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Overview to PCB etching – methods and properties

Overview-to-PCB-etching---methods-and-properties

What is PCB etching?

The removal of surplus copper from a printed circuit board is known as PCB etching. Nothing except the necessary circuit will remain on the PCB once the superfluous copper has been removed. The board layout is created so that it may be examined before the etching process begins.

The method of printing a printed circuit board’s intended layout is called photolithography (PCB). To determine which copper pieces need to be removed from the board, use this as a reference. The PCB’s top layer is protected from deterioration by tin plating.

On the other side, the photoresist guards against etching away the inner layer. There are typically two methods for etching a PCB’s inner and outer layers. Both dry and wet etching are possible. Wet etching, a kind of chemical etching, is done at ABL Circuits using a Tech Win Alkali Etching Machine.

What is dry etching?

The use of plasma in the dry etching process is common. The atoms at the laminate’s base and those on its surface can begin chemical reactions with the help of plasma. The copper that is no longer needed will degrade as a result of this procedure. Although plasma is the tool used in dry etching most frequently, lasers are another choice.

What is wet etching?

Using a solution, copper is dissolved through a series of chemical reactions in the wet etching process. This technique may use an acidic or an alkaline chemical, depending on the material being etched.

The merits and demerits of dry etching and wet etching

 ★ Merits of dry etching
Low chemical cost, anisotropy of the etching profile, less photoresist shedding, good etching uniformity, and anisotropy of the etching profile are all desirable characteristics.

 ♥ Demerits of dry etching
Harm caused by plasma, Limited alternatives for etching the underlying material, pricey equipment, and potential danger from plasma.

 ★ Merits of wet etching
Is homogeneous, cost-effective, and highly selective, stopping the etching process without damaging the films of the other materials below. It is suitable for most metals, glasses, and plastics among other materials. It also has a high degree of flexibility and is suitable for most metals, plastics, and glasses.

 ♥ Demerits of wet etching
The etched pattern’s precision is subpar, and it is difficult to control even the slightest of lines and an isotropic pattern of etching.

The process of Alkaline Etching

Using an alkaline solution as the solvent, the outer layers of a PCB are frequently removed. At ABE Circuits, where I work, that is also how we operate. A printed circuit board can be quickly and affordably etched using an alkaline solution.

But caution must be used when performing the procedure. This is due to the potential for permanent damage if the solvent is left on the circuit board for a long time. In a belt-moving high-pressure spray chamber, alkaline etching is frequently carried out. By doing this, the procedure is made as quick, efficient, and precise as possible. 

Using a fresh spray of etchant, the PCB is removed from the chamber. The process of etching ends once all of the unwanted copper has been eliminated. Usually, this is carried out in the centre of the spray chamber.

The process of Acidic etching

A rigid PCB’s core layers are frequently removed using an acidic method. In this method, cupric chloride or ferric chloride will be applied. Because it can be used frequently, has a consistent etching rate, and more accurately removes minute details, cupric chloride is the most popular solution. Acid is frequently applied to the inner layers.

This is so that the necessary component is not harmed by the acid, which does not react with the photoresist. In addition, undercuts—the sideways erosion of the etched material behind the tin or lead shield—are reduced to the absolute minimum. However, acid etching might take a lot longer than alkaline etching. Dealing with a lot of PCBs is therefore not always the best choice.

The-process-of-Acidic-etching

What is cupric chloride etching?

This solution uses potassium chloride instead of hydrochloric acid to etch cupric chloride. Contains cupric chloride. This has many advantages.

● Quicker: Etching a 35-um copper PCB at 50°C and room temperature is faster.
●More secure: The etch bath contains no free hydrochloric acid, so HCl vapors won’t make you sick.
●Simplified: Measure specific gravity to manage a bath. Titration and other complicated methods and tools are unnecessary.

Using this method, you can etch a PCB at home. Etching is fast enough with a simple container, so no extra equipment is needed. Due to constant etching velocity and minimal bath operator effort, results are consistent no matter how recently the etchant was used. The solution only needs to be used once or twice a week and doesn’t go bad easily. When etchant is increased, waste is minimal.

The process of Ferric Chloride PCB etching

Any copper on the board that isn’t covered by the marker’s ink will be corroded away by ferric chloride because it is an acidic and corrosive chemical. Apply a little ferric chloride to the board and then put it in a plastic container with a lid. A sufficient amount must be used to completely cover the board. The board ought to be usable in ten minutes. As you shake the container back and forth to mix the contents, make sure the lid is securely fastened.

Examine the board to see if there is any copper on it after 10 minutes. Put on a rubber glove and remove the copper from the board if there is none there. Repeat the process if copper is present. Use a disposable towel to dry wipe the board to get rid of any accumulated ferric chloride. Use acetone to rinse the board.
By using this technique, you can see your markings and safely remove the marker ink from your hands.

The-process-of-Ferric-Chloride-PCB-etching

Factors affect the etchant’s quality

★ Physical-chemical characteristics

1)Etchant quantity: based on the structure of the copper foil and the theory of metal corrosion; the etching liquid concentration should be chosen. The process must provide a variety of options.

2)Temp: the etching solution’s temperature can be checked in Celsius. Chemical reactions are impacted by temperature. It accelerates solution flow, lowers viscosity, and speeds up etching.

★ Mechanics
1)Resources: the etching liquid is impacted by the apparatus design. A PCB with a wide wire width is etched in an immersion tank. The design of this device doesn’t worry about precision. 

Spraying: a linked framework in the shape of a cone is required by the current general spray system. Different patterns of fan-shaped etchings are released from each nozzle.

★ Fluid dynamics:
The liquid might appear to have a tight film because of the limited surface area. The film shrinks at the molecular level. To keep this in mind, A surface-tangential force must be applied to the edge to prevent shrinkage in order to achieve a tight surface balance. This preserves the surface volume.

Conclusion

One of the most crucial steps in the production process is the etching of PCBs. To reveal the appropriate circuit arrangement, copper is scraped off the printed circuit boards (PCB) surface. All of the copper on the PCB is removed during the etching process, with the exception of the circuitry, which is covered in a layer of tin. The copper is polished until it is ready for use after the tin has been taken off. Despite how simple it may seem, etching PCBs is a highly complicated process that demands extreme precision. There are several techniques for etching PCBs, each with advantages and disadvantages.

The precision and caliber of high-density thin-wire images on printed circuit boards are influenced by the etchant selection. Pick your etchant wisely. Etching solution characteristics can be influenced by physical, chemical, and mechanical factors.

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