Wet process and PCB surface treatment

1. Abrasives abrasives, brush materials
Various materials used to clean and pre-treat the PCB surface and brush 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), etc. Call it Abrasives. However, the powder of this kind of sandy brush material is often implanted on the copper surface, which will cause problems in the adhesion and solderability of the subsequent photoresist layer or electroplating layer. The attached picture is mixed with sand grains
The schematic situation of the brush material fiber.

2. Air Knife
At the outlets of various process line units, there are often high-temperature and high-pressure air knife edges to blow out air knives, which can quickly dry the PCB board surface, making it easy to carry and reduce the chance of oxidation.

3. Anti-Foaming Agent
During the PCB manufacturing process, such as the washing process of the dry film developer, a large amount of organic film material is dissolved, and air is mixed in during the extraction and spraying action, resulting in a large amount of foam, which is very inconvenient to the process. Chemicals that reduce surface tension must be added to the bath solution, such as Octyl Alcohol or Silicone as a defoamer to reduce the trouble of on-site operations. However, silicone resins containing silicon oxide cationic surfactants are not suitable for metal surface treatment. Because once it touches the copper surface, it will not be easy to clean, resulting in problems such as poor adhesion of the subsequent plating layer or poor solderability.

4. Bondability bonding layer
Adhesive layer: refers to the surface to be bonded (or 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 washes weakly, so as to weaken the power of being attacked by the potion and reduce the degree of side erosion (Cmdercut) , is an important condition for fine line etching, and this agent is mostly a supplier’s secret.

6. Bright-Dip gloss impregnation treatment
It is a kind of metal surface that is slightly etched to make it appear smoother and brighter. It is called wet treatment with bath solution.

7. Chemical Milling
Metal materials are corroded to various degrees by the chemical wet bath method, such as surface roughening, deep etching, or selective etching after applying precise special resists, etc., to replace some mechanical The punching (Punch) operation of the processing method, also known as Chemical Blanking or PhotoChemical Machining (PCM) technology, not only saves expensive mold costs and preparation time, but also eliminates the trouble of residual stress in the product.

8. Coat, Coating film, surface layer
It often refers to the processing layer made on the surface of the PCB board. In a broad sense, it refers to any surface treatment layer.

9. Conversion Coating
It refers to the surface of some metals, which can be transformed to form a protective layer of compounds on the surface only after being soaked in a specific bath. Such as phosphating on iron surface, chromating on zinc surface, or zincating on an aluminum surface, etc., can be used as “priming” (Striking) of subsequent surface treatment layer. ), also has the effect of increasing adhesion and enhancing corrosion resistance.

10. Degreasing
Traditionally, metal objects need to remove a lot of oil stains left by mechanical processing before electroplating. Generally, “Vapor Degreasing” with organic solvents or immersion degreasing in emulsified solutions is often used. However, there is no need for degreasing in the circuit board process, because almost no oil is touched in all the processing processes, which is different from metal plating. It’s just that the “cleaning” treatment still needs to be used in the pre-treatment of PCB boards, which is not exactly the same as degreasing in concept.

11. Etch Factor etch factor, etch function
In addition to the front-to-side corrosion of copper, the etching solution will also attack the unprotected copper surface on both sides of the line, which is called undercut, thus causing etching defects like mushrooms. Etch Factor is etching An indicator of quality. The term Etch Factor in the United States (mainly IPC) is just the opposite of the interpretation in Europe. What the Americans say is “the ratio of the depth of positive erosion to the concavity of the side erosion”, so it is known that the greater the “etching factor”, the better the quality; the European definition is just the opposite, its “factor “But the smaller the better. It’s easy to get it wrong. However, for many years, IPC’s achievements in circuit board academic activities and publications have already firmly occupied the leading position in the world industry, so the definition it elaborates can be said to have become a standard, and no one can replace it.

12. Etchant etchant, etching
In the circuit board industry, it refers to the chemical bath solution used to etch the copper layer. At present, the inner layer board or single-sided board has mostly used acidic copper chloride solution, which has the advantages of keeping the PCB surface clean and easy to automate management (single-sided board is also There are those who use acidic ferric chloride as etchant). For the outer layer of double-sided or multi-layer boards, since tin-lead is used as the anti-corrosion agent, the quality of copper to be etched is also greatly improved.

13. Etching Indicator etching pointer
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 board to be etched, or several pieces of specially etched samples can be deliberately added in the operation batch, so as to understand and improve the etching process.

14. Etching Resist
Refers to the anti-corrosion film layer made on the copper surface to protect the part of the copper conductor that is not intended to be etched, such as electrophotographic photoresist, dry film, ink pattern for image transfer, or tin-lead plating, etc. agent.

15. Hard Anodizing
Also known as “hard anodizing”, it refers to placing pure aluminum or some aluminum alloys in a low-temperature anodizing solution (15% sulfuric acid, 5% oxalic acid, temperature below 10°C, lead plate for cold pole, The anode current density is 15ASF), after a long time of electrolytic treatment for more than 1 hour, an anodized film with a thickness of 1-2 mils can be obtained, which has a high hardness (that is, crystalline A12O3), and can be dyed and sealed again. A good anti-corrosion and decorative treatment for aluminum.

16. Hard Chrome plating
Refers to the thick chromium layer plated for wear-resistant and lubricating industrial purposes. Generally, decorative chrome plating can only be plated on the glossy nickel surface for about 5 minutes, otherwise it will cause cracks if it is too long. Hard chrome can be operated for several hours. The traditional bath composition is CrO3250 g/1+H2SO410%, but it needs to be heated to 60°C, and the cathode efficiency is as low as only 10%. Thereby other electric quantity will produce a large amount of hydrogen gas and bring out a large amount of harmful dense mist that is made up of chromic acid and sulfuric acid, and make water washing also form a large amount of yellow-brown serious waste water pollution. Although the waste water needs to be strictly treated to increase the cost, hard chromium plating is the wear-resistant coating of many shafts and rollers, so it cannot be completely abolished.

17. Mass Finishing A large number of whole surfaces and a large number of polishing
For many small metal products, before electroplating, the edges and corners must be carefully removed, scratches removed and the surface polished to achieve the most perfect base. Only after plating can the appearance be the best and have the best anti-corrosion effect. Usually, the polishing work of the pre-plating base can be done manually and with cloth wheel machinery for large objects. However, those with a large number of small pieces must rely on the processing of automatic equipment. Generally, the small pieces are mixed with “polishing stone” (Abrasive Media) made of ceramics of various shapes, and injected with various anti-corrosion solutions to place them obliquely. The way of slow rotation and mutual friction can complete the polishing and finishing of all parts of the surface within tens of minutes. After pouring out and separating, it can be loaded into a barrel plating tank (Barrel) for rolling electroplating.

18. Microetching
It is a stop in the wet process of circuit boards. The purpose is to remove foreign pollutants on the copper surface. Usually, the copper layer below 100μ-in should be removed by etching, which is called “micro-etching”. Commonly used microetching agents are “sodium persulfate” (SPS) or dilute sulfuric acid plus hydrogen peroxide, etc. In addition, when conducting “microsection” microscopic observation, in order to see clearly the structure of each metal layer under high magnification, it is also necessary to microetch the polished metal section, so that the truth can be revealed. This term is also sometimes referred to as Softetching or Microstripping.

19. Mouse Bite
Refers to irregular gaps appearing on the edge of the circuit after etching, like the gnawing marks after being bitten by a mouse. This is an informal term that has become popular in the US PCB industry these days.

20. Overflow overflow
The liquid level of the liquid in the tank rises beyond the upper edge of the tank wall and flows out, which is called “overflow”. In the washing stations of the circuit board wet process (Wet Process), a tank is often divided into several parts, which are washed from the dirtiest water by overflow, and can be soaked multiple times to achieve the principle of water saving.

21. Panel Process full plate electroplating method
In the orthodox Substractive Process of the circuit board, this is the method of obtaining the outer layer circuit by direct etching. The process is as follows: PTH-full board thick copper plating to 1 mil hole wall-positive dry film cover hole-etching – Remove the film to obtain the outer layer board of the bare copper circuit. The process of this positive film method is very short, no secondary copper is required, and there is no need for lead-tin plating and tin-lead stripping, which is indeed much easier. However, it is not easy to make fine lines, and the etching process is difficult to control.

22. Passivation passivation, passivation treatment
It is a term for metal surface treatment. It often refers to immersing stainless steel objects in a mixture of nitric acid and chromic acid to force a thin oxide film to further protect the substrate. In addition, an insulating layer can also be formed on the surface of the semiconductor to electrically and chemically insulate the surface of the transistor and improve its performance. The formation of such a surface film is also called passivation treatment.

23. Pattern Process line plating method
It is another way to manufacture circuit boards by shrinkage method. The process is as follows: PTH—>Primary Copper Plating—>Negative Film Image Transfer—>Secondary Copper Plating—>Tin Lead Plating—>Etching—>Tin Stripping Lead –> Get the outer layer of bare copper board. This pattern process of secondary copper and tin-lead plating by the negative film method is still the mainstream in various processes of circuit boards. There is no other reason, just because it is a safer way and less prone to problems. As for the longer process, additional troubles such as tin-lead plating and tin stripping are required, which are already secondary considerations.

24. Puddle Effect puddle effect
It means that when the PCB board is sprayed and etched up and down during the horizontal transportation, the etching liquid will accumulate on the upward facing PCB board and form a layer of water film, which hinders the effect of the fresh etching liquid sprayed down later and blocks the air. With the help of oxygen, the etching effect is insufficient, and its etching speed is slower than that of spraying on the lower PCB surface. The negative effect of this kind of water film is called Puddle Effect.

25. Reverse Current Cleaning (electrolytic) cleaning
It is an anode that hangs the metal work object in the cleaning solution, and uses a stainless steel plate as the cathode, uses the oxygen generated in the electrolysis, and cooperates with the dissolution (oxidation reaction) of the metal work object in the bath solution, and the surface of the work object Cleaning, this process can also be called “Anodic Cleaning” anodic electrolytic cleaning; it is a commonly used technology for metal surface treatment.

26. Rinsing washing, washing
In the wet process, in order to reduce the mutual interference of chemicals in each tank, the PCB board needs to be thoroughly cleaned in various intermediate transition sections to ensure the quality of various treatments. The other washing method is called Rinsing.

27. Sand blasting
It uses strong air pressure to carry various small particles ejected at high speed, and sprays them on the surface of the object as a method of surface cleaning. This method can be used to derust metal, or remove difficult dirt, etc., which is very convenient. The types of sand sprayed include gold steel sand, glass sand, walnut kernel powder, etc. In the circuit board industry, pumice powder (Pumice) is mixed with water, and sprayed together on the copper surface of the PCB board for cleaning.

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