When the function of a product can be disturbed by surface contamination it is important not to exceed a specified surface cleanliness level. The required final surface cleanliness level of the quality determining parts of the product can be found by a combination of a risk assessment and vulnerability tests.

Incoming parts of a product, that is assembled, should always be cleaner than the final product. Parts must be cleaned to achieve an initial surface cleanliness better than the final surface cleanliness level. A suitable method for the cleaning of parts must be selected and results should be measured. Useful standards for surface cleanliness are ISO 14644 part 9, 10 and 13. During assembly the difference between initial and final surface cleanliness level determines the maximum acceptable contamination from the environment and the required contamination control measures (ISO 14644-2 and 8).

After the initial investigations and the assurance of the obtained initial surface cleanliness, the manufacturing process can monitored by continuous real-time measurement of the particle deposition rate (ISO 14644-17).