PCB Corrosion: Causes & How to Prevent It
The most adverse effect manufacturers of circuit boards deal with — corrosion. Silver (tarnishes) and base metals (copper, lead, etc.) are prone to oxidation in a way. That’s why learning ways how to clean corrosion of PCBs and prevent corrosion is due.
Let’s find out what type of corrosion exists and how to deal with its effects. You’ll learn both basic and advanced tips, so stick with us here.
What is PCB Corrosion?
In the broad sense, corrosion is the process of happens that oxygen bonds with metals of circuit boards. It causes the process called oxidation, which all non-resistant metals are prone to. This way, the metal loses some of its chemical and mechanical properties and gradually turns to rust.
Different metals are prone to corrosion at different rates. Here are the ones that are resistant:
- Gold.
- Silver (still tarnishes).
- Nickel.
- Graphite.
- Carbon steel and galvanized steel.
- Aluminum.
And here are types of metals that should be protected against oxidation at any reasonable cost:
- Copper.
- Lead.
- Plated nickel.
- Iron and its alloys.
It’s considered that noble metals are resistant to corrosion. Yet, in PCB manufacturing, producers protect silver from forming metal ions bond with oxidation because it starts darkening or tarnishing quickly.
Now, let’s proceed with researching types of corrosion and ways to deal with them.
What Are the Distinct Types of Corrosion That Can Occur?
Forms of corrosion vary, depending on their nature. Here are ones that are distinguished in different types:
- General Attack or Atmospheric Corrosion. It is safe to say that atmospheric corrosion is the prevalent type of ionic contamination with oxygen atoms. It is provoked by the exposure of metal to open air. The reaction induces the formation of copper oxide, for one. It instantly affects electrical conductivity leading to the malfunctioning of electronic devices.
- Localized Corrosion. This form occurs in a small area, causing defects in circuit boards. Technically, there are three types of localized corrosion.
Filiform corrosion is the occurrence of oxidation because of moisture under the surface finish. It spreads throughout circuit boards, causing more damage.
Crevice corrosion is the affection of crevices under the hardware of circuit boards. It’s caused by flux residues, cleaning solutions, or other contaminants.
Pitting corrosion is what seems to be holes or cavities in copper. Localized galvanic reactions cause such a deterioration, also increasing the pit diameter and depth. THe end result of pitting corrosion is a PCB board’s failure.
- Galvanic Corrosion. Such deterioration occurs in the presence of electrolytes. This situation cause more resistant metal corrodes faster. For example, in the combination of tin and gold, in the case of galvanic contortion, gold deteriorates faster.
- Electrolytic. It’s that type of degradation that occurs in adjacent traces. Basically, its dendrite growth, when contaminated with ionic moisture, affects the electrical voltage between those traces. It results in the phenomenon of a short circuit.
- Fretting. This type of corrosion is the action of closing solder-plated switches conceiving wiping actions. It removes the surface oxide layer (for one, such as with aluminum). It causes the layer beneath to oxidize. It causes rapid rusting.
- Inter-Granular Corrosion. Such a type of corrosion occurs because of chemical reactions on the grain boundary of a copper trace. A typical cause — chemical exposure. Grain boundaries contain impurities that oxidize easily.
Take a look at what atmospheric corrosion may look like in the image below.
How to Clean Corrosion from PCB
Cleaning most types of corrosion, even localized or atmospheric, is a fairly complex process. The reason is the need to disassemble the entire board before even attempting to clean anything.
For one, here are the steps you should proceed with which should your electronics suffer from water and subsequent corrosion damage:
- Remove batteries, power connectors, and power supplies first. This way, you’ll reduce the chances of short-circuiting.
- Look for white or green areas on the device since water could have damaged other components but PCBs.
- Then, remove the circuit boards by disconnecting connections and power sources.
- Use a cleaning solution such as isopropyl alcohol or baking soda.
- Use a soft brush to apply a solution and leave till rust and dust become soft.
- Remove the drive using the same or another brush and distilled water.
- You may remove harder rust by applying more isopropyl alcohol.
- Clean the board with a microfiber rug and dry the bard using an air dryer.
- Install the PCB back into the electronic device.
Fortunately, at least solutions for cleaning are a no-brainer:
- Baking soda. It has abrasive and alkalinity properties making it a perfect cleaner of rust. It neutralized corroded areas.
- Deionized water. You should leave no contaminants on PCBs. Deionized water has no conductive properties and cannot possibly cause any electrical damage to your components.
- Household cleaner. Any phosphate-free cleaner may be of great assistance for you in removing dirt and corrosion. Phosphates act as water pollutants, so avoid them.
- Soft-bristle brush. Even if you do not have a specialized PCB cleaning tool, a toothbrush or paintbrush may do the trick. Soft bristles will not scratch a component’s surfaces.
- Lint-free towel. Regular fabrics leave fibers on boards. Fibers may act as contaminants, so using a lint-free towel is the way you prevent spreading fibers. Such clothing also absorbs water better.
- Oven. Use a regular household oven to dry a PCB. Use small temperature levels just to give a good dry and not to bake your electronic component.
Carefully combine the methodology for cleaning corrosion and the materials recommended to achieve an excellent result.
How to Prevent Corrosion on PCBs
As a professional PCB manufacturer, your role is to minimize the risks of corrosion. Since the presence of moisture and electronic contaminants are the primary causes of corrosion, pay them particular attention. Here is what you can do about it:
- Clean PCBs probably during the assembly process. Ensure that all flux residues have been removed. Dry boards, if necessary. Lower the relative humidity in the workplace.
- Perform conformal coating. Coating or applying one or more PCB finishes are great ways of reducing the probability of corrosion occurrence. Epoxy coatings, spray coatings, and soldering is all absolutely effective barriers against oxidation.
- Lay traces using gold or gold-nickel alloys. It’s an expensive decision, but it helps to nearly eliminate the risks of localized or electrolytic corrosion occurrence.
- Always take the operating environment of a PCB into consideration. Automotive and food processing industries set different corrosion-resistance requirements for PCBs.
- Avoid fingerprints on PCBs. You should be particularly careful about the way your handle your PCBs. Skin oil is what may easily spoil some boards of an entire batch.
- Mind the shelf and storage time. Some boards, such as ones with silver coating, must be assembled within a day after they were fabricated. The same concerns shelf life. Exceeding this parameter leads to unpredictable consequences.
Take good care of your components during the production stage, and your rejection rates will be close to zero.
Summary
Corrosion is the adverse effect that manufacturers deal with. It is mostly caused by oxygen ions, moisture, chemical residues, and other contaminants. To get rid of those and repair a PCB, you need to completely disassemble the electronics, apply cleaning liquids, and dry the board.
It’s way easier to prevent corrosion in the fabrication stage.
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