PCB Blog - Wet process and PCB Board surface treatment

1. Abrasives Abrasives, brushes

Various materials are used for pre-cleaning the PCB board surface and brushing the copper surface, such as polymer non-woven fabrics, non-woven fabrics mixed with emery, or various types of sand-free materials, and pumice powder (Pumice Slurry), etc. It's called Abrasives. However, the power 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. The accompanying drawing is a schematic view of the brush material fibers mixed with sand particles.

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 to facilitate carrying 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 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

Subsequent layer: refers to the surface to be bonded (or bonded), and must maintain good cleanliness in order 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 they can play a role in 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). , is an important condition for fine line etching, and this agent is mostly the secret of the supplier.

6. Bright-Dip gloss dipping 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 is called.

7. Chemical Milling

It uses the 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 The 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. Coat, coating film, the 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 lot 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 emulsified 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 a "clean" treatment, which is not exactly the same as degreasing in concept.

11. Etch Factor etching 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. The term Etch Factor is used in the United States (mainly IPC) to be the exact opposite of the European interpretation. Americans say it is "the ratio of positive etch depth to side etch concave degree", so the Americans say that the larger the "etching factor", the better the quality; the European definition is just the opposite, but the smaller the "factor", the better the quality. it is good. It's easy to get it wrong. However, over the years, IPC's achievements in circuit board academic activities and publications have already taken a leading position in the world's industry, so the definition of IPC can be regarded as a standard cost and no one can replace it.

12. Etchant etchant, etching

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 to 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.

14. Etching Resist

Refers to the part of the copper conductor that is to be protected from corrosion, and the anti-corrosion film layer made on the copper surface, such as image transfer photoresist, dry film, ink pattern, or tin-lead coating, etc. are all anti-corrosion resists agent.

15. Hard Anodizing

Also known as "hard anode treatment", it refers to placing pure aluminum or some aluminum alloys in a low-temperature anode treatment solution (sulfuric acid 15%, oxalic acid 5%, temperature below 10 ℃, lead plate for cold electrode, anode current Density is 15ASF), after long-term electrolysis treatment for more than 1 hour, an anodized film with a thickness of 1-2 mil can be obtained, which has high hardness (ie crystalline A12O3), and can be dyed and sealed again. It is an aluminum material A good anti-corrosion and decorative treatment method.

16. Hard Chrome plating

Refers to thick chrome plating for wear-resistant and lubricating industrial applications. Ordinary decorative chrome plating can only be applied to a glossy nickel surface for about 5 minutes, otherwise too long will cause cracks. 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℃, and the cathode efficiency is only 10%. Therefore, other electricity will generate a large amount of hydrogen and bring out a large amount of harmful dense fog composed of chromic acid and sulfuric acid, and also cause a large amount of yellow-brown waste water pollution in water washing. Although the waste water needs to be strictly treated and the cost increases, but hard chrome plating is a wear-resistant coating on many shafts or drums, so it cannot be completely abolished.

17. Mass Finishing A lot of whole surface, a lot of polishing

For many small metal products, it is necessary to carefully remove the edges and corners, eliminate scratches and polish the surface before electroplating, so as to achieve a perfect base, and the appearance will be beautiful and anti-corrosion effect only after plating. Usually, the polishing of the base before plating, large objects can be done manually and mechanically with cloth wheels. However, those with a large number of small pieces must rely on the processing of automatic equipment. Generally, the small pieces are mixed with "Abrasive Media" (Abrasive Media) specially made of ceramics of various shapes, and various anti-corrosion solutions are injected to rotate slowly at an oblique position. By rubbing each other, the polishing and finishing of all parts of the surface can be completed within tens of minutes. After being poured out and separated, it can be loaded into the barrel plating tank (Barrel) for rolling plating.

18. Microetching

It is a station in the wet process of the circuit board. The purpose is to remove foreign contaminants on the copper surface. Usually, the copper layer below 100μ-in should be etched away, which is called "micro-etching". Commonly used microetching agents are "sodium persulfate" (SPS) or dilute sulfuric acid plus hydrogen peroxide. In addition, when performing "microsection" microscopic observation, in order to see the structure of each metal layer under high magnification, it is also necessary to micro-etch 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

It refers to irregular gaps on the edge of the line after etching, like the bite marks after being bitten by a mouse. This is an informal term that has recently become popular in the U.S. PCB industry.

20. Overflow overflow

The liquid level of the liquid in the tank rises over the upper edge of the tank wall and flows out, which is called "overflow". In each washing station of the circuit board wet process (Wet Process), a tank is often divided into several parts, which are washed from dirty water by overflow, and can be dipped for many times to save water.

21. Panel Process full plate electroplating method

In the orthodox Substractive Process of the circuit board, this is the practice of obtaining the outer layer circuit by direct etching. The process is as follows: PTH-full-board thick copper plating to 1 mil on the hole wall-positive film dry film to cover the hole-etching -Remove the film to get the outer layer board of the bare copper circuit. The process of this positive film method is very short, and there is no need for secondary copper, no lead-tin plating and tin-lead stripping, which is indeed a lot easier. However, thin lines are not easy to do well, and the etching process is also difficult to control.

22. Passivation passivation, passivation treatment

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

23. Pattern Process circuit electroplating method

It is another way to manufacture circuit boards by reduction method. The process is as follows: PTH——>Copper plating——>Negative image transfer——>Secondary copper plating——>Tin lead plating——>Etching——>Tin lead stripping ——>Get the outer layer of bare copper plate. This pattern process of secondary copper and tin-lead plating by the negative film method is still the mainstream of various circuit board manufacturing processes. There is no other reason, just because it is a safer practice and less prone to problems. As for the long process, the additional troubles such as tin-lead plating and tin stripping are already secondary considerations.

24. Puddle Effect

It means that when the board is in the horizontal transportation, when the plate is sprayed and etched up and down, the upward surface of the board will accumulate etching solution to form a layer of water film, which hinders the effect of the fresh etching solution sprayed later, and blocks the oxygen in the air. Power boost, resulting in insufficient etching effect, and its corrosion rate is slower than that of spraying on the lower surface. The negative effect of this water film is called Puddle Effect.

25. Reverse Current Cleaning Reverse current (electrolytic) cleaning

It is an anode in which the metal work is hung in the cleaning solution, and the stainless steel plate is used as the cathode. The oxygen generated in the electrolysis is used to cooperate with the dissolution (oxidation reaction) of the metal work in the tank liquid, and the surface of the work is removed. Cleaning, this process can also be called "Anodic Cleaning" anodic electrolytic cleaning; it is a commonly used technology for metal surface treatment.

26. Rinsing wash, rinse

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

27. Sand Blast

It uses strong air pressure to carry various small particles ejected at high speed and spray it on the surface of the object as a surface cleaning method. This method can be used for rust removal of metal, or to remove difficult-to-tangle dirt, etc., which is very convenient. The types of sand sprayed are gold steel sand, glass sand, walnut powder and so on. In the circuit board industry, pumice powder is mixed with water and sprayed on the copper surface of the board for cleaning.

28. Satin Finish

Refers to the surface of the object (especially the metal surface) after various treatments to achieve the effect of luster. However, after this treatment, it is not a mirror-like full-brightness state, but a semi-gloss state.

29. Scrubber grinder, grinder

Usually, it refers to the equipment that produces brushing action on the board surface, which can perform grinding, polishing, cleaning, etc. The brushes or grinding wheels used are of different materials, and can also be carried out in a fully automatic or semi-automatic manner.

30. Sealing

After the aluminum metal is anodized in dilute sulfuric acid, the "cell layer" of the crystalline alumina on its surface has cell openings, and each cell opening can absorb dyes and be dyed. After that, it must be immersed in hot water again, so that the alumina absorbs a crystal water to make the volume larger, so that the cell opening is squeezed smaller and the color is closed to make it more durable, which is called Sealing.

31. Sputtering

Cathodic sputtering is the abbreviation of Cathodic Sputtering, which means that in a high vacuum environment and under high voltage conditions, the metal surface atoms in the cathode will be forced to leave the body, and form plasma in the environment in the form of ions, and then run to the surface. On the object to be processed at the anode, and accumulate into a layer of film, evenly attached to the surface of the work, called cathode sputtering coating method, is a technology of metal surface treatment.

32. Stripper stripper, stripper

Refers to stripping liquids for metal plating and organic films, or strippers for enameled wires.

33. Surface Tension

It refers to the molecular-level inward attraction on the surface of the liquid, that is, part of the cohesive force. This surface tension (shrinkage) force at the interface between the liquid and the solid will tend to prevent the liquid from spreading. As far as the cleaning bath liquid for the pre-treatment of the circuit board wet process is concerned, the surface tension (shrinkage) force should be reduced first, so that the board surface and the hole wall can easily achieve the effect of wetting.

34. Surfactant surface wetting agent

Chemicals used to reduce surface tension are added to various bath solutions in the wet process to assist the wetting of the pore walls of the through holes, so it is also called "Wetting Agent".

35. Ultrasonic Cleaning

The energy of ultrasonic oscillation is applied in a certain cleaning solution to generate semi-vacuum bubbles (Cavitation), and the friction force and micro-stirring force of this foam are used to make the dead corners of the objects to be cleaned also generate mechanical properties at the same time. cleaning effect.

36. Undercut Undercutting

The original meaning of the word means that in the early days of artificial logging, the ax was used to cut down the big tree gradually from both sides of the root, and it was called an undercut. In the PCB board, it is used for the etching process. When the surface conductor is sprayed under the cover of the resist, the etching solution will attack vertically downward or upward in theory, but because the effect of the potion has no direction, it is also Lateral corrosion will occur, causing the conductor line after corrosion to show indentation on both sides on the cross-section, which is called Undercut. But it should be noted that only under the cover of ink or dry film, is the side etching caused by direct etching of the copper surface is the real Undercut. Generally, after the secondary copper and tin-lead are plated in the pattern process when the resist is removed and then etched, secondary copper and tin-lead may grow outward from both sides. The loss of inward erosion can be calculated according to the line width of the negative, and the outward widening part of the coating cannot be included. In addition to this defect in the copper surface etching in the circuit board manufacturing process, there is also a similar side etching situation during the development of the dry film.

37. Water Break

When the oil stain on the board surface is cleaned, a uniform water film will be formed on the surface after immersion in water, which can maintain good adhesion with the board or copper surface (ie, the contact angle is small). Usually, it can maintain a complete water film for about 5~10 seconds when standing upright. The clean copper surface can be maintained for 10 to 30 seconds without breaking when the water film is placed flat. As for the unclean board, even if it is laid flat, it will soon "water break", showing a "Dewetting" phenomenon that is discontinuous and aggregated. Because the adhesion between the unclean surface and the water body is not enough to counteract the cohesion of the water body itself. This simple method of checking the cleanliness of the board is called the Water Break method.

38. Wet Blasting

It is a physical cleaning method for metal surfaces, driven by high-pressure gas, forcing wet mud-like abrasives (Abrasive) to spray on the surface to be cleaned to remove dirt. The wet spray pumice powder (Pumice) technology that has been used in the PCB board manufacturing process belongs to this category.