Have you ever wondered why almost all PCBAs are green? Apparently, the military, for whom the earliest boards were manufactured, requested that color. As it turns out, a green solder mask makes boards the most visible during the day and also allows for the smallest solder dams. The most important aspect of the solder mask, however, might be the protection it provides against board contamination and oxidation.
Protecting circuit boards is a topic that receives far less attention than is warranted. After all, PCBAs contain exposed copper which is susceptible to oxidation and other contaminants that can disrupt functionality and shorten the board’s operational lifecycle. While not a common topic of conversation for board development, several corrosion prevention best practices can be utilized to prevent contamination, erratic function and premature replacement.
Common Causes of Corrosion on PCBAs
Circuit boards are under threat from corrosion throughout their lifecycle. During fabrication, contaminants that can cause corrosion may exist within the materials. Prior to assembly, handling may be a major source of debris introduction that can eventually lead to board degradation and corrosion. While contamination can lead to corrosion and create significant problems for circuit board operation—especially for critical applications such as medical devices PCBAs—corrosion is normally caused by the introduction of moisture into or onto the board during fabrication, assembly or storage.
The 10 Best PCB Corrosion Protection Techniques
In many cases, developers elect not to protect boards against corrosion. For example, prototypes or single-use boards that will be used immediately often do not protect against corrosion. However, it is probably a better option to apply some kind of PCB corrosion protection for all board development. And the best techniques are listed in the table below.
|MOST EFFECTIVE PCB CORROSION PROTECTION METHODS|
|Order||Corrosion Protection Method||Stage||Description|
|1||Follow a controlled lamination procedure||Fabrication||During this important fabrication step, a desiccant drying agent should be used, and personnel should wear protective attire.|
|2||Use appropriate solder mask||Fabrication||The solder mask is an underrated protective element of board construction. However, the type of solder mask matters and should be chosen appropriately based on design considerations.|
|3||Use meshed copper planes||Fabrication||Meshed copper planes provide a good option, as well. They can prevent the movement of moisture between the planes of your stackup.|
|4||Use surface finishing||Fabrication||The best way to protect boards between fabrication and assembly is to use a surface finish. ENIG is the most popular but by no means the only option.|
|5||Baking||Assembly||To remove moisture, boards should be baked after assembly.|
|6||Use conformal coating||Assembly||Conformal coating, which is IPC regulated—primarily in IPC-CC-830B and IPC-A-610—should also be used. This applies especially to boards that will be used in hazardous environments.|
|7||Use thermal overmolding||Assembly||Another option is thermal overmolding or encasement. This is great for high-temperature environments.|
|8||Use micro-encapsulation||Assembly||Micro-encapsulation is the enclosing of certain components or board elements that are most susceptible to corrosion.|
|9||Use ESD bags for storage||Post-Assembly||Circuit boards should always be stored in ESD bags to isolate them electromagnetically. These bags can also aid in protecting against moisture accumulation.|
|100||Install board in an enclosure||Post-Assembly||Installing boards in an enclosure can also provide protection; however, it should be well vented to prevent moisture from being trapped.|
All of the PCB corrosion protections listed above are good options to extend board lifetime and ensure functionality when deployed. However, the appropriate options for your specific design depend upon your board’s installation environment.
Additional Notes About Protecting PCBAs
In addition to board protection, it is highly recommended that you ensure that your CM cleans your boards. Boards should be cleaned during fabrication (IPC-5704 provides guidance) and during assembly. Additionally, make sure that personnel wears gloves when handling boards. These simple steps can go a long way toward preserving your boards.
|Tempo's Custom PCB Manufacturing Service
Tempo Automation is committed to producing the highest quality boards at the speed of design. We wash every board that we manufacture and offer both in-house and outsourced PCB corrosion protection services.
And to help you get started on the best path, we furnish information for your DFM checks and enable you to easily view and download DRC files. If you’re an Altium Designer or Cadence Allegro user, you can simply add these files to your PCB design software. For Mentor Pads or other design packages, we furnish DRC information in other CAD formats and Excel.