P2 Tech
Cleanliness Measurement Review

Released January 1997


Unlike the previous three reviews in this series, this review does not present findings from case studies on the effectiveness of the different technologies but introduces the different methods. In addition, some of the methods discussed here are best applied in precision cleaning applications such as medical parts or electronics manufacturing. Precision cleaning applications require very accurate information about a part’s cleanliness to meet the design specifications of the unit being manufactured. Less precise cleaning applications like those done in automotive repair shops do not use most of the methods described herein.

Why Meaure Cleanliness?
Cleaning is part of many manufacturing operations. Parts may require cleaning before they can be electroplated or painted, before they can be soldered, or before they can be packaged and shipped for end use. But what is meant by "clean"? Even if its microscopic, there is still some contamination left on a part after it is cleaned.

In some cases a manufacturer defines how "clean" a part will be by specifying the process used to do the cleaning (i.e. dip Part A in Cleaning Solution B at Temperature C for X minutes), without regularly checking how clean parts actually are. This approach takes advantage of knowledge gained through experience with the cleaning process or through measurements taken during initial testing of the cleaning process. However, in many cases, it is more effective for a level of cleanliness to be specified and have that level checked by measuring cleanliness on a portion or all of the parts. This is especially true in precision cleaning applications. Another approach used is to monitor the contamination levels in the cleaning solution to determine when the solution needs to be replaced.

But if a level of cleanliness is to be specified, then a method of measurement must be specified at the same time for that level to have meaning. This leads to the all important selection of a cleanliness measurement method.

Measuring cleanliness not only helps ensure product quality, but is an essential part of implementing pollution prevention approaches related to cleaning. These measurement methods can be used to evaluate the performance of any alternative cleaning process, analyze parts during initial implementation of a new cleaning process to optimize the process, or be used to determine if better parts handling or other innovations can allow the cleaning process to be eliminated entirely. In addition, measuring cleanliness itself often prevents pollution by reducing rejects.

dot Issues Affecting the Selection of a Measurement Method

dot Types of Cleanliness Measurement Methods
Direct methods actually measure cleanliness on the part of interest by analyzing the surface of the part directly. These include: magnified visual inspection, black light, water break test, contact angle, gravimetric measurement, optically stimulated electron emission, direct oxidation carbon coulmetry, x-ray photoelectron spectroscopy, and other direct methods.
Indirect methods typically use a solvent of some type to extract the contaminants of interest from the part and the solvent then is analyzed for contamination. These include: gravimetric analysis, ultraviolet spectroscopy, optical particle counter, and other indirect methods.

dot Cleaning-related Projects in the Pollution Prevention Research Projects Database

dot Other Cleaning-related Internet Sites

dot Cleanliness Measurement Bibliography

© 1999, Pacific Northwest Pollution Prevention Resource Center
phone: 206-352-2050, e-mail: office@pprc.org, web: www.pprc.org