Extraction from the norm
Purpose of the norm
In order to achieve reliable performance of components and systems, control over the amount of particles introduced during the build phase is necessary, and measurement of particulate contaminants is the basis of control.
Based on a world-wide broadening and ongoing development of technical cleanliness issues this document is intended to:
- further improve the comparability of cleanliness inspection results;
- include new (extraction and analysis) techniques; and
- provide information on how to define cleanliness specifications and explain how to react when cleanliness limit values are exceeded
Cleanliness inspection principles
As reference test components with a defined level of contamination do not exists to assess the efficiency of extraction procedures, the effect of extraction conditions for cleanliness inspection needs to be investigated based on the following:
- Qualification of the extraction procedure (qualification test): the appropriate extraction procedure for a test component is determined by performing qualification tests. The qualification criteria are stated in this document. They serve to ensure that as many of contaminant particles are removed from the test component as possible. Finally the qualification results, requirements and parameters of the extraction procedure chosen are documented.
- Blank level: the cleaner a test component is (i.e. the lower the number of particles expected to be determined in a cleanliness inspection), the higher the risk that external contamination introduced into the test procedure will falsify results. The quantity of extrinsic particles permitted in a test is stated in this document. This permissible blank level is oriented towards the cleanliness requirements of the respective test component.
The cleanliness inspection is made up of the following steps:
- provision of the test component;
- removal of the particles from the test component (extraction);
- filtration of the particles (except with shortened analysis);
- analysis of the particles; and
- documentation of the inspection and results.
In order to perform cleanliness inspections, special equipment, suitable premises and skilled, experienced staff are required.
To be able to compare inspection results the same test fluid, the same extraction procedure and also same parameter settings for the analysis instruments shall be applied.
Annex 1 describes possible procedures to be taken when the result of a cleanliness inspection exceeds the permissible value stated in the cleanliness specification.
Selecting the inspection method
With respect to Figure1 the following shall be considered.
- Particle extraction: particles are detached from the component by means of a test fluid in a cleaning process. The extraction method is determined by the features of the test component(s), such as size, shape, accessibility to the surfaces requiring inspection, component material and type and adhesion of the contamination to be removed (see Clause 7)