A PCB etching solution is an acid solution used to remove excess copper from the inner layers of a rigid PCB. The solution contains various ingredients, including hydrogen peroxide, Chloride copper, and water. This method works on the inner layers of a PCB and is a cost-effective way to remove excess copper. One advantage of this method is that it is not reactive to photolithography, which means that the part will not be ruined.
Ammonia in PCB etching solution
Ammonia is used in PCB etching to control the etching rate. It can be used in combination with ammonium persulfate, which is safer than ferric chloride. This solution does not produce gas bubbles or float the board, and is therefore less harmful to electronic devices. The etching process takes about 20 minutes.
It is essential to ensure the etching solution has a high specific gravity, otherwise the process will fail. To adjust the specific gravity of the etching solution, ammonia and ammonium chloride in an aqueous solution are added. The concentration and pH value of the etching solution should also be adjusted according to process regulations.
Hydrogen chloride
Hydrogen chloride is an acid used for PCB etching. The acid is composed of a small amount of water. The PCB is immersed in the solution and allowed to sit for several minutes. The solution will turn a light green color and then will darken. The acid will eventually decompose into water and oxygen gas.
The solution is readily available at hardware stores and contains 30% hydrochloric acid. This acid is very dangerous and should be handled with respiratory protection. It is important to mix hydrogen peroxide with the acid, as this serves as an oxidizer. This allows the acid to eat away at the copper. Once the board is immersed in the solution, it should etch quickly.
Hydrogen peroxide
Hydrogen peroxide is used as an etching agent in several PCB processes. It is also used in through-hole plating of multilayers and in the microclean stage. The concentration of hydrogen peroxide is critical for the quality of the etched product, which is why it is critical to control the concentration in the bath. The concentration of hydrogen peroxide in the etching solution is checked several times daily to ensure that the proper amount is used.
Muriatic acid is a strong acid that is toxic, so it is important to wear protective clothing while handling it. The hydrogen peroxide helps the acid eat copper, which is the target of this etching method. The etching solution consists of a 1:1 ratio of HCl and H2O2, with one part of the two ingredients dissolved in the other. This ratio may not be easy to obtain, however.
Sulfuric acid
A PCB etching solution containing sulfuric acid may be dangerous to the environment. Free chloride ions may interfere with the ability of the sulfuric acid to etch printed circuit boards. These ions are present in typical untreated tap water, which can contain between 2 and 300 milligrams per liter. Therefore, water used to prepare an etching solution must be treated and purified. In addition, distillation and ion exchange methods must be applied to remove the free chloride ions.
There are several different types of PCB etching solvents. Common solvents used in this process are FeCl3 or nitric acid in a concentration of 1 part FeCl3 per volume of water. Other etching solvents may include hydrogen peroxide and iron chloride, or copper sulfate.
