How To Effectively Avoiding Excessive PCB Corrosion? ----14 Tips To Help You Easily Cope with

ⅠWhat is PCB corrosion?

PCB corrosion is the main cause of electronic product failures. At first, the effect of corrosion was to increase the resistance of copper traces on the circuit board, but as the degree of corrosion increased, the efficiency of PCB work would decrease or even stop working.

Corrosion is an oxidation process that occurs when oxygen combines with a metal, causing rust and causing the metal to peel off and lose its valuable chemical properties. Due to PCB being mainly made of metal and exposed to oxygen, it is prone to corrosion.

However, not all metals are equal in terms of corrosion. Some metals corrode almost immediately, while others seem to never corrode.

 Highly corrosion-resistant metals include:

   *Graphite

· *Gold

*Silver

· *Copper nickel alloy

Highly corrosive metals include:

* Tin plating

*Lead

*Copper

*Plate with nickel

Metals that are highly resistant to acid and corrosion, such as gold and silver, are called precious metals, while metals that are susceptible to corrosion, such as copper and tin, are called base metals.

ⅡPCB corrosion type

01 General attack corrosion (atmospheric corrosion or uniform corrosion)

The most common type of corrosion, also known as atmospheric corrosion or uniform corrosion, is usually caused by a chemical reaction between oxygen/water in the air and copper.

General corrosion attacks lead to the formation of copper oxide, and low conductivity can cause PCB problems, but mechanical properties remain unchanged, which is usually easy to diagnose and prevent.

02 Localized corrosion

✷Filamentous corrosion

Moisture entering below the surface finish can cause defects in copper, which may then spread to wider PCBs.

✷Crevice corrosion

Due to residual substances, the area below the components on the hardware or PCB may corrode in these gaps. The flux, cleaning solution, or other contaminants in this type of gap often lead to this type of corrosion.

✷Pitting

This type of corrosion is considered as voids or "voids" in copper. Local electrochemical reactions lead to degradation, resulting in an increase in the diameter and depth of pits, ultimately leading to failure. Compounds that produce corrosion often hide pits, making them difficult to detect.

03 Galvanic corrosion

When two different metals (such as copper and component metals, gold or tin) are coupled in a corrosive electrolyte, galvanic corrosion, also known as bimetallic corrosion, occurs.

This is similar to pitting, but the main difference is that electrochemical corrosion only occurs between metals with different electrochemistries, when they are in electrical contact and the metals are exposed to the electrolyte.

04 Formation of electrolytic dendrites

When there is ion contamination in the water, dendrites will form on the copper trace. When adjacent copper trace wires grow dendrites, they may short-circuit and cause PCB failure.

05 Inter-granular corrosion

When there are chemicals on the grain boundaries of copper traces, intergranular corrosion occurs. Grain boundaries typically contain higher levels of impurities, which are more sensitive to this type of corrosion.

06 Corrosion caused by residual solder mask

The flux residue left by welding has always been the main cause of corrosion. Flux is very important in the welding process because it can prevent oxidation during the welding process. Flux actually reduces the formation of metal oxides at the electrical contacts of welding due to heating. The flux also improves the wetting of the solder beads on the solder pads.

Older flux materials contain corrosive chemicals such as chlorine and must remove residues after welding. Newer fluxes use organic acids that decompose at high temperatures.

When using reflow soldering components, there is usually no residue of solder mask. However, using wave soldering, it is unlikely that the flux will reach the temperature required to decompose the acid. Any remaining flux residue is acidic and highly corrosive.

07 Microseismic corrosion

In micro corrosion, the action of turning off the welding switch will generate a wiping action to remove the surface oxide layer and oxidize the lower layer. Ultimately, excessive rust will accumulate and prevent switch activation.

Ⅲ Prevent PCB corrosion

01 Cover PCB with conformal coating

In cases where it is not possible to package the PCB in the casing, conformal coating can provide assistance. Different forms of conformal coatings, such as simple solder mask layers, aerosol spray coatings, or epoxy resin coatings, are effective anti-corrosion measures. However, for PCBs with components that generate heat, it may be necessary to wisely apply such conformal coatings to avoid hindering heat management.

02 Keep PCB dry

Make every effort to avoid moisture around the PCB. Try to place them in an environment that is not affected by humidity.

03 Prevent electrolyte from wetting PCB

By preventing moisture or other liquids from reaching the PCB, it is possible to effectively prevent PCB corrosion. There are many ways to achieve this, such as placing the PCB inside an enclosure with an appropriate IP rating.

04 Effectively remove solder residue on PCB

Older flux materials are notorious for producing chlorine or other harmful halogens, and unless the flux material is removed after the welding process, it can lead to pitting corrosion of copper traces. However, the organic acids in the new flux do not contain halogens, and they decompose at higher temperatures, such as during reflow soldering. However, circuit boards that undergo peak soldering may not reach the decomposition temperature, and residual flux residue may need to be thoroughly cleaned manually to prevent crevice corrosion.

Ⅳ How to remove corrosion on PCBs - commonly used chemical reagents?

01 Compressed air

Compressed air is a commonly used tool for cleaning electronic products. For simple repairs, compressed air provides an inconspicuous way to remove any dust from electronic devices or machine interiors and blow them out. Use a short-term spray to inject air into the ventilation opening. If you are not satisfied with the dust removed, you can open the device with a screwdriver and operate around the components, carefully cleaning the circuit with air.

02 Baking soda

Baking soda can be used to remove corrosion on PCBs. Baking soda contains sodium bicarbonate, which plays a role in collecting dirt and dust from PCBs, breaking down dirt into small particles. The mild grinding properties of soda water can eliminate corrosion without producing any side effects.

03 Deionized water

When you clean the circuit board with water, you must ensure that it is free of pollutants. Ions in ordinary water have conductive properties that reduce electronic performance. Meanwhile, deionized water does not cause any harmful pollutants or ions

04 Distilled water

Due to the absence of ions that conduct electricity to electronic devices, distilled water outperforms any other form of liquid when mixing cleaning solutions. Distilled water is specially treated to remove harmful pollutants, so it will not damage the PCB.

It may also be quickly contaminated by dirt on hands or in the air, and when not in use, it is necessary to seal the distilled water reserve and avoid contact with bare hands.

05 Isopropanol

When it comes to chemical cleaning agents, isopropanol or external alcohol can remove various dirt, debris, flux, and rust on circuit boards. Isopropanol is a good PCB cleaner because it is cheap and evaporates quickly. Compared to other cleaning agents used for similar purposes, alcohol contains fewer chemicals.

Importantly, the isopropanol content used for cleaning circuit boards should be 90% or higher. High concentrations of isopropanol in contact with the body can have adverse effects, so be careful when handling and use latex gloves and goggles.

Ⅴ Steps to remove PCB corrosion

After preparing all necessary cleaning agents and tools for the circuit board work, you can follow the given steps to clean the corrosion on the circuit board:

Step

1. Firstly, open the given electrical equipment or appliances and remotely control the PCB by disconnecting all connections and power sources.

2. Record the layout and configuration of the PCB, and it is necessary to remember every detail, as the PCB needs to be reassembled after cleaning.

3. When using the correct tools, it is necessary to refer to the user manual and use the tools correctly.

4. After removing the circuit board, use cleaning solutions such as isopropanol or baking soda.

5. Now, use a soft brush to apply it to the circuit board and keep applying until the rust and dust soften.

6. Then, a brush can be used to remove dirt, and further distilled water can be used to remove any remaining dust and corrosion.

7. If there is still hard corrosion on the circuit board, you can further apply more isopropanol as it is a stronger reagent.

8. Finally, clean the circuit board with ultra-fine fiber carpet and dry it with an air dryer, then install it back into the electrical equipment to remove all corrosion.