Before exploring the subject of cleanrooms in the electronics manufacturing industry, a cleanroom needs to be defined: 'A cleanroom is an environment in which microbial and particulate contamination is limited to prescribed levels.' In the electronics industry, microbial contamination is not relevant.
Cleanroom classes
There are different cleanroom classes with varying levels of cleanliness. The appropriate cleanroom class needs to be selected according to the requirements of the manufacturing process. Various cleanroom classification standards are in use. However, a new international standard, the ISO 14644 series, has been officially introduced to replace all the different national standards. This will go a long way to alleviate the confusion between the different standards. All the standards are based on the number of particulates of a certain size, per specified volume of air. A chart comparing some of the older standards, with the new ISO standards, is available from the author.
Why manufacture under cleanroom conditions?
Probably the prime reason is that it will lead to a better quality product. This makes economic sense if you are able to sell your better quality product at a higher price - an aspect that should appeal to the accountants. Manufacturing in an ideal environment will hopefully lead to fewer product rejects, improved production rates and enhanced operator satisfaction and comfort. Having a fully compliant, certified cleanroom manufacturing environment provides an added marketing advantage when trying to sell your product.
How do you achieve a cleanroom environment?
Creating a clean environment is not achieved by simply adding a filter to the supply air to the factory or laboratory. The following factors all contribute to achieving the cleanroom environment, and they all need to be in balance with one another in order to be effective:
* Air filtration.
* Air flushing rate.
* Directional airflow.
* Location of air terminals.
* Sequence of air handling components.
* Room pressure.
* Room layout.
* Room finishes.
* Room structural integrity.
* Production activity.
* Type of equipment.
* Number of staff.
* Staff discipline.
* Cleaning SOPs.
* Staff flow.
* Raw materials flow.
* Temperature and humidity.
Cleanrooms are not cheap. In order to get a cleanroom that works, one has to optimise all the aforementioned factors, into an integrated facility. One frequently finds that a logical balance has not been adhered to, and enormous expense is allocated to one aspect, and other vital features are ignored. To curtail costs ensure that the cleanroom environment is appropriate to the process or product being manufactured. A design overkill can result in unnecessary capital and running costs.
If you cannot afford the fully-integrated facility, put a plan in place to implement the project over time. However, the design and implementation must be open ended, so that future upgrades can take place without discarding work that has already been carried out.
Planning the cleanroom
A clear user requirement specification (URS) is required. This document stipulates in broad terms, all the basic requirements and design parameters for the manufacturing environment. Know what you want and why you need it before putting it in the URS - unnecessarily tight design parameters can lead to higher installation costs. From the URS, the design specifications and implementation documentation is developed.
Whether the project implementation is put out to tender, negotiated with a contractor or carried out in-house, one needs the above documentation for installation qualification purposes. You need to be able to verify.
Validation and qualification
The crucial aspect of 'knowing what you have got' is Validation and Qualification. The cleanroom facility needs to be validated to confirm that the conditions, as required by the client URS or design specifications, are being met. Part of the validation process is issuing a Certificate of Compliance.
Every new system needs to be qualified and validated, and system re-validation should be carried out on a regular basis to ensure that the parameters remain within specification on an ongoing basis. Without re-validation, conditions could drift resulting in non-compliance and possible product degradation. Validation comprises the following sub-sections, which need to be carried out in the sequence as listed:
DQ or design qualification entails assessing the design to ensure that it complies with the original Client URS and further assessing that the design is based on good cleanroom principles.
IQ or installation qualification is the process of verifying that the installation has been carried out and installed in accordance with the design specifications and drawings.
OQ or operational qualification consists of verifying that the critical parameters, which the design specification has stipulated, are being achieved. These are items such as temperature, relative humidity, room pressurisation, cleanroom classification filter integrity tests, room particle counts, etc.
PQ or performance qualification consists of verifying and documenting that the system provides acceptable operational control under 'full operational' conditions. This is carried out over time (usually 12 months) ensuring that a system is under control on a continual basis, regardless of ambient or seasonal variations.
Another vital aspect of a cleanroom installation is maintenance. Cleanroom installations involve sophisticated systems, and it is imperative that regular maintenance be carried out by competent individuals. Maintenance records form part of validation documentation. No ad hoc changes should be made, or any changes must be subject to change control procedures and documentation.
For more information contact Deryck Smith, Deryck Smith Consulting Engineers, +27 (0)12 991 4010, [email protected]
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