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Critical Cleanliness

Contamination
One common class of contamination problems arises when a manufacturer needs to verify that its product is suitably free of a specific kind or class of particulate contaminant, such as a toxic or abrasive material. The challenge in such cases is that the targeted particles are, one hopes, rare, or even absent entirely. To achieve the necessary statistical precision, a quite large sample area may need to be searched, and an inordinate amount of time could be wasted examining "benign" materials present. In such a "needle-in-a-haystack" problem, the challenge is to rapidly screen for candidate particles.

ASPEX's Perception AFA software is ideal for such applications. By appropriate selection of the back-scatter contrast thresholds and the dynamic search grid, large areas of "empty" sample can be rapidly traversed without sacrificing sensitivity to the "bad actors." The analysis can automatically terminate when the necessary precision is fulfilled, and go/no-go decisions can be automatically generated.

The more general class of contamination problem involves screening for "foreign" materials of a general and largely unpredictable nature. Here the challenge is to identify and classify large quantities of particles over a wide range of sizes, shapes, and compositions, realizing that the particles of greatest interest may not be known until after the analysis. For such applications, Perception CFA offers distinct advantages with its ability to accurately characterize particles of arbitrary shape. CFA, like AFA, can also rapidly characterize large numbers of particles, employing user-defined rules to automatically classify particles, in appropriate classes, and includes provisions for employing or suppressing elemental analysis and storing thumbnail images for post-analysis. The ability to relocate specific particles for manual inspection following the analysis can be a vitally important capability in such applications when unexpected particle types are encountered. Knowledge of particle morphology and composition becomes primary evidence in the identification of the contamination source.

Regardless of whether it's Perception AFA or Perception CFA that is employed, comprehensive reports can be generated and customized spreadsheet reports automatically generated by means of the Tabular Reporter. Population of an iStore database permits long-term trend analysis.


Critical Cleanliness
As the physical sizes and tolerances of precision devices continue to shrink, quality-conscious manufacturers find it increasingly necessary to ensure the critical cleanliness of their parts and processes. An important part of the challenge is to develop and monitor adequate cleaning procedures—but how does one know whether one's protocol is performing optimally?

A highly effective procedure is to filter the final rinse fluid to collect the residual particulate material. In critical cleaning applications, the mass of material collected may be too small for reliable weighing, but the number of particles may nonetheless be substantial when the air-dried filter is placed in the PSEM (without coating or other preparation) and automatically scanned. By performing repetitive rinsing, trends can be established that relate the observed particle counts following a rinse or procedure to a projection of the remaining material, thereby using the distribution of particulates by size, shape, and composition to establish the component's suitability for its intended use. Armed with such information, the efficiency of the cleaning method can be characterized, optimized, and regularly checked. Manufacturers of precision assemblies employ this technique to establish and enforce meaningful cleanliness specifications for their suppliers, and suppliers use it to optimize their procedures to ensure conformance without wasteful "overkill."

Whether to choose Perception AFA or Perception CFA for such applications depends on the amount of particle shape detail required. Typically, AFA provides adequate information with somewhat greater speed. Automatic population of an iStore database facilitates the accumulation and assessment of long-term trend data, and automatic generation of customized reports via Tabular Reporter provides convenient hardcopy records.