PCB circuit board is widely used in electronics, computer, electrical appliances, mechanical equipment and other industries. But it always faces a powerful enemy, which is PCB corrosion. A sufficiently corroded circuit board won’t work, and the steady advance of corrosion is inevitable. Corrosion increases the resistance of copper tracks on a PCB, and when sufficiently corroded, result in the board working inefficiently or stop working altogether.
What Is PCB Corrosion?
PCB corrosion is actually an oxidation process that occurs when oxygen is combined with metal. During this process, the PCB metal surface will rust and cause the metal to peel off and lose its valuable chemical properties. Since the main material of the printed circuit board is copper clad board, that is to say, the PCB is mainly composed of metal, and the PCB is exposed to oxygen for a long time, so the PCB always faces the problem of corrosion.
However, the degree of corrosion varies depending on the metal properties. Some metals will soon corrode, while others will never corrode. Here I list the highly corrosion-resistant metals, including: graphite, gold, silver, copper-nickel alloys. In contrast, highly corrosive metals include: tin, lead, copper, nickel. Therefore, when producing PCBs, we should choose acid and corrosion resistant metals to ensure the quality of the PCB.
What Are the Distinct Types of Corrosion That Can Occur?
The printed circuit boards can corrode in several ways, but mainly includes the following:
Atmospheric: In the atmospheric corrosion mechanism of circuit boards, the adsorbed liquid film on the surface of the material plays an important role. Corrosion is most serious when the thickness of the liquid film is more than 1 μm, and the electrochemical reaction occurs mainly under the liquid film. The common forms of corrosion of electronic equipment in the air are mainly local corrosion. Corrosion is concentrated in a small part of the surface of the metal material, and most of the remaining surface corrosion is slight or no corrosion occurs. Mainly due to the uneven surface state of the metal (coating defects, chemical composition, etc.) and the uneven distribution of the corrosive medium, the electrochemical properties are not uniform, that is, different parts have different electrode potentials, thereby forming potential differences and driving the generation of local corrosion. In the local corrosion process, the anode area and the cathode area are significantly different. Usually, a configuration of a small anode and a large cathode is formed, and the anode corrosion is severe.
Electrolytic: Electrolytic corrosion. When the adjacent conductors are closely spaced and biased, a strong electric field is formed. If there is a liquid film on the conductor at this time, the higher potential conductor will be electrolyzed by the solution, and the formed ions will migrate to another conductor, which will cause the insulation between the conductors to rapidly decrease, destroy the conductors, and eventually cause the equipment to fail.
Fretting: A special type of local corrosion, common galvanic corrosion on gold-plated components. Due to the existence of micropores or other defects on the surface of the coating, the intermediate transition layer and even the base metal are exposed to the atmosphere. Au and other metals form galvanic couples with large cathodes and small anodes, and electrochemical corrosion occurs. The appearance of corrosion products further leads to the increase of surface defects, and eventually to the destruction of the coating. Affected by the microporous corrosion products of the contact surface, the corroded area will show higher contact resistance and phase shift.From the above two points, we can see that when we store PCB, we need to vacuum-pack them with clean plastic bags, and then store the PCB in a cool and dry environment.
How to Clean Corrosion off a Circuit Board
When the PCB receives water damage or other sources of corrosion, cleaning it can be an important way to repair it.
Washing Water (commonly known as circuit board cleaning agent).
Washing water refers to chemical industrial cleaning agent potion used to clean the flux and rosin on the surface of PCB circuit board after soldering. The traditional method for cleaning printed circuit boards is to use organic solvents. A mixed organic solvent consisting of CFC-113 and a small amount of ethanol (or isopropanol) has a good ability to clean the residue of rosin flux, but because of CFC- 113 has a destructive effect on the atmospheric ozone layer and has been banned in 2013. The optional non-ODS cleaning processes include water-based cleaning, semi-water-based cleaning, and solvent cleaning.
In addition, you can also use a variety of tools to clean PCB corrosion. I list the following materials here, they will definitely help you.
The alkalinity and abrasiveness of baking soda make it an ideal cleaner for PCB corrosion. It can effectively remove all corroded areas without causing any damage to the PCB itself.
When we use ordinary water to clean circuit boards, we must ensure that the water is free of contaminants. However, we know that ions in ordinary water have electrical conductivity and reduce electronic performance. At this time, distilled water has a great advantage, because it has neither any pollutants nor any ions, so it will not cause damage to the PCB.
Phosphate-free household cleaners effectively remove dirt and corrosion. Because phosphates protect PCBs from corrosion, but they are also a major source of water pollution, we try not to use this method for cleaning.
How to Prevent Corrosion on PCBs
How can we prevent PCB corrosion? Slight corrosion is unavoidable. But if we take some effective measures, it can definitely reduce the degree of PCB corrosion.
Among these measures, the most important thing for us is to protect the PCB from ion pollution. And we need to keep printed circuit boards and their components clean and dry at all times.
We must also keep this in mind when producing PCBs, it is very important. That is to avoid leaving fingerprints or liquid on the surface of the PCB and ensure that the circuit board is manufactured in a clean and dry environment.
When we design a PCB, if the PCB is used in an environment that is easily exposed to liquid pollutants, such as the automotive industry, agricultural industry or many industrial environments, we should take measures to protect the PCB from pollution.
The above is the main content of PCB corrosion. If you have PCB and PCBA project, welcome to contact us. We have rich experience in this industry and can provide one stop service for you.