products are meeting end-user requirements. As an added step in the overall calibration, product samples are periodically reviewed to compare performance against Telcordia criteria.
In the past, manual operations typically have dominated the cable assembly process. While most assembly types still require some manual tasks, there is a trend towards increased automation throughout the process. Automation is especially effective where designs are standardized -- for instance, where a single cable and connector type are specified. Automated tasks result in greater consistency and can improve the throughput of the overall assembly line. The trend toward automation has helped to improve yields and performance in the overall process.
Manufacturers currently use automation in the stripping process to help improve consistency and eliminate fiber breakage. Automated crimps are used to overcome inconsistencies in hand operation by applying uniform and complete pressure, thus making the mechanical joining of fiber cord to connector much more reliable. Automated mixing and dispensing machines bring consistency to epoxy application. Newer automated curing ovens provide complete control of the cure temperature, thus providing a uniform temperature distribution and duration of cure. New cure cycles have been developed to provide optimized temperature and cure duration to ensure a totally cured epoxy. Each parameter of the polishing procedure is optimized to bring tighter controls to the assembly process. This includes specifying polishing pucks and paper to achieve high quality and following a prescribed algorithm for the polishing machine speeds and pressures.
With the improved automated assembly process, bar codes are used throughout to provide tracking of components and consumables, calibration data for equipment, test records, and the names of technicians responsible for carrying out the process. The process incorporates automated data acquisition and recording so that product performance can be monitored and improved using statistical process control (SPC).
Testing cable assemblies is still a critical part of the cable assembly process. Insertion loss testing and return loss testing are performed to ensure that products meet desired performance levels. Data are collected and used to monitor the assembly process and indicate where further improvements can be made.
The improved assembly process also institutes a geometry check on fiber ends using highly automated interferometers to ensure proper radius and fiber protrusion on the connector ferrule end face. The geometry data are recorded in a database as part of the permanent test record for the product. The geometry testing data are also correlated and used as feedback to continuously maintain tight controls over the endface geometry. Finally, inspection techniques have been developed that aid technicians in visual inspection resulting in end faces that are free of defects.
Particulates and contaminants of sub-micron dimension can adversely affect key fiber-optic cable assembly procedures such as polishing and testing. To achieve the high performance now required in fiber-optic cable assemblies, upgrades to manufacturing facilities are often needed to improve the assembly environment. This involves constructing a cleanroom environment to provide a controlled and monitored atmosphere for finishing and testing cable assemblies. It is often necessary to provide appropriate training and monitoring of cleanroom techniques to achieve maximum benefits from the new environment.
An updated training program is also instrumental in achieving new levels of performance. A thorough training program emphasizes proper techniques and procedures for cable assembly.
All technicians are required to complete a basic training course prior to handling fibers. Technicians are also retrained at a minimum frequency of once a quarter to ensure they are exposed to the latest techniques for high-performance assembly. In addition, specialized training courses are provided to certify technicians in polishing, testing or other procedures.
Quality control continues to be vital to the cable assembly process; in-process inspections and audits are used to ensure that proper procedures are being followed throughout. The improved assembly process incorporates in-process checks and requalification procedures that ensure consistent and ongoing adherence to proper procedures. These checks look at both procedural-based and performance-based criteria. This not only ensures that the cable assemblies are manufactured according to plan, but that they are being manufactured to performance standards defined by the customer. The checks are done in parallel to minimize rework, reduce the overall cost and improve manufacturing throughput.
Customers expect their fiber-optic cable assemblies to perform consistently throughout a rigorous installation and service life. One level of prediction of the product's ability to serve in the intended application is its ability to stand up under the performance and environmental tests found in Telcordia GR326-CORE. As such, fiber-optic cable assembly suppliers strive to satisfy this standard through independent testing. The goal is to provide customers with independent test data showing conformance to the requirements thus certifying to customers that products will meet requirements throughout their intended service life.
With the improved cable assembly process, manufacturers can satisfy the certification requirements and additionally achieved higher performance levels for almost all of the objectives set by Telcordia in GR-326-CORE, Issue 3. Improving the design along with the process for assembly offers customers new levels of performance and cost efficiencies.
Randy Reagan is director of product management and business development at FONS Corp. (Northboro, MA); www.fons.com.