Total effectiveness goes beyond cleanliness and sorbency.

Levels of cleanliness and relative sorbency are common measures used to compare cleanroom wipers, but neither metric addresses a wiper’s total effectiveness. The ability to reduce particle contaminants — contaminants that can become airborne and taint product — is another important differentiator betweenwipers, and one that can be measured and quantified.

THE PROBLEM WITH PARTICLES
Particle contamination can negatively affect yield in a variety of cleanroom situations. Particles can block circuitry in semiconductor facilities, contributing to product loss. Silicone contamination in particular is a problem in sensitive cleanroom environments, posing risks to facilities producing anything fromdisk drives to space shuttle components.

Particle contamination sources are as varied as the cleanroom industries they affect. Silicones find their way into cleanroom environments through methods ranging from a new plastic waste tub to a tech’s lotioned arm that peeps above her cleanroom glove. Silicone isn’t the only culprit, however. Trace elements in acids or solvents can cause metals contamination and paint surfaces on cleanroom workstationsmay eventually wear and flake.

SORBENCY AND CLEANLINESS: BREAD AND BUTTER WIPER METRICS
Perhaps the most commonly used metrics to compare consumables are sorbency and cleanliness. Sorbency, or the ability of a textile product to wick and hold liquid, can be a useful metric for cleanroom applications that may involve large liquid spills. An engineered cleanroom wiper removes liquid spillsquickly and efficiently; one engineered cleanroom wiper can do the job of multiplewipers with inferior sorbency.

In cleanroom applications, cleanliness is obviously vital; a wiper that contributes to particle contamination is counterproductive in a fine cleanroom environment. Wiper cleanliness is affected by the environment in which the product was manufactured, as well as the means by which the wipers are finished, cut, and laundered. Quality wipers are produced in an appropriate cleanroom facility to minimize outside particle contamination in the products. Some wiper designs also feature bound or sealed edges to prevent fraying and fiber release.

Highly sorbent wipers can more thoroughly remove liquid spills and do the job more quickly, potentially preventing solid contaminants from being left behind. Wipers that arrive contaminant-free, with measures in place to preventfraying textile material, avoid adding to the contamination problem.

But neither metric, that is, sorbency nor cleanliness, fully addresses a wiper’s ability to remove existing dry particle contamination from a cleanroom surface. Given the myriad potential entry points, particle contaminants including zinc, titanium, and silicone have a good chance of finding their way into a cleanroom facility. Effective removal can reduce the implication to a manufacturer’sbottom line, minimizing product loss and safeguarding yields.

ARRIVE CLEAN, LEAVE DIRTY
A cleanroom wiper should arrive clean and leave dirty. Desirable product performance involves entering a clean-room environment without contributing to contamination, performing effectively to collect any present contamination, and leaving the cleanroom with captured particles and liquids, to be discarded outside of the clean zone. One way to measure a wiper’s ability to do so isto perform a particle attraction (capture) and retention test.

The following is methodology used to test cleanroom wiper products with Particle Attraction Technology (P.A.T.). Though no specific protocol for measuring capture and release exists, such methodology could be adopted for use in cleanroom facility internal testing. Cleanroom operations could use the following tests to evaluate current wipers and consumables or potential new products for use.

TEST METHODOLOGY
In general, the testing process is very similar to IEST-RP-CC-004.2 section 5.2 in that it uses the same specified shaker, same duration of shaking time, and laser particle counter. The capture and release data is then calculatedfrom these results.