Corrosion is inevitable in the electronics manufacturing industry, to the point where it’s costing the manufacturing and industrial sector an estimated 17 billion dollars per year in the U.S. alone. The components of your product may take from a few months to a few decades to corrode, you need to be aware that product components all eventually will corrode.
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 will corrode eventually. The biggest factor in corrosion is exposure to moisture with ionic contamination. Keeping your PCB clean and dry can reduce the speed of corrosion. Using a conformal coating is an imperative step in helping to prolong the life of your PCB. But there are additional steps you can take to help avoid the process of corrosion for as long as possible.
Not All Corrosion is Created Equal
While all corrosion is inevitable, there are different ways in which your components may corrode and there are different ways to circumvent the inevitable. These are the most common types of corrosion for PCBs and flexible circuits:
- Atmospheric: The most standard type of corrosion occurs when metal is exposed to moisture, which contains oxygen. This results in a reaction where the metal ions bond with the oxygen atoms and create an oxide.
- Galvanic: When different types of metals are in the presence of an electrolyte, galvanic corrosion occurs. In these circumstances, the more resistant metal will actually corrode faster than the baser metal it’s in contact with, so, for example: when gold is in contact with tin, the gold will corrode much faster than usual.
- Electrolytic: Adjacent traces that have an electrical voltage between them may experience dendrite growth when ionic contaminated moisture infects this voltage, creating metal slivers that will inevitably result in a short circuit.
- Fretting: 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.
Not All Metals Are Created Equal
The most common metals used in electronics are copper, tin-lead, silver, gold, graphite and nickel. Some of these are more beneficial than others. If you want to help your products longevity, consider using different materials when possible.
Metals that are highly resistant to corrosion include:
- Graphite
- Gold
- Silver
- Copper-nickel alloy
- Copper 110
Metals to avoid include:
- Plated tin
- Lead
- Copper*
- Plated nickel
- Nickel-silver
Gold and silver are considered noble metals because they are highly resistant to not only corrosion but also acid, however, it’s not exactly cost-effective to use gold and silver in all your products. In the end, it will come down to weighing the cost of the metal you use to the cost of the speed of corrosion. While expensive, using gold and silver significantly improves the longevity of your components slowing down and resisting corrosion.
* Plumbers may find it strange to see copper on the list of metals to avoid because while copper experiences atmospheric corrosion very easily, it still retains its mechanical properties, so when copper pipes corrode, it doesn’t change the effectiveness. However, corroded copper does not retain its electrical conductivity, so this is a big problem for circuit boards.
Other Corrosion Considerations
Exposure to contamination can occur in other circumstances too. During the fabrication and assembly process, ionic contamination can stem from plating residues or even human fingerprints.
ACDi understands how important corrosion protection is. We meet IPC 6013 standards, ensuring a level of cleanliness to avoid contamination and other factors that may speed up the corrosion process. We’ll help you determine the most effective methods for designing electronic packages with flexible circuits to minimize corrosion issues.