This is part three of a three part series on fiber cleaning. For part two, click here.
From the August, 2014 Issue of Cabling Installation & Maintenance Magazine
By Sean Sheedy
Unless you are working in the tropics, never select a water-based fiber cleaner. It is very slow to dry and will freeze in cold weather.
One excellent characteristic of IPA is its ability to dissipate static. With a static charge, particulate will bind to surfaces surprisingly aggressively. For example, a large 500-micron (μ) particulate takes twice the force of gravity (2 G's) of "scrubbing" (mechanical action) to remove. But a 5-μ flake of solid residue takes 20,000 G's to break loose from the intermolecular grip the particulate has on the substrate. How do you get 20,000 G's of scrubbing force inside an LC connector? You don't. So solvents help solve the problem by neutralizing the static charge.
In the past decade there have been at least two studies looking at static on endfaces. iNEMI's results were presented in "Accumulation of Particles Near the Core During Repetitive Fiber Connector Matings and Dematings," at NFOEC in 2007. And during the development of the IPC-8497-1 standard, 18 researchers worked on the problem of static. Their findings were presented in "Cleaning Methods and Contamination Assessment of Optical Assembly," at NFOEC in 2006. This research clearly observed that wiping an endface with a dry wipe did not dissipate the static on the endface, and indeed may have added a triboelectric charge to the endface, which made the endface even more prone to attracting particulate. This problem was eliminated with a wet-dry cleaning process, in which a cleaning fluid was used to dissipate the static, and then a dry wipe was used to polish away any residual fluids. This is an excellent procedure and should be used by everyone in the fiber industry.
Remember, today's lasers are more powerful than previous designs. Applications such as WDM use lasers that are extremely sensitive to reflectivity and contamination. These new systems are not only reinforcing the importance of cleaning, but are requiring a migration to a next generation of cleaning materials that do not exchange one issue for another.
Cleaning during splicing
When it comes to splicing and connectorization, a common misconception is that one does not need to be concerned about cleaning, except at the very end of the assembly process. Not true. Once all the coatings have been stripped off from a fiber, it needs to be cleaned with a damp, lint-free wipe to remove any remaining debris. If the fiber is going to be spliced, the cleaned fiber will be placed in a cleave tool, cleaved, and then placed in the V-grooves of a fusion-splice machine or inserted into a mechanical splice. All of these components must be properly cleaned or the splice could be optically defective or mechanically weak.
If the fiber is going to be connectorized, the strand of cleaned fiber will be inserted through a connector body and ferrule. Given that singlemode ferrules have a tolerance of +/- 1 micron and multimode ferrules are only slightly more generous, any debris or moisture has the potential to clog the ferrule, which creates one of two following scenarios. And this is when things get messy.
Scenario 1: As the technician attempts to insert a dirty fiber through a connector, the contamination on the fiber exceeds the tolerances of the connector. This makes the path too restrictive and the fiber fails to pass freely through the ferrule. In most instances, the fiber binds and breaks off within the ferrule. The technician now needs to begin the process again, wasting time and inventory.
Scenario 2: During the connectorization process, the target connector always is prepared with very quick-curing anaerobic epoxy. If the bare fiber still has debris on it when the technician inserts the fiber into the connector, the debris will mix with the adhesive and clog the ferrule. This has the potential to slow the insertion of the fiber into and through the connector and the ferrule. If this delay exceeds the allotted curing time, which can easily happen, the epoxy will cure before the process is successfully completed. Once again, the technician's efforts are wasted, costing time and money.
The wet-dry cleaning technique is important for cleaning ports, as well as cleaning exposed endfaces. In the first photo, a technician dampens a cleaning swab with a nonflammable, fast-drying cleaning fluid. In the second photo he is inserting the cleaning tool into the port to ensure no residues remain on the endface.
Both of these scenarios can be avoided by proper cleaning.
One last threat-not as critical as those detailed above, but still worth mentioning-lies in the corrosive properties of certain cleaning materials. In years past this was not considered to be an area of concern or a threat to the network, but it is now. Damage caused by corrosive cleaners can include destabilizing the bonds of epoxies used to terminate connectors and pitting of newer ferrule materials. In addition, there is the very significant issue of chemically sensitive users and the evolving regulations affecting chemical handling, storage and shipping.
40 years of learning
We cannot say it often enough: Cleaning is essential for today's fiber networks. There are quality companies offering a wide selection of connector and splice cleaning products that have addressed all of these issues. The selecting of a cleaning product today is a very different process than it used to be. Though isopropyl alcohol is commonly used to clean off bare fibers for splicing, insufficiently pure IPA can leave a reflective film on the endface, has too slow an evaporation rate, and can be corrosive to connectors. Look for cleaning fluids that dry quickly (i.e. do not allow any moisture to remain on the connector or trapped in the alignment sleeve), do not have corrosive properties, and are nonflammable, easily transported, environmentally friendly and vapor-free. Look for wipes that are made with synthetic fibers, do not include cellulose and do not have glues in the paper. The best wipes should be small and easily disposable, so there is no inclination by the tech to re-use the wipe.
About the Author
Sean Sheedy has worked for more than 20 years as a fiber-optic installer, troubleshooter, system designer, emergency-restoration technician inspector, project manager, sales manager, and consultant. He holds 30 industry-related certifications and is a certified instructor with The Fiber Optic Association and The Electronics Technicians Association. He has also developed and teaches fiber optic/copper communications installation and troubleshooting training courses. His experience includes work in all divisions of the military, various government agencies, federal and state prisons, as well as the commercial markets. He can be reached at firstname.lastname@example.org.