Electronics PCB Board for LED Display
At present, the typical processing technology of printed circuit board (PCB) adopts the "graphic electroplating method", that is, the copper foil part to be retained on the outer layer of the board, that is, the graphic part of the circuit is pre-plated with a layer of lead and tin corrosion resistant layer, and then the rest of the copper foil is corroded by chemical method, which is called etching.
In the etching process, it is important to note that there are two layers of copper on the board. Only one layer of copper in the outer etching process must be completely etched out, and the rest will form the final circuit required. This type of graphic electroplating is characterized by copper plating only under the lead-tin corrosion resistant layer.
Another process is to coat the whole PCB with copper, and the parts other than the photosensitive film are only tin or lead-tin corrosion resistant layers.This process is called "whole plate copper plating process". Compared with graphic electroplating, the biggest disadvantage of whole plate copper plating is that every part of the PCB surface needs to be copper plated twice and they must be corroded out during etching. Therefore, when the line width is very fine, a series of problems will arise. At the same time, side corrosion will seriously affect the uniformity of the line.
In the process of printed circuit board outer circuit, there is another method, which is to use a photosensitive film instead of metal coating as the corrosion layer.This method is very similar to the inner layer etching process. You can refer to the inner layer etching process.
At present, tin or lead tin is the most commonly used corrosion resistance layer, used in the ammonia etching agent etching process.Ammonia etching agent is a commonly used chemical solution that does not react with common tin or lead tin. Ammonia etching agent mainly refers to ammonia water/ammonia chloride etching solution.In addition, ammonia water/ammonium sulphate etching solution is also available on the market.
Sulfate-based etching solution, after use, the copper can be separated by electrolysis, so it can be reused. Due to its low corrosion rate, it is not commonly seen in actual production, but it is expected to be used in chlorine-free etching. Experiments have been made with sulfuric acid-hydrogen peroxide as an etching agent to corrode the outer layers. Due to many reasons including economy and waste liquid treatment, this process has not been widely used in commercial sense.Furthermore, sulfuric acid-hydrogen peroxide, can not be used for lead tin corrosion layer etching, and this process is not the main method of PCB outer production, so most people are rarely interested in.