Wet Process and PCB Surface Treatment (1)

Wet Process and PCB Surface Treatment

1. Abrasives Brushes

Various materials used for pre-cleaning the board surface and brushing the copper surface, such as polymer non-woven fabrics, or non-woven fabrics mixed with emery or various types of sand-free materials, and pumice powder (Pumice Slurry) are all called abrasives. However, the powder of this kind of brush material mixed with sand is often implanted on the copper surface, thereby causing problems of adhesion and solderability of the subsequent photoresist layer or electroplating layer.

2. Air Knife

At the outlet of various process online units, there is often a knife edge with high temperature and high pressure air to blow out the air knife, which can quickly dry the board surface, which is convenient for taking and carrying and reducing the chance of oxidation.
3. Anti-Foaming Agent

During the PCB process, such as the flushing process of the dry film developer, a large amount of foam is generated due to the dissolution of a large amount of organic film materials, and the air is mixed in during the extraction and spraying action, which is very inconvenient for the process. It is necessary to add chemicals to reduce surface tension in the bath, such as Octyl Alcohol or Silicone as defoamer to reduce the trouble of on-site operation. However, silicone resins containing cationic interface active agents of silicon oxide compounds are not suitable for metal surface treatment. Because it will not be easy to clean after contacting the copper surface, resulting in problems such as poor adhesion of subsequent coatings or poor solderability.

4. Bondability Bonding Layer

Adhesion Layer: Refers to the surface to be bonded, which must be kept in good cleanliness to achieve and maintain good bonding strength, which is called “bonding”.

5. Banking Agent

It refers to the organic additives added in the etching solution, so that it can play a role of film adhesion on both sides of the line where the water flow is weak, so as to weaken the force attacked by the potion and reduce the degree of lateral erosion (Cmdercut). It is an important condition for fine line etching, and this agent is mostly the secret of the supplier.

6. Bright-Dip Treatment

It is a kind of slightly biting on the metal surface to make it appear smoother and brighter. The wet treatment of the bath liquid is called.

7. Chemical Milling

It uses chemical wet bath method to carry out various degrees of corrosion processing on metal materials, such as surface roughening, deep etching, or applying precise special resists, and then selectively etching through, etc., to replace some mechanical punching operation of the processing method, also known as Chemical Blanking or Photo Chemical Machining (PCM) technology, not only saves expensive mold costs and preparation time, but also eliminates the trouble of residual stress.

8. Coating Film, Surface Layer

Often refers to the treatment layer done on the surface of the board. In a broad sense, it refers to any surface treatment layer.

9. Conversion Coating

It refers to some metal surfaces, which can be transformed on the surface to form a protective layer of compounds only by simply soaking in a specific bath. For example, the phosphating treatment of the iron surface, the chromating treatment of the zinc surface, or the zinc treatment of the aluminum surface, etc., can be used as the “priming” (Striking) of the subsequent surface treatment layer. It also has the effect of increasing adhesion and enhancing corrosion resistance.

10. Degreasing

Traditionally, it refers to the need to remove a large amount of oil stains left by mechanical processing before metal objects are electroplated. Generally, the “Vapor Degreasing” method of organic solvent or the immersion degreasing method of emulsification solution is often used. However, there is no need for degreasing in the circuit board process, because almost no oil has been touched in all processing processes, which is not the same as metal plating. It’s just that the pre-treatment of the board still needs to use “clean” treatment, which is not exactly the same as degreasing in concept.

11. Etch Factor & Etching Function

In addition to the front-down etching of copper etching, the etching solution will also attack the unprotected copper surfaces on both sides of the line, which is called undercut, thus causing etching defects like mushrooms. Etch Factor is etching as an indicator of quality.

12. Etchant

In the circuit board industry, it refers to the chemical bath used for etching copper layers. At present, acid copper chloride solution has been used for inner-layer boards or single-sided boards, which has the advantages of keeping the board surface clean and easy to automate management (single-sided boards also have the advantage of Acidic ferric chloride being used as an etchant). The outer layer of the double-sided or multi-layer board uses tin and lead as the corrosion resistance, so the copper corrosion quality is also greatly improved.

13. Etching Indicator

It is a special wedge-shaped pattern that pays attention to whether the etching is over-etched or under-etched. This kind of specific pointer can be added on the edge of the plate to be etched, or several specially etched samples can be added in the operation batch to understand and improve the etching process.