What kind of image do you have about cleaning processes?
"It seems bad if something is dirty..."
"It seems to have better quality if it's clean..."
Many people probably have such impressions.
Some people may be using cleaning processes just because they have been in their own process for a long time, or using them with a kind of ritual meaning.
While these images are not necessarily wrong, the effects of cleaning go far beyond that. Cleaning in industry is a very important process that can bring out the original functions of products or provide them with new functions.
Specifically, it is used for the following four purposes:
- Improving product functionality and performance
- Pre-treatment for the next process / Stripping of resist, etc. in circuit formation
- Improving appearance characteristics
- Improving reliability
As described above, cleaning is not just about removing dirt, but is an indispensable process in modern industry.
We will introduce the basics of cleaning in a series.
The first installment is about dirt.
The cleaning process is the process of cleaning dirt from products during manufacturing, but dirt rarely just sits on top of objects. It exists while interacting with the surface of objects.
Such dirt can generally be divided into three types:
① Particle contamination - Dirt from fine powders such as dust in the air
② Organic contamination - Dirt consisting of organic substances such as oils. The most common in industrial cleaning.
③ Inorganic contamination - Dirt from inorganic substances such as metal oxide films. Often has strong adhesion between the surface and the dirt.
These three types of dirt are often mixed together. For example, in the cleaning of abrasives, there is composite dirt consisting of fillers as particle contamination existing within solvents as organic contamination. When cleaning this dirt, the composite dirt can be cleaned by removing the organic contamination. In this way, carefully examining the actual condition of the dirt is a very important perspective in cleaning.
Also, the way things get dirty varies depending on the object. For example, even a familiar television gets dirty for various reasons such as floating dust, fingerprints, and sebum.
Naturally, in manufacturing processes for making products, there are more complex types of dirt. For example, in objects with fine wiring such as semiconductors, even if there appears to be no dirt, some dirt may remain in parts of grooves and holes. Therefore, since the way things get dirty varies with each object, it is necessary to carefully observe the actual product.
The phenomenon of dirt being cleaned occurs through two types: "dissolution" and "separation". "Dissolution" refers to the removal of dirt, rust, etc. by solvent-based cleaning agents or acidic cleaning agents. It is a method of removing the target dirt through dissolution reactions with the cleaning agent. On the other hand, "separation" refers to the removal of oil stains, etc. by water-based cleaning agents containing surfactants. Through the action of surfactants, the surface tension between oil and the object's surface is strengthened, causing the oil to be repelled from the object, and finally the dirt is removed through separation.
There are also three levels of cleaning: "general cleaning," "precision cleaning," and "ultra-precision cleaning."
"General cleaning" means removing most of the dirt. "Precision cleaning" means completely cleaning the dirt, but with the interface between dirt and the object remaining. "Ultra-precision cleaning" means the dirt is completely cleaned and the surface of the object itself is exposed.
While it may seem that making all processes "ultra-precision cleaning" would be best, it is important to select a cleaning level that is necessary and sufficient for the process based on production costs and tact time. Also, in some cases, the surface is more chemically stable when thin dirt or an oxide film exists on the surface of the cleaned object. Therefore, if the cleaning level is raised too much, necessary dirt or oxide films may be removed, creating a risk of actually leading to defects. It is necessary to select the optimal cleaning level with consideration for the impact on the next process and final product.
If the dirt removal process is insufficient, what would happen?
For example, imagine a process of coating the surface of metal processed products. What would happen if you apply the desired coating to a metal surface where processing oil used during manufacturing remains? It would be easy to imagine that coating cannot be applied directly over the processing oil, resulting in partial peeling or appearance abnormalities. In this way, the process of removing dirt is indispensable in manufacturing processes, and careful process design is necessary to avoid affecting the next process.
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The cleaning process is not just about removing dirt, but is an important process that improves product functionality and performance. Dirt can be divided into three types: particle contamination, organic contamination, and inorganic contamination, and there are three cleaning levels: general cleaning, precision cleaning, and ultra-precision cleaning. There are two methods of cleaning: dissolution and separation, and it is important to select the optimal cleaning level. If the cleaning process is insufficient, defects may occur in the next process or final product, so careful process design is necessary.