Tuesday, March 18, 2014

CHAMBER CHARATERIZATION

Characterizing your coating chambers is one of the most important things you can do in your lab. There's an old saying, "A good craftsman never blames his tools". The same goes for coating and your equipment. Know your tools and their capabilities and use them accordingly. Whether you're implementing a new design or process or just maintaining your equipment, knowing your coating chamber's characteristics is key to keeping your processes, new and old, within tolerance.

The most important thing is to know your material characteristics. Keep a database on each materials refractive index and physical properties for each coating chamber in your lab. Knowing the characteristics of your materials throughout the day and throughout the year will minimize coating runs that are out of spec and ease the implementation of new coating processes.

Characterize your coating chambers once every quarter. Add it to your preventative maintenance program. The optical performance of thin films will change season to season as the environment outside and in your lab change. It should only take a day or two to run all the materials used in a particular chamber and a confirmation coating for verification. It's well worth the time.

Characterization of a coating chamber requires more than just knowing the optical and physical properties of the thin films you deposit. You have to know the chamber too. Put your hands on it. Front and back. Top and bottom. Feel for temperature and vibration. Get to know when your equipment isn't running the way it's supposed to. A change in temperature by just a few degrees can change the outcome of your thin films.

For example, if you cool your chambers and associated equipment on city water rather than a constant temperature chiller, your processes may change from winter to summer as the water coming in will change by several degrees. Based on the temperature change of your cooling water your processes may need to be changed as the characteristics of the chamber change with temperature.

You're the craftsman and your coating chambers are your tools. Know them and their characteristics well so you can use them accordingly, effectively and efficiently.

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