Fabricating printed circuit boards (PCBs) requires using many materials, including copper, solder, and specific chemicals, for etching copper traces.
While chosen for their durability and reliability, all these materials are susceptible to corrosion due to natural environmental factors like water and oxygen or exposure to certain chemicals.
Corrosion interferes with the performance and longevity of your board and appears as a rust-colored film on the surface of PCBs. Additionally, the cost to replace a corroded board is often higher than the cost of preventing corrosion in the first place.
So, no matter the application of your PCB, it is essential to understand everything about PCB corrosion, how it happens, and how to prevent it.
What is PCB corrosion?
Corrosion on PCBs is a common problem during fabrication, assembly, and storage. Any metal parts on a PCB are susceptible to corrosion, including copper traces and lands, integrated circuit packaging, tin-plated components, and solder joints.
Typically, corrosion on a PCB appears as an orange or brown discoloration on the board. This discoloration is caused by oxidation which occurs when oxygen molecules in the atmosphere interact with organic metals.
However, other colors may indicate other forms of corrosion. For example, white or blue-ish white corrosion may indicate mismatched metal alloys, while green corrosion indicates the presence of water-soluble salts, like those found in sea spray.
In some cases, corrosion may take on unique physical forms, featuring deep pits, grooves, and other deformations affecting the electrical continuity of your board. These extreme PCB corrosion issues are typically caused by prolonged exposure to acidic or alkaline solutions, low-quality manufacturing practices, or harsh environmental conditions.
How to prevent PCB corrosion
The best way to prevent PCB corrosion is to use high-quality materials designed and proven to resist oxidation, along with a proper assembly process. When possible, also consider using components or materials specifically developed for applications in harsh environments.
Other effective techniques for preventing corrosion include:
- Thin-film coatings. Applying special conformal coatings, such as acrylics and epoxies, can protect from environmental factors. Additionally, these coatings add an extra layer of insulation that helps prevent shorts on the board.
- Cleaning processes. Maintaining a clean environment is vital for preventing corrosion. Regularly cleaning your work area and PCBs will reduce the amount of dust, dirt, and other debris that cause corrosion.
- Temperature control. Extreme temperatures can accelerate corrosion by increasing the oxidation rate. For this reason, keeping your workspace and stored products in a temperature-controlled environment is essential.
- Handling awareness. Avoid leaving fingerprints, oils, and other substances on your PCBs. Additionally, use clean gloves when handling the board to prevent introducing corrosive elements during assembly.
Following these tips and using the right materials and processes can significantly reduce the risk of PCB corrosion. Furthermore, investing in regular inspections and maintenance will help ensure that your board is functioning properly for its entire lifespan.
How to clean PCB corrosion?
Even with the best preventive measures, preventing corrosion isn’t always possible. However, assuming the corrosion hasn’t caused too much damage, there are steps you can take to restore your board.
Step 1: Isolate the corroded area.
Disconnect all power sources from the board and isolate the corroded area with tape or other insulating materials.
Step 2: Clean the corrosion.
Gently scrape away any visible corrosion, followed by cleaning with an appropriate cleaner (deionized water, baking soda, household cleaning products) and a soft brush or lint-free towel. For more difficult-to-remove deposits, use a mild abrasive, such as a cloth and isopropyl alcohol or water-based flux remover.
Step 3: Evaluate the damage.
Once the area is clean, assess whether any permanent damage has been done to the board. If so, you may need to replace certain components, traces, or even the entire board. Otherwise, the board is likely ready to reassemble.
In the event that your boards have gotten wet and you want to reduce the amount of corrosion, you can also use a drying agent like silica gel or oven drying techniques.
Different Types of Corrosion on PCBs
Knowing the different types of corrosion helps understand the cause and provides insight into potential fixes and preventive measures.
Atmospheric Corrosion
This type of PCB corrosion affects the entirety of the board and renders circuitry, electrical connections, and components useless. Exposure to water, oxygen, and certain chemicals usually cause it. General atmospheric corrosion is known by many names, including uniform attack corrosion and atmospheric corrosion.
Galvanic Corrosion
Galvanic corrosion is also known as bimetallic corrosion and happens when two dissimilar metals are in contact with each other and an electrolyte, such as water, is present. One of the most common causes of galvanic corrosion on PCBs is mixing copper and aluminum traces on one board. This type of corrosion usually appears as a white or bluish-white film on the board surface.
Electrolytic Corrosion
When this type of PCB corrosion occurs, small dendrites called whiskers will form and grow on the circuit board. These dendrites cause electrical shorts, which lead to damage or malfunctioning of the board. Electrolyte solutions coming into contact with the circuitry and components, such as from humidity in the environment or spills, cause electrolytic corrosion.
Fretting Corrosion
Fretting corrosion occurs when switch components on a PCB break down the protective oxidative layer that prevents corrosion. As a result, the PCB cannot resist corrosion, which causes the surface to build an excess of red, brown, or black corrosion. Fretting corrosion is a serious (and costly) issue, requiring immediate attention the moment it is spotted.
Protect Your PCB
Printed circuit boards are essential to any project and require high-end protection against corrosion at all costs. Knowing the different types of corrosion, the signs to look for, and preventive measures helps ensure that your boards function correctly for their entire lifespan.
While some measures may not be preventative, such as drying agents for wet boards or corrosion-resistant coatings for harsh environments, other measures, such as proper storage and protection from environmental factors, help reduce the risk of corrosion damaging PCBs.
Taking steps to protect your printed circuit board against corrosion will save you time and money in repairs and keep your project running smoothly. With the proper precautions, you can make sure your boards remain in top condition for years to come.
Read one of our many in-depth PCB resources for more information on how to protect your printed circuit board from moisture.