1. The kinds of etching
Note that the board with two layers of copper etching. There is only a layer of copper in the outer layer etching process is must be etched away, all the rest will be formed finally the circuit you need. This type of pattern plating, its characteristic is the copper plating layer is confined to lead solder resist layer below. Another technique is the entire board copper plating, coating outside of the part is only a tin or lead solder resist layer. This process is called “whole board copper plating process”. Compared with the graphic electroplating, the biggest drawback is plate copper plating board face everywhere to two copper plating and etching must also drop their corrosion. So when very fine wire line width will produce a series of problems. At the same time, the serious influence line of lateral corrosion uniformity.
In the outer circuit PCB processing technology, there is another method, is made from photographic film to replace the metal coating corrosion layer. This method is very similar to the inner layer etching process, can refer to the inner process of etching. At present, tin tin or lead is the most commonly used, corrosion resistant layer used in ammonia etching process of etching agent. Ammonia etching agent is used widely in chemical liquid, lead and tin or tin without any chemical reaction. Ammoniacal etching agent is mainly refers to the ammonia/ammonium chloride etching liquid. In addition, also can buy in the market the etching liquid ammonia/ammonium sulphate. Sulfate as the base of etching solution, after use, the copper can be separated with electrolytic method, thus can be reused. Because of its low corrosion rate, generally in the actual production, but is expected to be in no chloride etching. Someone test using sulfuric acid etching agent – hydrogen peroxide do to corrosion outer graphics. Due to many reasons such as including economic and waste liquid treatment, this process has not been extensively used in commercial sense. Furthermore, sulfuric acid, hydrogen peroxide, cannot be used to lead solder resist layer etching, and this process is not PCB outer production, the main method, so the vast majority of people very few takers.
2. Etching equipment maintenance
Etching equipment maintenance is one of the most key factors to ensure the nozzle cleaning, no obstruction to jet flow. Obstruction or slagging under the effect of injection pressure impact. If the nozzle is not clean, so will cause uneven etching and makes the whole piece of PCB scrap.
Obviously, equipment maintenance is the replacement of damaged parts and wear parts, including the replacement of nozzle, the nozzle also has the problem of wear and tear. In addition, more key problem is to keep the etching machine does not exist and slagging, in many cases will appear slagging accumulation. Slagging accumulation is overmuch, may even affect the etching liquid chemical equilibrium. Also, if the etching liquid chemical imbalance, excessive slagging will more and more serious. Slagging accumulation can’t emphasize enough. Once the etching liquid suddenly appeared a lot of slagging, is usually a signal, the solution of the problems with balance. It should be with strong hydrochloric acid cleaning or solution for adding properly.
Residual material also can produce slagging, very little residual film dissolved in etching liquid, and then forming copper salt precipitation. The residual film formed by slagging way to membrane process not completely before that. Stripping bad is always caused by the edge membrane with a plating results.