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PCB Corrosion Causes

Corrosion is one of the major enemies of printed circuit boards. A sufficiently corroded circuit board won’t work, and the steady advance of corrosion is inevitable. But why do printed circuit boards corrode, and what are some of the most common causes of PCB corrosion?

What Is Corrosion?

Corrosion is the process of oxidation that happens when oxygen bonds with metal, producing rust and causing the metal to flake off and lose its valuable chemical properties. Since printed circuit boards are largely made of metal and are exposed to oxygen, they must corrode eventually.

However, not all metals are created equal when it comes to corrosion. Some metals corrode almost immediately while some seem to never corrode. Metals that are highly resistant to corrosion include:

  • Graphite
  • Gold
  • Silver
  • Copper-nickel alloy

Metals that are highly susceptible to corrosion include:

  • Plated tin
  • Lead
  • Copper
  • Plated nickel

Metals that are extremely resistant to acid and corrosion, like gold and silver, are called noble metals, while those that are susceptible to corrosion, like copper and tin, are called base metals.

What Are the Distinct Types of Corrosion That Can Occur?

The metal in your circuit boards can corrode in several ways, including:

  • Atmospheric: This is the most standard type of corrosion. Metal is exposed to moisture, which contains oxygen, causing a reaction where the metal ions bond with the oxygen atoms and create an oxide. Copper experiences atmospheric corrosion very easily, which is not a problem for copper plumbing because corroded copper retains its mechanical properties. It does not, however, retain its electrical conductivity, so this is a big problem for circuit boards.
  • Galvanic: Galvanic corrosion occurs when different types of metals are in the presence of an electrolyte. In these circumstances, the more resistant metal will actually corrode faster than the baser metal it’s in contact with, so when gold is in contact with tin, for example, the gold will corrode much faster than usual.
  • Electrolytic: In this type of metal degradation, adjacent traces experience dendrite growth when ionic contaminated moisture infects the electrical voltage between them, creating metal slivers that result in a short circuit.
  • Fretting: With fretting corrosion, the action of closing solder-plated switches creates a wiping action that removes the surface oxide layer, allowing the layer beneath to oxidize. Eventually, excessive rust builds up and prevents the switch from activating.


How to Prevent Corrosion on PCBs

So, how can you prevent printed circuit board corrosion? You can’t avoid corrosion forever, but it is possible to delay it beyond the expected life of the circuit board. What are some of the steps for doing this?

Your primary goal when trying to prevent PCB corrosion should be to avoid ionic contamination. Exposing circuit board components to moisture with ionic contamination is the leading cause of printed circuit board corrosion. Your first priority should always be to keep your printed circuit boards and their components clean and dry.

It’s very important to keep this priority in mind when manufacturing your printed circuit boards. Fabricators should avoid getting fingerprints or liquids on printed circuit boards and make sure to manufacture the boards in a clean, dry environment. Designers should take care not to let moisture bead up on exposed conductors.

If you’re designing any printed circuit boards for use in applications where they’re more than likely to be exposed to liquid contaminants — such as the automotive industry, agricultural industry or many industrial environments — you should take steps to protect your boards from the environmental hazards they’re likely to face.

Keeping PCBs clean and dry enough to ward off corrosion isn’t difficult with a little care and attention. Taking these preventative steps doesn’t guarantee none of your printed circuit boards will ever corrode, but it can make it significantly less likely. Taking measures to reduce the likelihood of corrosion as often as possible is invariably well worth the effort.

Learn More About Preventing Corrosion in Printed Circuit Boards

For information about how Millennium Circuits Limited works to make sure the printed circuit boards we distribute are as resistant to corrosion as possible, or to find out about our many other stringent quality assurance methods, contact MCL today.

 

PCB Glossary

  • Buried Via

    A via hole that does not extend to the surface of a printed board.