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.
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.
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 firstname.lastname@example.org 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.