What to do (and what NOT to do) in your fiber optic cable assembly polishing process

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As you probably know, the polishing
process is an extremely important step in the manufacture of fiber optic cable
assemblies. Your polishing process ensures your fiber optic connectors meet
certain geometric parameters, industry specifications, and/or customer
requirements.

 

When I visit fiber optic cable assembly
houses, I help our customers set up their polishing process and, together, we
determine the exact requirements for every step in the polishing process to
support their unique application. While training customers, I often address
common questions revolving around the polishing process: how to prevent film
from moving, how much water to use, and how to establish good cleaning
techniques to extend the life of the lapping (polishing) film.

 

Q. 
“HOW DO WE KEEP THE POLISHING FILM FROM MOVING?”

 

A. 
When fiber optic cable assembly houses set up a new polishing machine
and establish their polishing process, they often find that film slipping or
coming off the pad is an issue. To provide uniform polishing, film should never
move on the polishing pad. If the film moves with the revolutions of the
polishing machine’s platen (the turntable), then you’re not accomplishing
anything.

 

Everything may be spinning, but you’re
not actually polishing the connectors. It’s extremely important to overcome
this issue! In fact, this is the first thing I show people when I teach them
how to polish connectors. The following tips offer pointers.

 

Helpful tips:

 

The rubber polishing pad has two
surfaces that can be used: a highly polished side and a dull, unpolished side.
Place the lapping film on the polished side of the rubber pad – without any
liquids. This process relies on “stiction” (adhesion of the film to the pad).
First, though, you need to ensure the shiny surface of the polishing pad is
absolutely clean. Use a lint-free wipe and isopropyl alcohol (IPA) as a solvent
to remove dirt and oils. As long as the pad’s surface area is clean – and the
polishing film is clean – you will have successful stiction. After you lay the
film on the rubber pad, remove air bubbles by using a circular motion with the
lint-free wipe.

 

If you’re using a glass plate, that’s a
different animal! If your process requires the use of a glass plate with a
non-PSA-backed film, you can apply a thin film of liquid – a combination of IPA
and distilled water – to create stiction. Unfortunately, the IPA-distilled
water combination doesn’t provide a lot of strength to adhere the film to the
glass plate. Take time to remove air bubbles when laying the film on the plate.
This will give you adequate stiction to polish on a mechanized polishing
machine. Alternatively, you can use a spray-on adhesive, which can be quite
messy.

 

You don’t want the film to slip AND you
don’t want the rubber (or glass) pad to slip. During the cleaning process,
liquid may seep between the pad and the platen of the polishing machine. When
turned on, the spinning and downward pressure can make the pad slip, which can
cause poor results. To prevent this, make sure the pad and platen are
completely dry prior to the polishing step.

 

Q. 
“HOW MUCH WATER SHOULD WE USE?”

 

A. 
When polishing fiber
optic connectors on a fixed platen, water is used as a lubricant on the
lapping film. How you apply the water – and how much to apply – needs to be determined
when establishing your process.

 

The following tips address these
points. Next, it’s important to train your operators, so they apply water
consistently.

 

Helpful tips:

 

The majority of the fiber optic
industry uses a distilled/deionized-water mix and a few companies use a
combination of isopropyl alcohol and pure distilled water as the primary
lubricant. Another school of thought is to use soap (liquid detergent) and
water, because soap is slippery and creates very low friction. It’s a matter of
choice, plus the type of connectors you’re polishing can dictate which type of
lubricant you use. In rare applications, certain optical fibers cannot touch
water and require the use of exotic lubricants. (Contact Fiber Optic Center at
sales@focenter.com if you encounter such a situation.)

 

How much water should you apply to the
film? Some people use a squirt bottle to spray the film. However, squirt
bottles tend to flood portions of the film, and do not provide uniform
coverage. I prefer using a SPRITZ bottle, which sprays a fine mist uniformly
around the film. Using a spritz bottle, moisture is dispersed in a light and
even manner and doesn’t pool. How much water to spritz on your film is very
much dependent on your application. There’s no tried-and-true formula. I
actually define this when I’m with a customer. (Fiber Optic Center sells
16-ounce and 8-ounce ÅngströmSpray Spritzer Bottles.)

What if you use too much water? If too
much water is applied, you’ll risk overflow and flooding the platen. Liquid can
seep underneath the rubber (or glass) pad and start slipping, and that’s a risk
you want to avoid at all costs. Thankfully, today’s quality polishing machines
have plates that lock to prevent the pads from spinning, regardless of how much
water seeps underneath the pad. In that case, excessive water use won’t hurt
your process – if you lock the plate – but it is messier and takes more time to
clean between polishing steps. (Click here to view the polishing machines that
Fiber Optic Center sells.)

 

Can you polish successful dry – with no
lubricant? Some fiber optic cable assembly houses do, but I do not recommend
this.

 

Certain fiber optic applications
require continuous flow of water: one or two drops a second. The polishing
machines we sell at Fiber Optic Center have the ability to provide a constant
water drip – from one drop to a continuous flow. However, we strongly recommend
you do not use running water in your polishing process.