ApplicationNotesenko.com

Direct MT Angle Polishing for
MT Flat Ferrules
FEBRUARY 2021
Rev. 01

Issued by:EngineeringDepartment

Created by:
Bakar Bhatti
Andrei Vankov

Application Engineering Note
1.0

Introduction
Historically, when polishing MT ferrules on an angle, a two-step polishing process is performed:
first, a flat MT ferrule polishing fixture is used to remove epoxy beads making all ferrules uniformly
flat. Second, load the ferrules into an 8-degree angle polishing fixture to create a final result of anangled physical contact (APC). This is not efficient from a mass production standpoint as it adds
additional time to the process while unloading and reloading ferrules from the fixtures. Even after
polishing all the ferrules for a presumably flat shape from the first polish, the MT termination
process, the epoxy bead size and debris, the cleanliness of the fixtures and the operator’sexperience, all will play a major role. The less time that is spent handling the terminated cables thelesser the opportunity for error.
In some instances, pre-angled MT ferrules are introduced in hopes to simplify the polishing process
by promoting usage of only one angled fixture. In reality, the original angle will likely be alteredbased on the process variabilities outlined above. Also, the angle could be inconsistent across thesurface if the process does not allow sufficient time for removing ferrule material and is set up justto remove epoxy with the assumption of perfect ferrule placement. See Figure 1 where slight angle
variations can be seen. The blue line indicates an original angle from a ferrule manufacturer. Redline indicates an angle formed by a polishing process.
8.00-degree

8.10-degree

Figure 1: Pre-angle ferrule post polish angle possible variation

At Senko the polishing process for MT ferrules on an angle was developed using angled MT ferrule
fixture eliminating the use of a flat MT polishing fixture.

1

Application Engineering Note
2.0

Key points for successful MT/APC polish
2.1 Proper epoxy mixing
Successful polishing starts with proper manufacturing techniques. Proper epoxy mixing, applicationand curing is necessary for a successful result.
Senko’s recommended epoxy is S-123 which consists of Parts A and B that needs to be thoroughlymixed. After mixing the epoxy air bubbles will inevitably be present. A 7-to-10-minute spin cycle ina centrifuge will draw the air out. Failing to degas the epoxy could reduce the proper fiber to ferrulebond as the air expands at high curing temperatures. This reduces epoxy bonding strength, whichcauses the fiber to move during environmental temperature changes.

Figure 2: Epoxy on the left with air bubbles after mixing and on the right degassed in centrifuge

2.2 Proper epoxy application into ferrule and epoxy bead size2.1.1

Inject a small amount of epoxy into the MT ferrule covering all of the v-groves. It canbe done from the top window, but its more precise to inject it into the rear of the ferruleand spread it along the far wall covering all of the v-groves inside.
Epoxy should form
bead along this wall

Figure 3: Epoxy application using 20 AWG needle

2Application Engineering Note

Figure 4: Proper epoxy dispensing into MT ferrule

2.1.2

Install rubber mini boot closing ferrule rear opening. This prevents epoxy from flowing
out of the back of the ferrule.

2.1.3

You should see an epoxy bead on the front of the ferrule, clean the stripped fibers withisopropanol alcohol and a lint-free tissue. Carefully slide the fiber through the rear of
the ferrule until the exposed fibers emerge from the epoxy bead. It is important tocheck through the window of the ferrule to make sure the fibers are not bending or
meeting resistance as they are being pushed through. You should see fibers pushing
more epoxy out forming a uniform bead at approximately 0.2mm in thickness. Epoxy
must encapsulate the fibers completely at the ferrule/fiber bond on top.

Epoxy bead size
approximately 0.2mm

Figure 4: Proper epoxy bead

2.1.4

Once the fibers are properly inserted, slide them forward until you feel some resistance.
This is from the buffers hitting the end of the grooves (ferrule pedestal). Stop pushing at
this point. Move the ferrule back and force two-three times in order to distribute epoxy
evenly inside the ferrule. Ensure the ferrule boot snug and strait. No epoxy should leakthrough the edges of the boot. Retract the fibers from the end of the grooves leaving a3

Application Engineering Note
gap of 0.25 – 0.50mm between the groves and fiber coating. This is a necessary step,
because during heat curing the coated fiber could be pulled up over the pedestal ledge
creating microbends.

Figure 5: Proper space 0.25 to 0.50mm between the ribbon coating and MT ferrule pedestal inside

2.1.5

At this stage, if necessary, carefully apply a drop of epoxy to the window, but be sure
not to over fill. Be very careful not to get any epoxy on the outer surface of the ferrule,as this will affect how it sits in the polishing fixture. If necessary, carefully wipe off theoutside surface of the ferrule with an alcohol-soaked lint-free tissue to remove any
extra epoxy. The end-face epoxy lines must be consistent from ferrule to ferrule as thiswill be the key to successful polishing.

4Application Engineering Note

Properly Filled Acceptable

Overfilled – NotGood

Figure 6: Proper epoxy amount on MT ferrule window (left) vs overfill (right)

BadFigure 7: Epoxy outside of ferrule window

2.1.6

Some companies recommend using a vacuum pump to draw epoxy onto the endface. In the case of APC polishing, using the described technique is not necessary
as the polishing will reach the fibers inside the ferrule sufficiently recovering any
miscleaved fibers.

Ideal epoxy bead should beapproximately 1.2mm or lessin width
Figure 8 Good example of epoxy bead5Application Engineering NoteEpoxy bead should not extend to the guide holes as this will cause them to get contaminated.

Figure 9: Improper bead shown – Epoxy should not wick into the holes

3.0 Polishing directly on the Angle fixture
3.1 Polishing Preparation
3.1.1 Prior to loading of the ferrules into the polishing fixture, there should not be any excess epoxy
coming out of the MT ferrule window. Refer to Figure 7. Excess epoxy in the MT ferrule window cancause improper loading of the ferrules into the fixture which will cause bad polishing and 3D
geometry.
3.1.2 It’s important to load the ferrules properly into the angled fixture. During the loading of theferrules into the fixture, press the ferrule fully downwards and then tighten the torque screw to securethem in place. Different fixtures have different locking mechanisms. Make sure all the ferrules areat the same height after loading them into the fixture. Inconsistent heights can cause some of theferrules to be over-polished and some to not be polished enough.
3.1.3 Check the epoxy bead sizes and their consistency against each other in the polishing fixture.
Epoxy beads should be hand polished using 30um or 15um Silicon-Carbide film to reduce the beadheight and to be even more uniform in size. Operators should do this step once ferrules are loaded
into the fixture, unless another tool is used such as a laser or mechanical cleaver. See below imagefor guidance.

6

Application Engineering NoteFigure 10 Consistent bead size throughout fixture

3.2 Polishing on the angled fixture
3.2.1 Follow the SENKO recommended polishing procedure developed for the APC80XX. If your facility is using a different polishing machine, the procedure can vary. Theremay need to be pressure, rotation speed, and time adjustments. Contact your SENKO
representative for additional guidance.
3.2.2 MT SM ferrule polishing procedure is available upon request via your SENKO
Account Representative.
3.2 Ideal amount of polished surface
The proper angle is generated after the Silicon-Carbide steps. The steps that follow involve slurry
based polishing films and they add very little to the angle formation process. In theory, the SiliconCarbide steps should leave around 5% to 30% of unpolished surface area, T (Refer to Figure 11).
There is a common opinion that if the flat line is gone the ferrule is automatically considered to be overpolished, but is that true?
There is a perception that having a flat line indicates the manufacturing process is thought to be highly
under control. For clarity, a standardized polish and passing performance criteria depends on theoverall ferrule length that can be measured. For SM 8º MT/APC ferrules, the International Standard (IS)IEC 61755-3-31 identifies end-face geometry parameters and dimensional limits for 4 through 12 fiber
rectangular end-face ferrules to ensure effective optical performance. The IEC final dimensions for
MT/APC ferrules are shown below in Table 1. In summary, per IEC, it is perfectly acceptable not tohave a flat line as long as the overall ferrule length is over 7.9mm.

7Application Engineering NoteLL

Figure 11 Before (a) and After (b) MT ferrule profile

Figure #Description
Before Polish
After Polish

Dimention L, mm
Minimum
Maximum
8.0
8.1
7.9
8.1
Table 1: Ferrule Dimensions

Dimention T, mm
Minimum
Maximum
nana00.8

Acceptable flat region

Figure 12 Acceptable flat portion8

Contact us

USA

East Coast +1-508-481-9999
West Coast +1-858-623-3300
Texas +1-972-661-9080
Sales-Americas@senko.com
Mexico & Central America +1-858-623-3300
Sales-Mexico@senko.com
Brazil and South America +55-21-3736-7065
Sales-Brazil@senko.com

Asia-PacificHong Kong +852-2121-0516
Shanghai +86-21-5830-4513
Shenzhen +86-755-2533-4893
Thailand +66(0)2-163-2798
Australia +61(0)3 9755-7922
Sales-Asia-Pacific@senko.com

JapanUnited Kingdom

UK +44(0) 1256 700880
Sales-UK@senko.com

EuropeSpain & Portugal
Sales-Iberia@senko.com
Germany
Sales-Germany@senko.com
Italy
Sales-Italy@senko.com
FranceSalesfrance@senko.com
Other European Countries+44(0) 1256 700880
Sales-Europe@senko.com

Yokkaichi City +81-59-352-1121
Tokyo +81-3-5825-0911
Sales-Japan@senko.com

CALL 1-888-32-SENKO

www.senko.com