General description

This volume explains how to achieve the desired cleaning quality effectively by utilizing the production technology, based on the understanding of the principles and general rules of cleaning procedures in each production process.

Explanation

(1) Principle of cleaning

The following three rules apply to work performed in a clean room:

In the same idea, the cleaning principles can be described as follows:

(2) Production technology and cleaning

Each process of a production line is designed to deliver conforming items to the next production process. As for the cleaning quality, the specified quality on the product appearance must be guaranteed.

1) Do not add contaminants that cannot be removed
- The cleaning is performed in each process to remove the expected contaminants that may be generated during the process.
- Therefore, they must not generate excess contaminants that cannot be removed by the intended cleaning process.
- If heat, pressure, or chemical reactions are applied to the products in addition to these contaminants, the contaminants are difficult to remove.

2) Be sure to remove the contaminants
- The person in charge of production technology must consider measures to remove expected contaminants that could occur in each production process.
- For example, stubborn stains should be removed by a brush, or if it just contains floating contaminants, only the ultrasonic cleaning is used, and so on.

3) Do not allow removed contaminants to be reattached
- Since the reattachment of removed contaminants will likely to cause stains or burns, it must be avoided.
- Hardware and cleaning solution for the device must be appropriately selected. In addition, it is necessary to perform appropriate maintenance including the device software, and to replace cleaning solution and filters regularly.

In order for these principles to be steadily adopted in the LCA mechanism, the following agenda (1) and (2) must be resolved:

1) The purpose of the cleaning is to remove dirt and foreign particles that are mixed in during the process. However, depending on the cleaning process used, it may leave stains on the products.

2) If you dry this cleaning stain, a chemical reaction that occurs in the stained area could make this stain permanent.

3) Residual stains appear mostly because of the following two reasons: (1) Existence of residual contaminants that were not removed in the specified cleaning conditions, (2) Insufficient rinsing in the final cleaning process.

(3) Automation and insufficient cleaning

1) Cleaning stains - (2) occur mostly because the solution in the auto-cleaner's ultrasonic cleaning tank and rinsing solution in the rinse tank become more contaminated than the specified level. Therefore, it leaves small point-like stains on the product after rinsing (the process of exchanging dirty liquid with clean liquid, followed by drying.)

2) To prevent the situation described in 1), be sure to eliminate the residual cleaning solution on the workpieces to be cleaned before bringing them into the next cleaning tank. It is important to stabilize the cleaning quality for each cleaning tank appropriately.

3) Depending on the shape or state (e.g. overlapping, facing sideway, or upward/downward) of a workpiece, the contaminated cleaning solution is likely to enter from a small gap and spread by capillary action.

4) Therefore, it is recommended to place workpieces to be cleaned in a position where no residual liquid stays in, and to use a cleaning fixture that can hold the workpieces at a certain distance apart.