1. First, a layer of lead tin anti-corrosive coating should be applied to the copper foil to be retained on the PCB board. After this, the rest of the copper foil should be chemically etched, a process known as etching.
2. Next, let’s discuss the types of PCB etching and the etchants that are commonly used.
Types of PCB etching
1) Pattern electroplating method: During etching, there are two layers of copper on the board, with only one layer of copper completely etched, and the rest forming the final required circuit.
2) Full plate copper plating process: The entire plate is copper plated, with the parts outside the photosensitive film only having tin or lead tin corrosion resistant layers. Compared to pattern electroplating, its biggest disadvantage is that copper must be plated twice everywhere on the board, and must be corroded during etching.
3) The use of a photosensitive film as an anti-corrosion layer instead of a metal coating is similar to the inner layer etching process.
4) The photochemical etching process involves applying layers of photoresist or anti-corrosion dry film on the clean copper clad plate, and obtaining the power circuit image through exposure, development, film fixation, and etching. After the film is removed, it is mechanically processed, coated on the surface, and then packaged, printed, and marked as finished products. This processing technology is characterized by high precision graphics, short manufacturing cycle time, and suitability for batch production and multiple categories.
5) The wire mesh leak printing etching process involves placing a pre-prepared stencil with the required power circuit pattern on the copper surface layer of the clean copper clad plate, and leak printing the anti-corrosion raw materials on the copper foil surface layer to obtain the print pattern. After drying, the organic chemical etching process removes part of the bare copper and the printing material to reveal the required power circuit pattern. This method is suitable for large-scale professional production and manufacturing, with large production volume and low cost, but its precision is not comparable to the chemical etching process.
6) Rapid etching process for ultra-thin copper foil removal: This etching process is mostly applied to thin copper foil laminates. After plating with copper, the thickness of a part of the power circuit pattern and the metal material copper at the hole edge is about 30 μm, while the copper removal foil that is not part of the power circuit figure is still thin (5 μm). This method can produce high-precision and dense printed circuit boards, making it a new production process with a promising future.
What are PCB etchants
Ammonia etchant is a commonly used chemical solution that does not have any chemical reaction with tin or lead tin. Additionally, there is ammonia water/ammonia sulfate etching solution, where copper can be separated by electrolysis after use; it is generally used in chlorine-free etching. Others use sulfuric acid hydrogen peroxide as an etchant to etch the outer figure, but this has not been widely used.
In the transmission signal line of electronic devices, the resistance encountered in the transmission of high-frequency signals or electromagnetic waves is called impedance. Why must PCB have impedance in the manufacturing process? Let’s analyze the following four reasons:
1) PCB board must consider the connection and installation of electronic components, and the later SMT patch connection shall also consider the conductivity and signal transmission performance, so the lower the impedance, the better.
2) During the production process of PCB board, the process of copper deposition, electro tin plating (or chemical plating, thermal spraying tin), connector soldering, and other production links are involved. The materials used must have low resistivity to ensure that the overall impedance value of the PCB board meets the product quality requirements and can operate normally.
3) The tin plating of PCB is the most likely problem in the whole PCB production, and is the key link affecting the impedance; Its biggest defect is easy oxidation or deliquescence, poor solderability, which makes the circuit board difficult to weld, high impedance, resulting in poor conductivity or unstable performance of the whole board.
4) The conductor in the PCB will have various signals transmitted. The impedance value of the circuit itself will change due to different factors such as etching, stack thickness, and wire width, which will distort the signal and lead to the decline of the PCB board performance. Therefore, it is necessary to control the impedance value within a certain range.
2. Next, let’s discuss the types of PCB etching and the etchants that are commonly used.
Types of PCB etching
1) Pattern electroplating method: During etching, there are two layers of copper on the board, with only one layer of copper completely etched, and the rest forming the final required circuit.
2) Full plate copper plating process: The entire plate is copper plated, with the parts outside the photosensitive film only having tin or lead tin corrosion resistant layers. Compared to pattern electroplating, its biggest disadvantage is that copper must be plated twice everywhere on the board, and must be corroded during etching.
3) The use of a photosensitive film as an anti-corrosion layer instead of a metal coating is similar to the inner layer etching process.
4) The photochemical etching process involves applying layers of photoresist or anti-corrosion dry film on the clean copper clad plate, and obtaining the power circuit image through exposure, development, film fixation, and etching. After the film is removed, it is mechanically processed, coated on the surface, and then packaged, printed, and marked as finished products. This processing technology is characterized by high precision graphics, short manufacturing cycle time, and suitability for batch production and multiple categories.
5) The wire mesh leak printing etching process involves placing a pre-prepared stencil with the required power circuit pattern on the copper surface layer of the clean copper clad plate, and leak printing the anti-corrosion raw materials on the copper foil surface layer to obtain the print pattern. After drying, the organic chemical etching process removes part of the bare copper and the printing material to reveal the required power circuit pattern. This method is suitable for large-scale professional production and manufacturing, with large production volume and low cost, but its precision is not comparable to the chemical etching process.
6) Rapid etching process for ultra-thin copper foil removal: This etching process is mostly applied to thin copper foil laminates. After plating with copper, the thickness of a part of the power circuit pattern and the metal material copper at the hole edge is about 30 μm, while the copper removal foil that is not part of the power circuit figure is still thin (5 μm). This method can produce high-precision and dense printed circuit boards, making it a new production process with a promising future.
What are PCB etchants
Ammonia etchant is a commonly used chemical solution that does not have any chemical reaction with tin or lead tin. Additionally, there is ammonia water/ammonia sulfate etching solution, where copper can be separated by electrolysis after use; it is generally used in chlorine-free etching. Others use sulfuric acid hydrogen peroxide as an etchant to etch the outer figure, but this has not been widely used.
In the transmission signal line of electronic devices, the resistance encountered in the transmission of high-frequency signals or electromagnetic waves is called impedance. Why must PCB have impedance in the manufacturing process? Let’s analyze the following four reasons:
1) PCB board must consider the connection and installation of electronic components, and the later SMT patch connection shall also consider the conductivity and signal transmission performance, so the lower the impedance, the better.
2) During the production process of PCB board, the process of copper deposition, electro tin plating (or chemical plating, thermal spraying tin), connector soldering, and other production links are involved. The materials used must have low resistivity to ensure that the overall impedance value of the PCB board meets the product quality requirements and can operate normally.
3) The tin plating of PCB is the most likely problem in the whole PCB production, and is the key link affecting the impedance; Its biggest defect is easy oxidation or deliquescence, poor solderability, which makes the circuit board difficult to weld, high impedance, resulting in poor conductivity or unstable performance of the whole board.
4) The conductor in the PCB will have various signals transmitted. The impedance value of the circuit itself will change due to different factors such as etching, stack thickness, and wire width, which will distort the signal and lead to the decline of the PCB board performance. Therefore, it is necessary to control the impedance value within a certain range.
