Tuesday, March 3, 2015

Cleanroom Tip: Controlling Relative Humidity

Failure to properly measure and control relative humidity in the cleanroom can result in lower yields, increased scrap and waste, contaminated product inadvertently reaching consumers, customer lines down, increased liabilities, and decreased revenues—among other situations best avoided. Carefully monitoring and controlling the relative humidity in a cleanroom is an absolute requirement—with no options.

Particulate count. Temperature. Airflow. Humidity. These five words are among the environmental factors that must be measured and controlled in the cleanroom environment. Sometimes the ‘stickiest’ of these is humidity. Measuring and controlling it within prescribed parameters can be a challenge. Too little or too much RH can impact much more than the personal comfort of cleanroom employees. Too little humidity can be quite electrifying—creating issues of static build-up and discharge. Too much humidity brings its own woes: encouraging the growth of bacteria and microbes, corroding sensitive metals whether in products or equipment, and manifesting itself in moisture condensation and water absorption. Then there’s photolithographic degradation. Photoresist processes are among the most sensitive to humidity, and can be among  the most costly to control for, due to their tightly required parameters. The bottom line: any of these conditions can result in cost overruns, scrapped products, and shortened equipment life. In short, the diminution of cleanroom performance, which is costly in itself.

Simply put, because humidity is relative to temperature, controlling RH within very tight tolerances or at extremely low levels can end up costing you more money in both construction and operating budgets. It’s important to understand that target humidity and temperature control decisions impact costs. A cleanroom target temperature of 65 degrees will have a lower relative humidity than a target temperature of 60 degrees. The lower your controlled temperature goes, more is required to “dry out” the air to reach a set RH level. Driving lower moisture content drives cost.

No comments: