Soiled connector end-faces are responsible for more downtime and wasted time when managing fiber optic networks than any other single cause. Whether you are long haul or local network, CATV or Telco, Military or 911/DOT, you can prevent most of these problems if you know how to use the proper connector cleaning tools and procedures.
For anyone new to fiber optics, I’d first like to explain that a connector end-face is the tip of the connector ferrule. It is held in precise alignment with an “alignment sleeve” or precision pins that enable high speed light to be passed through the connection. This alignment enables the fiber to be mated properly with another fiber in a connector, adapter or equipment port. The point at which two mated fibers come together is potentially the “weakest link” in any fiber optic network. To work properly, each of the end-faces must be absolutely clean using proper procedures. Not all cleaning methods provide the best results.
The importance of inspecting the connector end-face with a video microscope before and after cleaning can not be over-stated. This practice enables the technician to decide whether to accept, re-clean, re-polish or replace a connector. Don’t rely on a power meter to determine whether or not connectors are clean.
The Science of Cleaning
“Clean-room grade” materials are required when cleaning fiber optics. These materials are designed to clean gently and effectively without leaving behind un-removed soils, lint or chemical residue. A cleaning process must not damage either the end-face or sensitive plastic components.
Paper and cotton are not acceptable as they easily tear or shred and can deposit lint-like residues. Acceptable are certain non-woven materials, high-quality microfibers and precision clean-room grade foam. Always seek “clean-room grade” products from established sources. Cleaners vary in terms of worker-safety, plastic compatibility, environmental impact, cost and most importantly the effectiveness of the cleaner itself. A higher price is not always an indicator of higher quality, yet lower cost items should always be scrutinized.
There are two well-known procedures for cleaning fiber optic connections, Dry Cleaning and Wet Cleaning. A relatively new cleaning procedure, Compound (Combination) Cleaning, combines the best procedures used in Wet and Dry Cleaning and removes the widest range of OSP and OEM soils.
Although tools and procedures may vary, all three cleaning methods can be used to clean connectors on the both the jumper side and backplane of equipment racks.
“Dry Cleaning” refers to the practice of cleaning a connector end-face (end-face) with a dry cleaning medium as opposed to “Wet Cleaning” which involves the use of liquid chemicals.
The Dry Cleaning technique is perhaps the best known cleaning method and is acceptable when the contamination is a light dust or hand oil. Dry Cleaning tools range from reel cassettes(fiber optic cleaner / cassette cleaner) to precision swabs(fiber optic cleaning swabs) and fiber optic inspection probes used for cleaning “back plane” connections. These tools should be made from clean room grade foam or high quality non-woven (lint-free) material, or specialty micro fiber. Cotton is not acceptable.
The Dry Cleaning technique was more acceptable when network demands were not as rigorous as they are today. As speeds and bandwidth have increased, the ‘dry method’ has proven to be less reliable than the more recently developed Compound (Combination) Cleaning process, which is explained in detail below.
One concern about the Dry Cleaning process is that it tends to move soils around the end-face rather than completely remove them. Dry Cleaning can also generate a static field that attracts dusty soils. Electrostatic Discharge (tribocharge phenomenon) can be created when two dissimilar materials are drawn over each other.
Dry cleaning is only marginally effective in removing complex soils such as gels or lubricants. Dry Cleaning effectiveness is limited to removal of some finger oils and light dust. Dry Cleaning rarely cleans the entire end-face edge-to-edge. Dry Cleaning is also a concern with dust soils, which can contain abrasive grit or sand. Should this method be chosen, video inspection of each connection is required.
Wet Cleaning involves the use of solvents to clean end-faces. One wet cleaning technique is to moisten a pad with high-purity IPA (Isopropyl Alcohol) and then to lightly wet the end-face by “dragging” or “spotting” the moistened pad on the end-face prior to precision cleaning. Precision swabs are also used for Wet Cleaning.
A fundamental concept in understanding contamination is that ‘soils tend to be attracted to moisture’. Liquid fiber optic cleaners are formulated to evaporate quickly, which reduces the likelihood that they will attract airborne contaminates during the cleaning process. However, some liquid fiber optic cleaners actually evaporate too quickly, which can leave a soil/cleaner residue. On the other hand, if used improperly, liquid cleaners can transport soils to the end-face and actually ‘flood’ the connector making it exceptionally difficult to dry. Should this method be chosen, video inspection of each connection is required.
For example, some technicians have been known to spray solvent directly onto the connector end-face. This practice is never recommended since it tends to over saturate the connector. Drying a flooded connector is not a simple matter. Excess solvent can leach from ferrule sides even though a typical 400-600 micron view of the end-face may show a dry end-face image. The best practice is use as small amount of solvent as possible with an integrated drying technique.
In 2005 a patent was issued for a new cleaning process. In this method a small amount of solvent is placed on a cleaning platform. The connector end-face is placed in contact with the moist area in an inverted position so that the solvent cannot enter the side of the ferrule. The end-face is then lightly drawn from “wet-to-dry” areas of the cleaning platform, which automatically dries the end-face surface.
Today, the Compound or Combination Cleaning process may vary somewhat but it remains essentially the same. The process integrates a lint-free wiping material with an appropriate solvent. The process also provides an ‘automatic drying’ step (of a minimal amount of liquid fiber optic cleaner) as part of the “wet-to-dry” cleaning procedure.
Advantages of Compound Cleaning
The Compound method cleans a wider range of ionic and non-ionic contaminants as well as those contaminants that exist in combination. When used with widely available applications specific tools Combination Cleaning also can clean the side of the ferrule as well as the end-face. The use of solvent also helps to reduce static fields. Finally, the amount of solvent (and actual solvent type selection) used is significantly reduced, which is an advantage both in terms of cost and environmental impact.
By Ed Forrest, ITW Chemtronics
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