Introduction to PCB etching technology

Wet etching is a etching process in which unwanted materials are dissolved when immersed in chemical solutions.

According to the erosion agent used, PCB manufacturer Tongyu adopts two wet etching methods:

1. Acid etching (iron chloride and copper chloride).

2. Alkaline etching (ammonia)

Acid etching process

The acidic method is used to etch the inner rigid PCB layer, which involves chemical solvents, such as iron chloride FECL3 or copper chloride (CUCI2). Compared to alkaline methods, acidic methods are more accurate, cheaper but more time-consuming. This method is suitable for the inner layer, because acid will not react with the photoresist, nor will it damage the required part. In addition, in this method, the bottom cut is the smallest.

The bottom cut is the horizontal corruption of the etching material below the most lead layer. When the solution encounters copper, it attacks copper and leaves a protected orbit. Use anti-corrosion electroplating or light shielding to protect the track. At the edge of the track, a certain amount of copper will always be removed below the resistance, which is called the bottom cut.

1. Copper etching

Copper chloride is the most widely used etching agent because it can accurately etch fewer characteristics. The ammonia process also provides a constant etching rate and continuous regeneration at a lower cost.

The maximum etching rate of the copper chloride system is a combination of copper hydride-sodium ammonia-HCI system. The combination provides a maximum turbid engraving rate of 55 seconds at 130 ° F. Therefore, this type of etching is used for the inner layer of etching the fine line

Note: The use of chlorine gas requires adequate ventilation, storage tanks and cylinders to store and leak detection equipment. In addition, it must be approved by the emergency agreement, personal protection equipment, trained operators, and the fire department.

2. Triscel oxide etching

Due to the high cost of copper etching agents, the use of iron chloride etching agents in industry is limited. However, iron chloride is an attractive spray etching because it is easy to use, the ability to maintain copper, and the ability to use it in rare batch applications. Iron chloride can be used with silk ink, lithography glue and gold pattern, but cannot be used with tin or tin/lead.

Generally, the iron chloride solution is dissolved in water, with a concentration range of 28-42% (by weight). HCI (5%) is also mixed with the solution to prevent the formation of insoluble hydroxide and iron oxide.

The iron chloride ratio is usually 36 BE, or about 4.0LB/Gal Feci3. The content (HCL) for commercial use is within 1.5 to 2%.

Alkaline etching process

Alkaline method is used to etch the PCB outer layer. Here, the chemicals used are copper chloride (CUCL2) ten hydrochloride (HCI)+hydrogen peroxide (H2O2)+water (H20) composition. The alkaline method is a fast process, and it is also a bit expensive. The parameters of this process must be carefully followed, because if you touch the solvents for a long time it will destroy the circuit board, the process must be well controlled.

The entire process is carried out in a high pressure air spray, and the PCB is exposed to the fresh etching spray. Some important parameters are required in the alkaline PCB etching. They are the amount of panel movement, chemical spray, and copper to be etched. This ensures that the etching process is completed uniformly through the straight end.

In the etching destruction, the points that are not required for copper etching are breakpoints. This is usually done from the midpoint of the atomicization chamber. For example, assuming the length of the atomization chamber is 2 meters, the breakpoint will be reached when the plate reaches the intermediate point.