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Surface treatment and wet process for PCB manufacturing
PCB Blog
Surface treatment and wet process for PCB manufacturing

Surface treatment and wet process for PCB manufacturing

2021-12-28
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Author:pcb

1. Abrasives

Abrasives are the materials used to grind and brush the copper surface before cleaning the PCB surface, such as polymer nonwoven or nonwoven cloth with diamond sand, various types of free materials of its sand, and pumice Slurry. However, this kind of brush material mixed with sandy materials, its powder will often be implanted on the copper surface, resulting in subsequent adhesion of the photoresistive layer or electroplating layer and soldering tin problems.

2. Air Knife

At the outlets of various process online units, a knife with high temperature and high pressure air is often installed to blow out the air knife, which can quickly dry the board surface for easy carrying and reducing the chance of oxidation.

3. Anti-Foaming Agent

During the flushing process of PCB processes such as dry film imaging fluid, a large amount of foam is produced due to the dissolution of a large amount of organic film materials and the mixing of air during the extraction and spraying, which is very inconvenient to the process. Chemicals that reduce surface tension, such as Octyl Alcohol or Silicone, must be added to the fluids to reduce the hassle of field operations. However, silicone resins containing silica oxide cationic interface activators are not suitable for metal surface treatment. Because once it touches the copper surface, it will not be easy to clean, resulting in poor adhesion of subsequent coatings or poor solderability.

4. Bondability

Next layer: refers to the surface to be bonded (or followed) and must be kept clean to achieve and maintain good bonding strength, which is called "bonding".

5. Banking Agent

An important condition for fine-line etching is the addition of organic additives to the etching solution, which act as a kind of skin film attachment on both sides of the line where the current washes away the weaker one, to weaken the power of being attacked by the drops and to reduce the degree of Cmdercut. This agent is mostly confidential to the supplier.

6. Bright-Dip

It is a slight bite on the metal surface to make it appear smoother and shinier, which is referred to as the wet treatment of the groove liquid.


PCB process

7. Chemical Milling

Metal materials are processed by chemical wet fluids in various degrees of corrosion, such as surface coarsening. By deep etching or applying precise special inhibitors, selective etching, etc. instead of the Punch operation of some machining methods, also known as the Chemical Blanking or Photo Chemical Machining (PCM) technology, can not only save the expensive cost of moulds and preparation time, but also free the distress of residual stress in the product.

8. Coat, Coating

This is often referred to as the processing layer on the outside of the board. Generally, it refers to any surface treatment layer.

9. Conversion Coating

It refers to the simple immersion of certain metal surfaces in a specific bath to form a protective layer of compounds on the surface. Such as Phosphating on iron surface, Chromating on zinc surface, or Zincating on aluminium surface can be used as "Striking" for subsequent surface treatment layers, as well as increasing adhesion and corrosion resistance.

10. Degreasing

Traditionally, metal objects have to be cleaned of excessive oil stains left by mechanical processing before electroplating. Vapor Degreasing, an organic solvent, or soaking degreasing in an emulsifying solution, is often used. However, there is no need for degreasing in the PCB process, as almost no oil has been touched during all processes, which is different from metal plating. Only the pre-treatment of boards still requires a "clean" treatment, which is not identical in concept to degreasing.

11. Etch Factor

In addition to the front-down etching of copper, the etchant also attacks unprotected copper surfaces on both sides of the line, called Undercut, resulting in a mushroom-like etching defect, the Etch Factor being a pointer to etching quality.

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12. Etchant

In the PCB industry, it refers to the chemical fluids used to etch the copper layer. At present, acid copper chloride is used in most of the inner or single panels, which has the advantages of keeping the panel clean and easy to automate management (single panels also use acid iron chloride as etchant). The quality of the outer layers of double or multi-layered panels can also be greatly improved due to the use of tin and lead as corrosion resistors.

13. Etching Indicator

It is a special wedge pattern that emphasizes whether the etching is excessive or insufficient. This specific pointer can be placed on the edge of the plate to be etched, or several etched templates can be deliberately added to the operation batch to improve the etching process.

14. Etching Resist

An anti-etching skin layer made on the surface of copper to protect the part of the copper conductor that is not intended to be etched, such as the Electro-resistance of image transfer. Dry membranes. Ink patterns, or tin-lead coatings, are anti-corrosive.

15. Hard Anodizing

Also known as "hard anodization", refers to placing pure aluminium or some aluminium alloy in a low temperature anodizing solution (15% sulfuric acid, 5% oxalic acid, below 10 C, with a lead plate for the cold pole and an anode current density of 15 ASF). After a long electrolysis process for more than an hour, a 1-2 mil thick anodized skin film with high hardness (i.e., crystalline A12O3) can be obtained, and then stained and sealed. It is a good anti-corrosion and decorative treatment for aluminium.

16. Hard Chrome plating

Refers to the thick chrome layer plated for wear-resistant and slippery industrial uses. Ordinary decorative chrome plating can only be applied on a glossy nickel surface for about 5 minutes, otherwise it will cause cracks for too long. Hard chromium can be used for hours. The traditional plating solution consists of CrO3250 g/1+H2SO410%, but the cathode efficiency is only 10% when heated to 60 C. As a result, other electricity generates a large amount of hydrogen, which brings out a large amount of harmful fog composed of chromium acid and sulfuric acid, and causes a large amount of yellow-brown serious waste water pollution from washing. Although wastewater needs to be treated rigorously to increase costs, hard chrome plating is a wear-resistant coating on many axles or drums and cannot be completely removed.

17. Mass Finishing

For many small metal products, the edges and corners must be carefully removed before plating, scratches and polished surfaces must be removed to achieve the best base, and the best appearance and anti-corrosion effect can be obtained after plating. Usually this pre-plating base polishing can be done by hand with a cloth wheel machine. However, a large number of small pieces depend on the processing of automated equipment, usually by mixing small pieces with Abrasive Media, which is specially designed for various shapes of ceramics, and injecting various anti-corrosive solutions, to finish polishing and finishing all parts of the surface in tens of minutes in a slanted, slow-rotating and interabrasive manner. After the pour-out separation is completed, the plating can be rolled back into the barrel.

18. Microetching

It is a station in the PCB wet process to remove foreign contaminants from the copper surface. Usually 100 should be removed by biting μ- The copper layer below in is called microetching. Common microetchants are "sodium persulfate" (SPS) or dilute sulfuric acid plus hydrogen peroxide. In addition, when microslicing is used for microscopic observation, the polished metal sections are also microetched in order to see the structure of each metal layer at high magnification. This term is sometimes referred to as Softetching or Microstripping.

19. Mouse Bite

An irregular gap in the edge of an etched line, like a rodent bited by a rat.

20. Overflow

The liquid level of the liquid in the groove rises over the upper edge of the groove wall and flows out, which is called "overflow". In each wash station of the wet PCB process, a slot is often separated into several parts and washed by overflow from the dirtiest water, which can be soaked several times to save water.

21. Panel Process

In the Substractive Process of PCB, this is a direct etching process to get the outer layers. The process is as follows: PTH-full plate coated with thick copper to hole wall 1 mil-positive dry film cover hole-etching-removing film to get the outer layers of bare copper lines. The process of this kind of positioning is very short. It does not require secondary copper, nor lead-tin plating or lead stripping. It is really a lot easier. However, thin lines are not easy to do well and the etching process is difficult to control.

22. Passivation

A term for metal surface treatment, often used to refer to stainless steel objects immersed in a mixture of nitric acid and chromium acid to force the formation of a thin oxide film to further protect the substrate. In addition, an insulating layer can be created on the surface of the semiconductor, which enables the transistor surface to be insulated electronically and chemically to improve its performance. The formation of such a surface cuticle is also known as passivation.

23. Pattern Process

It is another way to make PCB by reducing the shrinkage process as follows: PTH -> once plated copper -> negative image transfer -> twice plated copper -> tin lead -> etching -> tin-fading lead -> getting bare outer copper sheet. This patterning process of secondary copper and tin-lead plating is still the mainstream in various PCB processes. The reason for this is that it is safer and less likely to cause problems. As for the longer process, additional troubles such as tin-plated lead and tin stripping have been considered as secondary considerations.

24. Puddle Effect

When a board is being transported horizontally and sprayed up or down to form a water film, the upward side of the board deposits etching fluid, which hinders the effect of the fresh etching fluid sprayed down later and blocks the help of oxygen in the air, resulting in insufficient etching effect. The etching speed is slower than that of spraying above the lower side. This negative effect of the water film. This is called Puddle Effect.

25. Reverse Current Cleaning

It is an anode that hangs a metal work object in the cleaning fluid, and uses a stainless steel plate as the cathode. It uses the oxygen generated in the electrolysis to dissolve (oxidize reaction) the metal work object in the tank fluid, and cleans the surface of the work object. This process can also be called "Anodic Cleaning" anodic electrolysis cleaning. It is a common technology for metal surface treatment.

26. Rinsing

In the wet process, in order to reduce the interference of chemicals in each tank, the plates need to be thoroughly cleaned in various intermediate stages to ensure the quality of various treatments, such as Rinsing.

27. Sand Blast

It is a method of surface cleaning by using high pressure to carry small particles which are ejected at high speed onto the surface of an object. This method is very convenient for removing rust or hard-to-tangle scales on metals. The sand to be sprayed is gold and steel sand. Glass sand. Nutcracker powder, etc. In the PCB industry, pumice are mixed with water and sprayed together on the copper surface of the board for cleaning.

28. Satin Finish

Refers to the effect of various treatments on the surface of an object, especially on a metal surface, to achieve a gloss. However, this process is not a full-gloss Mirror-like situation, it is only a semi-glossy state.

29. Scrubber

Usually refers to a device that generates a brush action on the surface of a plate and can perform a brush. Polishing. Cleanup and other work, using different materials such as brushes or grinding wheels, can also be done in a fully automatic or semi-automatic way.

30. Sealing

After the aluminium metal was anodized in dilute sulfuric acid, the cell layers of crystalline alumina on its surface all had cell stomata, and the cell stomata were stained with absorbable dyes. It is then immersed in hot water to make alumina absorb one more crystalline water and make the volume larger, resulting in a smaller cell size and a more durable color closure called Sealing.

31. Sputtering

In other words, cathode sputtering, cathode sputtering, referred to as cathode sputtering, means that in high vacuum and high voltage conditions, the metal surface atoms in the cathode will be forced out of the body and form plasma in the ion form in the environment, then run to the objects to be processed in the anode, and accumulate into a skin film, which evenly adheres to the surface of crops, called cathode sputtering coating. It is a technology for metal surface treatment.

32. Stripper

Refers to the stripper for metal coatings, organic skins, etc., or for strippers other than enameled wires.

33. Surface Tension

A molecule-level inward attraction, that is, part of the cohesion, on the surface of a liquid. This surface tension (contraction) force tends to prevent the diffusion of liquid at the interface between liquid and solid. For cleaning fluids treated before PCB wetting process, the surface tension (contraction) force should be reduced first, so that the board and hole walls can be easily moistened.

34. Surfactant

Chemicals added to the various fluids used in the wetting process to reduce surface tension to assist in wetting the pore walls through the holes are also known as Wetting Agents.

35. Ultrasonic Cleaning

Applying the energy of the supersonic oscillation to a cleaning fluid produces a semi-vacuum bubble (Cavitation), and using the abrasive force of the foam and the power of micro-stirring, causes the dead ends of the items to be cleaned to have a mechanical cleaning effect at the same time.

36. Undercut Undercut

The original meaning of this word refers to the early artificial felling, when the axe from both sides of the tree roots, the upper and lower slopes to gradually cut down trees, known as Undercut. In PCB, it is used for the etching process. When a planar conductor is etched under the protection of a blocker, the etching fluid will theoretically attack vertically down or upward. However, due to the non-directional effect of the water, side etching will also occur, which will cause the conductor lines to appear in the cross section with the sinks on both sides, called Undercut. However, it should be noted that only under the cover of ink or dry mask, the side etch produced by direct etching on the copper surface is really Undercut. In general, when Pattern Process is etched after two times of copper and tin-lead plating and then after removing the anti-plating agent, secondary copper and tin-lead may grow outwards from both sides. Therefore, the part of side etching after finishing the etching can only be calculated for the upper line width of the negative, but the loss of its inward etching can not be included in the outward widening part of the coating. In addition to the defect of copper etching in PCB process, there is a similar side etching in dry film imaging.

37. Water Break

When the oil dirt on the board is cleaned very well, a uniform water film will be formed on the surface after immersion, which will maintain good adhesion with the board or the copper surface (i.e., very small contact angle). Usually the water film remains intact in upright position for about 5-10 seconds. The clean copper surface can be kept flat for 10 to 30 seconds without breaking. As for dirty surfaces, even if they are flat, they will soon "burst" and present a discontinuous and separate "Dewetting" phenomenon. Because of the adhesion between the dirty surface and the water body, it is not enough to counteract the cohesion of the water body itself. This simple way to check the cleanliness of the panel is called the Water Break method.

38. Wet Blasting

It is a physical cleaning method for metal surfaces, driven by high-pressure gases, that forces wet, muddy abrasives (Abrasive) to be sprayed onto the surface to be cleaned in order to remove dirt. This is the type of wet pumice technology used in PCB processes.

39. Wet Process

PCB is manufactured by dry drilling. Cohesion. Exposure and other operations; But there are also plated holes that need to be immersed in water. Copper plating, even imaging and film stripping in image transfer, are wet processes originally called Wet Process.