ApplicationNotesenko.com

MT Ferrule Epoxy Injection
Techniques
OCTOBER 2017
Rev. 01

Issued by:Engineering
Department

Created by:Andrei Vankov
Emmanuel Kolczynski

Application Engineering Note
1.0 Purpose of this document
The MT Ferrule has been around for over 20 years and throughout the years there havebeen many different processes and recommendations when it comes to terminating onto
this ferrule. The purpose of this document is to provide guidance on the control of epoxy
injection into the MT ferrule by providing a variety of options that have been proven towork. Additionally, this document will outline how epoxy can enable the MT ferrule angle
grinding without the need for a flat polishing step.
2.0 Epoxy Control
Epoxy can be injected into the window of the ferrule using an appropriate applicator at aslow steady rate, completely filling the window or from the back of the ferrule. Different
operators will have their own preference based on experience and ease of handling.
Automated dispensing equipment can help with the volume dispensed and increase
consistency.

Figure 1 Proper epoxy injection techniques

The amount of epoxy injected ideally should be level with the top edge of the window,
not above. Over injection of epoxy will form a dome of epoxy above the height of thewindow when fully cured. This dome of epoxy prevents the polishing fixture from1

Application Engineering Notesufficiently clamping the ferrule for polishing, thus, adversely affecting critical geometry
measurements.
After the epoxy injection, small beads of epoxy should be visible at each fiber hole. The
beads of epoxy should not run when the ferrule is placed horizontally on a flat surface.

Figure 2 Epoxy must be visible in the fiber holes

The fibers should then be inserted slowly and smoothly to prevent fiber damage orbreakage. If there is any resistance, back off and try again. There is a small pedestal insideof the ferrule that aids with the alignment of the fibers.

Figure 3 Ideal epoxy amount (left) and excessive epoxy amount (right)

Be very careful not to get any epoxy on the outer surface of the ferrule, as this will affecthow it sits in the polishing fixture. If necessary, carefully wipe off the outside surface ofthe ferrule with an alcohol dampened lint-free tissue to remove any extra epoxy. The endface epoxy lines must be consistent from ferrule to ferrule as this will be the key tosuccessful polishing. Even the smallest amount of epoxy can carry significant
consequences for the finished product.
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Application Engineering Note

Figure 4 Epoxy on the ferrule surface is bad

The ferrule should then be held vertically after fiber insertion to allow epoxy on the fibers
to flow down and accumulate on the ferrule surface. Epoxy must encapsulate the fiberscompletely at the ferrule/fiber bond on top.

Figure 5 Proper epoxy amountThe accumulated epoxy thickness for angle MT polishing ideally should be around 0.2mm.
Angled polishing exerts an angular force, that when applied to a tall, thin ridge of epoxy
has a high risk of fiber breakage. Controlling the height of this ridge of epoxy to 0.2mm
eliminates fiber breakage and allows direct angled polishing without the need for a flat
polish process to remove fibers and epoxy before angled polishing. The epoxy bead also3

Application Engineering Noteassists with the cleaving of the fiber. The epoxy encapsulates the fiber and when cleaving
will protect the fiber from cracking into the ferrule.
Ideal epoxy bead should beapproximately 0.2 to 1mm in widthand not close to the guide pin holes

Figure 6 Ideal epoxy bead thickness

Excessive epoxy leaks into
guide pin holes

Figure 7 Epoxy interference with guide pin holes

It’s important to note that multimode fibers have a larger core and are more susceptible
to core damage during epoxy curing. If the epoxy bead is too thick, core cracks may form
during epoxy curing stress and cannot be polished away. With thinner epoxy beads, cracks
will not likely to occur or occur not below the ferrule surface, which can be polished away.
It is important to remember to check the height of epoxy in the ferrule window before
curing. Insertion of fibers into the ferrule will draw some of the epoxy out of the ferrule
window. A pronounced dip/concave shape to the epoxy means a lack of epoxy, and it
must be topped up. Lack of epoxy will affect long term reliability.
3.0 Additional polishing advisory note
The higher the number of fibers, the higher the force required to produce and maintainphysical fiber contact. Therefore, control of ferrule length is critical making it imperative
to not over-polish. Over-polishing will affect the length of the ferrule, thus, affecting theforce exerted to ensure physical contact of mated end-face fibers.
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Application Engineering Note
IEC 61754-7 stipulates that the unpolished (flat) area of an angle polished ferrule (singlemode) can be a maximum of 0.8mm. Measuring this area is difficult, and removal of theferrule from the polishing fixture to do so is not recommended due to the adverse effecton end-face geometry. A simple rule of thumb is to polish until the angle has overlapped
the fiber by one fiber diameter, which can be “eyeballed”.

Here is can be clearly seen thethicker epoxy bead most likely
will not be polished away.
However, slight pressure with asharp blade can remove it.

Here is can be clearly seen thatthe polished angle has passed
the single row of fibers andguide pin holes

Figure 8 Epoxy interference with matingFigure 9 Ideal polishing result for MT/APC angle

For additional polishing advise, please refer to relevant SENKO polishing procedures orcontact your local representative.

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