Apr 09 2015
There are several ways to create a PCB and one of those ways is called acid etching. This PCB fabrication method works by chemically removing unwanted copper from the board. Resistances are placed on the portions of the copper board that one wants to remain after the etching process.
One chemical of choice is ferric chloride. This acid is usually a cheaper option than other chemical compounds used for etching. There are two types of this acid and one type is called hexahydrate ferric chloride. This type comes in a light yellow colored powder and is usually dissolved in water with about a tablespoon of salt for a clearer, easier inspection of the PCB when it is submerged in it. The other type is called anhydrous ferric chloride which is a green-brown colored powder. This is a more dangerous chemical and it is highly discouraged to be used but if one decides to, observe extreme caution when dissolving this in water as it creates a lot of heat. Never add water to the powder, add it to the water instead.
There is a chance that this chemical may not successfully etch the board, making it far from ideal for PCB fabrication. If this happens, one can add a small amount of hydrochloric acid and leave the board submerged in it for about two days. When using any of these etching chemicals, use a ceramic or a plastic container, be sure to use gloves and safety glasses when handling such chemicals as they can be damaging to the eyes and skin; also, avoid splashing at all costs.
Another acid of choice in PCB fabrication is sodium persulfate. This is a white-colored powder that is a good etching solution for copper printed circuit boards. This chemical has some advantages over ferric chloride and other similar copper-etching chemicals. Unlike ferric chloride, sodium persulfate does not stain clothes, skin, or containers. It leaves no residue in plain water and rinses quite easily. Its etching speed is faster and it maintains a good etching rate throughout its mixing life.
As to be expected though, this chemical also comes with disadvantages when compared with other etching chemicals. Sodium persulfate has a shorter mixing life (or, in a way, durability) when used in an etch tank; it has a maximum of three weeks regardless if it is being used or not. If ferric chloride triggers a potentially dangerous reaction with metals, sodium persulfate reacts in the same way upon coming into contact with natural fibers such as linen, cotton and wool.
In addition to those already mentioned, other chemicals can be used as etching agents for the PCB – these include hydrogen peroxide and hydrochloric acid. Same with ferric chloride, a non-metallic container is needed for this as well. Mix two parts of hydrogen peroxide with one part hydrochloric acid; by doing that you’ll create a good etching agent. While etching with these chemicals, make sure that the area is well ventilated. In addition to this, acetone is needed to remove the resist from the PCB after etching. Compared to the other methods discussed, this may be the safest for etching the PCB with chemicals. However, extreme caution should still be observed.
When using any of these PCB fabrication methods, always remember to be safe. Be cautious when handling dangerous chemicals and be sure to prepare everything that is needed to keep the etching area secure. Also, follow the instructions very carefully, including those about the proper disposal of such chemicals. Keep in mind that any mistakes can cause serious damage not only to one’s surroundings but even to oneself.