NEPCON West - Fiberoptic Expo Conference Proceedings


FROM SUPPLIERS TO EMS: REVIEW OF THE FACTORS AFFECTING CLEANLINESS OF FIBER OPTIC CONNECTORS

Author: Tatiana Berdinskikh et al.
Company: Celestica International, Inc
Date Published: 12/3/2002   Conference: NEPCON West - Fiberoptic Expo


Abstract: Optical interconnect technology is the preferred solution for high speed communications. A particular area of application includes Gigabit Ethernet. The current trend is the extension of Ethernet into metro networks, which will require reliable, low cost interconnect solutions.

Cleanliness of fiber optic connectors is recognized as a basic requirement for the successful operation of optical networks. The importance of cleanliness standards for fiber optic connectors has been realized. In many cases the specification used by the Fiber Optic Connector Supplier doesn’t exactly match the user/customer specification. These differences in specifications resulted in non-conforming material at user/customer sites. The acceptance of the customer specification by one of our optics suppliers improved the quality of the incoming parts by approximately 30%.

Extensive failure analysis data on contaminated fiber optic connectors is presented. The contaminants have been analyzed by Field Emission Scanning Electron Microscopy (FE-SEM), X-ray inspection, SEM-EDX, and Fourier Transform Infrared Spectroscopy (FTIR). Based on our data, some critical processes of cable manufacturing, pig tail termination, module assemblies (transmitter, receiver, transceiver), and board and system level assemblies that are affected by contamination of fiber optic connectors have been identified.

For example, it was found that the polishing of connector endfaces is one of the critical processes for cleanliness of fiber optic connectors. Improper control of the polishing process results in contamination of the connector endface with silicon dioxide (non-removable contamination) and metallic particles (stainless steel) trapped in the epoxy ring. Insufficient cleaning performed between the two stages of the polishing process resulted in a pitted appearance. In both these examples the performance of the installed component is affected.

Examples of contamination identified on OC-48 transceivers with SC duplex-type connectors and lens surfaces of 1.3 µm wavelength MQW-FP (Multiple Quantum Well Fabry- Perot) laser diodes are presented. It was found that the contamination of OC-48 transceivers with urethane was due to the conductive foam used as packing material for optical ports shipped without dust caps. The polyphenylene sulfide contamination of the Tx ports was identified as the same material in the inner housing of the Tx ports. The welding sleeve operation for laser manufacturing was identified as another critical process that resulted in the contamination of 32% of all parts.

Extensive experimental results are presented on the influence of dust caps on the cleanliness of fiber optic connectors. The quality of incoming parts was controlled by visual inspection of 32 parts per lot and monitoring of DPPM (defective parts per million). A correlation between the cleanliness and the type of dust cap has been identified. The Polyvinyl Chloride (PVC) dust cap was found to be one of the main sources of contamination, affecting about 80 - 90% of the parts protected with this type of cap. A significant improvement (70-80 %) in quality of incoming parts was achieved by the replacement of PVC dust caps with polyethylene ferrule-type dust caps. The DPPM level of incoming parts with different variations of the ferrule-type caps (materials and design) was in the range 200,000 to 300,000. The best results were achieved with a polycarbonate mouth-type dust cap, specially designed for ST connectors. The implementation of the mouth-type dust cap decreased the DPPM level of incoming parts to 60,000-70,000, about 80%.

Finally, the contamination of optical fiber connector endfaces caused by electrostatic charge (ESC) effects during the cleaning process has been investigated. The charged connector can attract metallic and dust particle contaminants from many sources including standard manufacturing environments, dust caps, adapters, matched connectors, etc. The ESC effect also results in the contamination of fiber optic connectors during the storage process, if the non-cleaned dust cap has been used. The improved cleaning process includes the application of air ionizers and cleaning cassettes with improved ESD capability. Prevention of the ESC effect is important at connector, module, board, and system level assembly, especially if the assembly process is not performed in a clean room environment.

The prevention of contamination of fiber optic connectors will result in the reduction of inspection and cleaning process times, elimination of dirty connector false failures during test, manufacturability improvement, and finally in cost reduction of product assembly.



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